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The January 17, 1995 Hyogoken-Nanbu

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Performance of Structures, Lifelines, and Fire

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NIST Special Publication 901 (ICSSC TR18)

The January 17, 1995 Hyogoken-Nanbu

(Kobe) Earthquake

Performance of Structures, Lifelines, and Fire

Protection Systems

Riley Chung, Team Leader and Editor

Donald Ballantyne Roger Borcherdt

Edward Comeau James Cooper

Thomas Holzer H. S. Lew

Daniel Madrzykowski Jack Moehle

Anshel Schiff Li-Hong Sheng

William Stone Andrew Taylor James Wilcoski

Ian Bucker

John Hayes

E. V. Leyendecker

Thomas O'Rourke

M. P. Singh

Michael Whitney

Building and Fire Research Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899-0001

July 1996

/ V %

California Department of Transportation Federal Highway Administration

National Center for Earthquake

Engineering Research

National Fire Protection Association

National Science Foundation

U.S. Army Construction Engineering

Research Laboratory

U.S. Geological Survey

U.S. Department of Commerce

Michael Kantor, Secretary

Technology Administration

Mary L. Good, Under Secretary for Technology

National Institute of Standards and Technology

Arati Prabhakar, Director
National Institute of Standards

and Technology

Special Publication 901

Natl. Inst. Stand. Technol.

Spec. Publ. 901

544 pages (July 1996)

CODEN: NSPUE2

U.S. Government Printing Office

Washington: 1996

For sale by the Superintendent

of Documents

U.S. Government Printing Office

Washington, DC 20402
ABSTRACT

The January 17, 1995 Hyogoken-Nanbu earthquake of magnitude 7.2 in JMA scale (Mw = 6.9),

which struck Kobe, Japan and its surrounding area was the most severe earthquake to affect that region this century. The earthquake resulted in more than 6,000 deaths and over 30,000 injuries.

Fires following the earthquake incinerated the equivalent of 70 U.S. city blocks. They together

destroyed over 150,000 buildings and left about 300,000 people homeless. The economic loss as a

result of this earthquake is estimated to reach $200 billion.

An investigation was conducted under the auspices of the Panel on Wind and Seismic Effects of the

U.S. -Japan Program in Natural Resources to observe, document, and summarize important lessons

from this earthquake that can be used to mitigate the potentially tragic impact of future earthquakes on modern urbanized communities. An 18-member team was in Japan from February 12 to February

18, 1995 to study seismology, geology, and geotechnical effects; as well as- the performance of

buildings, lifelines, and fire safety systems.

This document summarizes the information collected during as well as following this investigation.

Key findings of the investigation include needs for research and for improvements in practices to achieve earthquake loss reduction in the United States.

Key words: airports, bridges, buildings, building technology, engineering seismology, electric power, fires, gas, geology, geotechnology, harbor, highway, lateral spread, lifeline,

liquefaction, railroad, rapid transit, reinforced concrete, sewage, steel,

telecommunication, wastewater, water, wood frame construction

iii
ACKNOWLEDGMENTS

The authors wish to thank the following individuals for their extraordinary support during the

investigation team's visit to Kobe. Many of them also have provided valuable information through

followup correspondences that helped prepare this report.

Public Works Research Institute, Ministry of Construction, Japan

Dr. Hiroshi Sato

Dr. Yasuyuki Koga

Mr. Tomonobu Nakaoka

Mr. Takaaki Kusakabe

Mr. Yoshio Ninomiya

Mr. Shuji Tanaka

Dr. Koichi Yokoyama

Building Research Institute, Ministry of Construction, Japan

Dr. Shinsuke Nakata

Dr. Isao Nishiyama

National Research Institute for Earth Science and Disaster Prevention, STA

Mr. Keiichi Ohtani

Geographical Survey Institute, Ministry of Construction

Mr. Masaharu Tsuzawa

Kobe Waterworks Bureau, City of Kobe

Mr. Makoto Matsushita

Kobe University

Prof. Shiro Takada

Nippon Telegraph and Telephone Corporation

Mr. Kenichi Honda

Mr. Yasui Kuribayashi

Mr. K. Yamagami

Kansai Electric Company

Mr. K. Yasuda

Osaka Gas Company

Mr. Nobuhiro Kanatsuji

Mr. Chiaki (Jack) Gomi

Mr. Shimizu

Ms. Noriko Fukunaga

iv
Hanshin Expressway Public Corporation

Mr. Motohiko Nishibayashi

Japan Highway Public Corporation

Dr. Yuzuru Ito

Ministry of Construction, Naniwa National Highway Construction Bureau

Mr. Toshai Kato

Kobe Rapid Transit Railway Co., Ltd.

Mr. Toshi Aki Syo

Mr. Hiroshi Kishimoto

American Consulate General in Osaka

Mr. Robert G. Rapson

The authors also wish to thank Mr. LeVal Lund, and Dr. Bijan Mohraz and Ms. Ann Bieniawski of

the Building and Fire Research Laboratory, National Institute of Standards and Technology, for

their review of the manuscript; as well as the support that they have been receiving from Drs.

Richard Wright and Jack Snell, Director and Deputy Director, respectively, of the Building and Fire

Research Laboratory. Other individuals who have helped contribute the work of this investigation are specifically recognized in the acknowledgments in separate chapters.

v
CHAPTER CONTRIBUTORS

INTRODUCTION

Riley Chung

SEISMOLOGY, GEOLOGY, AND GEOTECHNICAL ISSUES

Roger Borcherdt

Thomas Holzer

PERFORMANCE OF BUILDINGS

John Hayes

H. S. Lew

E. V. Leyendecker

Jack Moehle

M. P. Singh

William Stone

PERFORMANCE OF TRANSPORTATION SYSTEMS

Ian Buckle

James Cooper

Thomas Holzer

Thomas O'Rourke

Anshel Schiff

Li-Hong Sheng

Andrew Taylor

Michael Whitney

James Wilcoski

PERFORMANCE OF LIFELINE SYSTEMS

Donald Ballantyne

Riley Chung

Thomas O'Rourke

Anshel Schiff

POST EARTHQUAKE FIRES

Daniel Madrzykowski

Edward Comeau

OBSERVATIONS, CONCLUSIONS, AND RECOMMENDATIONS

FOR RESEARCH

Riley Chung

vi
TABLE OF CONTENTS

EXECUTIVE SUMMARY

1. INTRODUCTION 1

1.1 Impact of the Earthquake 1 1.2 Overview of Report 3

2. SEISMOLOGY, GEOLOGY, AND GEOTECHNICAL ISSUES 5

2.1 Source Characteristics 5

2.2 Regional Geologic Stratigraphy 6

2.3 Geotechnical Overview - Kobe City Area 7

2.4 Strong Ground Shaking 9

2.4.1 Strong Motion Recordings 9

2.4.2 Attenuation 11

2.4.3 Amplification Effects of Soft-Soil Deposits 12

2.5 Ground Failure 14

2.6 Engineering Seismology and Geotechnical Lessons for the United States 15

2.7 Research Needs for Engineering Seismology and Geotechnical Engineering . . 16

2.8 Acknowledgment 17

2.9 References 4% /^i.r-i;«U'*ihL 17

Appendix 2.A . . . 55

3. PERFORMANCE OF BUILDINGS 61

3.1 Introduction 61

3.2 Development of Japanese Building Construction 62

3.2.1 Development of Japanese Building Seismic Requirements 62

3.2.2 Types of Construction in Japan 63

3.2.2.1 Wood Frame Construction for Traditional Houses 63

3.2.2.2 Reinforced Concrete Bearing Wall Construction , 64

3.2.2.3 Reinforced Concrete Frame and Frame-Wall Construction ... 64

3.2.2.4 Steel-Reinforced Concrete (SRC) Construction 65

3.2.2.5 Steel Construction 66

3.2.3 Lateral Force and Design Requirements 66

3.2.3.1 The Building Standard Law from 1950 through 1980 67

3.2.3.2 The Building Standard Law of 1981 67

3.3 Performance of Traditional .Wood Houses 79

3.4 Reinforced Concrete and Steel-Reinforced Concrete Buildings 87

3.4.1 Introduction 87

3.4.2 Description of Damage 88

3.4.2.1 Damaged Reinforced Concrete Shear Walls 88

3.4.2.2 Damage to Reinforced Concrete Frame Members 89

3.4.2.3 "Soft" First-Story Collapses 89

3.4.2.4 Mid-height Story Collapses in RC and SRC Mid-rise

Buildings 90

3.4.2.5 Other Observations 91

vii
3.5 Performance of Steel Buildings Ill

3.5.1 Introduction Ill

3.5.2 Description of Damage 113

3.5.2.1 Weld Fractures in Light Gage Steel Frames 113

3.5.2.2 Diagonal Brace Fractures 113

3.5.2.3 Buckling of Columns 114

3.5.2.4 Weld Fractures in Low-rise Buildings 114

3.5.2.5 Moment Frame Behavior: Mid-rise Buildings 114

3.5.2.6 Anchor Bolt Failure 115

3.5.2.7 Behavior of High-rise Buildings 116

3.6 Lessons for the United States 155

3.7 Research Needs 157

3.8 Summary 157

3.9 References 158

4. PERFORMANCE OF TRANSPORTATION SYSTEMS 163

4.1 Introduction 163

4.2 Highways and Bridges 171

4.2.1 Overview .171

4.2.2 Observed Damage 172

4.2.2.1 Damage to Superstructures Due to Bearing Failure 174

4.2.2.2 Damage to Concrete Substructures 177

4.2.2.3 Damage to Steel Substructures 183

4.2.2.4 Damage to Structures Due to Special Conditions 186

4.2.2.5 Performance of Other Highway Bridge Structures 188

4.2.3 Lessons for the United States 188

4.2.4 Research Needs and Opportunities 190

4.2.5 Summary 191

4.2.6 References 192

4.3 Railways and Rapid Transit System 235

4.3.1 Overview 235

4.3.2 What Happened 235

4.3.2.1 Shinkansen - Western JR 235

4.3.2.2 JR Main Line - Western JR 237

4.3.2.3 Hanshin Dentetsu 237

4.3.2.4 Hankyu 237

4.3.2.5 Kobe New Tram System 237

4.3.2.6 Underground Rapid Transit Systems 238

4.3.3 Lessons for the United States 240

4.3.4 Research Needs 242

4.3.5 Summary 242

4.3.6 References 242

4.4 Airports 261

4.4.1 Overview 261

4.4.1.1 Kansai Airport 261

4.4.1.2 Osaka Airport 264

4.4.2 What Happened 264

4.4.2.1 Kansai Airport 264

4.4.2.2 Osaka Airport 265

viii
6. POST EARTHQUAKE FIRES 497

6.1 Introduction 497

6.2 Fire Events Following the Earthquake 497

6.2.1 Fire Causes 498

6.2.2 Fire Spread 499

6.2.3 Performance of Fire Protection Systems 500

6.2.3.1 Active Systems 501

6.2.3.2 Passive Systems 501

6.2.4 Fire Service 502

6.2.5 Resident Self-help 504

6.3 Lessons for the United States 504

6.4 Research Needs 505

6.5 Summary 505

6.6 Acknowledgments 506

6.7 References 506

7. OBSERVATIONS, CONCLUSIONS, AND RECOMMENDATIONS FOR

RESEARCH 525

7.1 Introduction 525

7/2 Observations and Conclusions 525

7.2.1 Seismology, Geology, and Geotechnology 525

7.2.2 Buildings 526

7.2.3 Highways and Bridges 527

7.2.4 Railways and Rapid Transit System 528

7.2.5 Airports 529

7.2.6 Ports and Harbors 529

7.2.7 Water and Wastewater Systems 529

7.2.8 Gas Delivery System 530

7.2.9 Electric Power 531

7.2.10 Telecommunications 532

7.2.11 Hospitals 532

7.2.12 Post Earthquake Fires 532

7.3 Recommendations for Research 533

7.3.1 Seismology, Geology, and Geotechnology 533

7.2.2 Buildings 533

7.3.3 Highways and Bridges 534

7.3.4 Railways and Rapid Transit System 535

7.3.5 Airports 535

7.3.6 Ports and Harbors 535

7.3.7 Water and Wastewater Systems 536

7.3.8 Gas Delivery System 536

7.3.9 Electric Power 536

7.3.10 Telecommunications 537

7.3.11 Hospitals k 537

7.3.12 Post Earthquake Fires 538

APPENDIX Seismic Intensity Scale, Japan Meteorological Agency vs Modified Mercalli Intensity Scale 539

xi
5.4 Electric Power 387

5.4.1 Overview 387

5.4.1.1 Kansai Electric Company 387

5.4.1.2 System Description 387

5.4.1.3 Differences in Equipment, Facilities, and Practices

between Kobe and the United States 387

5.4.1.4 Seismic Design Criteria 389

5.4.2 What Happened 390

5.4.2.1 Seismic Environment at Power Facilities 390

5.4.2.2 Restoration of Service 390

5.4.2.3 Overview of Damage 391

5.4.2.4 Itami Control Center and Substation 392

5.4.2.5 Shin-Kobe Substation 396

5.4.2.6 Fukiai Control Center and Substation 396

5.4.2.7 Performance of Generating Facilities 397

5.4.2.8 Performance of High Voltage Transmission Lines 397

5.4.2.9 Performance of the Distribution System 398

5.4.3 Implications of Observations to the United States 398

5.4.4 Research Needs 399

5.4.5 Summary 400

5.4.6 Acknowledgments 400

5.4.7 References 400

5.5 Telecommunications 465

5.5.1 Nippon Telegraph and Telephone (NTT) Corporation 465

5.5.2 What Happened 465

5.5.2.1 Central Offices 465

5.5.2.2 Outside Plant 466

5.5.2.3 Network Operations 467

5.5.2.4 Restoration 468

5.5.2.5 Special Post-Earthquake Services 468

5.5.3 Lessons for the United States 468

5.5.4 Research Needs 468

5.5.5 Summary 468

5.5.6 Acknowledgments 469

5.5.7 References 469

5.6 Hospitals 481

5.6.1 Overview 481

5.6.1.1 Scope of Investigations 481

5.6.1.2 Kobe Medical College of the University of Kobe 481

5.6.2 What Happened 481

5.6.2.1 Kobe Medical College of the University of Kobe 481

5.6.2.2 Hyogo Medical Center 484

5.6.3 Lessons for the United States 484

5.6.4 Research Needs 484

5.6.5 Summary 485

5.6.6 Acknowledgment 485

x
4.4.3 Lessons for the United States 266

4.4.4 Research Needs 266

4.4.5 Summary 266

4.4.6 Acknowledgment 266

4.5 Ports and Harbors 287

4.5.1 Overview 287

4.5.2 What Happened 288

4.5.3 Lessons for the United States 289

4.5.4 Research Needs 290

4.5.5 Summary 290

4.5.6 References 290

5. PERFORMANCE OF LIFELINE SYSTEMS 299

5.1 Introduction 299

5.2 Water and Wastewater Systems 301

5.2.1 Overview of Water System 301

5.2.1.1 System General Overview 301

5.2.1.2 Supplies 302

5.2.1.3 Water Treatment Plants 302

5.2.1.4 Distribution 302

5.2.1.5 Distribution Reservoir and Pump Stations 303

5.2.1.6 Control System 304

5.2.1.7 Earthquake Monitoring and Control 304

5.2.2 What Happened to the Water System 305

5.2.2.1 Conditions Following the Earthquake 305

5.2.2.2 Damage to Water Facilities 306

5.2.3 Wastewater System Overview and Damage 308

5.2.3.1 System and Damage Overview 309

5.2.3.2 Higashinada Wastewater Treatment Plant 309

5.2.4 Lessons for United States and Research Needs 311

5.2.4.1 Overwhelming Conditions 311

5.2.4.2 Fire Following 311

5.2.4.3 Geotechnical Issues 311

5.2.4.4 Design 312

5.2.4.5 Recovery 312

5.2.5 Summary 312

5.2.6 Acknowledgments 313

5.3 Gas Delivery System 375

5.3.1 System Description 375

5.3.2 Observations 376

5.3.2.1 LNG Facilities and Trunklines 376

5.3.2.2 Medium Pressure Lines 376

5.3.2.3 Low Pressure Distribution System 377

5.3.2.4 Seismic Monitoring and Control System 377

5.3.2.5 Repair and Restoration 378

5.3.2.6 Intelligent Meters 378

5.3.3 Lessons for the United States 379

5.3.4 Research Needs 380

5.3.5 References 380

ix

The January 17, 1995 Hyogoken-Nanbu (Kobe) Earthquake

EXECUTIVE SUMMARY

INTRODUCTION

The January 17, 1995 earthquake of

magnitude 7.2 in the Japan

Meteorological Agency scale or Mw =

6.9, which struck the northwest, north,

and northeast shorelines of Osaka Bay

of Japan, was the most devastating

earthquake to affect the region this

century. The earthquake resulted in the

worst natural disaster since the 1923

Great Kanto earthquake devastated

Tokyo and Yokohama.

The earthquake resulted in more than

6000 fatalities and over 30 000 injuries.

Fire following the earthquake

incinerated the equivalent of 70 U.S. city

blocks. They together destroyed over

150 000 buildings and left about 300 000

people homeless. The economic loss of

this earthquake is estimated to reach

$200 billion, the costliest earthquake in

the world thus far, and its impact has

been felt worldwide.

Kobe and its surrounding area is about

50 km long east-west and about 1.5 km

to 6 km wide north-south with Rokko

Mountain to its north, peaking at about

1000 m, and Osaka Bay to its south.

This narrow piece of coastal plain is heavily urbanized and industrialized. It

is a modern urban setting with a population of about 15 million (about

15% of the total Japan population).

Kobe port is the third largest port in the

world and handles about 20% of Japan's

total trade. Most of the port consists of

three man-made islands: Port Island,

Rokko Island, and Maya Terminal. The

region is served by a number of modern

transportation systems, such as the bullet

trains, railways, expressways and elevated

highways, new tram systems, ferries, and

rapid transit systems. It is also served by

modern utility systems for water,

wastewater, electrical power, gas, and

telecommunications.

The earthquake brought the region's

livelihood to a standstill. Houses and

buildings were destroyed and surface

transportation systems paralyzed.

Emergency response and search and

rescue operations had to be carried out

under extremely difficult conditions.

Water line breaks cut off water and

depleted supplies for fire fighting. The

loss of electricity and telephone

communication put majority of

residences in the region into total

darkness.

The weeks and months after the

earthquake brought out further problems

for the local authorities, transportation

agencies, and utility companies. Traffic

jams became a normal part of daily

routine, for a while walking was the best

way to get from point "A" to point "B". The authorities tried to restore public

transportation systems as soon as

possible. Removing the debris from

xiii
fallen houses and buildings and damaged

highway bridges became a monumental

problem. Schooling had to be

suspended temporarily because many of

the school buildings had to be used as

shelters.

Meanwhile, crews from utilities worked

around the clock to repair broken water

lines, sewage lines, downed power and

telephone poles, and leaking gas lines.

Because of the lack of pre-earthquake

planning, often these activities had to be

carried out haphazardly. In fact, it is believed that early restoration in

electricity to some part of the Kobe City

was responsible for the ignition of

additional fires after the initial burst of

fires immediately following the

earthquake.

Reclaimed lands along the shoreline of

Kobe City settled significantly during the

earthquake. Liquefaction and lateral

spreading were the two prominent

factors contributing to the damage from

this earthquake in areas of reclaimed

ground. Restoration of the port

facilities is estimated to take 2 years to

complete. Meanwhile, goods have to be

transported to other neighboring ports

and harbors and then through surface

transportation to reach factories in

Kobe. This could turn out to cause a permanent loss of business; it remains

to be seen how much of the original'

share of business the Kobe Port can

recapture once it is again open for

traffic.

The earthquake brought out some of the

best qualities of human beings, as evidenced by the outpouring of support

and assistance from other communities.

Water trucks brought in drinking water

through mutual aid arrangement. Tens

of thousands of utility and construction

workers from all over Japan participated

in the restoration of lifelines.

Unfortunately, the earthquake also

highlighted the helpless expressions on

the faces of search and rescue workers;

something that has been witnessed in

every recent natural disaster.

This earthquake provided an unprecedented opportunity to learn

many valuable lessons that can help

prepare us to reduce the devastating

effects of future earthquakes. Many of

U.S. cities have a geographic setting

similar to the City of Kobe, i.e., a narrow strip of coastal land, soft soils

along the shore, and congested urban

buildup and transportation systems.

These cities include Seattle and Tacoma,

Washington; Long Beach, San Diego,

and San Francisco, California; as well as New York City; Boston; Charleston,

South Carolina; and Memphis,

Tennessee; all located in the eastern and

central regions of the United States.

The nature of devastation of Kobe by

this earthquake is perhaps most relevant

to the cities in the eastern and central

regions of the United States. This is because the difference between the

maximum credible earthquake and

the design earthquake is clearly veiy

large for the Kobe region of Japan; a

situation that also exists in the eastern

and central parts of the United States.

xiv
These parts of the United States may be

even more vulnerable to earthquake

damage since the urban areas in eastern

and central United States are much

older than the region where this

earthquake hit (Kobe was rebuilt after

World War II). Most of the U.S.

buildings have been constructed without

the benefit of modern seismic design,

likewise the lifeline systems. The Kobe

earthquake should serve as a wakeup to

the communities in those U.S. regions to

begin a concerted effort to reduce the

impact from future disasters.

The investigation of the Kobe area

described in this report was carried out

under the auspices of the U.S. -Japan

Cooperative Program on Natural

Resources (UJNR) Panel on Winds and

Seismic Effects. The panel's U.S. effort

is led by NIST and its counterpart in

Japan is the Ministry of Construction's

Public Works Research Institute

(PWRI).

To every member of the investigation

team, the visit to Kobe and the area

devastated by the January 1995

earthquake will be a lifelong experience.

It was through this visit that we came to

appreciate the awesome power of

nature, that we came to have direct

understanding of which mitigation

measures worked and which did not, that

we also came to feel for those families

whose lives were dramatically altered as the result of the earthquake. The visit

also provided us with another reminder

of our responsibilities to help our society

better prepare for future earthquakes.

SEISMOLOGY, GEOLOGY, AND

GEOTECHNICAL ISSUES

The Hyogoken-Nanbu (Kobe)

earthquake of January 17, 1995 occurred

in an area of complex faulting located near Awaji Island and the Hanshin area

of Japan. This area, which includes the

urban centers of Kobe City, is located

about 250 km from the Nankai trough,

which forms the boundary between the

Philippine Sea and Eurasian plates.

Coseismic crustal rupture associated with

the earthquake initiated on the Nojima

fault located on Awaji island. The

rupture extended to the ground surface

along a 9 km segment of the fault on

Awaji Island. Maximum surface

displacements of 1.7 m right-lateral,

horizontal and 1.0 m vertical were

observed. Aftershocks during the first 10 days suggest the seismic rupture

surface was between 35 km and 50 km

long. The shallowest seismicity occurred

beneath Awaji Island and downtown

Kobe City.

Most of Kobe City is built on a narrow

2 km- to 3 km-wide coastal plain

confined between Rokko Mountains and

the Osaka Bay. Soils of the coastal plain

divide into two major groups from a geotechnical perspective, natural soils

and man-made landfills. Much of the

recent growth of Kobe, however, has

been on sandy landfills that were

dumped into Osaka Bay.

The floor of Osaka Bay offshore of

Kobe is blanketed by a compressible

marine clay that existed before the

xv
modern landfills were emplaced. The

clay is up to 20 m thick in the Kobe

offshore area but it thins to about 2 m

near the natural shoreline. The water

content of the soft clay ranges from 70%

to 100% and the compression index

ranges from 0.2 to 0.6. Its shear wave

velocity is about 180 m/s.

Following emplacements of landfills,

settlements of about 4 m have been

measured on top of the upper clay

surface. Settlements are expected to

continue for many years. This has

prompted the use of pile supported

foundations for all heavy structures built

on the fill.

The first reclamation efforts filled 529

ha along the Kobe City shoreline from

1953 to 1970. Following these

reclamation efforts, Port and Rokko

Island were created. Reclamation of Port

Island started first and was done in two

phases. The first phase, which filled

436 ha, was from 1966 to 1980. The

second phase started in 1986, and

increased the size of the island by 390

ha. Rokko Island, which is 580 ha, was

reclaimed from 1973 to 1992.

The strong motion data from this

earthquake provides an exceptional set

of near source measurements of strong

shaking. Measurements at 10 sites

indicate peak ground shaking was near

or exceeded 0.5 g and reached levels

exceeding 0.8 g at two locations.

Records also show that on the average

the peak vertical accelerations were

about 62% or 2/3 of the corresponding

horizontal values. Peak vertical

accelerations that exceeded the peak

horizontal values are most evident for

sites near or on Port Island. These

larger vertical accelerations are

consistent with larger amplification

factors observed for vertical motion

above the liquefied layer on the Port

Island array.

When artificial fills were subjected to the

strong shaking of the earthquake, they

liquefied and expelled large quantities of

both sand and water. More than 17 km2 of land area was covered by vented

materials. Splash marks on walls and

other structures indicated that water

fountains typically reached 0.5 m and

reached heights of almost 2 m in a few

locations.

BUILDINGS AND HOUSES

The most serious damage was

concentrated within a narrow band about

0.5 km to 1 km either side of the fault

lines. This extended about 30 km, from

the northern tip of Awaji island, through

the central part of Kobe, toward

Nishinomiya City near Osaka. Within

this band many old wooden houses, over 30 years old, were interspersed among

commercial structures. Many of these

houses totally or partially collapsed

burying their occupants.

The walls of single family dwellings

provided little lateral load resisting

capacity, and could not support the

heavy clay tile roof load during severe ground shaking. Likewise, 2- and 3-story

dwelling structures with commercial

xvi
operations in the first story had few

interior walls to resist lateral loads,

thereby sustaining partial or total

collapse.

Major revisions to the seismic design

requirements took place in 1971 and

1981. Ductility was introduced in the

seismic design for the first time in 1981.

Many reinforced concrete buildings

constructed prior to 1981 sustained severe damage. Many buildings

sustained damage to the first story.

Shear failure of first-story columns and

collapse of soft first stories were most

common. A prominent mode of failure

of reinforced concrete multi-story

buildings was a partial or a total collapse

of an entire story at an upper level.

Many buildings that failed in this mode

were of steel-encased reinforced

concrete (SRC).

Similar to reinforced concrete buildings,

steel buildings constructed 20 to 30 years

ago sustained severe damage whereas

buildings designed and constructed

according to the 1981 Building Standard

suffered little. Welding failures at member connections contributed to

many of the building failures. Light steel

frame structures suffered member

failures, particularly diagonal bracing

members, with reduction in cross section

due to corrosion. Brittle fractures of

heavy steel columns with flange thickness

of 50 mm occurred in a post-1981 multistory complex in Ashiya city.

TRANSPORTATION SYSTEMS

Two important features of the Kobe

area had a major impact on the seismic

damage suffered by transportation

systems in the Hyogoken-Nanbu

earthquake: the coastal topography and

the surface soil conditions along the

Osaka Bay.

Many transportation routes are located

adjacent to or on top of one another.

Rail lines are also routed closely

together, with three separate rail systems

occupying the same right-of-way in some

locations. The tunnels of the municipal

subway system run beneath major urban

streets in Kobe. Cut-and-cover subway

stations collapsed during the earthquake,

causing surface subsidence.

Unfortunately this corridor lay directly

above the ruptured fault zone of the

earthquake, so all major transportation

routes in Kobe were severely damaged

by the earthquake.

Out of necessity newer transportation

routes have been constructed on

artificial fill in and around Kobe. For

example, the Wangan, or "Bay Shore"

route of the Hanshin Expressway system

rings the entire bay from Kansai

International Airport on the south to

Kobe on the north.

Highways and Bridges

The region is served by a complex

network of freeways and highways built

since the early 1960's. Damage to

highway bridges was both widespread

and catastrophic. Typical damage

xvii
included shear and flexural failures in

nonductile concrete columns, flexural

and buckling failures in steel columns,

unseated girders due to bearing failures,

and gross foundation movements due to

liquefaction. In addition, pounding

between spans occurred. Some special

structures also suffered atypical damage

such as the excessive rotation of a skew

bridge on pin-ended columns and the

loss of seismic energy dissipators in a

cable-stayed bridge due to the failure of

a wind shoe.

Most of this distress was confined to

older structures, built more than 30

years ago before the introduction of

modern seismic codes. The poor

performance of these older bridges and

elevated expressways confirms previous

lessons learned in California and

elsewhere, about the pressing need to

retrofit the existing inventory of deficient

bridges.

Some new bridges also suffered serious

damage which implies a need to

re-evaluate the design loads and

procedures in the current design

specifications.

The closure of three major expressways

in the Hanshin region has had a major

societal and economic impact on the

region. The estimated total repair cost

for one highway authority alone, the

Hanshin Expressway Public Corporation,

is $4.6 billion. Furthermore, it does not

include the loss of toll revenue while the

network is inoperative (estimated at $2

million per day) nor does it include the

indirect losses which are expected to

exceed the repair costs by the time the

system is fully operational.

Railways and Rapid Transit System

There are four electric rail service lines

between Kobe and Osaka. Two of the

rail lines are operated by Western Japan

Rail and the other two are owned by

private companies, Hanshin and Hankyu.

Most of the rail lines that run through

this corridor are on elevated

embankments and on elevated

structures. There are two guideway

systems in Kobe, the Port Liner from

Sannomiya to Port Island and the Rokko

Liner from Sumiyoshi to Rokko Island.

There are five other railways and transit

systems in Kobe including the Kobe

Kosotku, Kobe Dentetsu, Kosoku Kobe,

Sanyo Dentetsu, and the Kobe Subway.

The Kobe Rapid Transit Railway, or Kobe Kosotku, is owned and operated

by the Kobe Rapid Transit Railway

Company, Ltd. The system was

constructed between 1962 and 1968.

Underground sections were built by

means of cut-and-cover techniques.

Running tunnels are reinforced concrete

box structures with center column

support.

The Kobe Municipal Subway, or Metro,

is operated by the City of Kobe and is composed of 22.7 km of elevated,

surface, and underground railway.

All four railways between Kobe and

Osaka and two guideway systems in

Kobe were seriously damaged. It is

xviii
obvious that the number of casualties

would have been much higher if the

earthquake had occurred during the day

time or rush hour.

The inability to resist the applied lateral

load for the elevated structures which

collapsed can be attributed to a lack of

confining steel within the critical

reinforced concrete column and joint

regions. The unexpected higher ground

accelerations over a wide area caused

damage to miles of elevated structures.

Insufficient seat length caused the

Rokko Liner to lose one span. Modern

steel columns performed well with minor

local buckling.

Airports

The Kansai area is served by three

airports: Kansai International Airport,

Osaka International Airport, and Yao

Airport. The Terminal Radar Approach

Control (TRACON), which is located at Kansai Airport, controls airplanes in the area before each is turned over to the

respective control towers. Kansai

Airport was opened for service on

September 1, 1994, and primarily serves

international flights. Osaka Airport

primarily serves domestic flights and a few international flights. Neither of

these airports allows general aviation,

which is served by Yao Airport. The

Kansai airport is built on a 511 ha island

of reclaimed land in Osaka Bay. It is located 27 km southeast of the

epicenter.

Kansai control tower was well

constructed with an innovative method

of leveling the tower should it be

subjected to differential settlement. This

tower also had columns in the interior of

the cab to support the roof and resist

lateral motion of the cab, thus protecting

the windows. The columns appeared to cause little visual interference. The

cooling system for the emergency

generator was provided with a large local

water supply. The tower sustained no

damage from the low level ground

motion in this earthquake. The peak

ground acceleration measured on the

runways was less than 0.2 g and at the

building foundations less than 0.1 g.

Both administration building and control

tower at the Osaka Airport sustained

minor damage. Damage included a crack in a window in the cab of the

tower, minor damage to shear walls in

the administration building and

temporary loss of use of the elevators.

Ports and Harbors

Kobe has been one of the world's most

expensive ports to construct. Two major

man made islands, Port and Rokko

Islands, cost about $2 billion to create.

The port contains 152 berths with an

aggregate wharf length of 27 km. The

Port operates 400 dockside gantry cranes and derricks to load and unload cargo.

Most of the quay walls forming the

wharfs are sand-filled caisson structures,

although a few consist of cellular steel

sheet piles. The foundation for each

caisson was prepared by excavating the

natural silt layer on the sea floor and

replacing it with sand fill. A gravel pad

xix
was placed on the fill and then the

10 m-tall concrete caisson was lowered

into place and filled with local sandy

material. The waterside crane rail rests on the caisson. Most of the gantry

cranes have rail spans of 30.5 m, but a few of the older cranes at Port Island

and Maya Wharf have rail spans of 16 m. The 30.5 m-rail girders are supported either by a concrete slab

placed on engineered fill or a concrete

pile supported wall and the 16-m-rail

girders rest on a concrete pile supported

wall. The crane rails were not

structurally connected to each other.

Liquefaction during the 1995 HyogokenNanbu earthquake disabled the port of

Kobe. Permanent ground deformation

caused failure of quay walls and

differential displacements of crane rails

causing crane operations to stop.

Lateral spreading was restricted to the

margins of the port facilities, usually

extending less than 100 m from quay

walls. Vertical settlements of 30 cm to

50 cm were widespread inland, but did

not do great damage because of their

uniform character.

LIFELINES

Lifelines are vulnerable to natural and

man-made hazards such as earthquake,

extreme wind, flood, accident, and

terrorism. Proper performance of

lifelines is important to assure public

safety, vitality of economic activity, and

quality of life. However, lifelines and

their importance to our way of life generally are not recognized until their

failure causes deaths and destruction,

impedes emergency response following a major disaster, hinders post-disaster

recovery, or paralysis to a community.

Disruption of regional lifeline systems as the result of a major natural disaster,

such as this earthquake in Kobe, can have a profound effect on the entire

nation because of the economic

interdependence of lifeline systems and

the functions they support.

Water and Wastewater Systems

The City of Kobe water system serves 608844 households including 1.5 million

people. The system was started in 1900,

as the 7th modern water system in

Japan. The Water Department began

actively using computers in 1987,

inputting water pipe drawings and boring

log data for 4000 borings in 1988.

Water is pumped to the water

purification plants and runs by gravity to

the west at an elevation starting at 90 m

above sea level through Kobe's tunnel

system. The tunnel system operates in

the open channel flow or low pressure

regime. The first tunnel, 1.8-m diameter

and built in the 1930's, is constructed in

rock with an unreinforced concrete

lining. The second tunnel, 2.5-m

diameter, was built in the 1950's and is lined with reinforced concrete. Water

used at an elevation above 90 m

(apparently 15% of the demand) is pumped from the tunnel system.

The Kobe water system is designed to

provide both water for drinking and fire

protection. There is no dedicated water

system for fire suppression, although one

xx
was under consideration in 1993.

There are a number of cisterns located

throughout the City for use for fire

suppression. The urban area is laid out

on a 400 m by 400 m grid. Three

quadrants of the grid each has a fire

hydrant, and the fourth quadrant has a

cistern. There is one special radio

system for communication between the

water and fire departments during

emergency response situation.

Kobe Water has an earthquake

monitoring and control system in place

to isolate water from the system and to

maintain it in selected reservoirs for

drinking following an earthquake. The

system is also designed to maintain

water for fire suppression. There is no

capability, however, to isolate major

lines crossing vulnerable areas, such as

lines to the reclaimed land areas.

There are dual reservoirs at each of the

21 sites, one has an isolation valve to be

controlled following an earthquake and

the other does not. This concept allows

shutdown of one reservoir while

maintaining service should an

inadvertent shutdown signal be received.

The earthquake left one million

households without water following the

event, with only 70% restoration in 3

weeks. Water for fire suppression was

substantially exhausted after 6 hours.

The two large diameter transmission

lines carrying water from the Yodogawa

River to the water purification plants

failed in ten locations. There were no

tank failures reported for the 239 tanks

located at 119 sites. There was some

connecting piping failure at one tank.

However, it should be noted that these

tanks were in the hills surrounding the

city and in areas of relatively low ground

motion.

Nearly 90% of Kobe's water distribution

system was made of either welded steel or ductile iron pipe, both thought to be

resistant to earthquakes. This unusually

high percentage of earthquake resistant

pipe resulted from an aggressive pipeline

replacement program initiated in the

mid-1960's. Even with this in place, an

estimated 1800 pipeline failures occurred

in distribution piping. It is speculated

that much of this damage is associated

with joint separation from liquefactioninduced lateral spread.

Kobe has eight wastewater treatment

plants, three of which were damaged by

the earthquake. There are 23 pump

stations; 20 were damaged or inoperable

from power loss, building damage, or

caisson damage. Most were operable

when power was restored.

Collection system pipe is 70% concrete,

20% PVC, and 10% VCP. Kobe uses Fiber Reinforced Plastic for large

diameter pipe and PVC for smaller

diameter pipe in liquefaction areas.

The Higashinada Wastewater Treatment

Plant provides one-third of Kobe's

treatment capacity. Liquefaction or

lateral spreading failures resulting in

movement of a retaining wall 2 m to 3 m

towards a waterway dropping the entire

xxi
site an average of 1 m. The result was

devastating. A 2 m x 2 m effluent

channel separated in four places. The

control and filter buildings moved, and

equipment and piping settled as the soil

moved away from under them. The

plant was placed into temporary

operation using an open channel as the

sedimentation basin.

Gas Delivery System

The Osaka Gas Company provides gas

to more than 5.6 million metered

customers, accounting for 30% of the

total gas sales volume in Japan. Major

trunk lines, pipelines, and distribution

mains total 49 430 km. The Osaka Gas

system is comparable in size to the gas

delivery network operated by the

Southern California Gas Company,

which is the largest U.S. gas supplier

with approximately 4.6 million metered

customers and nearly 74 000 km of

transmission, distribution supply, and

distribution pipelines. Liquefied natural

gas (LNG) accounts for about 94% of

the Osaka Gas system feedstock. Most

of the supply is imported.

Three LNG terminals provide the

primary sources for distribution. Gas is conveyed regionally through a system of

major trunk lines, which operate at internal pressures of 4 MPa.

Transportation of gas also is accomplished through what is termed a "medium pressure" system of A lines, at internal pressures of 0.3 MPa to 1.0

MPa, and B lines at internal pressures of

0.1 MPa to 0.3 MPa.

The Osaka Gas system is divided into

what company personnel call "super

blocks." The eight super blocks of the

network are large areas which can be

isolated through telemeter control by

closing valves activated by compressed

carbon dioxide. Closing valves with

carbon dioxide allows for control

independent of electric power supply.

The system can be subdivided further

into about 55 "middle blocks," each of

which may provide service to hundreds

of thousands of customers. The middle

blocks must be isolated by means of

manually operated valves. The low

pressure pipeline system within the

middle blocks can be subdivided again

into sectors, each provides service to

between 3000 and 4000 customers.

There was no significant damage

reported at the Senboku and Himeji

LNG terminals, and at the gas

distribution stations.

Osaka Gas personnel reported that there

was a total of 35 and 61 repairs to

medium pressure A and B lines,

respectively. No major damage was

reported in these lines. Medium

pressure steel pipelines were subjected

to large permanent ground deformation

at several locations, but no leakage was

observed.

The low pressure distribution system

which operates at internal pressures

equivalent to 150 mm to 210 mm of

water column, or about 1.8 kPa

sustained the greatest earthquake

damage. There were 43 895 km of low

pressure lines at the time of the

xxii
earthquake. In Kobe and adjacent

communities, the low pressure system is composed predominantly of steel pipe

with threaded steel couplings, or screw

joints. A small portion of the low

pressure system, approximately 5%, is composed of polyethylene mains and

services. Some steel piping with

restrained mechanical joints and

polyethylene linings was deployed in areas of artificial fill as a seismic

countermeasure.

There was no observed failure in the

bodies of steel pipe segments, and only

36 locations of ruptured cast iron pipe

walls. There was a total of 5190 repairs

to distribution mains and branches

within city streets, compared with 10 161

damaged service lines and 11 108

locations of damage at piping attached

to buildings. There were no repairs in

polyethylene piping.

The Osaka Gas Company operates a system of seismic sensors throughout its service area to provide rapid feedback

about the likelihood of earthquake

damage to pipelines and associated

facilities. Thirty four sensors had been

installed at the time of the earthquake.

The company plans had been

implemented to install an additional 30

sensors by the end of March 1995.

About 74% of customers were equipped

with intelligent meters according to

Osaka Gas personnel. The meter is equipped with a seismic sensor triggered

by acceleration exceeding 0.2 g, a pressure sensor, and a flow rate

transducer. A microcomputer monitors

the incoming signals and shuts off flow,

if required. A lithium battery is used as a power supply. Gas company personnel

report that the intelligent meters appear

to have functioned as intended.

Electric Power

Established in 1951, the Kansai Electric

Power Company is one of the nine major

investor-owned electric utilities in Japan.

The company serves four major cities:

Osaka with 2.5 million, Kyoto with 1.39

million, Kobe with 1.47 million, and

Nara with 0.35 million people. In the

earthquake impacted area the

transmission and sub-transmission

voltages are 500 kV, 275 kV, 154 kV,

and 77 kV. The 500 kV system lies

primarily to the north, northeast, and

east of the earthquake impacted area. These lines cany power from major

nuclear generating stations on the Japan

Sea, and large pumped storage facilities.

There are eight fossil-fuel generating

facilities on Osaka Bay east of the

epicenter. The primary distribution

voltage is 6.6 kV, although there are some 22 kV and 33 kV distribution lines.

Aerial lines and towers are used for

most high voltage lines, although there

are more 275 kV cables in urban areas than is typical for 230 kV in California.

Distribution is primarily aerial on

concrete poles, with cables in steel

conduit in central business areas like

Kobe.

The overall performance of power

systems, as measured by the extent and

duration of disruption, was very good.

xxin
Service was restored to most customers

who could use power about one day

after the earthquake. This earthquake

indicated that if sites are subject to

liquefaction, it is important that flexible

bus be used with liberal, but manageable

slack. Transformer anchorage frequently

failed. There was relatively little damage to high voltage substations as compared to what was observed in the

Loma Prieta and Northridge

earthquakes. The subsidence of

substation sites appears to have

contributed to the failure of bushings

connected to vertical conductor drops, as

little slack is typically provided. There

was uniformly high quality use of good

design and installation details in station

batteries.

Most disruption of power was associated

with the damage to the distribution

system. Spun, thin-wall concrete poles

were severely damaged by ground

vibrations, subsidence in liquefied soils,

and secondary damage when hit by

falling houses. There was extensive

damage to conduit in downtown Kobe

due to ground deformation associated

with liquefaction, but cable in the

conduit was generally undamaged.

Telecommunications

The telephone communication system is dominated by Nippon Telegraph and

Telephone Corp. (NTT), although

independent companies are now

providing long-distance services.

Welded steel conduit is exclusively used

in Japan as current measures for

improving the earthquake resistance of

conduit joints. This is in contrast to the

United States, where plastic conduit is used. Central offices are connected by

optical fiber, copper cable and

microwave trunks. Tunnels are used to

carry communication trunk lines. NTT

has two types of tunnels: bored or shielded tunnels make up 60% of the

tunnel system, and cut and cover tunnels

make up the other 40%. In addition,

there are joint utility tunnels built by the

government that have separate sections

for communication, power, and gas lines

that are paid for by a utility tax. These

tunnels are costly, but are encouraged by

the government because they reduce the

impact of surface transportation caused

by the installation of tunnels or repair of

buried lines.

There was relatively little service-disrupting damage to central

offices. Emergency power was disrupted

due to the loss of water at central

offices, which caused the loss of service

to 285 000 lines. There was extensive

damage to outside plant. A massive

restoration effort was required to restore

service and the restoration of conduit

and other facilities continues, two

months after the earthquake. Total cost

of damage from the earthquake is estimated by NTT at $3 billion.

Hospitals

The investigations of hospitals focused

on the impact of lifeline disruption on

hospital operations. The Kobe Medical

College of the University of Kobe was

visited. A limited amount of

xxiv
information about the Hyogo Medical

Center was also obtained through a brief

interview.

The quality of lifeline facilities and their

installation, from an earthquake

engineering perspective, was very high as compared to U.S. installations. Few

U.S. hospitals would have a large

emergency water supply as existed at Kobe Medical College. The loss of

water had a large impact on hospital

operations. The loss of water disabled

one generator at the hospital and caused

the loss of all emergency power at another medical facility. The

dependence on gas for food preparation

was disruptive to hospital operations.

FIRES

The earthquake resulted in 148 fires in

the Kobe city area, between January 17

and 20. Approximately 660 000 in2

, occupied by more than 6900 buildings,

were damaged by fire. Due to the large

number of simultaneous fires, disrupted

water supplies and blocked roads, fire

fighting efforts were largely ineffective.

The fire spread was limited primarily by

wide roads, open spaces, noncombustible walls, fire resistive building

construction and favorable weather

conditions.

The earthquake demonstrated the

potential for significant fire damage

following an earthquake even though

favorable weather conditions kept fire

intensities relatively low and helped to

limit fire spread. New fire ignitions and

spread continued for days after the

earthquake as a result of electric power

restoration and the need for open fires

by earthquake survivors.

OBSERVATIONS AND CONCLUSIONS

Some key observations and conclusions

are summarized below.

Seismology, Geology, and Geotechnical

Issues

The earthquake reemphasized that

moderate to large earthquakes directly

beneath densely urbanized areas can

cause catastrophic loss of life and

property.

Proximity to the earthquake crustal-ruptiire zone Strong-motion recordings show

that peak acceleration values attenuated

from values greater than 0.8 g near the source zone to values less than 0.25 g at some sites at distances near 20 km on

firm soils. This rapid attenuation of

strong shaking appears to have been an

important factor influencing the

confinement of damage primarily to the

Awaji Island, Kobe City and Nishnomiya

areas.

Amplification effects of soft-soil deposits

The amplification effects of Holocene

soil deposits appear to have contributed

to increased peak amplitudes and

duration of strong shaking at many

sites. The increased levels of shaking

contributed to direct structural failures

and liquefaction induced ground failures.

Liquefaction susceptibilities of reclaimed

land and soft soil deposits From the

xxv
geotechnical viewpoint, the liquefaction

of about 17 km2 of land underlain by

artificial fill highlights' the seismic hazard

of loose sandy soils. The experience

during the 1995 earthquake reaffirmed

the proclivity of areas built on these fills for large permanent ground

deformations when they are strongly

shaken. Many artificial fills in coastal

and river areas of the United States are

similar to the loose sandy fills in Kobe,

which performed so poorly. Much

artificial land has been created in the

United States by dredging or dumping

sand into open water without

compaction. These older fill areas in

ports and harbors, both in seismically

active areas and areas of low seismicity, are vulnerable to earthquakes. As the

1995 earthquake demonstrated, this

vulnerability can extract a steep price

when these areas are strongly shaken.

Buildings

The earthquake offers an excellent

opportunity to reflect on several general

issues.

Poor performance of traditional wood

frame houses The majority of the

casualties in this earthquake were caused

by the collapse of old Shinkabe and

Ohkabe houses made of wood. They

were built primarily to support gravity

loads. Many severely damaged houses

had heavy ceramic roof tiles set on soil as bedding, which contributed a great

deal to their collapse.

Damages to older reinforced concrete

buildings Many older reinforced

concrete (RC) moment frame buildings

experienced full or partial floor

collapses. The damaged low to mid-rise

RC buildings that were observed could

easily have been U.S. buildings that were

constructed in the 1950's and 1960's,

particularly in zones of low to moderate

seismicity. The large amount of damage

that occurred in Kobe points out the

high vulnerability of these older, poorly

detailed structures. These older and less

ductile RC structures will require

significant rehabilitation to be made less

vulnerable.

Good performance in new RC buildings

No evidence of collapse in any of the

newer (post-1981) engineered RC

structures was evident. The 1981

Japanese code improvements is quite

similar to the intent of current U.S.

building codes that focus on life safety, or collapse prevention, in the one-time

severe seismic event. This earthquake is a vindication of the current code

philosophies in both countries and the

technical changes that have occurred in

those codes as a result of the RC

research since the early 1970's in both

the United States and Japan.

Performance-based design philosophy A

somewhat more subtle issue regarding

new construction is whether there should

be standards that provide better building

envelope integrity than the basic

one-event life safety standard that we

have today. The event should fuel

further debate about weighing initial

construction costs against potential

xxvi
future earthquake losses.

Avoiding stiffness or mass irregularities

Many older building collapses could be

at least partially attributed to the

presence of "soft-stories" as weak links.

Performance of steel frame structures

Although there was extensive damage in

many of these structures, particularly low

to mid-rise apartments and offices, few

collapsed and egress means were

maintained. The extensive base metal

and weld failures observed at the AHST

complex in Ashiya City echo problems

first observed in steel structures in the

United States following the January 17,

1994 Northridge earthquake.

Highways and Bridges

Lessons for bridge design in central and

eastern United States The predominant

type of bridge in Japan is the steel girder

superstructure supported by bearings on

concrete columns and foundations. This

class of bridge is also found throughout

the central and eastern United States.

Bridges in California tend to be concrete

box girders with monolithic bents and

integral abutments especially in shorter

bridges. The performance of Japanese

bridges is thus of particular relevance to

states east of the central and eastern

United States.

The difference between the maximum

credible earthquake and the design

earthquake is clearly very large for this

region of Japan, which is a situation that

also exists in the eastern and central

United States.

The closure of arterial highways and

bridges affects emergency relief and

business recovery and can have a major

economic impact on a region and its ability to survive such a disaster.

Capacity design procedures, ductile

details and generous seat widths are necessary to prevent catastrophic

collapse during large earthquakes.

Critically important structures must be

designed to a higher level of

performance than that provided by

current specifications, if full service is to

be maintained after a large earthquake.

Lateral spreading due to liquefaction can

lead to span collapse even in modern

structures with massive foundations

(caissons) and well-engineered fills.

Railways and Rapid Transit System

Damage to elevated structure sections

Rail services suffered more damage

along the elevated structure sections

than along the elevated embankment

sections. Most damage to the elevated

structures occurred at columns either at the bottom of superstructures or at a

joint region. The damage was similar to

unretrofitted column damage observed

in past California earthquakes.

Better performance of Port and Rokko

Liners The Port Liner and the Rokko

Liner were built with modern codes.

But they did suffer localized failures.

Need for systematic retrofit techniques for

RC structures With the vast amount of

elevated old RC structures in need of

repair and retrofit, systematic and cost

effective retrofit techniques is needed.

xxvii
Collapse at the Daikai Station The

failure of the Daikai Station is the first

instance of catastrophic earthquake

damage to a modern cut-and-cover

subway station. Shear distortion and

vertical accelerations apparently led to

collapse of the center reinforced

concrete columns at the Daikai Station.

The lack of significant confining steel at

failed reinforced concrete columns

suggests that attention to confinement

and ductility can play an important role

in strengthening underground structures

against earthquake effects.

Airports

Good performance of airport facilities at Kansai Airport The braced frame

structural system in the recently

completed Kansai control tower appears

to have an effective seismic design, but it has not yet been put to a severe test. The leveling system provided in the

basement of this building is an

innovative approach to provide for the

possible uneven ground settlement that

may be caused by liquefaction or

consolidation. The use of interior

columns to support the roof of the cab

in the Kansai control tower did not

appear to be a significant visual

impediment. Its use in the United

States should be explored to reduce

earthquake window damage frequently

observed in this country.

Ports and Harbors

Seventy of damage Loose sandy fills have been widely used in both the

United States and worldwide to reclaim

ground for port development and

expansion. The earthquake illustrates

once again the potential for these fills to

liquefy and generate large permanent

ground displacements when shaken by

earthquakes. It further illustrates the

ability of such liquefaction to totally

disable a port.

Ground improvement of loose sandy fills The localization of lateral spreading

around the margin of the Port and

Rokko Islands suggests that the hazard

of permanent horizontal ground

deformation can be substantially reduced

by improving only the outer margins of

these loose fills. Modern pile-supported

structures on Port and Rokko Islands

performed well.

Consideration of multi-style of design By

repeatedly using the same type of quay

wall designs that were vulnerable to

lateral spreading, operation of the entire

port was left vulnerable to this hazard.

Water and Wastewater Systems

Overwhelming Conditions Utility

decision makers need to be thinking in

terms of consequences similar to the

Kobe event. For example, what happens

when you have no records because all

utility buildings are destroyed or become

inaccessible? What happens if the plan

is to dispatch crew to isolate critical

pipelines to save water or shut off

natural gas, but the fastest way to get

there is by walking?

Water Supply for Fire Fighting The use of

monitoring and control systems should

xxviii
be considered to enable the timely

control of a water system following an

earthquake to increase the probability of

delivering water to suppress fires. Water

purveyors and fire departments should

use permanent ground deformation

mapping to identify areas where

pipelines will likely fail so that plans can be made to isolate damaged areas and/or use alternate water supplies.

Geotechnical Issues In Kobe,

geotechnical failures governed the poor

performance of the water system.

Landslides, consolidation, and

liquefaction or lateral spread stopped

the flow of water from the source; damaged two major and one small water

treatment plants; and tore the

distribution system apart.

Recovery The three Kobe Water

Department buildings storing records

were destroyed or damaged to limit access. The probability of this occurring

is very low. In the United States, we

should make sure that our resources are

distributed so that the loss of any one

facility will not substantially impact our

ability to respond to an earthquake.

Gas Delivery System

Coordination in restoration process In

Kobe, it appears that there was no prearranged coordination between gas and

electric company personnel to restore

electric service in concert with shutting

off and venting gas in areas severely

damaged by the earthquake. It appears

that early restoration of electric power in

some areas of Kobe with leaking gas

may have contributed to additional fires.

Emergency plans should be developed

and specific, formal communication

procedures should be established

between gas, electric power, water

supply, and fire department personnel.

Gas service restoration can be a timeconsuming process Restoration of gas

service can be difficult and timeconsuming and is especially critical in

winter, as it was in Kobe. It may be

advantageous to provide for remote

control and other rapid means, such as through microzonation, for isolation of

smaller, more manageable areas of the

gas system. Hazard mapping and

scenario earthquake planning can be

especially valuable to identify and isolate

troublesome areas.

Electric Power

Poor performance of high voltage bushings

Leaks and porcelain failures of

transformers and circuit breaker

bushings has contributed to the poor

seismic performance of high voltage

substation equipment in the United

States and Japan.

Flexible couplings for transformer radiators

The use of flexible couplings in piping

connections of the transformer radiator

to the transformer body may reduce

problems with leaks observed in the

United States.

Better performance of instrumentation

transformers The performance of

instrumentation transformers in Japan

xxix
appears to be better than in the United

States. Some units acted as lower

restraints to suspended wave traps, and

still performed better than those in the

United States.

Need for adequate slack At potentially

liquefiable sites, the need for adequate

slack was demonstrated. Slack needs to

be provided in vertical drops at sites that are vulnerable to subsidence.

Performance of concrete poles The use of

concrete poles appear to increase the

vulnerability of the aerial distribution

system. In the 1992 Cape Mendocino

earthquake over 600 wooden poles were

about to be replaced because they were

weakened due to dry rot, and none of

these failed.

Telecommunications

Performance of microwave towers A

striking feature about communications

towers in Japan is their mass

construction considering large wind loads

associated with typhoons, compared to

those constructed in the United States.

The damage to Japanese towers suggests

that those in the United States are

vulnerable, particularly where central

offices are built on poor soil.

Effect of loss of water The loss of water

to communication facilities and its effect

on emergency power further

substantiates this vulnerability of U.S.

facilities.

Hospitals

Need for emergency water supply The loss

of water supply at Kobe Medical College

indicates that hospitals need to establish an emergency water use policy and

normal water use in hospitals is well

beyond what one could expect in

resupply after a major earthquake.

Post Earthquake Fires

Effectiveness ofpassive fire protection

Passive fire protection systems need to

be designed on a city wide basis. A

network of wide roadways would serve

as fire breaks and provide ample egress

and emergency access. Consideration

must be given to buildings which border

the egress routes and its components

such as bridges. The buildings should be

designed to withstand earthquake forces

and should be built of noncombustible

materials.

Effectiveness in using wire glass exterior

windows Wired glass exterior windows

appeared to be effective in reducing the

fire spread. These windows with small

gauge wire are common in Japan but are

rare in the United States.

Alternative water delivery systems

Alternative water delivery systems need

to be developed and utilized. One such

system might consist of caches of high

volume, diesel powered (or other

independent power supply), portable

pumps located near natural sources of

water around the city.

xxx
Fire fighting with aircraft Fire fighting

with aircraft dropping water or Class A

foam should be examined. Although

aircraft dropped water cannot attack

interior fires it may be effective on fires

in rubblized buildings. Fire fighting

from the air may be a method of

overcoming the problem of accessing the

fires due to blocked roads.

Information regarding preparation for post

earthquake fires Information necessary

for residents to prepare for postearthquake fires needs to be further

developed and disseminated to the

public.

RECOMMENDATIONS FOR

RESEARCH

Research needs in each of the technical areas are identified as follows:

Seismology, Geology, and

Geotechnology

Availability of strong-motion data set in

soft-soil deposits The large set of

recordings on Holocene soil deposits

provides a unique set of in-situ

measurements of the response of softsoil deposits at high input ground

motion levels. These data provide a

potentially important data set for

research on: (a) the location and nature

of the crustal-rupture process, (b)

development of an improved

understanding of the response of softsoil deposits at high input ground

motion levels, and (c) improved

estimates of the response of soft-soil

deposits for purposes of code revisions

and site-specific design analyses.

The extensive lateral spreading around

the margins of the artificial fills placed

in Osaka Bay provides an opportunity to

clarify the mechanism of horizontal

ground displacements associated with

soil liquefaction. The widespread

damage to engineered works should

permit documentation of details of

deformation fields associated with lateral

spreading. This understanding should

improve the design of countermeasures

to minimize the impact of liquefaction on engineered works. Areas of ground

improvement need to be documented.

Evaluation of the performance of these areas should increase confidence in our

ability to reduce the hazard from

liquefaction of sandy soils.

Buildings

Improvement of performance of existing

RC buildings The most urgent research

need for RC buildings is the extensive

research on seismic vulnerability

assessment, rehabilitation, and retrofit

for older, non-ductile RC moment frame

and shear wall buildings. Rehabilitation

techniques need to be cost-effective and

nonintrusive for building owners and

users. Research into less traditional

techniques for rehabilitation, such as supplemental energy dissipation and the use of newer structural composites,

should be conducted.

Steel frame structures The behavior of

heavy steel frame highrise structures

under strong low cycle lateral loading

should be examined. Given the wealth

xxxi
of data concerning the design

procedures, weldment details, and

material specifications for the AHST

complex in Ashiya City, research should

be conducted into the behavior of builtup steel column sections and truss

weldments under very low cycle fatigue.

This would augment research programs

already underway in the United States

following the Northridge earthquake.

Highways and Bridges

Study of bridges with strong-motion

records Conduct correlation studies on

those bridges with strong motion records

to calibrate theoretical models against

actual behavior. Valuable insight into

the performance of these two important

types of bridges would be derived from

such studies.

Case studies of steel bearings and

earthquake couplers Develop a detailed

database on the performance of steel

bearings and earthquake couplers

(restrainers) followed by case studies on

selected bridges in which these devices

failed. Results from such a study would

help determine the need for a review of

current U.S. design criteria for

connection forces and restrainers.

Study of superstructure-foundation

interaction Analyze structural response

due to large foundation movements

during liquefaction and lateral spreading

and the development of optimum

mitigation measures to minimize

structural impacts.

Performance of retrofitted bridges

Perform case studies on those bridges

that had been retrofitted before the

earthquake to determine the

effectiveness of the retrofit measures.

Development ofperformance-based design

approach Develop multiple-level

performance criteria which define

expected damage and serviceability

states for various earthquake scenarios

and the corresponding design

strategies/structural options necessary to

satisfy these criteria.

Study of bridges with steel substructures

The relatively large number of damaged

steel substructures provides an

opportunity to calibrate proposed new

methods for the seismic design of steel

bridge columns. In particular, their

capacity for ductile actions and the

identification of their limit states should

be investigated with the objective of

refining the R-factors in the U.S. bridge

codes for these components.

Railways and Rapid Transit System

Ductility study between RQ Steel, and

SRC columns Because of the low

redundancy of single column structures,

the structural layout and substructure

performance becomes more important

for those structures than for structures

with multiple column bents. Research is needed to compare the ductility between

reinforced concrete, steel and steel

reinforced concrete composite columns.

A damage index should be developed to assess the repairability of columns after an earthquake. Force levels

xxxii
encountered at collapse sites should be

compared to current U.S. design forces

to validate current designs.

Study of transient shear distortion The

severity of racking in underground

structures resulting from strong motion

with high amplitude and relatively long

periods needs to be understood better,

and the combined effects of racking and

high vertical accelerations needs

additional clarification.

Study of differential lateral movements

Site response needs to be investigated in

terms of differential lateral movements

which occur during earthquake loading

at sites with thick deposits of soft to

medium clay and loose sand. The

effects of depth and soil liquefaction on

soil shear distortion and structural

racking also need further research.

Airports

Development of methods for improving the

performance of control towers The

Kansai Airport control tower

incorporated columns in their design

that did not appear to significantly

adversely effect the functionality of the

tower. Practical methods are needed to

upgrade these towers in a way that will

not interfere with the function of the

towers.

Ports and Harbors

Better design and construction of quay

walls The extensive damage to the quay

walls that disabled the port operations

indicates that the failure mechanism of

these structures needs to be understood.

The localization of lateral spreading near

the quay walls suggests that only

portions of the fill need to be improved.

The development of such guidelines

would facilitate remedial efforts at other

ports with similar exposure.

Study of ground deformation due to liquefaction The large vertical

settlements observed in sandy fill during

the earthquake also provide an excellent

opportunity to develop a case history of

ground deformation associated with

liquefaction.

Water and Wastewater Systems

Study of water treatment plant design In

general, water treatment plants and

service reservoirs performed well. We

should study Japanese design approaches

for these facilities. Their tank designs

are somewhat different from those used

in the United States and apparently had

no damage when subject to high peak

ground acceleration.

Study of the performance of S-joint pipe

Pipelines were heavily damaged, except

that preliminary information on

performance of the ductile iron S joint

pipe indicates that it had no or few

failures. If it is confirmed, we should

introduce it to the United States. If it did not perform well, we should find out

why, and improve U.S. pipe design based on those findings.

xxxiii
Gas Delivery System

Study of interaction among lifelines Of

special importance is the relationship

between gas system disruption as a potential source of flammable substances

and the damage to and restoration of

electric power as a potential source of

ignition. There is a need to evaluate

and optimize the use of water and fire

protection relative to gas and electric

system vulnerabilities and operational

characteristics.

Performance of intelligent gas meter The

performance of the intelligent gas meter

should be investigated to provide a more

complete database with respect to the

earthquake operation and effectiveness

of seismic gas shutoff valves.

Electric Power

Study of the performance of transfoimers

and circuit breaker bushings The

performance of transformers and circuit

breaker bushings in the United States

and Japan is just the opposite of each

other. That is, in Japan circuit breaker

bushings failed due to slipping and

transformer bushings did not. Study

should be conducted to find out whether

there is a difference in design and

installation procedures in the two

countries.

Study offailure mechanism of bolted

transformers Several bolted transformers

moved, even though they appeared to

have substantial anchorage. While new

transformers are typically welded to

embedments in the United States, bolts

are often used for retrofit. The design

and actual loads on the equipment that

failed and the cause of the anchorage

failures should be evaluated.

Study of the performance of

instrumentation transformers It would be

interesting to explore the reasons for the

relatively good performance of

instrumentation transformers in Japan as compared to those in the United States.

While these components appear to be

larger in Japan, they also appear to be

supported on more rigid structures. The

differences in design and installation

should be explored.

Study of substation performance with

respect to strong-motion records It would

be veiy beneficial to review the

performance of equipment at these sites

using the response spectra for the site

and more detailed information that

derived from site conditions.

Telecommunications

Study of the performance of outside plant

There is a need to get a better

understanding of practices used for

outside plant in Japan and to review in

detail their earthquake performance.

The collection and analysis of this data

on outside plant damage can provide

insight into the outside plant in the

United States, particularly in the

Midwest where liquefaction is expected

to be a serious problem.

xxxiv
Hospitals

Review to establish guidelines for

minimum levels of service for each lifeline

There is a need to review lifeline needs

at critical facilities, such as hospitals, and

establish guidelines for minimum levels

of service for each lifeline. Alternative

facilities and equipment that can

mitigate the effect of the loss of lifeline

service should be evaluated and

guidance provided to facility designers.

Post Earthquake Fires

Passive fire protection systems There is a need to examine current construction

requirements for fire resistive buildings,

especially the protection of openings

such as windows and doorways. Special

efforts should be taken toward materials

or systems which could be retrofit to

existing structures. The concepts of fire

resistive egress corridors for cities should

continue to be investigated.

Alternative water supplies and delivery

systems Wildland fire agencies utilize a wide variety of methods to move water

. to the fire location. Their methods

should be examined for applicability to an urban conflagration.

Predictions of post-earthquake fire losses

Case studies of the fire propagation and

the fire suppression activities from this

earthquake could provide a basis for

further post earthquake fire model

development.

xxxv

CHAPTER 1 INTRODUCTION

1.1 Impact of the Earthquake

The January 17, 1995 earthquake of

magnitude 7.2 in JMA scale (Japan

Meteorological Agency) or Mw = 6.9, which

struck the northwest, north, and northeast

shorelines of Osaka Bay near Kobe, Japan, was the most severe local earthquake to

affect the region this century. The

earthquake resulted in the worst natural

disaster since the 1923 Great Kanto

earthquake devastated Tokyo and

Yokohama. Several names have been used

to refer to this earthquake, including the

Hygoken-Nanbu earthquake, the Great

Hanshin earthquake, the Hanshin-Awaji

earthquake, or simply the Kobe earthquake.

This report uses the "Hyogoken-Nanbu

(Kobe) earthquake" which is the official name now being used in Japan. It also

highlights Kobe, which was devastated by the

earthquake.

The earthquake resulted in more than 6000

fatalities and over 30000 injuries. Nearly

150 fires following the earthquake

incinerated the equivalent of 70 U.S. city

blocks. Together they destroyed over

150,000 buildings and left about 300000

people homeless. The total loss, including

direct and indirect and economic losses, of

this earthquake is estimated to reach $200

billion, making it the costliest earthquake in

the world thus far, and its impact has been

felt worldwide.

Kobe and its surrounding area is about 50

km long east-west and about 1.5 km to 6 km

wide north-south with Rokko Mountain to

its north, peaking at about 1000 m above sea

level, and Osaka Bay to its south. This

narrow piece of coastal plain is heavily

urbanized and industrialized. It is a modern

urban setting with a population of about 15

million (about 15% of the total Japan

population). It is the third largest port in

the world and handles about 20% of Japan's

total trade. Most of the port consists of

three man-made islands: Port Island, Rokko

Island, and Maya Terminal. The region is served by a number of modern

transportation systems, such as the bullet

trains, railways, expressways and elevated

highways, new tram systems, ferries, and

rapid transit systems. It is also served by

modern utility systems for water, wastewater,

electrical power, gas and

telecommunications.

The earthquake brought the region's

livelihood to a standstill. Houses and

buildings were destroyed and surface

transportation systems paralyzed.

Emergency response and search and rescue operations had to be carried out under

extremely difficult conditions. Water line

breaks cut off water for fire fighting. The

loss of electricity and telephone

communication put majority of residences in the region into total darkness.

The weeks and months after the earthquake

brought out further problems for the local

authorities, transportation agencies, and

utility companies. Traffic jams became a normal part of the daily routine and for a while walking was the best way to get from

point "A" to point "B". The authorities tried to bring public transportation systems back

to functioning as soon as possible; however,

removing the debris from fallen houses and

buildings and damaged highway bridges

l
became a monumental problem. Schooling

had to be suspended temporarily because

many of the school buildings had to be used

as shelters.

Utility crews worked around the clock to repair broken water and sewage lines, down

power and telephone poles, and leaking gas

lines. Because of the lack of pre-earthquake

planning, often these activities had to be

carried out haphazardly. In fact, it is believed that early restoration in electricity to some parts of Kobe City was responsible

for the ignition of additional fires after the

initial burst of fires immediately following

the earthquake.

Reclaimed lands along the shoreline of Kobe

City settled significantly during the

earthquake. Liquefaction and lateral spreading were the two most prominent

factors contributing to the damage from this

earthquake in areas of reclaimed ground.

Restoration of the port facilities is estimated

to take a couple of years to complete. Kobe

was a hub port. Some of hub business went

to Hong Kong and Seoul, Korea.

Meanwhile, goods have to be transported to other neighboring ports and harbors and

then through surface transportation to reach

factories in Kobe. This could turn out to be

a permanent loss of business; it remains to be seen how much of its original share of

business the Kobe Port can recapture once it

is again open for traffic.

The earthquake also brought out some of

the best qualities in human beings, as evidenced by the outpouring of support and

assistance from other communities. Water

trucks brought in drinking water through

mutual aid arrangements. Tens of

thousands of utility and construction workers

from all over Japan participated in the

restoration of lifelines. Unfortunately, the

earthquake also highlighted the helpless

expressions on the faces of search and

rescue workers; something that has been

witnessed in every recent natural disaster.

This earthquake was the first earthquake in recent history that occurred directly

underneath a modern urban city and

resulted in unprecedented damage and

economic loss. Nevertheless, it provided an unprecedented opportunity to learn many

valuable lessons that can help prepare us to reduce the devastating effect from future

earthquakes.

Exactly one year previous to this earthquake,

the Northridge earthquake occurred in

Southern California with a similar

magnitude (1VL, = 6.8). The epicenter of the

Northridge earthquake was about 30 km

northwest of downtown Los Angeles. The

occurrence of these two earthquakes in a span of one year offered a unique chance to compare and contrast the impact of an

earthquake on the built environment

developed by two different countries, half a globe apart. Many of our cities have a geographic setting which is similar to the

City of Kobe, i.e., narrow strip of coastal

land, soft soils along the shore, and

congested urban buildup and transportation

systems. These cities include Seattle and

Tacoma, Washington; San Francisco Bay,

Long Beach, San Diego, California; along

the west coast; as well as New York City;

Boston, Massachusetts; Charleston, South

Carolina; and Memphis, Tennessee; all located in the eastern and central regions of

the United States. The nature of

devastation on Kobe by this earthquake is perhaps even more relevant to the cities in the eastern and central United States. This

is because the difference between the

maximum credible earthquake and the

design earthquake is very large for the Kobe

region of Japan; a situation that is also

considered to exist in the eastern and central

2
parts of the United States. Bridges in these

parts are more like those in Japan than

those in Califorynia, therefore the

performance of Japanese bridges is of

particular relevance.

Adding to the vulnerability of these regions

is the fact that urban areas in eastern and

central United States are much older than

the region where the earthquake hit (Kobe

was rebuilt after World War II). Most of

the buildings and lifeline systems were

constructed without the benefit of modern

seismic design. The Kobe earthquake can

serve as wakeup call to the communities in

these U.S. regions to begin a concerted

effort to prepare their communities to reduce the impact from future disasters.

1.2 Overview of Report

After the earthquake, the National Institute

of Standards and Technology's Building and

Fire Research Laboratory (BFRL)

dispatched an advance team of three BFRL

members, followed by a larger team of 18

members made up of individuals from a number of federal agencies and others

affiliated with national earthquake

engineering research centers. The teams were to observe, document, and summarize

important lessons from this earthquake.

These lessons can be utilized to mitigate the

potential tragic impact of future earthquakes on urbanized communities around the world,

especially urban centers in seismic-prone

areas of the United States.

This investigation was carried out under the

auspices of the U.S. -Japan Cooperative

Program on Natural Resources (UJNR)

Panel on Winds and Seismic Effects. The

panel's U.S. effort is led by NIST and its counterpart in Japan is the Ministry of

Construction's Public Works Research

Institute (PWRI). It was the extraordinary

efforts of the colleagues at PWRI and its sister agencies in Japan that made the

team's investigation trip a success.

The 18-member team was in Japan from

February 12 to February 18. The

investigation was carried out by dividing the

Team into five groups, each focusing on one

or two special technical areas. These groups

were:

- Seismology/Geology

- Buildings

- Transportation

- Lifeline/Geotechnology

- Fire

Team members and their assignments are

given below:

- Seismology/Geology

Roger Borcherdt, Thomas Holzer

- Buildings

William Stone, John Hayes,

H.S. Lew, E.V. Leyendecker,

Jack Moehle, M.P. Singh,

James Wilcoski

- Transportation Systems

James Cooper, Ian Buckle,

Michael Whitney, Li-Hong Sheng,

Andrew Taylor

- Lifelines/Geotechnical

Riley Chung, Donald Ballantyne,

Thomas Holzer, Thomas O'Rourke,

Anshel Schiff

- Fires

Daniel Madrzykowski, Edward Comeau

The team was briefed by staff of the hosting

agencies upon their arrival. They then

launched a three-day intensive field

investigation, working together with their

Japanese colleagues.

3
To every team member, the visit to Kobe

and the area devastated by the January 1995

earthquake will be a lifelong experience. It was through this visit that we came to appreciate the awesome power of nature,

that we came to have direct understanding

of what mitigation measures worked and

what did not, that we also came to feel for

those families whose lives were dramatically

altered as the result of the earthquake. The

visit also provided us with another reminder

of our responsibilities to help our society

better prepare for future earthquake events.

The report is divided into seven chapters.

Chapter 2 addresses issues related to seismology, geology, and geotechnology.

Chapter 3 assesses the performance of

various types of buildings, old and new. Chapter 4 takes a close look of the

performance of different types of

transportation systems. Chapter 5 examines

the impact on the community by the

disruption of utility systems; water and

wastewater, gas, electric power, and

telecommunications. It also reviews the

performance of hospitals in Kobe. Chapter

6 studies the operation of fire suppression

following the earthquake. And finally,

Chapter 7 summarizes the lessons and

conclusions learned from the investigation

and lists research that the earthquake

community should undertake in order to learn from this earthquake to reduce future

losses.

4
CHAPTER 2

SEISMOLOGY, GEOLOGY, AND GEOTECHNICAL ISSUES

2.1 Source Characteristics

The Hyogoken-Nanbu (Kobe) earthquake of

January 17, 1995 (5:46:52 JST) occurred in an area of complex faulting located near

Avvaji Island and the Hanshin area of Japan

(34.607 N, 135.043 E, depth 14.3 km; Japan

Meteorological Agency, JMA). The area which is near the urban centers of Kobe City

and Osaka is located about 250 km from the

Nankai trough, which forms the boundary

between the Philippine Sea and Eurasian

plates (Figure 2.1.1). The earthquake of

magnitude 7.2 (JMA) is the most severe earthquake to affect the region this century.

The largest previous earthquake near Kobe

City was a magnitude 6.1 which occurred in 1916 on or near the same fault. Other large

but distant earthquakes occurred in 1944

and 1946 along the plate boundary (Figure

2.1.1). Numerous faults known to be active

in the Quaternary extend throughout the

affected region (Figure 2.1.2). However,

prior to January 17, 1995 the area was

characterized by relatively low seismicity

compared with areas near the plate

boundaries (Figure 2.1.1). This 1995

earthquake having occurred at considerable

distance from the plate margin, can be

considered an intraplate event.

Coseismic crustal rupture associated with the

earthquake initiated on the Nojima

fault located on Awaji island. The rupture

extended to the ground surface along a 9 km

segment of the fault on Awaji Island.

Maximum surface displacements of 1.7 m

right-lateral, horizontal and 1.0 m vertical were observed [T. Masaharu, personal

communication, 1995]. No surface rupture

associated with the fault system had been

confirmed in Kobe City.

Aftershocks during the first 10 days suggest

a rupture surface extending between 35 km

and 50 km. Comparison of the seismicity

pattern with mapped surface faults suggests

that the rupture zone extends about 46 km

from about 19 km southwest of the epicenter

to about 27 km northwest of the epicenter.

The aftershock locations suggest the rupture zone slightly increases in average depth to the northeast. The shallowest seismicity

occurred beneath Awaji Island and

downtown Kobe City.

Source rupture characteristics inferred from

teleseismic and regional data by Kikuchi [1] suggest three subevents (Figure 2.1.3, Table

2.1.1). The subevents are inferred to have

moment magnitudes of 6.8, 6.3, and 6.4 and

predominantly strike-slip source mechanisms.

Relative locations of the subevents (Figure

2.1.3) suggest the third subevent is located

beneath Kobe City near the region of

shallow seismicity apparent in the aftershock

distribution. The source mechanism inferred

by Kikuchi suggests that rupture for the first subevent was bilateral, then the rupture

proceeded unilaterally with the two

subsequent events in a northeasterly

direction beneath Kobe City. Duration of

total rupture is about 11 seconds with

average depth inferred at 8 km. Hypocentral

depth or depth of rupture initiation is 14.3

km.

Comparison of source characteristics for the

Loma Prieta (Ms 7.1, Mw 6.9) and

Northridge (Ms 6.8, Mw 6.7) earthquakes

suggests the Hyogoken-Nanbu earthquake

(Ms 7.2, Mw 6.9) is about the same

5
magnitude, but slightly longer rupture

duration (11 seconds as opposed to 6 to 8 or

9 seconds for the other events). The rupture

mechanism is predominantly strike slip or

horizontal for the Hyogoken-Nanbu

The rupture mechanism for the

Hyogoken-Nanbu Earthquake is

predominantly strike-slip or

horizontal compared to relatively

larger vertical motion associated with

reverse and thrust faulting for the

Loma Prieta and Northridge

Earthquake.

earthquake compared to relatively larger

vertical components of motion associated

with reverse and thrust faulting for the

Loma Prieta and Northridge earthquakes.

The average depth of rupture and

hypocentral depth for the Hyogoken-Nanbu

earthquake are less than those for Loma

Prieta and Northridge earthquakes. Rupture

for the Hyogoken-Nanbu earthquake

reached the surface on Awaji Island and

may have come within 4 km of the surface

beneath Kobe City. Rupture was inferred

not to extend closer than 6 km to 8 km of

the surface for the Loma Prieta and

Northridge events.

2.2 Regional Geologic Stratigraphy

Southwestern Japan is geologically divided

into the "Inner Zone" and "Outer Zone" by

the east-west trending Median Tectonic

Line, a major structural and lithologic

geologic boundary. Kobe lies in the Inner

Zone about 60 km north of the line. The

geology and geologic history of the Kobe

region have been described by Huzita and

Kasama [6, 7, 8] and Huzita and Maeda [9].

Basement rocks of the Inner Zone chiefly

consist of Paleozoic and Mesozoic

sediments. In the Kobe region, these

sediments are intruded by large bodies of

Late Cretaceous granite and granodiorite.

These intrusive rocks compose the mountain

massif north of Kobe. They consist of the

Nunobiki Granodiorite, a medium-grained

hornblende-biotite granodiorite, and the

Rokko Granite, a coarse to fine-grained

biotite granite with pinkish feldspar.

Downwarping within the Inner Zone during

the Cenozoic created sedimentary basins

bounded by the basement rocks. Kobe sits on the northwestern margin of one of these

basins, the Osaka Basin (Figure 2.4.1). This

area has subsided at a high rate throughout

the Plio-Pleistocene and consequently has

accumulated a thick sequence of nonmarine

and marine sediment. The Osaka Basin is superimposed on an older large depressional area within the Inner Zone that contains

sediment of the Miocene Kobe Group.

Formations within this group sporadically cover the uplifted mountainous areas and

presumably are the basal part of the

sediments filling the Osaka Basin. Members

of the Kobe Group range from lacustrine to pyroclastic deposits.

The Quaternary Osaka Group sediments

and the overlying alluvium, and the geologic

units filling the Osaka basin, are of

particular engineering significance in the

Kobe area because they underlie most of the

urban and industrial development. These

sediments are exposed along the foot of the

Rokko Mountains and thicken abruptly

toward the subsurface of Osaka Bay. They

are more than 600 m thick. The Osaka

Group is divided into three subgroups,

Lower, Middle, and Upper. These subgroups

6
unconformably overlap each other. The

Lower Subgroup is of Pliocene age and

contains primarily lacustrine facies. The

Middle Subgroup is of early to middle

Pleistocene age, and contains alternating

marine and nonmarine sediment. It unconformably overlies the Lower Subgroup.

The Upper Subgroup also locally

unconformably overlies the Middle

Subgroup. It contains 50-m-thick gravel beds

intercalated with marine clay beds. The

Upper Subgroup, which is middle

Pleistocene in age, is believed to have been

deposited during marine transgressions that

buried an erosional surface incised into the

Middle Subgroup.

The Osaka Group is overlain by up to approximately 80 m of Late Pleistocene and

Holocene alluvium that was deposited in two

cycles of deltaic sedimentation. The alluvium

in the eastern part of the Osaka Basin

beneath the Osaka Plain consists of two

coarse-grained layers separated by a marine

clay which reaches a thickness of 10 m. The

clay bed was deposited during the Holocene

global rise in sea level that ended about

6000 years ago, which is known in Japan as the Jomon Transgression. The underlying

coarse-grained material is believed to have

been deposited following the last major

regression before the Jomon Transgression.

Much of the coast in the Kobe and Osaka

regions was reclaimed from Osaka Bay by

filling. Significant land reclamation occurred

in the Osaka region before 1868 and has

continued to the present. Land reclamation

along the Kobe shoreline occurred later,

primarily after 1953. Landfill in the Kobe

region is from quarries in the weathered

Rokko Granite and the Kobe and Osaka

Groups.

2.3 Geotechnical Overview - Kobe City

Area

Most of Kobe City is built on a narrow 2-km

to 3-km-wide coastal plain. The landward, or

northern, margin of the coastal plain is the

Rokko Mountains, and the shoreward

margin is Osaka Bay. Soils of the coastal

plain divide into two major groups from a geotechnical perspective, natural soils and

man-made landfills. The natural soils range

from clays to gravels. A lot of the recent

growth of Kobe, however, has been on sandy

landfills that were dumped into Osaka Bay.

In the Kobe area, the predominant rock of

the mountain is granite. The granite is intensely sheared and deeply weathered.

Figure 2.3.1 is a generalized soils map of the

Kobe area. The inner part of the Kobe

coastal plain is underlain by an

approximately 2-km-wide zone of soils that were deposited by the streams that discharge

from the Rokko Mountains. Near the

modern stream channels, soils tend to be

coarser grained, frequently containing beds

of stream gravels. These stream channel

deposits range from 10 m to 20 m in thickness. Interchannel areas are underlain

by both sandy and clayey deposits. On their

southern margin, these alluvial deposits are truncated by a prehistoric shoreline that

roughly parallels the modern shoreline. This

shoreline is marked by a 4-m-high erosional

scarp. The erosional scarp was cut at the

end of the Jomon marine transgression into

Osaka Bay. Bayward of this old shoreline is an approximately 1-km-wide flat plain that is underlain by alternating littoral sands and

lagoonal clays. These sands and clays, which

are only a few meters thick, represent postJomon deposition and progradation of the

coastal plain.

The floor of Osaka Bay offshore of Kobe is blanketed by a compressible marine clay that

7
was deposited during the Jomon

transgression. The clay is up to 20 m thick in

the Kobe offshore area, but thins to about

2 m near the natural shoreline that existed

before the modern landfills were emplaced.

The base of the marine clay layer slopes

gently bayward (Fig 2.3.1). The water

content of the soft clay ranges from 70% to 100 % and the compression index ranges

from 0.2 to 0.6. Its shear wave velocity is about 180 m/s. The soft clay is underlain by

a complex interbedded gravel, sand, and clay

sequence. This sequence was deposited

during the low stand of sea level before the

Jomon transgression as indicated by multiple

layers of peat that have been dated by

radiocarbon. They are correlative with the

sediments of the inner coastal plain. The

thickness of this sequence ranges from 20 m

to 40 m in the Kobe Harbor area. Field

blow counts are highly variable in this sequence, ranging from 10 to 50. Another

marine clay, presumably representing a preJomon sea transgression, underlies the sand

and clay sequence. It is about 20 m thick.

Although its water content is slightly lower

than the upper marine clay, 40% to 55%,

field measurements of the vertical

distribution of consolidation contributing to land-surface settlements on Port Island

indicate that approximately 40 percent of the

total settlement was caused by compression

of the lower clay layer. Figure 2.3.2 shows a representative boring log from the harbor

area.

The compressibility of the marine clays has

created two problems for reclamation and

construction. Following emplacements of

landfills, settlements of about 4 m have been

measured on top of the upper clay surface.

Because of the low permeability of the clay

layers, settlements are expected to continue

for many years. This has prompted the use

of pile supported foundations for all heavy

structures built on the fill.

The fill used to reclaim ground was obtained

from outcrops of the Kobe and Osaka

Groups and weathered granite in the

adjacent Rokko Mountains. Fill was

excavated from several large scrapping areas

east and west of Kobe. The first reclamation

efforts filled 529 ha along the Kobe City

shoreline from 1953 to 1970. Following these

reclamation efforts, Port and Rokko Island were created. Reclamation of Port Island

started first and was done in two phases.

The first phase, which filled 436 ha, was

from 1966 to 1980. The second phase started

in 1986, and increased the size of the island

by 390 ha. Rokko Island, which is 580 ha, was reclaimed from 1973 to 1992.

Construction of Port Island is described by

Nakakita and Watanabe [12]. Sand fill was dumped in standing water that had an

average water depth of 12 m. Filling

continued to an elevation of about 4 m

above water level. The upper and lower

parts of the fill were placed using different

techniques. The lower part of the fill was dumped into standing water from a trapbase barge with no compaction effort to within 2 m of high water level. It was

created in 2 m to 4 m thick layers. The

upper part of the fill was emplaced by

scooping from barges that were moored to the quay wall, transporting to the interior of

the island by a movable conveyor, and

spreading with modest compaction by

rolling. No significant effort was made

during reclamation to compact the sandy fill to increase its liquefaction resistance.

Preearthquake field blow counts typically

ranged from 5 to 10.

Most of the multistory buildings on Port

Island were built on piles to reduce postconstruction settlement. For some of the

single-story buildings, slab foundations were

used and the fill was improved by vibrocompaction. This technique increased field

8
blow counts from an average of about 10 to 22 [8].

2.4 Strong Ground Shaking

The Hyogoken-Nanbu earthquake generated

an outstanding set of strong motion data.

The data were recorded on stations installed

and maintained by a variety of private,

government, and university affiliated

agencies. Data assimilation and distribution

is provided by each agency with coordination

provided for several of the agencies and

organizations by The National Research

Institute for Earth Science and Disaster

Prevention of the Science and Technology

Agency. All of the data and results reported

here have been derived from information

supplied by the various agencies and the

"Prompt Report on Strong Motion

Accelerograms No. 46." A conscious effort

has been made to report the results

accurately with appropriate credit to the

agencies, which made this outstanding data

set possible. Any omissions or inaccuracies

are not intentional, but some are sure to

exist due to language translation difficulties. This compilation is intended to provide an

overview of this excellent data set with the

understanding that additional and more

accurate information should be incorporated

to improve the result as it becomes

available.

2.4.1 Strong Motion Recordings

Locations for the strong-motion stations,

superimposed upon the 1:1000000 scale

geologic map are shown in Figure 2.4.1. The

geologic map was derived digitally from the

published map for Japan in digital format on CD-ROM. Coordinates for the stations are given in Table 2.4.1. Coordinates for some

stations were provided by the agencies and

for others, inferred from projected map

images. The locations inferred from map

images are considered least accurate and

should be updated, when additional

information becomes available. Projection

of available maps is expected to have

introduced location errors in general less than 100 m; however, other sources of error may have contributed to larger uncertainties

for some sites.

Station identification and various measures

of distance and peak amplitude data are tabulated (Table 2.4.1). Measurements

exceeding full scale at two stations are

indicated. Measurements reported by the

Committee on Earthquake Research and

Observation in the Kansai region were

detected with velocity transducers. Peak

accelerations reported by the Railway

Technical Research Institute [10] and Osaka

Gas represent the maximum value of the

vectorial sum of the two perpendicular

horizontal components. Other agencies

report the maximum value of the three

orthogonal components, while others report

the maximum value of only the horizontal

components. An effort has been made to tabulate peak horizontal values (PGA in Table 2.4.1) as reported by the individual

agencies. It is not possible at this writing to resolve all of the differences in reported

values; rather, resolution of these differences

as additional information becomes available

is needed to reduce uncertainty.

Conclusions derived from these data should

account for variations due to differences in reported values, differences in the types of

instrumentation, and possible uncertainties

in station locations.

The strong-motion data from the HyogokenNanbu earthquake provides an exceptional

set of near source measurements of strong

shaking. The mapped locations of the

stations indicate that 20 measurements are

within 20 km of the surface projection of the

9
inferred rupture surface. Twelve of the

stations are within about 10 km. About 60%

of these three-component measurements are

located on relatively soft soil deposits of

Holocene age. Measurements at 10 sites indicate peak ground shaking was near or exceeded 0.5 g and reached levels exceeding

0.8 g at two sites. The measurements

represent the first extensive set of near- source measurements on soft soils. As such,

they provide an important data base for

inferring strong shaking on soft soils near

the source of future strike-slip earthquakes.

The strong motion data from this

earthquake provides an exceptional

set of near source measurements of

strong shaking. Measurements at 10

sites indicate peak ground shaking

was near or exceed 0.5 g and reached

levels exceeding 0.8 g at two

locations.

Record sections showing the north-south,

east-west, and vertical components of

motion as recorded at stations located at increasing distance from the fault are shown

in Figure 2.4.2. These recordings, shown

with the same amplitude scale, indicate a well-defined velocity pulse near 1 second

period. They suggest that the peak

amplitude of ground velocity decreases

rapidly within the first few kilometers of the

projected surface rupture, with the duration

of shaking extended from about 11-15

seconds for a site on Pleistocene deposits

(KC-KBU) near the source to more than 60

seconds at several sites on Holocene soil deposits (see e.g. sites KC-FKS, KC-YAE,

KC-SAS).

Acceleration, velocity and displacement time

histories as derived by Nakamura [13] for

four locations are reproduced in Figures

2.4.3a through 2.4.3d. These analyzed

versions illustrate effects of source rupture, wave propagation and local geology on the

resultant motions. Corresponding response

spectra are provided by Nakamura [13].

The acceleration time histories recorded at the Kobe Ocean Meteorological Station JMKBM) are shown in Figure 2.4.3a. The peak

acceleration amplitude of 818 gal on the

north-south component is one of three

recording sites near the source region for

which motions exceeded 0.8 g. The

measurements at the JM-KBM site were

obtained using accelerometers and 16 bit

digital recorders (K. Ohtani, personal

communication, 1995). These recordings were obtained on a concrete pier inside a

single story concrete building. The building

is located atop a hill with a steeply dipping

slope near the building. The station is located near the boundary of Holocene and

Pleistocene deposits. Inspection of the site revealed a collapsed brick wall outside the

instrument structure, but relatively minor

amounts of damage to structures located at the base of the hill. Detailed studies to infer

the role of topographic amplification at this

site are needed.

Response spectra were provided by the

Building Research Institute for several

significant earthquake recordings (Figure

2.4.4 a, b, c) . They show that the JM-KBM

spectra are greater than the other spectra in

the period band 0.8 seconds to 2.0 seconds.

Comparison of the spectra with those used

for tall building design in Japan (Figure

2.4.4c) shows that the JM-KBM spectra

exceed the design spectra in the period band

0.25 seconds to 2.0 seconds by about a factor

of 2 at periods near 1 second.

10
Measurements obtained from a threecomponent vertical borehole array of sensors

located on Port Island at a distance of about

4 km from the projected surface rupture are of special importance. They provide

measurements of shaking at the ground

surface and at depths of 12 m, 27 m, and

79 m. With liquefaction occurring at this

site, these measurements provide an

exceptionally important data set for inferring

the in-situ response characteristics of soils at ground-motion levels sufficient to induce

failure. Receipt of the digital recordings will permit a thorough investigation of this important set of recordings by many

investigators. Some preliminary observations

follow.

Ground motion measurements obtained on

the vertical array located on Port Island are shown in Figure 2.4.5. This figure also gives

the simplified geologic log and velocity

profiles for the site. The site is underlain by

about 13 m of fill, which in turn is underlain

by at least two thick layers of clay and

several layers of interbedded sands and

clays. Depth of bedrock at the site is thought to exceed 100 m.

Peak acceleration, velocity and displacement

values inferred at the various depths

(Figures 2.4.6a, b, c) reveal several effects of

the soil deposits on resultant ground

motions. Horizontal motions at the surface

above the liquefied layer show a marked

reduction in high-frequencies, but a

significant amplification of low frequency

motion. The peak horizontal accelerations

increase slightly as they propagate upward

toward the bottom of the liquefied layer, but

are reduced by factors of 1.7 and 1.9 in the

north-south and east-west directions

respectively, upon reaching the surface.

Peak horizontal velocities atop the liquefied

layer are comparable to those at the bottom

of the layer, which are larger than those at

depth by factors of 1.7 and 1.3. Peak

displacement values inferred at the surface are about 1.5 and 1.9 times larger than

corresponding values measured at a depth of

79 m.

Each measure of vertical motion

(acceleration, velocity and displacement) is larger at the surface than at depth. The

vertical motions probably are predominantly

dilatational energy. The various measures of

vertical motion are amplified by the

liquefied layer by factors of 1.0 for

acceleration, 1.9 for velocity, and 1.6 for

displacement.

The shear-wave velocity profile shows that

the velocity of the near-surface fill, clay, and

interbedded sands and clays within the first 30 m of the surface range between 170 m/s,

210 m/s and 245 m/s, resulting in an average

shear velocity to a 30 m depth of 196 m/s.

These velocities clearly illustrate that the

upper shear-wave velocity limit of 183 m/s as

it has currently evolved for consideration in the proposed NEHRP and UBC site definitions should be reinstated at a minimum of 200 m/s as initially proposed

[1]. Otherwise, soft-soil sites with

interlayered sands and clays with a high

failure potential, such as this site, will be

inappropriately classified.

The excellent set of recordings obtained on

the Hagashi-Kobi Cable stayed bridge are provided in Appendix 2. A.

2.4.2 Attenuation

Peak horizontal accelerations as reported for

the Hyogoken-Nanbu earthquake (Table

2.4.1) are plotted versus the closest distance

to seismogenic rupture approximated to be

at a depth of about 4 km beneath Kobe City

(Figure 2.4.7). Peak horizontal accelerations

from the Northridge earthquake with a

11
minimum depth to seismogenic rupture of

6 km are superimposed. Also superimposed

are attenuation curves developed by Boore

et al. [5] and Campbell and Borzognia [4].

Velocity measurements from Port

Island vertical array illustrate that

the upper shear wave velocity limit of

183 m/s, as it has currently evolved

for consideration in the proposed

NEHRP and UBC site definitions

should be reinstated at a minimum

of 200 m/s as initially proposed.

The peak values for the Hyogoken-Nanbu

earthquake tend to be less than those for the

Northridge earthquake for sites within 4 km

to 20 km of the seismogenic source, but

greater at distances exceeding about 30 km.

These differences in amplitude are roughly

consistent with differences in source mechanism and types of geologic site conditions. The source mechanism for the

Northridge earthquake is predominantly

vertical movement on a reverse fault. Such

source mechanisms typically generate higher

peak accelerations near the source than

comparable sized strike-slip mechanisms.

The geologic conditions beneath a majority

of the recording sites for the HyogokenNanbu earthquake are soft-soil (Holocene)

deposits with higher amplification

capabilities for ground motions near one

second period than the stiff Pleistocene

deposits beneath many of the recording sites for the Northridge earthquake.

Consequently, the high frequency motions

near the source might be expected to be

larger for the Northridge earthquake, but

the longer period motions at some distance

from the source might be expected to be

larger for the Hyogoken-Nanbu earthquake.

The peak acceleration values plotted as

linear function of distance (Figure 2.4.8)

emphasize the rapid decrease in peak

acceleration values with distance. The

recent attenuation curves derived by Boore,

et al.[5] when extrapolated to soft

soils using an average shear-wave velocity of

200 m/s fit the data quite well. Peak values

observed at sites in a +_ 22.5 degree window

centered along strike with apex at the

epicenter are superimposed on those

observed in a + 67.5 degree window

centered at the epicenter perpendicular to

strike. Similar trends in each data set suggest

that a significant directivity effect is not

apparent in these two samples of peak

acceleration values. However, a similar

comparison of peak velocity values reflecting

the mid-period characteristics of the ground

motion might be expected to yield a

different result.

Comparison of the peak vertical acceleration

recorded at each of the sites with the peak

horizontal (Figure 2.4.9) shows that on the

average the peak vertical accelerations are about 62% or 2/3 of the corresponding

horizontal values. Peak vertical

accelerations that exceed the peak horizontal

values are most evident for sites near or on

Port Island (MC-PRI, MC-PIA). These

larger vertical accelerations are consistent

with larger amplification factors observed for

vertical motion above the liquefied layer on

Port Island array.

2.4.3 Amplification Effects of Soft-Soil

Deposits

The geologic classification of the sites shown

in Table 2.4.1 provides a basis for a preliminary evaluation of the effect of local

site conditions on recorded peak

accelerations. The geologic classification

12
was inferred from superposition of the

strong-motion station location coordinates on the 1:1,000,000 scale geologic map of

Japan. The resultant classification is dependent on both the accuracy of the

station coordinates and the published map

scale. Consequently, the geologic

classification for sites inferred from map

projections and associated results must be

regarded as preliminary.

Observations from this earthquake

suggest that amplification factors

currently being suggested for the

NEHRP and UBC code provisions

should be modified so as to reduce

the influence of nonlinearity on site

factors for which the potential for

ground failure is low.

Site-specific amplification factors were computed for each site by normalizing the

peak values by corresponding peak values

observed at the nearest station on rock or

firm alluvium at seismogenic-rupture

distances (SR-Dis, Table 2.4.1) of about

4 km, 25 km, 50 km and 75 km in 45 degree

azimuthal windows centered along strike of

the fault with apex at the epicenter. The

amplification factors also are normalized by

the reciprocal ratio of the seismogenicrupture distances for each site. Sites for

normalization were chosen from those for

which coordinates had been provided by owner agencies. If chosen normalization

sites were not on rock [SC-Ib, 2], then

corresponding average amplification factors were used to adjust resultant amplifications

to rock.

The mean and standard deviation for

amplification factors inferred for Holocene

sites in the azimuthal window of 45 degrees

centered along strike are 1.8 and 1.5,

respectively. Corresponding values inferred

for the azimuthal window of ±_67.5 degrees

perpendicular to strike are 1.7 and 1.5. The

Holocene sites are thought to be categorized

as soft-soil sites as defined by Borcherdt [2]

(classified as SC-IV) or as D sites as initially

proposed for the NEHRP code revisions.

The preliminary 1.8 value is slightly smaller

than the 2.0 value for SC-IV sites as initially

inferred from the Loma Prieta strongmotion for input ground motion levels near

0.1 g [3].

As a preliminary attempt to quantify the

response characteristics of the Holocene

deposits at high input ground motion levels near the source, amplification ratios were computed with respect to the Shin-Kobe site (JR-SNK) for which a peak acceleration of

0.57 g was recorded at a distance of about

4.1 km from the seismogenic source. The

geologic map and site coordinates imply that

the site is underlain by geologic unit QP3

(gravels, sands, and clays of Late Pleistocene

age). The amplification ratios, normalized by

the reciprocal ratio of the seismogenicrupture distance, are plotted for sites along

strike at distances less than 22 km (Figure

2.4.10). The mean and standard deviation

for the amplification factors are 2.0 and 1.1,

respectively. The linear trend fit to the data

do not show a tendency to decrease with

increasing peak acceleration level. Liquefaction induced ground failure is known to have reduced the amplification at only the Port Island vertical array station.

These preliminary observations suggest that

the amplification factors for these Holocene

sites do not decrease with increasing peak

amplitude. Confirmation of this important

result with further analyses would suggest

that amplification factors currently being

13
suggested for the NEHRP and UBC code

revisions should be modified so as to reduce

the influence of nonlinearity on site factors

at sites for which the potential for ground

failure is low.

2.5 Ground Failure

The 1995 Hyogoken-Nanbu earthquake

caused extensive liquefaction of the artificial

fills that had been placed in Osaka Bay near Kobe. As was noted in Section 2.3, most of

these fills consist of sands that were dumped

into standing water and left uncompacted.

Consequently, when they were subjected to the strong shaking of the earthquake, they

liquefied and expelled large quantities of

both sand and water (Figure 2.5.1). More

than 17 km2 of land area was covered by

vented materials (Figure 2.5.2). Splash

marks on walls and other structures indicated that water fountains typically

reached 0.5 m and reached heights of almost

2 m in a few locations.

The severity of ground shaking on the

artificial fill was recorded at two locations, one without any reported liquefaction and

one with liquefaction. A recording of ground

shaking on reclaimed ground in Kobe north

of Port Island is shown in Figure 2.5.3. The

station is free field. It is located at the Port

of Kobe Construction Office near the

shoreline that existed before land

reclamation. No evidence of liquefaction was

reported at this station. The peak horizontal

acceleration is 502 gals (0.51 g). Figure 2.4.5

illustrates that liquefaction reduced the

strength of shaking at the land surface on

Port Island. The Port Island station is 1860

m south of the Construction Office station

where sand and water vented to the surface.

The peak horizontal acceleration at the land

surface was only 341 gals (0.35 g) at the Port

Island site despite a peak acceleration of 565

gals (0.58 g) at the base of the sandy fill.

Post-liquefaction consolidation and expulsion

of particulate matter caused regionally

extensive settlements. Settlements ranged

from 30 cm to 50 cm throughout the area

underlain by artificial fill, and locally

exceeded 100 cm. Settlements were easy to detect because many of the structures built on reclaimed ground are supported by piles or columns that extend through the zone

that liquefied. Figure 2.5.4 shows differential

settlements between columns of the Harbor

Expressway, and Figure 2.5.5 shows

settlements between columns of a covered

parking structure. At many locations, the

former position of the ground surface was

obvious on the walls of pile-supported

structures.

Lateral spreading was common along the

perimeters of the artificial fill and usually

involved failure of quay walls (See Section

4.5). Maximum permanent horizontal ground

deformation from lateral spreading was

about 2 m. Ground deformation from lateral spreading diminished rapidly in severity

inland from the quay walls, although ground

cracks extended as much as 100 m inland

from some walls.

Despite the rugged terrain of the Rokko

Mountains, only a few landslides were

reported. Unpublished reconnaissance maps

provided by the Geographical Survey of

Japan, although of limited areal coverage of

the mountain front near Kobe, showed only

12 landslides. Most of these slope failures were inland from Nishinomiya. The largest

and most damaging slope failure was next to the Nikawa-Yurino Filtration Plant (Figure

2.5.2). The failure killed 34 people.

Embankment failures were also noted along

streams in the coastal plain.

14
Another significant ground failure occurred

above the underground Daikai railroad

station in Nagata-ku in Kobe City (Figure

2.5.2). The station is operated by the Kobe

Express Railroad Company as part of the

Japanese National Railroad. The station and

adjacent running tunnels were constructed

by the cut-and-cover method. The reinforced

concrete columns in the station, which

supported the roof of the station and 4.8 m

to 5.2 m of overlying soil, buckled and

caused 1800 m2 of land to settle in an

approximately 100 m long elongate

depression. Maximum settlement was 2.5 m.

Collapse was localized above the 17 m wide

underground station and did not extend into

the narrower 9 m wide running tunnels on

either end of the station.

2.6 Engineering Seismology and

Geoteehnical Lessons for the United

States.

The Hyogoken-Nanbu earthquake has

reemphasized that moderate to large

earthquakes directly beneath densely

urbanized areas can cause catastrophic loss of life and property.

Important factors contributing to these

losses from an earth science perspective are:

(a) proximity to the earthquake crustalrupture zone A large number of vulnerable

structures experienced especially strong

levels of ground shaking in a zone thought

to be directly above a portion of the crustalrupture area. Strong-motion recordings

show that peak acceleration values

attenuated from values greater than 0.8 g near the source zone to values less than

0.25 g at some sites at distances near 20 km

on firm soils. This rapid attenuation of

strong shaking appears to have been an

important factor influencing the confinement

of damage primarily to the Awaji Island,

Kobe City and Nishnomiya areas.

(b) amplification effects of soft-soil deposits

The amplification effects of Holocene soil deposits appear to have contributed to increased peak amplitudes and duration of

strong shaking at many sites. The increased

levels of shaking contributed to direct

structural failures and liquefaction induced

ground failures. The amplification effects of

the Holocene soil deposits are consistent

with those inferred empirically from the

Loma Prieta earthquake. With the exception

of those sites experiencing liquefaction, the

amplification effects appear to be greater

than those currently predicted by numerical

models for levels of input ground motion

near 0.3 g to 0.5g.

(c) liquefaction susceptibilities of reclaimed

land and soft soil deposits Where clean,

water-saturated, granular layers exist near

the surface, shaking-induced or ground

failure associated with liquefaction was a

significant contributor to damage

experienced by port and harbor facilities.

Refinements in U.S. building codes that

should be considered for evaluation in order

to better account for these factors are:

(a) incorporation of "near-source factors" to account for high levels of shaking at sites near the crustal-rupture zone,

(b) increase the amplification factors for site class SC-IV (D,E) at high input ground

motion levels according to empirical results

derived from strong-motion recordings of

the Hyogoken-Nanbu earthquake, and

(c) increase the upper shear-wave velocity

limit for site class SC-IV horn 183 m/s to at least 200 m/s in order that soft-soil sites with

a high liquefaction susceptibility are not

misclassified.

15
From the geotechnical viewpoint, the

liquefaction of about 17 km2

of land underlain by artificial fill highlights

the seismic hazard of loose sandy soils. The

experience during the 1995 earthquake

reaffirmed the proclivity of areas built on

these fills for large permanent ground

deformations when they are strongly shaken.

Large differential horizontal displacements were observed around quay walls where

lateral spreading occurred. Regional and

localized differential vertical displacements

also were observed throughout the area of

artificial fill. The Kobe Port and other

engineering works such as wastewater

treatment facilities were crippled by these

deformations.

Many artificial fills in coastal and river areas of the United States are similar to the loose

sandy fills in Kobe, which performed so

poorly. Much artificial land has been

created in the United States by dredging or dumping sand into open water without

compaction. Until three to four decades

ago, the seismic hazard of soils placed by

these techniques was not widely recognized.

Consequently, many older fill areas in ports

and harbors, both in seismically active areas and areas of low seismicity, are vulnerable to earthquakes. As the 1995 earthquake

demonstrated, this vulnerability can extract a

steep price when these areas are strongly

shaken.

2.7 Research Needs for Engineering

Seismology and Geotechnical

Engineering

The Hyogoken-Nanbu earthquake has

provided an especially important set of

strong-motion data for purposes of

earthquake engineering. The large set of

recordings on Holocene soil deposits within

5 km to 20 km of the crustal rupture zone

are unprecedented. They provide a unique

set of in-situ measurements of the response

of soft-soil deposits at high input ground

motion levels. These data provide a

potentially important data set for developing

improved site factors for site-specific designs

as well as revised building codes.

Important engineering-seismology issues for

further research are: (a) the location and

nature of the crustal-rupture process as it can be inferred from augmentations to the

seismological and strong-motion data sets, (b) compilation, analyses, and distribution of

the strong-motion recordings obtained by all contributing agencies, (c) compilation of

detailed seismic and geotechnical logs at as many of the strong-motion stations as resources permit, (d) thorough analyses of

surface and borehole strong motion

recordings to develop an improved

understanding of the response of soft-soil

deposits at high input ground motion levels,

and (e) interpret improved estimates of the

response of soft-soil deposits for purposes of

code revisions and site-specific design

analyses.

The extensive lateral spreading around the

margins of the artificial fills placed in Osaka

Bay provides an opportunity to clarify the

mechanism of horizontal ground

displacements associated with soil liquefaction. The widespread damage to engineered works should permit

documentation of details of deformation

fields associated with lateral spreading. This

understanding should improve the design of

countermeasures to minimize the impact of

liquefaction on engineered works. The large

and readily documentable settlements of the

land surface provide an excellent

opportunity to check and improve

techniques to predict magnitudes of postliquefaction consolidation. By determining

engineering properties of soils at sites where

16
settlements were well documented, the

empirical data base can be substantially

augmented. Finally, areas of ground

improvement need to be documented.

Evaluation of the performance of these

areas should increase confidence in our

ability to reduce the hazard from

liquefaction of sandy soils. To date, field

experience with the dynamic response of

improved ground is limited to relatively low

levels of seismic shaking.

2.8 Acknowledgments

The authors are especially appreciative of

the information and data provided by numerous agencies and colleagues on which

this report is based. In particular, data and

information provided by colleagues of The

Public Works Research Institute; The

National Research Institute for Earth

Science and Disaster Prevention, Science

and Technology Agency; The Disaster

Prevention Research Institute, Kyoto

University; the Earthquake Research

Institute, University of Tokyo; Department

of Civil Engineering, Gifu University; the

Port and Harbor Research Institute; the

Architectural Institute of Japan; The

Committee on Earthquake Observation and

Research in the Kansai Area; Osaka Gas;

Japan Railway; Japan Highways; Japan

Meteorological Agency; Building Research

Institute; Geological Survey of Japan and

others are appreciated. A special note of

thanks is expressed to Y. Iwasaki, H.

Kameda, Y. Koga, Y. Ninomiya, K. Ohtani,

M. Sugito, M. Watabe, and numerous other

colleagues for information and personal

contributions. The efforts of C. Wentworth

in compiling the geologic map were essential

for the preparation of Figure 2.4.1 and

subsequent geologic classifications of the

strong-motion stations. Manuscript reviews

by W. Joyner and D. Boore are appreciated.

Translations of Japanese text to English by

Yoko Takauchi and Yoshiko Suzu were

helpful.

2.9 References

1. Borcherdt, R.D., 1994a, Simplified

site classes and empirical

amplification factors for site- dependent code provisions,

Proceedings NCEER, SEAOC, BSSC

workshop on site response during

earthquakes and seismic code

provisions, University of Southern

California, Los Angeles, California,

November 18 - 20, 1992.

2. Borcherdt, R.D., 1994b, Estimates of

site-dependent response spectra for

design (Methodology and

Justification), Earthquake Spectra, 10,

p. 617-653.

3. Borcherdt, R.D., and Glassmoyer,

G., On the characteristics of local

geology and their influence on

ground motions generated by the

Loma Prieta earthquake in the San

Francisco Bay region, California:

Bulletin of the Seismological Society of

America, 82, p. 603-641, 1992.

4. Campbell, K. W. and Bosorgnia, Y.,

Near-source attenuation of peak

acceleration from worldwide

accelerograms recorded from 1957 to 1993, Proc. Fifth U.S. National

Conference on Earthquake

Engineering, Chicago Illinois, 1994.

5. Boore, D.M., Joyner, W.B., and

Fumal, T., Estimates of response

spectra and peak accelerations from

western North American

earthquakes; an interim report part 2

17
(with insert), U. S. Geological Survey 11. Open File Report 94-127, 39 pp., 1994.

6. Huzita, K., and Kasama, T., Geology

of the Osaka-Seihokubu District, 12. Scale 1:50,000: Geological Survey of

Japan, 1982.

7. Huzita, K., and Kasama, T., Geology

of the Kobe District, Scale 1:50,000:

Geological Survey of Japan, 1983.

8. Huzita, K., and Maeda, Y., Geology 13. of the Suma District, Scale 1;50,000:

Geological Survey of Japan, 1984.

9. Huzita, K., and Maeda, Y., Geology

of the Osaka-Seinambu District,

Scale 1;50,000: Geological Survey of

Japan, 1985.

10. Maxi mum accelerations observed by

JR, JR Earthquake Information No.

23a, Internet.

Kikuchi, M., The Mechanism of the

Hyogoken-Nanbu earthquake of

January 17,1995, in YCU

(Yokohama City University)

Seismology Report No. 38, 1995.

Nakakita, U., and Watanabe, Y., Soil

stabilization by preloading in Kobe

Port Island, in Proceedings of the 9th

International Conference on Soil

Mechanics and Foundation

Engineering, Tokyo, Case History

Volume, p. 611-622, 1977.

Nakamura, Y., Waveform and its analysis of the 1995 HyogokenNanbu earthquake, JR Earthquake

Information No. 23c, 46 pp., 1995.

18
Table 2.1.1

Source parameters inferred for the Hyogoken-Nanbu earthquake

(Kikuchi,1995)

Subevent

Parameter 12 3 Total

6.8 6.3 6.4 6.9

Area (km2 ) 24x12 9x5 12x6 40x10

Slip(m) 2.1 2.5 2.7 2.1

Stress Drop (MPa) 9.3 13 24 10-20

MQ (newton-m) 2.5x10

19
Table 2.4.1 A preliminary list of strong motion stations for the Hyogoken-Nanbu earthquake

Station Name Sta Geol. Site N. Lat. E. Long. Azm E-dist H-dist Surf-Dis SR-Dis PGA Sta H1 H2 UD

Code Clas (deg) (deg) (deg) (km) / Ism \ (km) (km) (km) (gal) Azm (gal) (gal) (gal) Fukiai OG-FUI Qp-Q3 III •34. flU 7 JO. ZUZ oz I 0.0 Z0.4 ft A U.4 a n OJJ

Shin-Kobe JR-SNK Qp-Q3 III J4./U4 inn 1 J5.ZUU DJ IO.U ZZ.a n q U.o A 1 4.1 DDI NS -OJU -ZD/ 1 A A -o44 Kobe Marine JM-KBM Qh IV 34.688 135.180 54 15.4 21.0 0.9 4.1 817 NS 817 617 332 Kobe University KC-KBU Qp-Q3 III 34. 725 135.240 54 22.3 26.4 1.3 4.2 305 NS 270 305 447

Takatori JR-TKT Qh IV 34.649 135.139 62 9.9 17.4 1.7 4.3 616 NS 635 553 175 PHRI Kobe PH-KOB Qh IV 34.697 135.225 59 19.4 24.1 2.7 4.8 394 NS 394 169 275

Port Island MC-PRI Qh IV 34.691 135.226 61 19.1 23.9 3.3 5.2 341 NS 341 284 557 Kobe Motoyama KC-KOB Qh IV 34.718 135.273 60 24.4 28.2 3.8 5.5 775? NS 421? 775? 379?

Port Island Array MC-PIA Qh IV 34.669 135.206 65 16.4 21.8 4.0 5.6 340 NS 340 282 567

Nishinomiya OG-NSM Qh IV 34.732 135.346 63 31.0 34.1 7.5 8.5 792

Takaraduka JR-TKD Qh IV 34.809 135.344 51 35.5 38.2 8.5 9.3 601 NS 595 530 377

Nishi-Akashi JR-NSA Qh IV 34.664 134.964 311 9.7 17.2 10.1 10.8 481 NS 481 -389 338 Amagasaki 1 KC-AMG Qh IV 34.718 135.408 70 35.6 38.3 13.4 14.0 >321 NS 271 322 328 PHRI Amagasaki PH-AMG Qh IV 34.689 135.388 74 32.9 35.8 13.4 14.0 475 NS 475 320 312 Amagasaki 2 MC-AMG Qh IV 34.715 135.410 70 35.7 38.4 13.7 14.3 310 TR 310 274 336 Amagasaki 3 JH-AMO Qh IV 34.724 135.432 70 37.9 40.4 15.3 15.8 580 NS

Inagawa River TD-OKI Qh IV 34.826 135.426 55 42.6 44.9 15.8 16.3 421 Hokko OG-HOK Qh IV 34.666 135.432 80 36.2 38.9 18.1 18.5 266

Fukushima KC-FKS Qh IV 34.681 135.446 78 37.8 40.3 18.3 18.8 212 NS 180 212 195 Yodo R (Ooyodo MC-YRO Qh IV 34.688 135.458 77 39.0 41.5 18.9 19.3 336 TR 150 200 300

Hitokura Dam TD-HTD sed I 34.900 135.408 46 46.7 48.7 19.8 20.2 478 Toyonaka KC-TYN Qp-Q1 III 34. 800 135.492 62 46.3 48.4 20.6 21.0 NS

Senri OG-SEN Tp-N3 I 34. 801 135.501 63 47.1 49.2 21.4 21.8 312 Minoogawa Dam TD-MND sed I 34. 860 135.475 55 48.5 50.5 21.6 21.9 127

Shin-Osaka(SS) JR-SNO Qh IV 34.737 135.516 72 45.6 47.7 22.5 22.8 245 NS -218 -217 56 Kakogawa Ozeki MC-KGO Qh IV 34. 791 134.913 330 23.8 27.7 23.9 24.2 139 TR 136 139 114 Osaka JM-OSK Qp-Q3 III 34.678 135.522 80 44.5 46.7 24.7 25.0 80 NS 80 66 -65 Kansai Int'l. Airp KA-KIA Qh IV 34.421 135.212 143 25.8 29.5 25.2 25.6 160 247 Kakogawa JR-KKG Qh IV 34.764 134.843 314 25.3 29.0 25.7 26.0 229 NS 165 262 98 Abeno KC-ABN Qp-Q3 ill 34.636 135.519 86 43.7 45.9 26.6 26.9 226 NS 217 226 136

Morikawachi OG-MKW Qh IV 34.678 135.545 80 46.5 48.6 26.6 26.9 210 NS 210 123 159 Kawachi OG-KAW Qh IV 34.732 135.574 74 50.5 52.4 27.8 28.1 177

Sakai S KC-SAS Qh IV 34.564 135.469 97 39.3 41.7 28.4 28.7 150 NS 150 125 100

Sakai N OG-SKN Qh IV 34.573 135.487 95 40.8 43.2 28.8 29.0 173

Fujiidera OG-FU2 Qh IV 34.501 135.387 111 33.6 36.5 28.9 29.2 168

Shin-osaka KC-AHN Qh IV 34.679 135.572 81 49.0 51.0 28.9 29.2 243 NS

Minami-Osaka JH-MNO Qh IV 34.755 135.600 72 53.5 55.3 30.0 30.3 202

Izumi OG-IZ1 Qh IV 34.498 135.409 110 35.6 38.4 30.5 30.7 178

Iwasaki OG-IWS Qh IV 34.632 135.567 87 48.1 50.1 30.6 30.9 185 Yodo River (Hira MC-YRH Qh IV 34.803 135.614 67 56.6 58.3 31.6 31.9 253 TR 144 253 57 Tadaoka KC-TAD Qp-Q3 III 34.480 135.408 113 36.3 39.0 31.9 32.2 290 NS 290 190 137 Yae KC-YAE Qh IV 34.680 135.612 81 52.7 54.5 32.4 32.6 155 NS 155 145 127

Izumi 2 OG-I22 Qp-Q3 III 34.406 135.324 131 34.0 36.9 33.2 33.4 240 Sasayamaguchi JR-SMG sed I 35.053 135.180 14 51.2 53.0 33.5 33.7 195 NS 139 -177 39

Higashi-Kishiwad JR-HGK Qp-Q3 III 34.445 135.388 120 36.3 39.0 33.7 33.9 149 NS -110 -144 49 Shirahama OG-SHR Qh IV 34.779 134.729 304 34.5 37.3 33.7 34.0 189 189

Shijonawate OG-SHJ Qh IV 34.734 135.639 76 56.3 58.0 33.8 34.0 224 Yodo River, Hira TD-HKC Qh IV 34.810 135.645 68 59.5 61.1 34.5 34.8 313

Hashiramoto OG-HSM Qh IV 34.860 135.634 63 60.9 62.5 34.8 35.1 251

Onji OG-ONJ Qh IV 34.625 135.624 88 53.2 55.0 35.6 35.9 169

Fujiidera OG-FJ3 Qp-Q3 III 34.567 135.594 95 50.6 52.5 36.5 36.7 149

Shin-Takatsuki(S JR-SNT Qh IV 34.859 135.654 63 62.5 64.0 36.6 36.8 323 NS

Matsuo OG-MTS Qh IV 34.241 135.150 167 41.8 44.2 36.7 36.9 180 Shikama KC-SHM Qh IV 34.799 134.691 304 38.7 41.2 37.7 37.9 253

Fujiidera OG-FU1 Qp-Q3 III 34.558 135.611 96 52.3 54.1 38.4 38.6 149 Kino-Kawa Ohas TD-KKO Qh IV 34.231 135.167 165 43.3 45.6 38.6 38.8 150

20
Table 2.4.1 (continued)

A preliminary list of strong motion stations for the Hyogoken-Nanbu earthquake

Himsji KU-HIM vole I *>A B*>C 4 *}A 700 -511 J1 1 38. o 41.3 38.9 39.1 189

d r\d 1 1 (Jb 1 1 1 1 1 Id IV 7 OO. 7 i7 7 1 AO *fO.U AC *i 40. J in o

oa. o oa.O 1 VVdrVdydind Dl jn-vvpvi un IV/ IV / JJ.£ / 7 i oy AO o AA C n*4.0 jy. j O9.0 1 no Dimn^aka-Kamp >—/ II 1 IUOuiNQ 1 \UI 1 Iv JH-OMK Qp-Q2 III 34.983 135 fiOQ 51 UU. J R7 Q Ov7.D Sonobo JR-SNB Qh IV 35.100 135.487 37 68.2 69.6 42.4 42.6 163 NS -102 163 -47

Keiji Bypass JH-KJB Qh IV 34.898 135.741 63 71.5 72.8 45.4 45.6 249

Tatsuno JH-TSN vole I 34.871 134.626 308 48.2 50.2 47.7 47.9 136

Fushimi OG-FUS Qh IV 34.941 135.772 61 76.2 77A 49.8 49.9 206

Chihaya KC-CHY ig/meta I 34.439 135.659 108 59.4 61.1 50.4 50.6 109 NS 91 109 74

Nijo JR-NJO Qh IV 35.007 135.744 55 77.9 79.1 51.0 51.1 84 NS

Nara JR-NRA Qh IV 34.677 135.821 84 71.6 72.9 51.1 51.2 113 NS 112 104 -36 Amagase Dam TD-ANID Qp-Q1 III 34.875 135.815 67 76.6 77.8 51.2 51.3 172

Kyoto OG-KYO Qh IV 35.012 135.755 55 79.1 80.2 52.1 52.3 67

Higashiyama JR-HGY sed I 34.978 135.797 59 80.3 81.4 53.6 53.8 113 NS

Shirakawa Dam TD-SKD TmN1/2 II 34.615 135.858 90 74.6 75.9 56.1 56.2 169 Fukuchiyama JR-FHY Qh IV 35.293 135.121 5 76.7 77.8 60.7 60.8 110 NS 72 107 21 Ikuno JR-IKN vole I 35.160 134.792 339 65.7 67.1 62.1 62.2 59 NS -36 53 20

In JR-IN vole I 34.750 134.227 282 76.3 77.6 66.9 67.0 101 NS -36 53 20

Kusatsu OG-KUS Qh IV 35.008 135.956 62 94.5 95.5 68.2 68.3 6 Gobo JR-GBO sed I 33.904 135.162 172 78.9 80.1 69.9 70.0 170 NS -111 132 26

Ritto JR-RTO Qh IV 35.028 135.996 62 98.8 99.7 72.4 72.5 67 NS

Nishi-Maiduro JR-NSM sed 1 35.438 135.333 16 96.1 97.0 75.4 75.5 87 NS -60 79 -20 Maizura JM-MAZ ig/meta 1 35.448 135.320 15 96.9 97.8 76.4 76.5 67 NS -67 -52 -40

Himeji JR-HMJ vole 1 34.821 134.075 285 91.7 92.7 82.9 83.0 125 NS 82 125 48 Tsuge JR-TSG Tp-N3 III 34.843 136.259 77 114.2 114.9 90.6 90.7 97 NS 77 -67 33 Obama JR-OBM Qh IV 35.488 135.749 33 117.2 117.9 91.7 91.8 74 NS 70 -57 -24 Gokasou JR-GOK vole 1 35.139 136.184 61 119.7 120.4 93.1 93.2 128 NS -125 119 -44 Toyooka JR-TYK TmN1/2 II 35.541 134.800 348 106.2 107.0 96.7 96.8 124 NS 103 -90 -27 Shin-Malbara(SS JR-SNM Qh IV 35.316 136.293 56 138.5 139.1 111.6 111.6 227 NS 217 135 -25 Kji-Nagashima JR-KNG sed 1 34.205 136.342 111 127.2 127.9 116.0 116.1 46 NS

Matsuzaka JR-MTZ Qh IV 34.573 136.538 92 136.9 137.5 117.7 117.8 49 NS

Kumancshi JR-KUM vole 1 33.889 136.105 130 126.1 126.8 123.5 123.6 52 NS

Yokkaichi JR-YKC Qh IV 34.960 136.633 75 150.4 150.9 126.2 126.2 65 NS

Sekigahara JR-SKH Qh IV 35.360 136.472 58 154.8 155.2 127.9 128.0 95 NS

Shin-Sekigahara( JR-SNS Qh IV 35.354 136.483 58 155.3 155.7 128.4 128.5 106 NS 106 72 -29 Hashima JR-HSM Qh IV 35.326 136.675 62 168.8 169.2 142.3 142.4 57 NS 57 -31 10 Kisogawa JR-WS Qh IV 35.343 136.783 63 178.4 178.8 152.0 152.1 67 NS

Biwajima(SS) JR-BWJ Qh IV 35.195 136.867 69 178.7 179.1 153.1 153.2 21 NS -21 18 -7 Odaka(SS) JR-ODK Tp-N3 III 35.066 136.953 74 181.6 182.0 157.0 157.1 18 NS -17 -14 -7 Anjo(SS) JR-ANJ Qp-Q3 III 34.929 137.099 80 191.2 191.5 167.8 167.8 26 NS -22 -19 -7 Okazaki JR-OKZ Qp-Q3 III 34.920 137.160 80 196.5 196.8 173.2 173.3 9 NS

Mino-Ota JR-MNO Qh IV 35.443 137.022 63 202.8 203.0 176.3 176.4 50 NS

Tajimi JR-TJM TmN1/2 II 35.330 137.122 68 205.8 206.0 179.9 180.0 15 NS

Toyohashi JR-TYH 34.760 137.385 86 214.8 215.0 193.1 193.1 12 NS

Gero JR-GRO 35.802 137.242 57 239.9 240.1 213.0 213.0 10 NS

Nakatsugawa JR-NKT 35.495 137.505 67 244.9 245.0 218.9 218.9 14 NS

Nagiso JR-NGS 35.596 137.612 66 258.3 258.3 232.1 232.1 19 NS Takayama JR-TKY 36.138 137.254 50 263.0 263.0 235.9 236.0 7 NS

Shin-lwata(SS) JR-SHI 34.723 137.901 88 261.7 261.8 240.3 240.3 14 NS 10 13 -4 Hiraoka JR-HRK 35.271 137.857 75 266.9 267.0 242.2 242.2 8 NS

Ida JR-IDA 35.517 137.825 69 272.7 272.7 246.9 246.9 18 NS KC - Kansai Committee for Earthquake Observation and Research OG - Osaka Gas

JR - Japan Railway JH - Japan Highway

MC - Ministry of Construction

PH - Port and Harbor Research Institute JM - Japan Meterological Agency

KA - Kansai International Airport TD - To be Determined

Bold faced coordinates provided by agencies.

Italicized coordinates inferred from maps

21
i— ••

•

• f ; _ m *»••

'

:

; i 130 135 140 145

Map showing seismicity for Japan for time period 1961-1994, plate margins and

approximate rupture zones for the large 1944 and 1946 earthquakes (compiled by

G.Marshall).

22

Figure 2.1.1
Figure 2.1.2 Map showing Quaternary faults and seismicity for a two day time period

including the occurrence time of the Hyogoken-Nanbu earthquake (from

Earthquake Research Institute, University of Tokyo via ftp, Observation Networks

of Disaster Prevention Research Institute, Kyoto University, and Faculty of

Science, Kochi University).

23
Subevent Distribution Source Time Functions

Figure 2.1.3 (a) Map showing aftershock distribution in plan and cross section views (from

Disaster Prevention Research Institute, Kyoto University) and (b) source mechanism for inferred subevents (from Kikuchi, 1995).

24
Figure 2.3.1 Soils map of Kobe City area (generalized from Huzita and Kasama, 1983).

25
Land Surface

Reclaimed Ground

K.P. +4-+7.5

K.P. ±0

-12

L.W.L -0

Fill N=5-10

-25

-55

-75

H.W.L -1.7

Marine Clay

q u =0~10

kgf/cm^

Interlayered

Sand and

Clay

N=10-50

Marine Clay

q u =1.5-5.5

kgf/cm^

Interlayered

Sand and

Clay

K.P.±0

-10

-20

-30

-40

-50

-60

-70

-80

N-Value

0 20 40 60

0.2

0 6

1 0

-J:

c

1.0

&5.0

q u (kgf/cm'1

q u (kgf/cm 2

)

Figure 2.3.2 Representative soil boring from Port Island showing fill overlying natural soils (Nakakita and Watanabe, 1977.

26
3O

So

.5 3 § 8

Cu

C

Oh

O

T3 5 c E * J

g.ac

i—

Q 

8 e _ C

«J

O *-» i—

r" *-> O

6/3 2 Q

CX(Jo

<oo"o

.2 ^ o _u E «5y oU, S03rv

1/5 5s c o

"5b E 13 •§ « O DC O

6X)~ ^ »8 f ° o E

-C o

Oh ~—

P3

C/i 3

bJ3 — ; C 8 E .2 TJ « t< 15 •= <u .« E o u d *

Oh

O 03

Uh3

27
NS

0. 00

KOBE-UN I V

KOBE

AMACASAK

I

FUKUSH IMA

MOR I CAWACH

YAE

SAKA 1

TADAOKA

CH I HAYA

ABENO

(a)

55. 109 Um/t)

40. 000 (cm/i)

40. 000 (cm/i)

30. 981 lti/il

27. 056 (cm/i)

21. 201 Icm/i)

15. 8G5 lt»/i)

24. 4 37 (cm/jl

5. 182 (cin/j)

21. 370 (cm/i)

25. 00

T I ME (sec. ) 50. 00 75. 00

i 100.

Figure 2.4.2 (a) Record section showing ground velocity in the NS (a) direction (from The

Committee on Earthquake Observation and Research in the Kansai Area,

CEORKA).

28
EW

o. oo

ir 3). 042 Urn/,) KOBE-UNI V

KOBE

AMAGASAK

FUKUSH 1 MA

MOR I GAWACH

YAE

SAKA I

TADAOKA

CH I HAYA

ABENO (b)

40. 000 (m/il

40. 000 (c»/>)

29. 811 (cn/il

24. 673 (em/.)

21. 817 (cm/i)

15. 664 len/il

14. 713 (cm/i)

4. 861 (co/i)

24. 889 (cm/j)

25. 00

Tl ME (sec. ) 50. 00

J 75. 00

i 100. 00

I

Figure 2.4.2 (b) Record section showing ground velocity in the EW (b) direction (from The

Committee on Earthquake Observation and Research in the Kansai Area,

CEORKA).

29
UD

0. 00

I KOBE-UN I V

KOBE

AMAGASAK

1

FUKUSH IMA

MOR ICAWACH

I

YAE

SAKA1

TADAOKA

CHIHAYA

ABENO

(c)

33. 173 (cm/»)

40. 000 (cm/i)

26. 095 Ura/i)

9. 607 (cm/i)

6. 106 (cm/i)

6. 979 Um/j)

6. 597 U»/i]

5. 923 (cm/i)

2. 466 (cm/»)

6. 277 (cm/»)

25. 00

I

TIME (sec. ) 50. 00

i 75. 00

i

Figure 2.4.2 (c) Record section showing ground velocity in the UD (c) direction (from The

Committee on Earthquake Observation and Research in the Kansai Area,

CEORKA).

30
1000

•95 01.17 05.46 3436135.00 20.0 7.2 19.2 KOBE(JMA)

w . re , . . .

-1000

iooo0". £V

-1000

1000°

-1000

10 20 Time(sec)

(1(1) Acceleration

Ma*. 81 8.0 Gal

RTRj/SDAC

-i—'——•——|- Nfo. 6173 Gal

Max.332.2 Gal

RTRJ/SDAC

30 40

hwOBiW- 1-M o ffn- i i(im oi J]))

100'

•95 01.17 05.46 34.36 135.00 20.0 7.2 19.2 KOBE(JMA)

-100 100*1

-100 100'

-100

10 20

Time(sec)

(2) Velocity

30

Max. 84,1 kine

Max. 70.3 king

Max. 38,4 kine RTR1/SDAC

40

Figure 2.4.3 (a) Three-component (1) acceleration, (2) velocity, (3) displacement, and (4)

displacement loci inferred by Nakamura (1995) from strong-motion

recordings at site (a), Kobe Marine (JM-KBM).

31
"95 01.17 05.46 34.36135.00 20.0 7.2 19.2 KOBE(JMA)

20", . ^

-2020

-2020

-20 20

Timc(sec)

(3) Displacement

40

rrm Ow l»5- UU tOSi 31 <Sr* V«.i.l(lWiM J|))

N

17.68

17.68X^5

17.68 U

17.&8

17.68 E - 17.68

- 17.68

- 1768

17.68 E

(4) Loci of Displacement

(UNIT: cm)

17.68 U

W F(JMA)

KOBE

Figure 2.4.3 (a) Three-component (1) acceleration, (2) velocity, (3) displacement, and (4)

displacement loci inferred by Nakamura (1995) from strong-motion

recordings at site (a), Kobe Marine (JM-KBM). (Continued)

32
"95 01.17 05.46 3436 135.00 20.0 7.2 13.8 TAKATORI

-800

-800 800 , .UP

-800 10 20

Time(sec)

(1) Acceleration

30

tyax.64j.7Gal

Max. 28?.7Gal

KTRJ/SDAC

40

hnm Om im- 2-1' 12*0J- 0jt - V«JjpmfilJl))

•95 01.17 05.46 34.36135.00 20.0 7.2 13.8 TAKATORI

150 *1 ^-r-T-r- , , ,

|

-150 150^1 E^U

-150 150^ .UP ,

-150

Max. 138.0, kine

10 20 Time(sec)

(2) Velocity

Max. 131.2 kinc

tyax. 20,1 kine RTRI/SDAC

30 40

*+mOm im- 1>M DJi 1 (Xf* - V«.U(W5AU1U

Figure 2.4.3 (b) Three-component (1) acceleration, (2) velocity, (3) displacement, and (4)

displacement loci inferred by Nakamura (1995) from strong-motion

recordings at site (b), Takatori (JR-TKT).

33
•95 01.17 05.46 34.36135.00 20.0 7.2 13.8 TAKATORI

50 o»

r_1_fcJ$_

20

Time(sec)

(3) Displacement

Kfo. 42,0 9m

40

OMim- 2->a ISiJ 15 (S^ = Va ) 1(1W101 J]))

N

42.0

42T ' ^

42.0

- 420

- 42.0

420 E

(4) Loci of Displacement

(UNIT: cm)

TAKATOR

I

42.0 U

Figure 2.4.3 (b) Three-component (1) acceleration, (2) velocity, (3) displacement, and (4)

displacement loci inferred by Nakamura (1995) from strong-motion

recordings at site (b), Takatori (JR-TKT). (Continued)

34
"95 01.17 05.46 3436 135.00 20.0 7.2 39.2 TAKARAZUKA

800°*, .F$ ,,,,,,, |

, , ,

-800

800*

-800 800 (

-800

Ml

10 20

Time(sec)

(1) Acceleration

Nfor. 694.2 Gal

tyajf. 587-2 Gal snu/SDAC

Maj,41Q.5,Ga,l

RTRJ/SDAC

30 40

ha Om iwj- 2- j* aax {Sj* - v«xi(iM3.0Uij)

•95 01.17 05.46 34.36 135.00 20.0 7.2 39.2 TAKARAZUKA

100 ""

1 , ^5 N?ax. 75.0 kine

20

Time(sec.)

(2) Velocity hMOa im- 1-14 ujui (Sr>- *«-Uomjijij)

Figure 2.4.3 (c) Three-component (1) acceleration, (2) velocity, (3) displacement, and (4)

displacement loci inferred by Nakamura (1995) from strong-motion

recordings at site (c), Takarazuka (JR-TKD).

35
•95 01.17 05.46 3O6135.00 20.0 7.2 392 TAKARAZUKA

30 ~r^-m-

-30

30

-30

30

-30 20

Time(sec)

(3) Displacement

Max, ?

4 , ,6ym, RTRl/SDAC

40

N

26.52

26^2

- 26.5

26.52

- 26.52

26.52

(4) Loci of Displacement

(UNIT: cm)

TAKARAZUKA

26.52 u

- 26.52

Figure 2.4.3 (c) Three-component (1) acceleration, (2) velocity, (3) displacement, and (4)

displacement loci inferred by Nakamura (1995) from strong-motion

recordings at site (c), Takarazuka (JR-TKD). (Continued)

36
"95 01.17 05.46 3436 135.00 20.0 7.2 8.0 N1SM-AKASH1

400°", , E§

-400

400°^, Eg

-400

400 W

-400

10 20

Time(sec)

(1) Acceleration

30

tyax. 397.3 Gal

40

«C»m5- 2-14 14:1X50 (Sp* V«.Ll(imJL3]))

95 01.17 05.46 34.36 135.no 20.0 7.2 8.0 N1SHI-AKASH1

40 **

f

. i

, i

-40

40

-40

40 "1 W

-40

10 20

Time(sec.)

(2) Velocity

30

NJax. 39,2 kine

— r—. . 1 1 , . 1 r RTR1/5DAC

1 i i . . . . tyaa. 18,0 kine RTRVSDAC

40

. o- mv- i-i J »J*»ffr»- v« i i<t«5fliJi»

Figure 2.4.3 (d) Three-component (1) acceleration, (2) velocity, (3) displacement, and (4)

displacement loci inferred by Nakamura (1995) from strong-motion

recordings at site (d), Nishi-Akashi (JR-NSA),

37
•95 01.17 05.46 3436135.00 20.0 7.2 8.0 NISHI-AKASHI

10 P$

-10

10

-1010

-10

20

Time(scc)

(3) Displacement

bfzx. 7-6 op

hwOwim- >-)4 M:CeU(Sfl« VnLI|)mdUI))

- 7.57

7.67 E

- 7.67

7.67 E

(4) Loci of Displacement

(UNIT: cm)

N1SHI-KASHI

7.67 U

- 7.67

Figure 2.4.3 (d) Three-component (1) acceleration, (2) velocity, (3) displacement, and (4)

displacement loci inferred by Nakamura (1995) from strong-motion

recordings at site (d), Nishi-Akashi (JR-NSA). (Continued)

38
Response Spectra for Recent Devastating Earthquakes

(Pseudo Response Spectrum with 5% Damping)

o

(D

V)E

o

o

o

CD >

o

-o

13CD

co Q_

1 00

7-

6'5-

4-

3-

2-

1 ~

7-

6-

5-

-

i ryrr// i.

j / ! ! j //

A ; ji _ ;

— Tarzana 1994.1.17 (090) --• El Centro 1940.5.18 (NS) — Taft 1952.7.21 (EW)

• - - Kushiro JMA 1993.1.15 (EW)

Pacoima Dam Abutment 1994.1.17 (104) — Kobe JMA Observatoryl 995.1 .17 (NS)

— - Hachinohe City Hall (Sanriku) 1994.12.28 (164) -- Hachinohe Harbor 1968.5.16 (EW)

< «. . -.j....

(a)

i—i—i i i 5 6 7 8-I 1 1—I I I I 3 4 5 6 7 8 0.1 1 Period (sec)

1—i—r-t-r

5 6 7 8

1 0

Figure 2.4.4 (a) Pseudo Velocity Response Spectra for recent devastating earthquakes for

the horizontal components (a), (from Building Research Institute, courtesy

M. Watabe).

39
Response Spectra for Recent Devastating Earthquakes

(Pseudo Velocity Spectrum with 5% damping)

o

COE

o

o

o>

o

T3

13

<D

CO CL

1 00

1 0 —

Period (sec)

Figure 2.4.4 (b) Pseudo Velocity Response Spectra for recent devastating earthquakes for

the UD component (b). (from Building Research Institute, courtesy M.

Watabe).

40
Kobe JMA Record 1995.1.17

vs Design Spectra for Tall Buildings in Japan

o

CDw

E

o

o

o

CD >

o

"D

=3CD

CO CL

1 00

1 o4-

3-

2-

1 ~

h=0.05 !

~\—7~

Kobe JMA 1995.1.17 (NS) original TM

El Centro 1940.5.18 (NS) 50 kine

' Taft 1952.7.21 (EW) 50 kine

Hachinohe Harbor 1968.5.16 (EW) 50 kinei

i—i—i i i I 5 6 7 8 0.1

(C)

n 1—i—riii

4 5 6 7 8

1 Period (sec)

i—i—

4 5 6

1 1 1

| 7 8

1

1 0

Figure 2.4.4 (c) Pseudo Velocity Response Spectra for recent devastating earthquakes for

design spectral for tall buildings (c). (from Building Research Institute,

courtesy M. Watabe).

41
100 200 300 400 1000 2000

LW.L

Fill (gravel)

Alluvial Clay

Interlayered

Sand & Clay

Diluvial Clay

Interlayered

Sand & Clay

Shear-Wave Velocity (m/s)

10 —i 1—i 10

0 0

10 -10

20 -20

30 -30

40 -40

50

-50

60

-60

70

-70

80

-80

90

-90

P Wave Velocity (m/s)

Boreholes

Geologic and seismic logs for the Port Island vertical array site (modified from

logs provided by The Committee on Earthquake Observation and Research in the

Kansai Area, CEORKA, courtesy Y. Iwasaki).

42
Figure 2.4.6 (a) Strong motion recordings obtained on the Port Island vertical array at the

surface and at approximate depths of 12, 27, and 79 m for the NS (a)

component (from The Committee on Earthquake Observation and

Research in the Kansai Area, CEORKA, courtesy Y. Iwasaki).

43
Port Island N090E 1995/01/17 05:46 accelera^n

u .

(b)

100-1 —, , , ,—, , , , , 10 15 20

TIME, S

Figure 2.4.6 (b) Strong motion recordings obtained on the Port Island vertical array at the

surface and at approximate depths of 12, 27, and 79 m for the EW (b)

component (from The Committee on Earthquake Observation and

Research in the Kansai Area, CEORKA, courtesy Y. Iwasaki).

44
Port Island UP

20-

1995/01/17 05:46 ACCELERATION

* T1995/01/17 0*46:46.74

U

m/s/s

gal cm/s cm

27

208 27 11

H 40

Q_

111 Q

60

80

173 28 12

(c)

100

10 15

TIME, S

20

Figure 2.4.6 (c) Strong motion recordings obtained on the Port Island vertical array at the

surface and at approximate depths of 12, 27, and 79 m for the UD (c)

component (from The Committee on Earthquake Observation and

Research in the Kansai Area, CEORKA, courtesy Y. Iwasaki).

45
10.000 r

Hanshin-Awaji & Northridge Earthquakes

*

' ao1

i—

i

Uo

1o

-a

Phu

boa

><

1.000

0.100 :

0.010 — - Alluvium (Campbell & Bozorgnia; (1994) o Northridge PGA

• Hanshin-Awaji PGA

Soft Soil, 200 m/s Boore, et al., 1994 PGA-StdDev

PGA + StdDev

Hard Rock, 1350 m/s Boore, et al., 1994

0.001 -I I I I I I

10 100

Distance to Seismogenic Rupture (km)

Figure 2.4.7 Preliminary compilation of peak horizontal acceleration as a function of closest

distance to seismogenic rupture for the Northridge and Hyogoken-Nanbu

earthquakes (attenuation curves courtesy of K. Campbell for evaluation of

Northridge data).

46
1.0

• Along Strike +/- 22.5 deg

0 50 100 150 200

Distance to Rupture Projected to Surface (km)

Figure 2.4.8 Preliminary compilation of peak horizontal acceleration compiled along strike (±

22.5 degree) and perpendicular to strike (+ 67.5 degrees).

47
1.0

c

o

1

1 0.5

<

o

>

0.0

0.0 0.5

Maximum Horizontal Acceleration (g)

1.0

Figure 2.4.9 Preliminary compilation of peak vertical and peak horizontal acceleration.

48
X>o

e

IE

00 J2

• Holocene Soil Deposits, <22 km,

Along Strike

Linear Trend (mean = 2.0; sd =1.1)

c

oO

00

t •

0.2 0.4 0.6 0.8

Peak Horizontal Ground Acceleration

1.0

Figure 2.4.10 Amplification of peak horizontal acceleration with respect to corresponding value

at Shin-Kobe station (0.57g) as normalized by the reciprocal ratio of respective

distances to seismogenic rupture for sites within a +/- 22.5 degree azimuthal

window of fault strike (51°).

49
50
Figure 2.5.2 Generalized areas where liquefaction vented material at the land surface. Areas

are inferred primarily from aerial photographs and unpublished maps by the

Geographical Survey of Japan.

51
500

-500

500

-500

500

-500

0 10 20

Time (s)

3C

Figure 2.5.3 Kobe-Awaji strong ground motion record at Port of Kobe Construction Office

from January 17, 1995, Hyogoken-Nanbu earthquake (source: Port and Harbor

Research Institute).

52
Figure 2.5.4 Differential ground settlement in artificial fill along the Harbor Freeway. Postliquefaction consolidation cause ground to settle between bridge columns.

Columns extend through the liquefied zone. (Photograph by Carol S. Prentice,

USGS).

53
Figure 2.5.5 Differential settlement of about 1 m between columns of parking structure on

reclaimed ground near the bridge to Port Island.

54
Appendix 2.A

This appendix provides copies of strong motion recordings obtained on the Higashi-Kobe bridge.

These recordings were provided to I. Buckle and J. Cooper by officials of the Hanshin

Expressway Public Corporation, Japan.

55
56
s k m 7 ff 1 17 B 05 Bf 46 ft m m

m & m VI

CH- 1 G 1 X 304.5 gal

CH- 2 Y 442.9 gal

CH- 3 G2X 281.2 gal CH- 4 Y 327.3 gal

CH- 5 Z 395.6 gal

CH- 6 K 1X 2.8 gal

CH- 7 Y 3.2 gal

CH- 8 Z 354.7 gal

CH- 9 V 1

K. 2 X 333.9 gal CH-10 Y 389.2 gal

CH-11 T 1 X 1000.0 gal J£UCH-12 Y iooo.o gai jy±

CH-13 T2

X 384.6 gal

CH-14 Y 964.8 gal

CH-15 T3

X 595.3 gal

CH-16 Y 821.8 gal

CH-17 Z 804.4 gal

CH-18

CH-19 Wl m/s

CH-20 a/s

CH-21 D 190.8 mm

CH-22 S 1

X gal

CH-23 Y gal

CH-24 Z gal

CH-25 C 1 gal

CH-26 gal

CH-27 C 2

gal

CH-28 gal

CH-29 W 1

m/tn

CH-30 m/m

CH-31

Cll-32

57
„X : HICRSHIJCOBEJOHHFISHI. TIME i 1195/17^05 46:51:80 Cl.X_ ICh 305. B

MAX

304.595

IGHLJ

Cl.Y 2Ch 443.0

HflX 442.993£CAU

C2.X 3Ch

MRX

28:. 219CCRLJ

C2.Y 4Ch 327.5

MAX

327.331

CCRL J B

C2.Z SCh

HRX 395.692 „

CCRL] B

-396 Kl.X 6Ch

3. a r

2.863 :cru

KI.Y 70

3.234

L

3.5f

|

i

i igrl ] a

;

1 Jl A A. a . — . _ _

y

—r-i ^ \y \J *7 " " ' ~

=3*

mi

Kl.Z 8Ch

MIX

354 . 75

355 .0 r

ccrli a

;

-355.3 ^/VvV^V - 1

—

1

L

1 1_ 0-000 15.000

1 1 -—

30. ^3 45.323

58
: HICflSHI_KOB£_OHHHSHI. TIME : I995'17'25 46:5::83

K2.X SCh

ra.x isch

M.RX 384. 674

CGRL] 8

T2.Y !4Ch 965.2 ["

USX

CCfiL)

n.x isch 595.5 r

M9X 535.397 i CCAU B '

-595.5 ! T3.Y l6Ch

MAX

321 .363CCRL)

-822 .0 L 1^U/jH^

^^

H^4*^

•5.222 S3.3C

I Sec

59
«MC t HIGflSHI_KOBE_OMMSSHl. TIME : I395'17'05 46:51:00

T3.2 l?Ch

HHX

804.4-13f J

MI !8Ch

804.

5

-804 .5

nflx 0.329 a

C«/-S.eJ "

-0.5

Ml l9Ch

MRX

0.018 CwSbcJ

Ml 20Ch

MRX 0.027

2 ICh

I 14 .5 [~

MAX

I 14 . I3S

SI .X 22Ch

-1 14 .5

(_

3 .sr

MRX

0. 133 ccru fflfflhi^flli lj( |ljfl^tl i liij Kl i(l ^

Si . r 23Ch a.sf

MRX

0. 133 CCRL) a .

:

SI .Z 24Ch

-0.5(_

0.5T

MRX

0. 133

-0.5 |

S0. 320

60
CHAPTER 3

PERFORMANCE OF BUILDINGS

3.1 Introduction

The magnitude 7.2 (JMA) earthquake

occurred at 5:46 a.m. when most people were still in their homes. As described in

Chapter 2, severe ground shaking along with

surface ruptures occurred in densely built

urban areas resulting in the partial or total

collapse of many structures. The most

serious damage was concentrated within a narrow band about 0.5 km to 1 km either

side of the fault lines. This extended about

30 km, from the northern tip of Awaji

island, through the central part of Kobe (the

Sannomiya area), toward Nishinomiya City near Osaka (Figure 3.1.1). Within this band

many old wooden houses, over 40 years old, were interspersed among commercial

structures. Many of these houses totally or

partially collapsed burying their occupants.

Over 5,500 people were crushed to death by

the collapse of their houses.

Both reinforced concrete (RC) and hybrid

steel-reinforced concrete (SRC) structures

built prior to the 1971 building code revision

sustained severe damage. Many of these

structures experienced a complete collapse

of an entire story at the mid-height of the

building. Japanese engineers stated that this

type of collapse most likely occurred at a

story where stiffness discontinuity was

present, particularly in SRC buildings in

which columns changed from a composite

section to a reinforced concrete section. In

recent past U.S. earthquakes, however, it was more common to observe collapse or

severe damage of a "soft" first story.

Detailed investigation of damaged RC and

SRC buildings is needed to reveal the causes of collapse of the buildings at their

mid-height.

Most steel buildings which experienced some

form of distress were 20 to 30 years old.

Observations showed many welded

connection failures. In some cases, beams

which were directly fillet welded to columns

pulled away from the column face. Tubular

columns of multi-story buildings fractured near the base without signs of inelastic

deformation. Slender buildings that

experienced a significant amount of lateral swing exhibited anchor bolt failures at the

column base. In general, many non-ductile

failures were observed.

The walls of single family dwellings

provided little lateral load resisting

capacity, and could not support the

heavy roof load during severe ground

shaking. Likewise, 2- and 3-story

dwelling structures with commercial

operations in the "soft" first story had

little interior walls to resist lateral

loads, thereby sustaining partial or

total collapse.

This chapter provides documentation of

damages observed by U.S. investigators

during two reconnaissance visits (January 23

to 26 and February 13 to 18, 1995).

Probable causes of failure are discussed

where possible. To better understand the

performance of buildings, the evolution of

Japanese seismic building code requirements

is presented.

61
3.2 Development of Japanese Building

Construction

3.2.1 Development of Japanese Building

Seismic Requirements

The modern era of Japanese building

construction was ushered in with the Meiji

Restoration in 1868. At this time Japan was

eager to embrace foreign culture and

sciences, including adoption of some foreign

building construction practices. The AD

(Architectural Institute of Japan) was

founded in 1886, and by 1888 the first city

planning legislation was in place. Formation

of the Earthquake Investigation Committee

following the 1891 Nobi earthquake was an

early step toward developing modern

earthquake resistant construction technology

in Japan [8] (Table 3.2.1).

Observations on building performance in earthquakes during this period strongly

influenced development of modern

earthquake engineering construction [Otsuki;

1956]. Masonry construction, introduced in the British form to reduce fire hazards

associated with traditional wood

construction, suffered many collapses in 1891 and 1894 earthquakes, slowing

development of this construction form.

Following the 1923 Great Kanto earthquake,

engineers noted that steel frames withstood

earthquake loads but could not stand up to the subsequent fires, contributing to development of SRC (Steel-Reinforced

Concrete) construction in which reinforced

concrete encloses structural steel sections. In the same earthquake, observations of

poor performance of reinforced concrete

construction without hooks at ends of

reinforcement led to abandonment of this practice. Generally good performance of

wall buildings in this same earthquake

contributed to the development of this construction form.

In 1915, Riki Sano introduced the concept

of the seismic coefficient, which defines a

lateral force for seismic design as the

product of a coefficient and the structure weight. The 1923 Great Kanto earthquake

led to the addition of an article in the Urban

Building Law which required the seismic

design of all buildings for a seismic

coefficient of 0.1. This law, which applied to certain urban districts, was a landmark in

seismic code development worldwide.

During World War II, because of a shortage

of construction materials, allowable stresses were relaxed. In 1943, the Urban Building

Law was suspended entirely, except for some | fire restrictions. Bombing during World

War II took a grim toll on many Japanese

cities, and Kobe was not spared significant

losses. As a consequence, the majority of

medium and high-rise building construction

in Kobe dates from after this war.

Following World War II the Urban Building

Law was restored briefly, but was replaced

when the 1950 Constitution of Japan

stipulated the Building Standard Law. This

law applied to building construction

throughout Japan, as opposed to limited

districts. Under this law, the seismic

coefficient was increased from 0.1 to 0.2. The net effect on proportioning materials was minimal, as there was a simultaneous

increase in allowable stresses for materials.

The increase in design lateral forces

represented a significant change in

overturning moment requirements. This

effect was especially notable in the postwar

building boom when many buildings were

proportioned to be more slender than

prewar buildings [12].

Later changes of significance included the

abolishment in 1963 of the height limit of

30 m. At the same time, the ministry of

construction recommended that buildings

62
over six stories in height should be

constructed of hybrid steel-reinforced

concrete (SRC) [10]. A very significant

change in the reinforced concrete (RC) code

to require closer spacing of column

transverse reinforcement was imposed in

1971 in response to heavy damage to RC

buildings in the 1968 Tokachi earthquake

[4]-

In the period 1972-1977 the Ministry of

Construction directed a project for

development of a new seismic design

method, resulting in a proposal in 1977 [8]. The 1978 Miyagiken-Oki earthquake,

causing serious damage in Sendai City and

demonstrating the effects of a strong

earthquake on an urban area, accelerated

the adoption of the proposal in 1981. The

new Building Standard Law included a

seismic coefficient that varied with structural

vibration period, and introduced a two level design procedure. The first level design,

which is similar to the design method used

in earlier codes, is intended as a strength

check for frequent, moderate events. The

second level design, which had not been

included in previous codes, is intended as a check for strength and ductility for a maximum expected event. This same code was in effect at the time of the HyogokenNanbu earthquake.

3.2.2 Types of Construction in Japan

Figure 3.2.1 [4] shows types of construction

common in Japan and the number of stories

commonly used for each type. Not shown is masonry building construction, which is relatively uncommon in Japan. As shown,

wood frame construction is the predominant

form of traditional house construction,

commonly being one or two stories in height. Reinforced concrete bearing wall

construction is the most common form for

apartment house construction; typical

heights are from three to five stories,

although it may be used up to eight stories.

Reinforced concrete frame structures, with

or without shear walls, are used for a variety

of structures, with common heights up to seven stories but with recent examples up to 50 stories. SRC construction is common for a wide range of construction, and is most

common for structures above six stories in

height. Steel structures may be used over

the height range and are the predominant

form for modern high-rise buildings.

Each of these construction forms and

materials has its own development history. In many cases, the history is unique to Japan. Some key aspects of each are described below. The discussion emphasizes

aspects that were predominant in the period

from the end of World War II to the

present, and therefore had most significance

for construction in Kobe.

3.2.2.1 Wood Frame Construction for

Traditional Houses

Traditional wood-frame construction for

houses was relatively unchanged from the

beginning of this century until the 1970's. Two forms were in widespread use, the older

being Shinkabe and the more recent being

Ohkabe. More recently, prefabricated

timber houses have become more common

[6].

Shinkabe construction uses a post-and-beam

framing, with lateral resistance being

provided by a mud-filled lattice of bamboo

in the walls. The need for additional

bracing was recognized by the Architectural

Institute of Japan (AD), although the

specification merely recommended that such

bracing, having dimension not less than half

the column dimension, be placed wherever it would not impair the external appearance of

the dwelling [1]. In Ohkabe construction

63
the bamboo is replaced with a narrow-plank

lathe, preferably placed on both sides of the

wall, nailed to the posts, and covered with

stucco. Diagonal bracing was also

recommended. Connections between posts

and beams are often by wood joiners rather

than nailing or connectors. Roofs commonly

are of relatively heavy tile, set in a relatively

thick mud mortar.

3.2.2.2 Reinforced Concrete Bearing

Wall Construction

Observations of building performance

following the 1923 Great Kanto earthquake

revealed the value of constructing low-rise

buildings relying on reinforced concrete

bearing walls.

As described by the AIJ [1], the emphasis in

design of bearing wall construction is on

proper layout and proportioning of the

structural system, as opposed to structural

calculations. Minimum wall thicknesses were required to range from 120 mm or h/25

(h = wall height) for one-story construction

to 180 mm or h/22 for four-story

construction. The required ratio of wall

length (parallel each principal direction) to floor area was 15 cm/m2 for the first story in

four-story construction, and 12 cm/m2 for all other floors. Web reinforcement ratios of

0.15%, 0.20%, and 0.25% were required for

the top story, the second-from-top story, and

all other stories, respectively.

Studies of building damage following the

1968 Tokachi-oki earthquake demonstrate

that bearing wall construction provides good

protection against severe damage [4] (Figure

3.2.2). The curves plotted in this figure

correspond to limits defined in the current

(1981) Building Standard Law. Regularly

configured wall buildings whose parameters

fall within the limits are exempt from the

check for ultimate lateral load carrying

capacity of that Law.

3.2.2.3 Reinforced Concrete Frame and

Frame-Wall Construction

Reinforced concrete frame construction in

Japan is commonly taken to include both

pure frame construction and combined

frame-wall construction. Although both

types are prevalent, experience in performance of RC frames has led to recommendations to combine frames and

walls [1]. Wall construction may include

solid walls framed by beams and columns, or walled frames that consist of deep girders

and wide columns.

Concrete may include normal weight

aggregate concrete or lightweight aggregate

concrete [1]; apparently in the 1960's the

lower mass associated with lightweight

aggregates led to some applications in

seismic zones similar to what occurred in the

U.S. at the same time. According to the

AIJ Structural Standards of the time, the

minimum strength was not less than

135 kg/cm2 for normal weight aggregate

concrete or 120 kg/cm2 for lightweight

aggregate concrete. In the Osaka-Kobe

area, builders began to use crushed stone for

aggregate around 1970, and exclusively since

1975. In the transition period, both crushed

stone and river gravel were used [3].

Plain reinforcement were used in Japan

prior to 1960. Starting around 1960,

builders in the Osaka-Kobe region began to use deformed longitudinal reinforcement

bars, and this became compulsory after 1970.

Deformed transverse reinforcement was

used 6 years to 7 years after the introduction

of deformed longitudinal reinforcement [3]. Five grades of reinforcement were used

then, with minimum yield stresses of 24

kg/mm2

, 30 kg/mm2

, 35 kg/mm2, 40 k/mm2

, and 50 kg/mm2 [1].

64
Pre-1971 construction details include

haunched beams with maximum transverse

reinforcement spacing not to exceed 30 cm

and 2/3D or 3/4D (D = overall depth of

beam). Columns were required to have

hoops with maximum spacing not exceeding

30 cm, minimum column depth, and 15

times the diameter of the main

reinforcement. Walls were required to have

minimum thickness of 12 cm, and two layers

of reinforcement were required where wall

thickness exceeded 20 cm. Maximum

spacing of wall reinforcement was 30 cm. Maximum allowable shear stress was oneeighth of the concrete compressive strength

[1]. Common practice had been to hook the

ends of all reinforcement, although Otsuki

[12] reports a trend away from hooks. In

the 1960's, hooks were only required for

plain bars, except deformed bars required

hooks in high stress areas and in stirrups

and hoops [1]. Reinforcement splices could

be either by lapping or welding. In recent

decades, rebar splices are almost always

done by gas pressure welding [3]. In this process, bars are aligned, butted together,

and fused by a combination of heat and

pressure applied by mechanical devices,

causing bars to flare out at the splice.

In 1971, following damage to RC

construction in the 1968 Tokachi-oki

earthquake, there was a partial revision of

the Building Standard Law and a large scale

revision of the AIJ Standards incorporating

ultimate strength design in shear of

reinforced concrete [4]. Perhaps the most

notable change in RC construction was the

requirement that maximum spacing of hoops

in columns be reduced to 15 cm, except in

column end regions the maximum spacing was further reduced to 10 cm.

3.2.2.4 Steel-Reinforced Concrete

(SRC) Construction

Steel-reinforced concrete construction in Japan grew out of observations of

performance during the 1923 Great Kanto

earthquake [11]. Bare steel frame

construction, while highly resistant to earthquake forces, was less resistant to fire. In steel frames encased in bricks, the bricks

failed, exposing the steel. Steel frames with

concrete casing, or with walls, performed

well. This led to an ascendance of SRC

construction using steel encased in

reinforced concrete.

The original form of SRC construction,

known as the full web form, used steel "I" or "FT sections. Later, in the interest of

maximizing section modulus and minimizing

rolled section consumption, built-up sections

with a smaller quantity of steel sections

became more common.

Some examples of SRC construction details

from the 1950's and 1960's are in Figure

3.2.3. The need for continuity of the steel framing members at joints was well

established, and was provided using welded

or riveted plates. Splice plates were commonly riveted or welded (Figure 3.2.3a).

Butt welds were considered unsuitable for

field work at the building site [AIJ; 1970].

Two types of connections were common at the foundation level: non-embedment type,

where a steel base plate was anchored using

anchor bolts, and embedment type, where

the steel extends into the RC foundation

with special detailing (Figure 3.2.3b). In 1963, when the 30 m height limit was

eliminated, the Ministry of Construction

recommended use of SRC for buildings over

six stories in height. While it is unclear

whether this recommendation led to a practice where SRC was used for the first seven stories, with either RC or steel used

65
for the remaining stories, it was reported

that many buildings over seven floors had

RC in upper floors supported by SRC in the

lower seven stories [3].

The 1958 ALT Standard for Structural

Calculation of SRC Structures was the first standard for SRC in Japan. Until that time,

many different types of SRC were built [10].

Subsequent revisions were published in 1963,

1975, and 1987. The current standard

approach is to calculate allowable loads as the sum of the allowable loads for the steel and the concrete sections, with the RC part

designed according to the RC standard, and

the steel part designed according to the steel standard except local buckling is ignored.

Because of observed superior behavior of

full web construction in the laboratory, the

1975 revision to SRC building code

recommended full steel webs [3]. The 1987

revision recommended use of the

embedment type steel base [3]. It also

showed how to evaluate lateral load resisting

capacity as required by the 1981 law [9].

3.2.2.5 Steel Construction

The applications of steel in building

construction grew rapidly in the years after

World War II. According to Chiba [5], early

steel products were light gauge steel. The

next developments took place around 1961

when rolling mills began to produce

standard column and beam sections.

Developments in welding technology enabled

production of box sections by welding

starting in 1969. Square hollow steel sections began to be produced around 1977.

Allowable stresses for design of buildings in the 1950's to 1990's were similar to those of

the AISC (American Institute of Steel

Construction) Specification during the same

time period. With the introduction of higher

strength steels by the mid-1960's, a wide

range of steels was available for building

construction. Allowable stresses were

related to a nominal stress limit F, defined

as the lesser of the nominal yield stress and

70% of the nominal ultimate stress [2]. A

wide range of structural details was used

over the period of interest. Figure 3.2.4

shows a variety of connection details from

the 1960's [1]. In the 1970's and 1980's, steel box sections became increasingly popular.

These were produced directly for use as columns starting in 1977, or could be

constructed by welding together light gauge

steel sections, rolled parallel flange channel

sections, or thick steel plates; some examples

are in Figure 3.2.5 [5]. It was typical to shop weld the connections at the beamcolumn joint and to use rivets or bolts in the

field away from the joint.

3.2-3 Lateral Force and Design

Requirements

In 1915 Sano introduced the seismic

coefficient concept, which offered an

earthquake resistant design approach in which the structure was designed for a

lateral force equal to the product of a

coefficient and the weight. No specific value was assigned to the seismic coefficient, and

the procedure was not part of law, until

after the 1923 Great Kanto earthquake. In 1924 the Urban Building Law added an

article to require a seismic coefficient of 0.1. The height limit of 33 m (100 ft) remained

unchanged from earlier times. This law

governed construction in major cities until

1943, when it was suspended during wartime.

The law was reinstated in 1948, and replaced

by the Building Standard Law in 1950 [12].

This law, and the 1981 revision, governed

lateral force requirements for the majority of

the Kobe region buildings that were in place

during the 1995 Hyogoken-Nanbu

earthquake. Some aspects of these two laws

are detailed in the following paragraphs.

66
3.2.3.1 The Building Standard Law from

1950 through 1980

3.2.3.2 The Building Standard Law of

1981

The basic seismic coefficient during this

period was set at 0.2, or double the value

that had been used since 1924. As described

by Otsuki [12], the doubling of the seismic

coefficient caused problems in design related

to overturning, and this was the subject of

great debate among engineers. The

outcome was not a decrease in the

overturning moment, but instead an increase

in the seismic coefficient for portions of the

building over 16 m above ground. The

Building Standard law was modified in 1955

to include reductions to account for the

seismicity of the region and the subsoil at the site.

According to the code [1], the design

horizontal seismic coefficient K for the

superstructure must be at least equal to the

quantity K = K0a/3, where the product a/3*

must not be less than 0.5, Ka is 0.2 for the

first 16 meters above the foundation and is increased by 0.01 for each additional 4

meters (Figure 3.2.6), a = a modification

factor for ground condition and type of

construction, and 0 = modification factor

for seismicity of the region (1.0 for the Kobe

region). Values of a are in Table 3.2.2, with

simplified descriptions of relevant

conditions.

In the period 1972 to 1977 the Ministry of

Construction conducted a project aimed at establishing a new seismic design method.

The method was released in 1977, and

generally accepted by 1978 [7]. The 1978

Miyagiken-Oki earthquake provided

momentum for implementation of this proposal, which was enforced in June 1981

as part of the Building Standard Law [4].

The design method features a two-level

procedure. The first phase design follows

the traditional allowable stress design

approach, with steel allowable stress equal to the yield stress and concrete allowable stress equal to two-thirds the specified compressive

strength. The second phase design is a

direct and explicit evaluation of strength and

ductility, and may be regarded as a check of whether these are sufficient for severe ground motions [4]. A flow chart of

the design process is in Figure 3.2.7. Timber

structures, and low-rise structures satisfying

rigidity, eccentricity, and detailing limitations

need not be checked using the second phase

design. Other structures, including all structures of height between 31 m and 60 m,

must be checked by both phases. Structures over 60 m in height are subject to special

approval. Details of this innovative design

procedure are summarized by Aoyama [4].

67
Table 3.2.1

Some Events in the History of Japanese Seismic Code Development

Date Event Code Change

1868 Meiji Restoration - Japan sets course of

modernization

1886 AD founded

1888 First city planning legislation in Japan

1891 Nobi earthquake (M7.9) causes extensive

damage

1892 Earthquake Investigation Committee founded

1894 Earthquake shakes Tokyo and causes damage

1906 San Francisco earthquake (M8.3)

1915 Riki Sano proposes concept of seismic

coefficient 1919 City Planning Law and Urban Building Law

enacted for six major cities. First structural standards. Great Kanto earthquake (M7.9) and fire 1924 Urban Building Law adds article to require

seismic coefficient of 0.1. Height limit of 100

ft unchanged.

1925 Earthquake Investigation Committee

rechartered as the Earthquake Research

Institute 1933 Muto proposes D-value method to calculate

stresses under horizontal forces 1937 Japan-China War puts Japan under war

condition

1943 Urban Building Law suspended except for some fire restrictions. Relaxation of

allowable stresses due to wartime shortage of

construction materials. Dual allowable

stresses introduced

uruaii ouuuiiig Law resioreu. 1950 Constitution of Japan Building Seismic Law replaces Urban

Building Law. Seismic coefficient increased

to 0.2, allowable stresses under temporary

loads set at twice the allowable stress under

permanent loads

1958 First standard for SRC

1963 Height limit of 100 ft abolished. Ministry of

Construction recommends use of SRC for buildings over 6 stories in height.

1964 Niigata earthquake (M7.5)

68
Table 3.2.1 (Continued)

Some Events in the History of Japanese Seismic Code Development

1968 Tokachi earthquake (M7.9) causes heavy

damage to RC buildings. First high-rise

building in Japan

1970 Steel code revised 1971 San Fernando earthquake (M6.4) Concrete code revised to require closer spacing of transverse reinforcement

1972- 77

Ministry of Construction project for development of new seismic design method,

resulting in 1977 proposal

1978 Miyagiken-Oki earthquake (M7.5)

1981 Building Standard Law changed. Main

features include seismic coefficient that varies with period and two-level design

Table 3.2.2

Values of a

Soil Wood Steel RC and SRC

Rock, hard sandy gravel 0.6 0.6 0.8 Sandy gravel, sandy hard clay,

loam, classified as diluvial

0.8 0.8 0.9

Alluvium 1.0 1.0 1.0 Bad or soft ground 1.5 1.0 1.0

69
Figure 3.1.1 Kobe City and the Hanshin Area.

70
60

50

40

30

25

20

CO 18

LU 16

14

cco

i-co

LLO

CC -|2

m

I

10

Z

8

6

4

2

co

Q_

O

I

CO

CO

LJJ o

LL

LLO

CO

_i

O

O

I

o

CO

CO

CO

LUCO

Z> I

o

I

TIMBER

LU

CC<

Q_

<

i 1

i ' T

Q_

CO

O

CO

I-z

LJJ

CC<

Q_

<

CO" _l

LU

I-o

co~

LJJ O

RC FRAME

CO

LJJ O

o

RC WALL

I

STEEL

SRC

Figure 3.2.1 Types of construction in Japan {Aoyama, 1993).

71
a= X 2-5 A, +

1

0.7

A

c - W, b = £ + X 0.7AC - 0.75 W , c = £ 1 .8^ + £ 1 .8A - W

Figure 3.2.2 Wall area index and average shear stress in walls and columns, following results

from Shiba (Aoyama, 1993).

72
Figure 3.2.3 Examples of SRC construction.

73
(a) Diaphragm Type

(b) Vertical Stiffener Type (c) Flat Rib Type

Figure 3.2.4 Some steel beam-column joint details (AIJ, 1970).

74
Figure 3.2.5 Some steel beam-column joint details with box columns (Chiba, 1989),

75
16m

Figure 3.2.6 Lateral seismic coefficient from the Building Standard Law in the 1950's (Otsuki,

1956).

76
1. Timber construction

Others, as specified by

Ministry of Construction

I

2. h < 31m and

other than 1 31m < h <60m

4.h > 60m

5. Conventional structural design including

first phase design for earthquakes

6. Check for storey drift

Second Phase

design for earthquakes

7. Check for

rigidity factor

and eccentricity

8. Use of specifications of Ministry of Construction

I

9. Check

ultimate

capacity for

lateral load

10. Approval by building officials of local government body

1 1 . Special

approval

required

Figure 3.2.7 Flow chart for seismic design according to the 1981 Building Standard Law

(Aoyama, 1993).

77

3.3 Performance of Traditional Wood

Houses

The majority of the casualties reported in

this earthquake were primarily due to the

collapse of old Shinkabe and Ohkabe houses

made of wood. Most of the damaged

houses were of non-engineered type

construction, primarily built to support the

gravity loads. As described in Section 3.2.1,

prior to World War II, the code of practice

called the Urban Building Law was used to regulate building construction primarily in

the six largest cities, including the city of

Kobe. This older code apparently lacked

detailed guidelines about seismic resistant

structural construction; such details became

available only in the later codes. During

wartime and several years after the war, even the existing building construction "law was not enforced due to wartime conditions"

[13]. The Ministry of Construction initiated

the revision of the defunct Urban District

Building Law in 1949. The revised version was finally adopted as the Building

Standards Law in 1950. It appears that

heavily damaged wood houses in this

earthquake were constructed in the post-war

period, but before the Building Standards

Law became applicable. Due to postwar

scarcity of adequate building material and

immediate need to rebuild, the residential

units were perhaps made with substandard

materials and construction practices, and

perhaps without any code regulations.

The number of collapsed houses constituted

about 10 percent of the houses in the Kobe

area. It was reported [3] that nearly 55000

houses collapsed and over 35000 houses were partially destroyed. These included

both Shinkabe and Ohkabe houses. Typical

damaged houses are shown in Figures 3.3.1 and 3.3.2.

In general, more Shinkabe houses sustained

complete collapse. The Shinkabe

construction employed walls of bamboo

thatch tied with rope and packed with mud.

The outside facade consisted of stucco or some light coverings with no structural

resistance. Figure 3.3.3 shows a damaged

two-story Shinkabe construction and Figure

3.3.4 shows a completely collapsed Shinkabe

house. In Ohkabe construction, the columns were joined by thin wooden slats (80 mm x 20 mm) placed horizontally (see Figure

3.3.5). Some parts of the Ohkabe houses were also reinforced by light wooden cross braces, and they performed better than the

unbraced parts (see Figure 3.3.6). There

were no indications of plywood or particleboard shearwalls being used in these

constructions, as is a common practice in the

United States. Only a few wood houses had

some type of diagonal bracings, and a majority of the wood houses had essentially no significant lateral load carrying capacity

to withstand earthquake loads.

Many severely damaged houses had heavy

ceramic roof tiles set on soil as bedding (see

Figure 3.3.7). It is believed that heavy tiled

roofs were preferred not only for the

aesthetic and architectural reasons, but also

because they could not be easily dislodged

by gusty winds in a typhoon. The heavy

roofs of these houses have contributed a

great deal to their collapse. On the other

hand, some of the older houses which used

less elaborate and less expensive synthetic

roofing made of light material performed

well in this earthquake.

The Building Standards Law of 1950 went

through a series of major revisions in the

1960's primarily to respond to the growing

demand for and planned construction of

high-rise buildings. In 1960, code provisions

for bearing walls were introduced and a minimum wall ratio of the wall area to the

79
floor area was established. The 1971-code

provided regulations for the "frame wall

construction method", also called the

"two-by-four construction method" (because

it used 2x4 lumber in the construction). It has been reported [3] that such two-by-four

construction and the residential houses

which followed the 1971 and later code

regulations performed rather well in this

earthquake. Figure 3.3.8 shows a frame

house under construction using 2x4's which

survived the earthquake.

80

Figure 3.3.3 A damaged two-story Sake factory with Shinkabe construction.

82
Figure 3.3.4 A completed collapsed Shinkabe construction-type house.

83
Figure 3.3.5 An Ohkabe house with only architectural design. Note a shadow of diagonal

bracing on the left side of second story.

84
Figure 3.3.6 Intact upper story (braced) of a collapsed unit - Ohkabe construction.
Figure 3.3.8 A new "two-by-four" construction replacing a destroyed residential unit.

86
3.4 Reinforced Concrete and SteelReinforced Concrete Buildings

3.4.1 Introduction

Reinforced concrete (RC) and steel- reinforced concrete (SRC) structures are most common for medium- and high-rise

buildings in this region. SRC involves

structural framing elements encased in RC.

It is difficult to discern whether a building is RC or SRC type based on visual

observation. However, based on Japanese

common design practice, it is reasonable to assume that offices, hotels and apartments

are SRC type if they are 7 stories and higher

[4]. Both RC wall- and frame- structures range from 2 to 7 stories (see Figure 3.2.1).

Reinforced concrete buildings

constructed prior to 1981 when the

concept of ductility was introduced

sustained severe damage. A

prominent mode offailure of RC

multi-story buildings was the partial

or total collapse of an entire story at

an upper level. Many of these failed

buildings were of steel-encased RC

(SRC) buildings.

In the central part of Kobe where a large

number of buildings sustained damage, RC

and SRC buildings comprised about 60

percent of about 2680 engineered buildings

[3]. The Kyoto University survey showed the

following damage distribution for RC and

SRC buildings in the central part of Kobe:

Developed collapse: 5%

mechanisms

Severe damage: 8%

Moderate damage: 11%

Minor damage: 21%

Slight damage: 55%

The distribution of severe damaged and

collapsed RC frame structures in the central

part (Chuo ward) of Kobe city is shown in

Figure 3.4.1. In this figure the block

numbers represent 20 damage survey zones

in the central part that was used by the

Kyoto University investigation team. Blocks

10 and 11 include the area near Sannomiya

station and the city hall. These two blocks

include the Kobe business district which had

many mid- and high-rise commercial

buildings, and consequently suffered a large

number of damage.

The Kyoto University survey revealed that

damage patterns closely paralleled the

improvements of the seismic provisions in

Japanese building code over time. It showed

the following percentages of buildings that

suffered severe damage or collapse:

Constructed before 1970: Over 55%

Constructed from 1971 to 1975: 30%

Constructed between 1976 & 1980: 10%

Constructed after 1980: None

These percentage figures clearly indicate the

positive impact of improved building code

provisions on the performance of buildings.

The Kyoto University survey also noted that no RC building that primarily relied on

shear walls for lateral load resistance

collapsed. This trend of decreased damage

of buildings with newer construction date

and the general lack of collapse or damage

to shear wall buildings were also noted by

the survey team.

87
Types of damage observed ranged from

shear failure of columns to total collapse of an entire floor. As observed in other

earthquakes, many buildings sustained

damage to the first story. Particularly, many

structures which were built prior to the 1971

revision of the Building Standard Law

sustained severe damage to first-story

columns. In most cases, shear failure of

these columns resulted from the lack of

column transverse reinforcement. As pointed

out in section 3.2.1, closer spacing of column

transverse reinforcement was introduced first

in the 1971 revision.

An uncommon mode of failure observed in

this earthquake is a total collapse of an

entire story at a mid level of a building. One

of the most likely causes of this type of

failure is abrupt changes in the lateral

stiffness at that story. Failure of splice of

longitudinal reinforcement by "gas-pressure

welding" also caused column failure of

several buildings. Some buildings suffered

significant damage due to shear failure of

walls and short wall-columns or piers.

3.4.2 Description of Damage

Typical damage to reinforced concrete and

steel- reinforced concrete buildings are described in the following.

3.4.2.1 Damaged Reinforced Concrete (RC)

Shear Walls

Shear walls were used commonly in large

mid-rise engineered buildings as major

lateral load resisting elements, as well as in low-rise buildings. While no shear

wall-related collapses were noted in larger

engineered structures, numerous smaller

structures with shear walls suffered

collapses.

Figure 3.4.2 shows the east end of the

second story of the seven-story Kobe Central

Post Office. The structure had a dual shear

wall and SRC moment frame system. Large

diagonal tension cracks can be seen in the

shear wall, and a thin masonry veneer can be seen to have fallen off. The height of the

first and second story are about 5 m and 4m,

respectively. Loss of concrete cover on some

ground-level columns revealed smooth

longitudinal reinforcement and wide column

tie spacing; the building is estimated to be

approximately 30 to 35 years old.

Figure 3.4.3 shows a multistory office

building in the western section of Chuo ward

of Kobe. The building has suffered diagonal

tension cracks in lower four stories, with the

severity of damage increasing toward the

ground level, paralleling increasing story

shear. Figures 3.4.2 and 3.4.3 illustrate the

typical damage seen in engineered shear

walls; no collapses were seen, even in

apparently older structures.

Figure 3.4.4 shows damage to window levels

in a five story apartment building in the

Nishinomiya area, which is several

kilometers NE of the downtown Kobe area. The reduced cross-sectional areas in the

window regions have suffered diagonal

tension cracks, due to "short column" effects

caused by the partial height infill walls.

Figure 3.4.5 shows a complete shear wall

failure in a low-rise apartment building in

the Nishinomiya area. The failed wall was

very lightly reinforced. This was an

apparent "soft-story" failure, as the ground

floor was a parking area (a situation that was very common). The entire story

collapsed. The two sections of the failed

wall, seen in the left side of the figure, were

laterally separated by almost a meter.

88
3.4.2.2 Damage to Reinforced Concrete

Frame Members

The many RC structures that combined both

"soft" first story and poor column details

suffered severe damage throughout the

Kobe area. Figure 3.4.6 shows a first story

column in a low-rise storefront structure. The column racked excessively to cause loss

of concrete integrity at its base. When the

concrete integrity was lost, the longitudinal

reinforcement buckled locally. Note the

widely spaced ties and smooth longitudinal

reinforcement. In Figure 3.4.7, a structure very similar to that in Figure 3.4.6, the

smooth bars with widely spaced ties have

buckled at the mid-height of the column.

As column detailing techniques were

improved for newer (post-1971) structures,

damage in newer structures was less severe. Figures 3.4.8 and 3.4.9 show columns with

much more closely spaced hoops, and with

deformed reinforcement. Figure 3.4.8 shows

a column that suffered complete

deterioration of the core, but the

reinforcement integrity was generally

maintained, preventing collapse. Figure

3.4.9 shows a column with only minor

damage, scabbing of the cover. This column

was in a building that was located in the

vicinity of the Sannomiya station where

ground motions were intense.

Figure 3.4.10 illustrates classic "short

column" failures through shearing of

columns that have been stiffened over

partial heights by infill walls. This structure was the Otaki Building in downtown Kobe.

It was a nine-story RC structure with a penthouse on top. This cracking pattern

extended over the entire building height,

though its severity decreased with height.

Figures 3.4.11 and 3.4.12 also illustrate

classic short column damage. These are views of the ground floor in the Fukae

Mitsuku Housing Project, in the

Nishinomiya area. This 9-story SRC building

has partial height infill walls which stiffened

the first-story columns that led to shear

failure. A close view of Figure 3.4.12 shows

that a wide flange section is placed at the

column centerline. With the severe amount

of damage that is shown, it is likely that this building would have completely collapsed

had it not been SRC.

An unusual problem was seen in downtown

Kobe. Figure 3.4.13 shows a collapsed

six-story RC building. It was located

between two other buildings that appeared

to be damaged only cosmetically. It is likely

that pounding, caused by N-S motions,

contributed to the collapse, but note the

relative size of the columns with respect to the girders. It appears that, with the almost

universal failure of the columns, that a

"strong girder-weak column" system existed.

3.4.2.3 "Soft" First-Story Collapses

A significant number of RC structures with

collapsed first stories was observed. It is common Japanese practice to use first story

and basement areas of both office and

apartment buildings as parking areas or other open spaces (e.g., for street level shops). This frequently leads to flexible first stories that predominately or solely resist lateral loads by the first story columns. The

upper stories are stiffened by the presence

of walls. The stiffer upper portions of such

structures will tend to translate and/or twist on the softer first story columns, leading to severe column damage or full story collapse.

This problem has repeatedly arisen in past

earthquakes around the world. In the Kobe

area, this was exacerbated by the deficient

detailing practices for RC members built

during the pre-1971 era. First story columns

that had collapsed typically showed small

and widely spaced ties. Ties were often

89
completely broken or otherwise displaced.

Column longitudinal reinforcement suffered

varying degrees of distress in such instances.

In some minimum damage cases, the

concrete cover had spalled off the

longitudinal bars. Damage in other

instances ranged from loss of all cover, complete shattering of the column core

concrete over significant lengths of columns,

and to complete buckling of the longitudinal

reinforcement. Another significant poor

practice was seen in a large number of RC

buildings. The longitudinal column

reinforcement was undeformed, or smooth.

In many of these instances, reinforcement

that was stubbed up from the column

footings into the first floor columns was

deformed, while the column reinforcement was not. This practice was discontinued in

the 1960's. The use of smooth bars reduces

bond strength, weakening all aspects of

reinforcement performance. Complete

buckling of the longitudinal reinforcement

bars in such columns was quite common.

Figures 3.4.14, 3.4.15, and 3.4.16 illustrate

the typical collapses that occurred in RC

buildings due to soft first story. These

collapses were generally confined to smaller

commercial or apartment buildings that were

five stories or less. The buildings shown in

Figures 3.4.14 and 3.28 are apartment

buildings location in Chuo ward of Kobe,

while the building in Figure 3.4.15 shows a commercial building in downtown Kobe.

3.4.2.4 Mid-height Story Collapses in RC and SRC Mid-rise Buildings

A substantial number of RC and SRC frame

buildings suffered partial or full story

collapses at upper floor levels. In several

cases, the collapses probably resulted from

plan and stiffness irregularities; this phenomenon has been observed in almost

every major earthquake. Figure 3.4.17

shows the Miyagi Hospital in the Ashiya

area, which suffered a second floor collapse.

The ground floor of this building was

populated by shear walls, making it stiffer than the second floor framing. Immediately

above the second floor, the plan size

reduced considerably with a setback. The

second floor was thus stiffer than the next

floor up but not as strong as the ground

floor. In Figure 3.4.18, the fourth floor of a ten story apartment building in the Ashiya

area has collapsed. The fourth floor was the

first setback floor above the larger plan of

the lower three floors. In Figure 3.4.19, a

five-story commercial building in downtown

Kobe has suffered an almost complete

collapse of its second story. The ground

floor was a parking garage. It appeared that

the ground floor was considerably stiffer than the second floor because of large

columns and shear walls there. Since the

building is in a street corner location, it is possible that its walls away from the street have fewer penetrations than the street

walls, resulting in an uneven stiffness

distribution, which could induce torsion in

the structure. Figure 3.4.20 shows a 10-story

SRC building, in which the third floor has

collapsed. In Figures 3.4.21 and 3.4.22, an

eight story (with offset penthouse) building

in downtown Kobe has suffered an almost

complete collapse of its seventh floor level. The offset penthouse may have contributed

torsional effects in this structure. In Figure

3.4.23, in a building in downtown Kobe, the

setback penthouse structure's shear wall has

failed, and the penthouse is leaning

noticeably.

A significant number of RC and SRC frame

mid-rise buildings suffered partial or complete collapses of a single story at upper

floor levels, where no obvious plan changes

or eccentricities could be seen. This failure

mode was particularly prevalent in

downtown Kobe. Because the failures had

90
occurred well above the ground level, thus

prohibiting close examination of damage

mechanisms. For example, Figure 3.4.24

shows the 8-story old city hall building which

experienced a total collapse of the sixth

story. This SRC structure was completed in

1957. As can be seen in this figure, the

building was not readily accessible. However,

it was stated by the city engineer that

encased structural steel section in concrete

columns extended to the fifth story.

As described previously, Japan has the

unique SRC construction, which when used

properly, may enhance ductility. However,

the Japanese host engineers indicated that it was typical in earlier times to discontinue

the embedded structural steel elements

above certain story levels, resulting in

stiffness or strength discontinuities that

could contribute to structural failures. If the

framing system extending above the cutoff

level for the embedded steel were made of

RC, initial stiffness of the upper level may

have been essentially the same as that below,

while strength was lower. If the framing

system extending above the cutoff level for

the embedded steel were structural steel only, the stiffness properties would change.

Both techniques, using steel alone and using

RC alone, above the cutoff level, have been

used, although RC is apparently the more

prevalent system.

Another potential contributing factor in the

observed upper story collapses may have

been the uniform lateral load distribution

used in earlier Japanese seismic design.

Post-1981 practice involves using lateral load

distributions that more closely resemble the

modal responses of a building structure to ground motions. A uniform lateral load

distribution would tend to result in upper

story members that are under-designed for

the story shears and moments that are

actually present, while lower story members

would be less likely to be overstressed. It seems plausible that both the load

distribution and SRC embedment cutoff

would contribute to upper floor collapses.

One building that suffered an upper story

collapse was the West Kobe Citizens

Hospital. The hospital was an interlinked

multi-building complex. The middle building was a 7-story structure, and a significant

length of the north end of its fifth story

suffered an almost complete collapse.

Figure 3.4.25 shows a view of the NE corner

of the collapsed area, while figure 3.4.26

shows its NW corner. The north end of the

structure collapsed completely, while the

south end, away from the pounding zone

that it had with the northernmost building was relatively intact. The south end of the

collapsed building was bordered by what

appeared to be a three story addition on its southwest corner, which may have provided

a stiffening effect on the level below the

collapsed story. While pounding with the

adjacent building to the north is apparent, it

is unclear that the pounding alone caused

the severe collapse mechanism, and no

major structural irregularities are noticeable.

The floors above and below the collapsed

floor are relatively undamaged. The failed

columns in the collapsed floor appear to be

pure RC.

3.4.2.5 Other Observations

There were several buildings which wee

completely overturned due to large sway

motion. One such building is a 9-story SRC

building located on Flower Road, north of

the Snnomiya station. Tin's box-shaped

building had two bays in the east-west

direction and five bays in the north-south

direction. Three sides of the building had

shear walls and the side facing the main

street (east side) was consisted of moment

resisting frames. Immediately following the

91
earthquake, the building was leaning

considerably toward east (Figure 3.4.27). In the evening of the same day, January 17, the

building collapsed onto the six-lane street severing traffic flow (Figure 3.4.28).

According to a report by Takenaka

Corporation, torsional motion of the

building caused the first story columns on

the east side to fail in shear, thereby causing

the building to lean toward east. Both the

west side shear wall and SRC column

connections failed in tension. The cause of

the collapse is not clear. It is possible that

aftershocks triggered the collapse.

92
Figure 3.4.1 Collapsed and severely damaged RC frame structures in Kobe.

93


Figure 3.4.6 Failure of older column - local bar buckling.

96
Figure 3.4.7 Failure of older column - general bar buckling.

97
Figure 3.4.8 Failed column in commercial structure.

98


101
Figure 3.4.14 Collapsed first story near JR Line.

102
Figure 3.4.15 Collapsed first story.

103
Figure 3.4.16 Collapsed first story - downtown Kobe.

104
Figure 3.4.17 Second story collapse - Miyagi Hospital.

I

Figure 3.4.21 Upper story collapse - Downtown Kobe.

Figure 3.4.22 Upper story collapse - Downtown Kobe.

107
Figure 3.4.23 Collapsed penthouse structure.

Figure 3.4.24 Collapsed upper story, north end - Kobe City Hall Annex.

108
Figure 3.4.25 Collapsed upper story, northeast corner - West Kobe Citizens' Hospital.
Figure 3.4.27 A leaning 9-story SRC building on Flower Road prior to total collapse.
3.5 Performance of Steel Buildings

3.5.1 Introduction

As was described in the introduction and in

Section 3.2, Kobe is a rather unique

situation from an engineering viewpoint in

that it was essentially re-built from scratch

following World War II. Code development

for steel structures essentially followed that

for reinforced concrete with regards to design loads. When the new two-phase

design procedures were introduced in 1981

(see Figure 3.2.7) the procedures to be

followed for steel frame construction were

identical to those for reinforced concrete

with two important exceptions:

(a) The present code permits the

construction of a particular class of steel frame structures without meeting the

second phase code design requirements,

provided that:

1) It is not more than three stories tall, including a basement.

2) Not more than 13 m in total height

and not more than 9 m at the elevation

of the eaves.

3) The horizontal distance between

major vertical structural supports is not

more than 6 m.

4) The total floor area is not more

than 500 nr.

5) The design seismic shear force in

the first phase design is calculated with

the standard shear coefficient taken not

less than 0.3. 6) All end connections and joints of

lateral (diagonal) braces which carry

horizontal earthquake forces must not

fracture when the bracing member is yielding.

(b) For steel frame structures not exceeding

31 m in height and which do not meet

the criteria described in (a) above, the

following criteria apply:

1) If the building includes stories

(except the basement) that are braced

to carry horizontal forces (as opposed

to moment resisting welded and/or

bolted frames), the force in the

members of each of those stories due to the design seismic force must be

increased by the factor B as follows:

When 0 is < 5/7 B = 1 + 0.7/3

For |8 > 5/7 B = 1.5,

where /5 is the ratio of horizontal force

carried by the braces to the entire story

shear in the story being considered.

2) It must be shown, when necessary,

that columns, girders, and their

connections, do not lose their loadcarrying capacity rapidly due to local

buckling or fracture.

Three major types of steel buildings were

noted in the Hanshin area: 1) braced frames

in one lateral direction, 2) braced frames in

both lateral directions, and 3) moment

resisting frames without lateral braces. A

damage survey carried out by the Steel

Committee of Kinki Branch of the

Architectural Institute of Japan [3] reported

that, among 988 buildings which they

investigated, 134 buildings had bracings in one direction, 34 buildings had bracings in

two directions, 432 buildings had moment

frames, and 388 contained unidentified

framing systems. However, it is believed

that moment frames comprised of about 70

111
percent of the buildings of the unknown

framing system category. With this

assumption, it can be conclude that over 70% of steel buildings investigated contained

moment frames.

Similar to RC buildings, steel

buildings constructed 20 to 30 years

ago sustained severe damage,

whereas buildings designed and

constructed according the 1981

Building Standard suffered little.

With the relaxed design procedures

permitted under (a.l) above, prefabricated

steel moment frame buildings are common

in the Hanshin area and elsewhere in Japan.

Typically these frame involve shop fabricated

columns in 3-story segments shipped to a construction site with integral beam stubs

projecting about 0.5 m. In this way, no field

welding is required and the frames are

rapidly assembled on site by connecting

beam segments to the stubs by means of

high strength bolts. An example of one such

new construction is shown in Figures 3.5.1 and 3.5.2. As shown in these figure, the

columns are usually made of cold-formed

square tubular sections. The beam stubs are welded to the through diaphragms as shown

in Figure 3.5.3. In some cases, wide-flange

sections are also used for columns. Usually,

the floor framing is comprised of cast-inplace concrete. External facades are commonly prefabricated autoclaved

lightweight concrete (ALC) panels,

approximately 0.5 m wide and 3 m high, or one story height. The ALC panels are attached to welded clip angles on the steel frame. Because the attachment hardware is not intended for structural resistance to seismic load, and because the panels are less

ductile than the supporting steel frames,

there is an inherent displacement

incompatibility in this type of design under

seismic loading. The response of this type

of construction during the earthquake is discussed in further detail below.

For steel structures the minimum

requirements, in theory, result in assurance of increased strength and ductile behavior of

braces, and ductile behavior of frames when

the frames carry some portion of the lateral loads. Clearly the intent of the code in the case of braced frames is to have the cross section of the main brace yield before any

weld or bolt failures in the attachment to the main vertical load bearing frame to occur. Many dramatic partial collapses in

the Hanshin area were a result of failure of

the as-built structures to meet this performance criteria.

For buildings greater than 60 m in height,

elastic and inelastic dynamic response

analyses are required on a case-by-case

basis. In these analyses, the input ground

motion with maximum acceleration of 0.2 g

to 0.3 g for elastic response and 0.3 g to 0.5 g for inelastic response. During this earthquake, no building greater than 10

stories collapsed. However, some sustained

severe damage.

Figure 3.5.4 shows the distribution of

damage of 988 steel buildings surveyed by

the AIJ Kinki Branch [3]. The figure reveals

that 3- and 4-story buildings sustained most

damage. Figure 3.5.5 shows the distribution

of collapsed steel buildings throughout

Kobe. In this figure, the block numbers

represents zones where the damage survey s were conducted in the central part of Kobe

as described in section 3.4.1. Figure 3.5.5 shows clearly that most collapses occurred in Chuo ward of Kobe city where commercial

buildings are concentrated. Comparison of

112
Figure 3.4.1, the damage distribution of

concrete buildings, and Figure 3.5.5, the same for steel buildings, indicate that the

number of collapsed and severely damaged

buildings of steel and of concrete are about

the same.

3.5.2 Description of Damage

A variety of failures were observed in steel frame structures. These included:

a) complete joint failures in low rise, older

buildings with severely corroded light gage

sections and/or cold formed steel; b) fracture

of diagonal braces; c) buckling of first floor

columns; d) weld fractures at beam-column

joints in medium-height prefabricated

moment frames; and e) fractures in virgin

column material and in beam joint welds in high rise structures. In addition there were some column base failures and anchor bolt

pullouts in slender buildings and large

permanent story drifts in the upper parts of

buildings. Detailed examples with discussion

of each of these follow below.

3.5.2.1 Weld Fractures in Light Gage

Steel Frames

A large number of failures occurred in low

rise steel frame structures constructed using

light gage or cold formed steel. These were

popular forms of construction in the 1960's

when there were shortages of steel for

general construction in Japan. In almost all cases, these were older (pre-1971) buildings

with less than three stories and typically

exhibiting significant corrosion and rusting

(See Figures 3.5.6 and 3.5.7). The degree of

corrosion in these older steel structures was

surprising, despite evidence that the steel had originally been shop painted (usually red

or orange) and was covered by various layers

of cladding. This corrosion may possibly be

related to Kobe's location as a port city on

the south coast, where typhoons may drive

airborne salt water mist inland.

3.5.2.2 Diagonal Brace Fractures

Braced frame structures are very common in

the Hanshin area although they seem to be

less prevalent in more recently constructed

buildings which tend to be prefabricated

moment frame designs. The braced frame

structures which failed were generally either

garage buildings or low- to mid-rise office

buildings. The low-rise buildings (Figure

3.5.8) often had masonry block infilled walls

(Figure 3.5.9). Even with the added rigidity

of the infill walls there were failures in the

braces. Although the present (post-1981)

code provides specific language concerning

the designs of welds and bolted connections

to insure first yielding of the braces, there were many such failures in the welds.

Those braced frame structures which did not

have infilled walls were more flexible. One

of the more striking failures in downtown

Kobe was a seven-story braced frame system

(Figure 3.5.10) with autoclaved lightweight

concrete panels for cladding (Figure 3.5.11).

This building had a very narrow platform

with one bay in the east-west direction and

two bays in the north-south direction.

However, the building drifted severely

toward north (stiffer direction) due to fracture of numerous braces (each

approximately 6 mm x 75 mm in cross

section) at bolted connections to gusset

plates which are welded to the columns. In the upper floors, it can be seen that the

braces in tension, which attempted to prevent displacement of the building toward

the north, fractured through the bolt hole.

The building remained standing only due to the presence of bolted shear connections for

the beams, which managed to resist some

lateral load.

113
Figures 3.5.12 and 3.5.13 are of a rather

unique braced frame failure in Higashi Nada

ward. This was originally a two story Ohkabe

type traditional dwelling, as evidenced by the

exposed slat timber wall construction

beneath the stucco in Figure 3.5.12. At

some time a third story was added. To do

this, an exterior steel braced frame was used.

During the earthquake the cross braces (18

mm round bars) failed. These were attached

to the steel frames apparently by means of

field welded clip angles (Figure 3.5.14). The

clip angle welds failed and the third floor

shifted westward by approximately 300 mm.

3.5.2.3 Buckling of Columns

Column buckling in steel structures was a

relatively rare event, with the notable

exception of some unusual failures in transportation infrastructure. An example of

column buckling in an 8-story building was a parking garage in downtown Kobe (Figure

3.5.15) . This structure (NO.2 South Parking

Building) is comprised of tubular columns

(16 mm wall thickness) and wide-flange

beams with diagonal braces. The first two

floors of the northeast corner of the

structure has a large unobstructed open

space for the gas station. It was the

northeast steel column that buckled (Figure

3.5.16) . An unusual architecture (large

eccentric open space on the first floor)

contributed to the excessive loads

experienced by column.

3.5.2.4 Weld Fractures in Low-rise

Buildings

Next to reinforced concrete, shop fabricated

steel moment frame construction seems to be a close second in terms of the number of

buildings in the Kobe area. The main

advantages are the speed of erection in the

field, since the columns are shop fabricated

in 3-story units with 0.5 m long beam stubs.

These eliminate the requirement for field

welding. Furthermore, special provisions in

the 1981 code ease the design process for

buildings less than 31 m (10 stories) and

particularly for buildings of three or fewer

stories.

In many instances, evidence of damage to

steel structures was somewhat difficult to recognize, since steel members are hidden by

more layers of exterior cladding. The most

common cladding is autoclaved lightweight

concrete (ALC) panels. These 0.5 m x 3 m x

a 75 mm thick panels are attached to the

steel frame by means of welded clip angles.

One example of moment frame structures which did suffer severe damage was a sevenstory Nari Hiro Building in downtown Kobe

(Figure 3.5.17). Figure 3.5.18 shows a closeup view of the southwest column,

second story junction showing lateral buckling of the first story column. This,

however, was a result of more dramatic weld

failures on the east face of the building.

Figures 3.5.19 show details of a beam stubto-column connection failure on the east face of the same building. Figures 3.5.20

and 3.5.21 show first floor column to second

story column joint fillet weld failure.

A 3-story steel frame building (Tanigawa

Building) on Flower road in downtown Kobe

also suffered beam-to-column connection

failures (Figures 3.5.22 and 3.5.23). It is clearly seen that weld joint failure caused Hshaped girders to fall.

3.5.2.5 Moment Frame Behavior: Mid-rise

Buildings

Figures 3.5.24 through 3.5.34 show behavior

of mid-rise steel moment prefabricated

frames that are representative of this class of

structure in the earthquake. In no case was

114
the structural integrity of the building

threatened. The steel frame, in all but a

very few instances, did not yield. However,

there is an apparent stiffness incompatibility

between the precast exterior cladding and

the ductile moment frame which led to widespread damage to the cladding. This

damage was concentrated mostly at the corners between adjacent panels and in some cases the racking motion that induced

the damage caused one or more panels to shear free of their attachment clips.

Figure 3.5.24 shows the west face of the

Liberty apartment complex located in

Higashi Nada ward. This eight story steel moment frame was typical of the

performance of mid-rise steel structures designed according to post-1981 procedures.

The columns were comprised of

approximately 300 mm steel tube. The

south face of the building had an artificial brick veneer on the extended patios from

each floor and the remaining sides were

faced with architectural autoclaved

lightweight concrete paneling.

Figure 3.5.25 is a closeup view of west face

steel moment frame of the Liberty

apartments. The shop welded frame shows

no damage but autoclaved lightweight

concrete cladding suffered brittle failures

along panel edges. Figures 3.5.26 and 3.5.27

show details of the east face of this same

building. In this case one beam-column

joint showed flaked paint indicative of local

yielding.

The seven story Silver Heights hotel, also in Higashi Nada ward and located

approximately 500 m east of the Liberty

apartment complex, was similar in both

design and behavior. Figures 3.5.28 and

3.5.29 show details of cladding damage.

The nine story Pacific Power Corporation

building in downtown Kobe was yet another

example of a tubular steel column frame

which exhibited cladding failures. At first

. glance (Figures 3.5.30 and 3.5.31) this

appeared to have suffered a significant

failure of a reinforced concrete frame in the

first story. Closer inspection (Figure 3.5.32)

revealed that this was only the failure of

elaborate corner cladding and that the 300

mm tubular steel column hidden inside was undamaged.

A much older example of steel moment

frame behavior is shown in Figures 3.5.33

and 3.5.34. This apartment building had

four bays in the east west direction and

three bays in the north-south direction. The

frame shows significant rusting and extensive

cladding damage but was not considered to be in danger of collapse. It had two open

garage entryway on the southwest corner and an open accessway on the first floor at the northwest corner. Neither of these

apparently affected the performance of the

structure. However the cosmetic artificial brick veneer and the precast window panels

served as stress concentrators and, because

of their brittle nature, were severely

damaged.

3.5.2.6 Anchor Bolt Failure

Because of extremely high land costs, many

of the newer Japanese structures are sited on very narrow lots; such buildings are often

tall and narrow. Most of these structures seemed to be relatively undamaged in the

earthquake, but a few sustained damage to anchor bolts for column base. One such

building in downtown Kobe is shown in Figures 3.5.35, the SAGA building. This

building is located adjacent to the

overturned SRC building described in Section 3.4.2. It is a seven story building,

one-bay wide and three-bay deep, sited on a

115
narrow corner lot. The north side of the

building suffered large uplift forces; the

anchor bolts for the northwest corner column were stretched, with plastic

deformation estimated at over 10 cm (see

Figure 3.5.36). The building suffered minor

damage to the exterior ALC panels and

concrete footing.

3.5.2.7 Behavior of High-rise Buildings

The tallest building in downtown Kobe is the

new 30-story city hall (Figure 3.5.37). This

frame building appeared to have sustained no damage to the exterior. There were

minor cosmetic damage to the interior

finishing. It is not clear as to the structural

framing system, whether moment resisting

frame or braced frame. There was a damage to the sky bridge structure connecting the new and old city hall (Fig

3.5.38). The fifth-story collapse of the old

city hall is described in Section 3.4.2.

Unexpected large column fractures were

seen at the "Ashiya Hama Seaside Town"

apartment complex (Fig. 3.5.39). There are

14-, 19-, 24-, and 29-story buildings. The

main load carrying system is comprised of a

truss-like frames made of heavy steel sections (Fig. 3.5.40). The exterior columns

are welded square tubular sections and the

interior columns are H sections. These

columns are supported on concrete piles

some of which are 35 m long. The

dimensions of some of the exterior tubular

columns are 500 mm x 500 mm x 50 mm

thick. The diagonal braces are either Hsections or circular tubular sections. The

prefabricated concrete dwelling units are attached to the main structural members.

Most damage occurred in 19-story and 24-

story buildings. Many columns sustained

complete fracture through the entire cross section without any sign of inelastic

deformation. Figure 3.5.41 shows a complete

fracture through a column section and

extended into the bracing member. Figures

3.5.42 and 3.5.43 show repaired columns. In Figure 3.5.43, the fracture is not only

repaired with full-penetration weld but also

added stiffeners.

116
Figure 3.5.1 Typical modern 3 story new steel frame building being erected near Hanshin

Expressway #3 east of Kobe. Columns are pre-fabricated so that no field welding

is required.

Figure 3.5.2 Field joint assembly of prefabricated steel frame structure east of Kobe using all high strength bolted connections. Beam stubs, approximately 0.5m in length, are shop-welded for quality control improvement.

117
Column

Figure 3.5.3 Beam-column construction detail.

118
400

350

300

<v

| 250

D

C^ 200

V4-I ° 150

u

0)

I 100

50

0

Kobe Building Damage Statistics as a Function of Building Height

Collapse

Severe

Moderate

Minor

3 4 5 6 7 8

Number of Stories

10

Figure 3.5.4 Damage distribution of steel buildings.

119
Figure 3.5.5 Kobe Damage Survey: Collapsed and severely damaged steel frame structures.

120
Figure 3.5.6 Three-story brick-faced light gage steel apartment. Has roll up door. Closeups

(Fig 3.5.7) show that there is a great deal of rust at the connections at the second

floor which connect 8 inch light gage wide flange columns. Rust clearly was at

fault in the failure, not the steel frame itself... this is a common type of failure

that seems peculiar to this form of light gage steel frame construction... perhaps it

is the salt atmosphere of a port city that leads to such extensive corrosion.

121
Figure 3.5.7 See caption for Figure 3.5.6: a closeup showing the rusted joint.

122
Figure 3.5.8 Braced steel frame, 5-story, in downtown Chuoku (Kobe). Masonry infill walls

appear to have saved this structure while a neighboring structure did not fare as

well.

123
Figure 3.5.9 Many braced frame structures had failures of the diagonal braces at the welded

connections. This photo shows a weld fracture between the turnbuckle rod and

the gusset plate.

124
Figure 3.5.10 Partial failure of a 7-story steel braced frame structure. Braces failed in tension

at the bolted connections. Significant rust is evident in most closeups (see next

four slides) around the vicinity of these bolt holes which may have permitted

widespread fracture of the brace plates (approximately 6mm x 75mm plate).

125
Figure 3.5.11 West side of the building shown in Figure 3.5.10.

126
Figure 3.5.12 Two-story traditional Ohkabe construction house with a third story add-on

supported by a steel braced frame near the Mikage metro station, Nada ku.

127
Figure 3.5.13 Detail showing drift in the building shown in Fig. 3.4.16 when diagonal braces

failed.

128
Figure 3.5.14 Detail of brace failure: angle plate weld to the steel frame failed (not the tension

diagonal rod).

129
Figure 3.5.15 Northeast corner of a Mitsubishi/Sogo garage/gas station located just one block

east of Kobe City Hall. Main steel tubular column at the northeast edge of the

first floor opening buckled.

130

Figure 3.5.17 "Nairo Hiro" Building, a seven-story steel moment frame structure in downtown

Kobe.

132

Figure 3.5.19 Beam Stub-to-CoIumn weld failure on the east face of the Nairo Hiro building.

134
Figure 3.5.20 First floor column to second story column joint fillet weld failure on the east side

of the Nairo Hiro Building, downtown Kobe.
Figure 3.5.22 Collapse of the 3-story Tanigawa building on Flower Road in Kobe. This two-way

steel frame was constructed of H-shape beams welded to columns.
Figure 3.5.24 West face of the Liberty apartment complex in Higashi Nada-ku. This eight-story

steel moment frame was typical of the performance of mid-rise steel structures designed according to post-1981 procedures.

137
Figure 3.5.25 Closeup photo of west face steel moment frame of the Liberty apartments. Shop

welded frame shows no damage but autoclaved lightweight concrete cladding

suffered brittle failures along panel edges.

138
Figure 3.5.26 East face of the Liberty apartments.

139
Figure 3.5.27 Closeup photo showing locally yielded third floor column joint in the Liberty

apartment complex.

140
Figure 3.5.28 Seven-story Silver Heights Hotel in Higashi Nada-ku. This was another steel moment frame mid-rise building with cracking in the precast lightweight cladding.

141
Figure 3.5.29 Closeup of cladding cracking at the Silver Heights Hotel.

142

Figure 3.5.31 Detail of southeast corner of Pacific Power Corporation building.

144
Figure 3.5.32 Closeup photo revealing steel moment frame beneath failed cladding of the

Pacific Power Corporation building.

145
Figure 3.5.33 Older 5-story steel moment frame building showing extensive cladding damage to

brittle cladding in Nada-ku near the Mikage metro station.

146

Figure 3.5.35 Seven-story steel frame SAGA Building - Flower Road in Kobe
Figure 3.5.37 New Kobe City Office building. A 30-story steel frame structure without reported

damage. The adjacent old Kobe City Office building sustained severe damage.

149
Figure 3.5.38 Sky bridge structure connecting the old and new City Hall buildings.

150
Figure 3.5.39 "Ashiya Hama Seaside Town" apartment complex.
Figure 3.5.41 Complete fracture through a steel column section.

Figure 3.5.42 A repaired column immediately after the earthquake (Portland Cement

Association)

.

152
Figure 3.5.43 A column repaired not only with full-penetration weld, but also with stiffeners

added.

153

3.6 Lessons for the United States

With the exception of the unique SRC

construction type, the construction and

detailing practices of Japanese buildings

have generally evolved in a manner that

closely parallels U.S. practice. Code

improvements, while not identical, have

occurred at the same general pace in both

countries. This is not surprising, as many of

the more prominent Japanese researchers

and practicing engineers have studied in the

United States, and there has been an open

interchange of ideas in the seismic area for

many years. Engineers in the two countries

have good rapport, and cooperation is quite

good. The Hyogo Ken Nanbu earthquake,

therefore, offers an excellent opportunity to

reflect on several general issues.

First, and foremost, is the serious damage

that older RC moment frame buildings

suffered; many buildings experienced full or

partial floor collapses. Both the cost of

damage to the built environment and life safety are at issue. And, this event, with a magnitude of 7.2, was not the proverbial "big

one," though strong ground motions clearly

existed in the Kobe area. With the

exception of the abOve-noted smooth

longitudinal column reinforcement, the

damaged low to mid-rise RC buildings that were observed could easily have been U.S.

buildings that were constructed in the 1950's

and 1960's. The 300 mm column hoop

spacing is quite similar to U.S. practice of

that era, particularly in zones of low to moderate seismicity. The large amount of

damage that occurred in Kobe points out

the high vulnerability of these older, poorly

detailed, structures. This problem is not

only one of concern for the zones of higher

seismicity in the Western United States, but

it is also one of concern for the lower

seismicity zones in the Central and Eastern

United States, where detailing practices in

many cases have not kept pace with Western

U.S. practice. These older and less ductile

RC structures will require significant

rehabilitation to be made less vulnerable.

. Such a rehabilitation effort will no doubt be

expensive; building owners and the general

public should be apprised of the risks and

costs, so that they might make informed

decisions concerning rehabilitation,

replacement, or status quo.

While damage to older RC buildings was

severe, no evidence of collapse in any of the newer (post-1981) engineered RC structures was evident. The 1981 Japanese code

improvements that added the second phase

of seismic design that addresses ultimate

capacity is quite similar to the intent of

current-era U.S. building codes that focus on

life safety, or the prevention of collapse, in the one-time severe seismic event. In this

light, the Hyogoken-Nanbu earthquake is a vindication of the current code philosophies

in both countries and the technical changes

that have occurred in those codes as a result

of the RC research that has occurred since

the early 1970's in both the United States

and Japan. The research investment seems

to have generally paid for itself many times

over. A somewhat more subtle issue regarding

new construction is one that arose after the

1994 Northridge, CA, earthquake, which was

similar in magnitude to this most recent

event. That is, should there be standards

that provide better building envelope

integrity than the basic one-event life safety

standard that we have today? Because of

time limitations, the survey team was unable

to enter numerous newer buildings to observe what more subtle types of damage

might have occurred on the interior

elements of newer buildings. It was clear

from the external envelope surveys that

racking had caused many windows in newer

155
structures to crack or pop out of their

frames. Also, facade cracking and other

minor damages were present. These less severe damages represent costs to the

building owners, and in many circumstances can also pose life safety dangers from falling

debris (since this event and the one in

Northridge both occurred in the early

morning hours, commercial districts were

not yet active). Once more detailed damage

estimates are available, the HyogokenNanbu event should fuel further debate in

both the United States and Japan about

weighing initial construction costs against

potential future earthquake losses.

One general philosophical issue that is also

tied to the poor performance of the older

RC structures is the need for special

standards for hospital and other facilities that are essential to post-earthquake disaster

response. At least two Kobe-area hospitals

suffered catastrophic floor collapses. While

the State of California has commendably

implemented special earthquake safety

requirements for hospitals, not all U.S.

jurisdictions have done so. This event

should reinforce the need for such special measures.

While it seems that every major earthquake

illustrates these problems, thus perhaps

making the observation redundant, the

Hyogoken-Nanbu event again pointed out

the need for avoiding the use of "soft" stories and stiffness or mass irregularities

either in plan or elevation. Many of the

older building collapses could be at least partially attributed to the presence of such

weak links. Particularly in the densely built

downtown areas, the need to eliminate

pounding of adjacent buildings was also

evident; separation is the obvious solution,

but, when it is not provided, the interactions

of adjoining buildings must be considered.

From what the survey team members

observed, the Kobe area had no significant

pre-earthquake seismic rehabilitation

initiatives. Likewise, there apparently were no newer energy dissipation technologies,

such as base isolation or supplemental

damping, used in any of the Kobe buildings.

The poor performance of steel frame

structures was generally prevalent to low- to mid-rise structures constructed with light

structural members. Types of welded

connections that failed are not common in

the United States. However, as many

welded connection failures we have seen in the Northridge earthquake, we should not over look at types of welded connection

failures occurred in Kobe. The use of

precast autoclaved lightweight cladding for

light steel frame structures is not common

practice in the United States. It does,

however, indicate that extensive monetary

damage can be inflicted on a structure in the

form of cladding failures. In this respect it will generally be the purview of the building owners to decide whether such loss,

following a major design-level earthquake, is tolerable. If not, then displacement

compatibility studies will need to be

undertaken to insure that large racking

motions, which can be tolerated by the

ductile steel frames, are limited to that

which is tolerable by the more brittle

cladding.

A final note concerning steel structures are the questions raised by the extensive base

metal and weld failures observed at the

Ashiya Hama Seaside Town (AHST)

complex in Ashiya City. A number of thick

column sections and diagonal bracing

members sustained brittle failures. These

failures echo problems first observed in steel structures in the United States following the

Northridge earthquake.

156
3.7 Research Needs

Paralleling the "lessons learned," the largest

overall research need for RC buildings seems to be the need for extensive research on seismic vulnerability assessment,

rehabilitation, and retrofit for older,

non-ductile RC moment frame and shear

wall buildings in the three to ten story range.

These buildings are numerous both in Japan

and the United States, so they represent a

substantial area of risk and potential damage

cost. More accurate models of existing

non-ductile structures are needed,

necessitating research on older member and

system capacities. Most U. S. research has

focused on developing more ductile

members and elements for new construction.

Rehabilitation techniques need to be

cost-effective and non-intrusive for building owners and users. Continued focus on

improving the deformation capacities of

columns, girders, and joints in moment

frames is needed. Beyond this, continued

research into less traditional techniques for

rehabilitation, such as supplemental energy

dissipation and the use of newer structural

composites, should be conducted, both to provide architectural flexibility and to reduce

costs to affordable levels.

Two areas of unique potential study involve

the contrasts in Japanese and U.S.

philosophies. First, as was described above,

current Japanese design techniques result in

stiffer but less ductile RC structures than in the United States. A study of these two

differing approaches would seem to be

appropriate. Second, the distinctive

Japanese practice of SRC construction

should be studied. Disregarding the

apparent problems that existed with

discontinuities in these systems, it is important to examine whether the use of

such composite construction does enhance

ductility in RC beyond that provided by

current U.S. RC detailing techniques, and if so, to determine its cost-effectiveness with

respect to current detailing techniques.

A final area of needed research relates to the behavior of heavy steel frame, high-rise structures under strong low cycle lateral loading. Given the wealth of data

concerning the design procedures, weldment

details, and material specifications for the

Ashiya Hama Seaside Town complex in Ashiya City, research should be conducted

into the behavior of built-up steel column

sections and truss weldments under very low

cycle fatigue -- one cycle to yield followed by an immediate reverse cycle to yield in the

opposite direction. This would augment

research programs already underway in the

United States following the Northridge

earthquake.

3.8 Summary

The 7.2 magnitude Hyogoken-Nanbu (Kobe)

earthquake claimed more lives than any

other recent earthquakes in Japan. Eighty

nine percent of over 6000 casualties resulted

from collapsed residential buildings. Many of

these buildings were over 40 years old and

had little lateral load resisting capacity. The

walls of single family dwellings provided

little lateral load resisting capacity, and

could not support the heavy roof load during

severe ground shaking. Two- and threestory dwelling structures with commercial

operations in the first story had little interior

walls to resist lateral loads, thereby

sustaining partial or total collapse.

As presented in Section 3.2, major revisions

to the seismic design requirements took

place in 1971 and 1981. For the first time,

the ductility was introduced in the seismic

design in 1981. As a result, many reinforced

concrete buildings constructed prior to 1981

sustained severe damage. Many buildings

157
sustained damage to the first story. Shear

failure of first-story columns and collapse of

soft first stories were most common. A

prominent mode of failure of reinforce

concrete multi-story buildings was a partial or a total collapse of an entire story at an upper level. Many buildings failed in this

mode were of steel-encased reinforced

concrete (SRC) buildings. The distribution

of collapsed and damaged concrete buildings

from Kobe to Ashiya city is shown in Figure

3.8.1. It is seen that most damage occurred

in the central part of Kobe where

commercial structures are concentrated.

Similar to reinforced concrete buildings,

steel buildings constructed 20 years to 30

years ago sustained severe damage which

buildings designed and constructed

according to the 1981 Building Standard

suffered little. Welding failures at member

connections contributed to many of the

failures. Light steel frame structures suffered

member failures, particularly diagonal

bracing members, reduction in cross section

due to corrosion. Brittle fractures of heavy

steel columns with flange thickness of 50

mm occurred in a multi-story complex in Ashiya city. This is the first known case of

brittle fracture of multi-story building

columns during earthquakes. The

distribution of steel building damages

throughout the Kobe area is shown in Figure

3.8.2. The shape of distribution of steel building damage is similar to the one for the

concrete buildings. Furthermore, the severity

of damage of concrete and steel buildings are about the same.

The degree of damage of reinforced

concrete and steel buildings with respect to the year of construction are shown in Figure

3.8.3. These two plots are constructed based on damage observations of about 100

buildings in the central district of Kobe. It

is seen that both reinforced concrete and

steel buildings constructed prior to 1971

suffered severe damage beyond repair or

collapse, while the buildings constructed

after 1981 sustained no severe damage or

collapse. This clearly attests that upgrading

of building codes is a most important factor

in improving the performance of buildings

during earthquakes.

3.9 References

1. Design Essentials in Earthquake Resistant

Buildings, (English translation of 1966

publication in Japanese), Architectural

Institute of Japan, Tokyo, 295 pp., 1970.

2. Design Standard for Steel Structures,

English translation of the 1970 Japanese

publication, Architectural Institute of

Japan, Tokyo, 113 pp., 1979.

3. Preliminary Reconnaissance Report of the

1995 Hyogoken-Nanbu Earthquake,

English Edition, Architectural Institute of

Japan, Tokyo, 1995.

4. Aoyama, FL, "Outline of Earthquake

Provisions in the Recently Revised

Japanese Building Code," Japan

International Cooperation Agency,

Tsukuba International Center, Japan, 34

pp., 1993.

5. Chiba, N., "Building in Steel in Japan,"

Proceedings, from the International

Symposium entitled "Building in Steel - the Way Ahead," British Constructional

Steelwork Association, London, 1989.

6. The Hyogo-Ken Nanbu Earthquake,

January 17, 1995, Preliminary

Reconnaissance Report, Earthquake

Engineering Research Institute, 1995.

158
7. Ishiyama, Y., "Aseismic Design Method

and its History in Japan," summary of

oral presentation, Proceedings of the 3rd

U.S. -Japan Workshop on the Improvement

of Building Structural Design and

Construction Practices, ATC-15-2, Applied

Technology Council, Redwood City,

California, pp. 8, 1989.

8. Ishiyama, Y., and Y. Ohashi, "History of

Structural Regulations in Japanese

Building Codes and Outline of WindResistant and Seismic Regulations," Wind

and Seismic Effects, Ed. N. Raufaste,

NIST SP 776, NIST, Gaithersburg,

Maryland, pp. 335-347, January 1990.

9. Morino, S., I. Nishiyama, and N.

Sakaguchi, "Hybrid Structures in Japan - Research and Practice," SSRC annual

meeting, Lehigh University, 1994.

10. Naka, T., M. Wakabayashi, and J. Murata, "Steel-Reinforced Concrete

Construction," IABSE preliminary

report, Amsterdam, May, 1972.

11. Naka, T., M. Wakabayashi, S. Takada,

"Quake Resisting Design of Composite

Structures in Japan," Proceedings of the

Second World Conference on Earthquake

Engineering, V. 3, Tokyo, pp. 1811-1826,

1960.

12. Otsuki, Y., "Development of

Earthquake Resisting Building

Construction in Japan," Proceedings of

the First World Conference on

Earthquake Engineering, Berkeley,

California, pp.16.1-16.17, 1956.

13. Mizukoshi, Y., "The New Illustrated

Building Code," Shin-Nihon

Hoki-Shuppan Co., Ltd., Tokyo, Japan,

1978

159
CO

-a

300

250

5 200

a

<—o

1—U

J5E3

Z

150

100

Collapse Severe

Moderate

Minor

Slight ; Damaged RC Building Profile

4 5 6 7 8 9 10 1 1 12 13 14 1 5 16 17 18 19 20

"Block" Number (West to East)

Figure 3.8.1 Kobe Damage Survey: All damaged RC frame structures.

160
140

120

| 100

o

u 80

60 Q

o

<u X>E

3

Z

60

40

20

Collapse

i Severe

Moderate

Minor

Slight Damaged Steel Building Profile

L

4 5 6 7 8 9 1 0 1 1 12 1 3 1 4 1 5 1 6 1 7 1 8 1 9 20

"Block" Number (West to East)

Figure 3.8.2 Kobe Damage Survey: All damaged Steel frame structures.

161
Reinforced Concrete Structures

CD

£=

CJ CDT3

CDCD

COE

CC Q

CD£

40

35

30

25

20

15

10

5

0

.>. ».''.

^ Slight Damage or No Damage

H Minor Damage

^ Moderate Damage

O Collapse or Severe Damage

Up to 1971 1972 - 1981

Construction Period

1982 or Later

Steel Structures

40 F

!

t5 30

Slight Damage or No Damage

Minor Damage

Moderate Damage

Collapse or Severe Damage

0

CD

Up to 1971 1972 - 1981 1982 or Later Construction Period

Figure 3.8.3 Damage level of RC and Steel structures with respect to the year of construction.

162
CHAPTER 4

PERFORMANCE OF TRANSPORTATION SYSTEMS

4.1 Introduction

The Hyogoken-Nanbu earthquake caused

damage to transportation facilities throughout the Kansai region, severely

hampering rescue and recovery operations

and crippling the flow of commerce.

Observations on the performance of selected

highway, rail, airport and port facilities are given in this chapter.

The elevated expressways and rail systems in

the region were completely severed, creating

extreme hardship to the public. Although

rail service is being rapidly restored, it will be several years before the highway and rail systems are fully operational. Predominant

types of observed bridge damage included

massive shear and flexural failure of

reinforced concrete columns and piers, local

buckling of steel columns, numerous failures

of both moveable and fixed bearing

supports, and probable failure of

foundations from lateral spreading of the

ground and liquefaction.

The new Kansai International Airport

performed well, with no reported structural

damage to the air traffic control tower, while

the older Osaka airport experienced cracking

of a runway. The Osaka air traffic control

tower experienced cracked shear walls,

cracked glass, and had an inoperative

elevator following the earthquake.

Permanent ground deformation and

liquefaction disabled facilities at the Port of

Kobe, the world's third largest port. Lateral

spreading around the cargo loading areas of

the port resulted in severe damage to most

of the dockside gantry cranes, thus closing

the port facility. Complete restoration is estimated by Japanese engineers to take

about three years.

The earthquake caused severe damage to transportation facilities

throughout the Kansai region,

severely hampering rescue and

recovery operations and crippling the

flow of commerce.

There are two important features of the

Kobe area which had a major impact on the

seismic damage suffered by transportation

systems in the Hyogoken-Nanbu earthquake.

The first is the coastal topography of the

Kobe area; the second is the surface soil conditions along the margins of Osaka Bay.

The general layout of Kobe is shown in Figure 4.1.1. Kobe is squeezed into a narrow strip of land, bounded by mountains on the north and Osaka Bay on the south.

The city is aligned roughly in an east-west

direction, and all surface transportation

routes are located within a band only three

kilometers wide in some areas. The

Shinkansen, or "Bullet Train" line, also runs near Kobe, through an east-west tunnel in

the mountains just north of the city. The

transportation routes shown in Figure 4.1.1 not only serve Kobe, but they are also the

primary links between the eastern and

western parts of Japan's main island,

Honshu.

163
Because land and space is at a premium in Kobe, many transportation routes are

located adjacent to or on top of one

another. For example, over a distance of

about 30 km, National Route 43 and the

Kobe Line of the Hanshin Expressway (also

known as Route 3), occupy the same

alignment: Route 43 runs along the surface,

and the Kobe Line runs along a viaduct

above. In locations where the elevated

Kobe Line collapsed or was severely

damaged during the Hyogoken-Nanbu

earthquake, both the surface Route 43 and

the elevated Kobe Line were impassable.

Rail lines are also routed closely together,

with three separate rail systems occupying

the same right-of-way in some locations.

The tunnels of the municipal subway system

run beneath major urban streets in Kobe.

Cut and cover subway stations collapsed

during the earthquake, causing surface

subsidence of over 1 m in some locations.

Bridges in the central and eastern

United States are more like those in

Japan than those in California. The

performance of Japanese bridges is

therefore of particular relevance to

states east of the Sierra Nevada

mountains.

Thus, because the local topography dictates

that all major transportation routes pass

through a narrow corridor, the routes are crowded together. Unfortunately this corridor lay directly above the ruptured fault zone of the earthquake, so all major

transportation routes in Kobe were severely

damaged by the earthquake. This crippled

not only the transportation infrastructure in Kobe, but also the main cast-west transportation corridor on the island of

Honshu.

The second characteristic which strongly

in 11 ue need the seismic performance of

transportation structures in Kobe was the

presence of poor ground conditions,

especially along the bay shore. Historically,

the land area of Kobe has been extended by

lllling the bay. Over the years the shoreline

of Osaka Bay has been reshaped with numerous port and industrial facilities constructed on reclaimed land. Figure 4.1.2 shows the extent of artificial fill in Osaka

Bay. Some areas along the shoreline were

filled over two centuries ago. The largest

recent reclamation projects include Port

Island (No. 10 on the map), Rokko Island

(No. 12), and Kansai International Airport

(No. 50).

Many artificial fill deposits, especially older

"non-engineered" fill, are prone to liquefaction and lateral spreading during

earthquakes. However, out of necessity

transportation routes have been constructed on artificial fill in and around Kobe. Figure

4.1.2 shows that several major highways are constructed on reclaimed land. For

example, the Wangan, or "Bay Shore" route

of the Hanshin Expressway system rings the

entire bay from Kansai International Airport on the south to Kobe on the north. (The

portion of the Bay Shore route shown in Figure 4.1.2 to the west of Rokko Island is planned, but has not yet been constructed).

Several bridges on the Bay Shore route to the east of Rokko Island were damaged

during the Hyogoken-Nanbu earthquake.

Figure 4.1.3 shows the soil profile around

the perimeter of the bay, along the

alignment of the Bay Shore route. The

rectangular blocks at the top of the soil strata indicate filled areas. The fill depth

along the Bay Shore route is up to 15 m. The figure also shows that the natural soil

164
stratum underlying the fill layer is alluvial

clay, 10 m to 15 m thick in the Kobe area.

Soft clay layers such as this tend to filter earthquake ground motions, concentrating

the energy of the earthquake at certain

frequencies.

The difference between the maximum

credible earthquake and the design

earthquake, is clearly very large for

this region of Japan - a situation

that also exists in the United States.

I

To illustrate in more detail the typical bay

side soil conditions near Kobe, a soil boring

log from the site of the Nishinomiya Ko

bridge, located on the Bay Shore Route to the east of Rokko Island, is shown in Figure

4.1.4. The eastern approach span of this

bridge collapsed during the earthquake. A

major cause of the collapse was probably

liquefaction of the 10 m to 15 m of granular

artificial fill soil at the site. When the fill on

both banks of the river channel liquefied

each bank moved towards the center of the

channel. This lateral movement caused the

two end piers of the main span to move

towards one another, pushing the approach

span off its support.

Poor soil conditions in Kobe are not limited

to the immediate shore line of the bay. In Figure 4.1.5, two soil profiles along lines

perpendicular to the shoreline are plotted.

Profile (a) is in the Suma Ward at the west

end of Kobe, and profile (b) in Higashinada

Ward at the east end of Kobe. The profiles

show that soil conditions are highly variable

in the area, and that deep clay deposits can

occur in areas away from the shore line. Thus, transportation structures throughout

Kobe are founded on a variety of soil conditions, ranging from soft clays to competent granular materials, sometimes

underlain by soft clay strata.

165
Figure 4.1.1 Major transportation routes through Kobe.

166

Figure 4.1.3 Soil profile around the perimeter of Osaka Bay. along the alignment of the Bay

Shore Route. Reproduced from HEPC (1^0).
N -VALUE

0 10 20 30 40 50

— 20

— 30

— 40

GRAVEL

GRAVEL

Figure 4.1.4 Soil boring log at the Nishinomiya Ko bridge, near Nishinomiya Port (Courtesy of

the Public Works Research Institute, Ministry of Construction Tsukuba Science

City, Japan).

80 m r

SAND;

-20 m

2 km

(b)

Figure 4.1.5 Soil profiles along lines perpendicular to the shoreline of Osaka bay. (a) at Suma

Ward, at the west end of Kobe; (b) at Higashinada Ward, (b) at the east of Kobe.

(Courtesy of the Public Works Research Institute, Ministry of Construction,

Tsukuba Science City, Japan).

169

4.2 Highway and Bridges

4.2.1 Overview

The Hanshin region comprises parts of the

Hyogo, Kyoto and Osaka Prefectures to the

north and east of Osaka Bay. The

population of 12.5 million people living and

working in the region is served by a complex

network of freeways and highways built since

the early 1960's. These major transportation

routes generally run parallel to the shoreline

of Osaka Bay with major links to the east to Nara, to the northeast to Kyoto, and to the

west to Himeji. As the mountains behind

Kobe approach the Bay shoreline, the

east-west routes are forced into a narrow

corridor which is barely 3 km wide in some

parts and which must be shared with three

major rail lines. Soil conditions vary

throughout the region but most of the

highway structures are founded on

sand-gravel terraces (alluvial deposits) which

overlie gravel-sand-mud deposits at depths

of less than 10 m. Liquefiable soils are present along the shoreline and in most

ports and channels. As a consequence piled

foundations are used extensively and caisson

foundations are common for those large

bridges that are in port areas or cross shipping channels.

Responsibility for the design, construction

and maintenance of these highway routes is divided between the Ministry of

Construction and two Public Expressway

Corporations. Highways under the

jurisdiction of the Ministry of Construction

are free for public use whereas those owned

by an Expressway Corporation are toll roads

and road user fees are collected. These

latter Corporations are independent but are nevertheless subject to government control

and regulation.

The Ministry of Construction (MOC),

through the Naniwa National Highway Work

Office, has oversight for the National

Highways (NH) in the region. These include

Routes R-2 and R-43 which join Osaka with

Kobe, as well as several other trunk roads

such as Routes R-428 (Kobe to Chugoku

Expressway), and R-171 (Nishinomiya to Kyoto and Route R-l). These arterial

highways are generally surface routes but

with some notable elevated sections. These

include the Route 2 Hamate Bypass on the

Kobe waterfront, the Port Island Connector

and the 6.6 km-long, Airport Access

Highway to the new Kansai International

Airport in Osaka Bay.

One of the two Expressway Corporations

noted above is the Japan Highway Public

Corporation (JHPC) which is responsible for

at least three major freeways (expressways)

in the region. These are the Meishin

Expressway (the first such expressway in Japan built in the early 1960s) and the

Chugoku and Kinki Expressways. The

Meishin runs in a northeasterly direction

from Osaka Bay (at Nishinomiya) to Kyoto.

Both the Chugoku and Kinki Expressways

start from Suita City, just to the north of

Osaka City, and run west and south

respectively.

The second Expressway Corporation noted

earlier, is the Hanshin Expressway Public

Corporation (HEPC). It is one of the

largest such Corporations in Japan and is, today, responsible for approximately 200 km

of freeway-standard highway throughout the

Hanshin region. Opened in 1964 with an

initial length of 2.3 km in Osaka, it has

grown in both size and capacity during the

intervening 30 years. Almost a million

vehicles per day used the system in 1994

with the highest traffic counts (131500 per

day) being recorded on the four lane, loop

expressway in the center of Osaka City. For

171
the fiscal year 1993, the average income

from tolls was ¥340 million per day

(approximately $3.4 million). More than

90% of the system is elevated, supported on

about 8500 spans. Of these, 83% are steel and 17% are concrete spans [1]. Most

substructures are single column concrete

bents but single and multi-column steel bents are also used to a significant degree.

Major routes under the jurisdiction of the

HEPC are Route 3 (Osaka - Kobe Route)

and Routes 4 and 5 (Wangan Route). The

Kobe Route was constructed from

Nishinomiya to Kobe from 1965 to 1970.

The link to Osaka was from 1981 to 1985.

The Wangan (Bayshore) Route, which links

Kansai Airport in the south (Route 4) to Rokko Island in the east (Route 5), was

completed in 1994 although parts of Route 4

had been completed as early as 1990. Both

routes were major technical

accomplishments at the time of their

construction. Average peak weekday traffic volumes in 1994 were 63000 and 18500 for

Routes 3 and 5 respectively.

Route 3 is elevated over its entire length

and runs above NH 43 from Osaka to Kobe.

It is generally supported on single column

bents, except at interchanges where ramps

and adjoining structures demand additional

width and the use of multi-column bents.

At the time of its construction it was highly

regarded for both its engineering

achievement and its aesthetic appeal.

The Wangan Route is also elevated over much of its length but its most remarkable

feature is the number of world-class, long

span bridges included in its construction.

Some of the more notable bridges include:

(1) the Minato Gerber truss bridge (510 m

center span, the third longest truss span in

the world); (2) three cable-stayed bridges

including the Higashi-Kobe bridge (485 m

center span, the eighth longest cable-stayed

span in the world); (3) two Nielsen-Lohse

tied-arches including the Nishinomiya-ko

bridge (252 m span); and (4) two Lohse

tied-arches including the Rokko Island

bridge (217 m span).

The HEPC has an active maintenance

program and currently spends about ¥30

billion per year (approximately $300 million)

in this area [1]. It also has an ongoing

seismic retrofit program and has for many

years used earthquake couplers to restrain

the free ends of simply supported girders.

The Corporation has recently begun to investigate the use of steel jackets for

improving the performance of concrete

columns and has installed some trial jackets on single column bents at the west end of

Route 3.

Seismic design criteria for new structures meet or exceed those required by the Japan

Road Association [2,3]. Furthermore the

HEPC has been proactive in the use of

energy dissipators in bridges and, as early as 1981, completed the Yoshino-Tamagawa

Viaduct on Route 3 in Osaka, using viscous

shearing dampers. More recently, the

HEPC has constructed two menshin (base

isolated) bridges on Route 4 (the Wangan

Route near the new Kansai Airport). These

are the 4-span, Matsunohama bridge (1994)

and the 6-span, Izumisano bridge (1994);

both use lead-rubber bearing (LRB)

isolators. The Matsunohama bridge is instrumented for strong ground shaking with

9 accelerometers and a 23-channel data

acquisition system.

4.2.2 Observed Damage

A large number of bridges were damaged in

this earthquake and one estimate of the

affected number is on the order of 60% of

the total inventory. An exact number is

172
difficult to count because of the use of long

elevated sections that are tens of kilometers

in length and the line where one bridge (or

segment) ends and another begins is difficult to determine. Furthermore, several

structures at the same interchange may be

identified, in some damage reports, as one

"bridge." Accepting these limitations, the

number of highway "bridges" that sustained

major damage (including collapsed spans) is of the order of 27. Many more suffered

moderate-to-minor damage such as pounding, spalling of cover concrete and

settlement of approach fills.

The 27 structures that were severely

damaged by this earthquake, are listed by

route number in Table 4.2.1 and by name in

Table 4.2.2. Figure 4.2.1 shows the location

of 16 of these structures. These sites were

visited by the UJNR team from February

13 to 17, 1995.

It is seen in Table 4.2.1 that the HEPC

suffered the largest loss, most probably

because it has the largest inventory of

elevated structures of any agency in the

Hanshin region. The HEPC estimate for

the direct cost of this damage is ¥460 billion

(approximately $4.6 billion). Average traffic counts fell from 920000 to 500000 vehicles

per day leading to a loss in toll revenue of

¥200 million per day. According to the

Hyogo Prefectural Police, 16 persons died in

vehicles on the Hanshin Expressway and 280

vehicles were abandoned. The number of

piers sustaining moderate-to-large scale

damage on Route 3 has been estimated to be 637. Corresponding numbers for spans

and bearings are 552 and 679 respectively. If

all categories of damage are included, the

HEPC estimates that the number of

damaged spans on Route 3 is in excess of

1300 [4].

Of the two routes, R-3 and R-5, Route 3 is older by about 30 years and this probably

accounts for the higher damage rate compared to that on the newer Route 5. Approximately 700 columns on Route 3 will be temporarily repaired and about 50 spans

will be replaced before it is opened to

traffic. Eventually, about 200 of these 700

columns will be replaced and the remainder

will be strengthened to meet new seismic

design criteria. By contrast, Route 5

performed considerably better despite

poorer soils and difficult foundation

conditions. The most likely reason is the

improvement in the seismic codes during the

intervening 30 years and the fact that a major revision was completed to the design

specification in 1990 [2,3]. This revision was

in effect during the design of some, but not

all, of the structures on this route.

The most likely reason that Route 5

performed much better than Route 3

is the improvement in the seismic

codes during the intervening 30 years

and the fact that a major revision

was completed to the design

specification in 1990.

Typical damage sustained by these structures includes shear and flexural failures in nonductile concrete columns, flexural and

buckling failures in steel columns, steel support bearing failures under lateral load,

and foundation failures due to liquefaction. In addition there was pounding between

spans, failure of several earthquake couplers

and settlement of many approach fills. Not

so typical was the failure of a skewed bridge on pin-ended columns and the fracture of a

set of holding down bolts in a wind shoe of

173
a cable-stayed bridge, which then led to

failure of the seismic energy dissipators and

other hardware at this location. This

performance is described in the following

sections.

4.2.2.1 Damage to Superstructures Due

to Bearing Failures

Many bridge bearings were damaged during

this earthquake and in general these failures can be grouped into three categories:

(a) primary bearing failures which caused

member distress elsewhere in the bridge and,

in extreme cases, triggered collapse.

(b) secondary bearing failures which were

the result of structural failures elsewhere in the bridge and caused by the redistribution

of load for which the bearings were not

designed and which led, in extreme cases, to collapse; and

(c) fuse-like bearing failures of either the

primary or secondary kind that relieved the

supporting substructures of load, protecting

them from major damage and preventing

collapse.

Four examples of Type (a) damage, i.e., examples of bearing failures which appear to have been the primary reason for bridge

damage and/or collapse, are given below.

They are the Nishinomiya-ko, Rokko Island,

Mukogawa and Hamate Bypass bridges.

Other sections in this report note secondary

failures (Type(b)) and Section 4.2.2.3

presents an example of Type (c) behavior.

The Nishinomiya-ko bridge (8)* carries

Route 5 over one of the shipping entrances

to the port of Nishinomiya (Figure 4.2.2a).

It is one of the longest Nielsen-Lohse Arch

bridges in the world with a main span of 252

m and a rise of 42 m. Constructed in 1993,

this all-steel tied-arch weighs approximately

8000 tonnes and is supported on 4 bearings:

2 fixed bearings at the west end (Pier 110)

and 2 expansion bearings at the east end

(Pier 111). Both Pier 110 and 111 are steel towers that are approximately 25 m high

from top of foundation to bearing level. Each foundation is a concrete caisson

extending to depth of about 23 m below

ground level. Soils include reclaimed gravels on alternating layers of saturated clays,

sands and gravels. N-values range from 2 to 20 over the first 20 m.

At the east end, the first two approach spans

(Piers 111 - 112 and Piers 112 - 113) are simply supported steel girders on steel piers

and are 54 m and 62 m long respectively.

The next three spans (Piers 113 to 116) are a continuous steel box girder of total length

183.5 m; they are also supported on steel piers that are about 23 m high. Support

conditions for these piers are given in Table

4.2.3. Earthquake couplers are provided in the longitudinal direction at all movement

joints. In general these are a pair of 25 mm

steel plates that have either one or two

slotted holes to accommodate up to +300

mm before engagement. Plate sizes vary but

are on the order of 950 mm x 250 mm.

Damage sustained during the earthquake

included failure of one of the fixed bearings

under the arch span at Pier 110 and collapse

of the first span on the eastern approach

(Figure 4.2.2b). This simply supported span

fell from its support at Pier 111 but retained

its seating on Pier 112. Ground movements

measured after the event showed permanent

offsets in the position of several piers

probably due to lateral spreading of the soils during liquefaction. Secondary damage

* Numbers in parenthesis refer to bridge

sites shown in Figure 4.2.1

174
included anchorage failure in one of the

cables between the arch rib and tie beam;

failure of all of the restrainers at Pier 111;

and failure of the bearings, couplers and

expansion joints at Pier 112 and Pier 113

(Figure 4.2.3). It seems likely that the

collapse began with the failure of one of the

fixed bearings at the western end of the arch

span (i.e., at Pier 110). These bearings have

a gravity load rating of 4500 tonnes each.

Their lateral load capacity is 2800 tonnes in

the longitudinal direction and 1400 tonnes in

the transverse direction. Since the weight of

the span is in excess of 8000 tonnes, the

longitudinal capacity of the pair of fixed

bearings is about 70% of the weight. Given

the high ground accelerations in the area, and the probable uneven distribution of load

between the pair of bearings, it is quite

possible that the capacity of one of the pair was exceeded, leading to its failure. If this occurred during a half cycle of loading

towards the west, then substantial

longitudinal loads would have been

transferred to the opposite end of the arch

tearing the restrainers out of the webs of the

girders in the approach span (Figure 4.2.4).

At the same time the fixed bearings at this

pier (Pier 111) would have been heavily

overloaded and failure would follow

immediately. In subsequent cycles the

reversed motion of the arch and the lateral movement of Pier 111 towards the center of

the channel led to the unseating of the

approach span and its collapse from Pier

111.

The Rokko Island bridge (11) at the west

end of Route 5, was completed in 1992 and

gives access to Rokko Island in Osaka Bay.

This single span, steel, tied-arch spans 217 m

and rises 36 m above its springings (Figure

4.2.5). It varies in width from 16.25 m at the south end (Rokko Island) to 26.5 m at the north end (Ashiya City) to accommodate

on ramps to the expressway. It follows that

the ribs of the arch, although vertical, are not parallel to each other. They are held in

this position by transverse floor beams at the

deck level and by crossbracing members in the plane of the rib. The arch is supported

at each end on two multi-column steel bents

which are about 26 m high. All major

structural members (archribs, tie beams and

bent columns) are boxed, single cell, steel members fabricated from 50 mm plate and

stiffened internally.

The arch weighs 6450 tonnes and is supported on four steel bearings, two at each end of the span. The fixed bearings

are at the northern end (the wide end); the

expansion bearings are at the southern end.

Reaction loads are greater at the fixed end

because of its greater width. Rotation is permitted but translation prevented (both

transversely and longitudinally) at all bearings except at the south end where the

expansion bearings permit longitudinal

movements to occur. These expansion

bearings use nested rollers to accommodate

movement in this direction and guide rails to prevent movement normal to the span. The

guide rails are expected to transfer wind and

seismic loads that are normal to the span of

the arch. Normal practice is to design these

restraints to resist a seismic load equal to 1.5 times the product of the seismic coefficient

and the dead load reaction.

During the earthquake the guide rails at the

expansion bearings failed under transverse

loading, allowing the south end of the truss

to displace laterally a distance of about 3 m

to the east across the bent cap (Figure

4.2.6). The arch came to rest with the east

rib overhanging the end of the cap beam

and as a consequence twisted the

superstructure about its longitudinal axis

(Figure 4.2.7). The racking of the

superstructure caused buckling in the

crossbracing in the plane of the ribs

175
particularly in those panels just to the south

of the midspan cross-member (Figure 4.2.8).

When constructed 3 years ago, this bridge was prefabricated in a shipyard to the west

of Akashi-Kaikyo (Akashi Strait),

transported by barge to the site and lifted into place by six floating cranes. Repair is also expected to involve floating cranes and

the lifting of the south end off of the

damaged bearings, followed by realignment on the supporting bent. Replacement of the

buckled crossbracing and the damaged

expansion joints will then be possible.

The Mukogawa bridge (13) on the Meishin

Expressway, is a dual carriageway, six-span

steel girder structure on concrete,

single-column bents (Figure 4.2.9). Built in 1963, each carriageway is an independent

structure and comprises three, 2 m deep

plate girders with concrete deck slab and

diagonal crossbracing in the plane of the

lower flange. Two 3-span continuous

segments make up the six spans. The length

of each span is 46.5 m and is skewed to the

support line by about 30°. The total length

of the bridge is slightly over 280 m with an

overall carriageway width of about 10 m.

All substructures are single, circular,

concrete columns with hammerhead cap

beams. Each column is tapered to a depth

of about 7 m, at which point it is founded on a single large-diameter shaft that extends

a further 24 m to stable gravel beds and stiff clays. The abutments are also founded on

large-diameter shafts. The columns for Piers

1 and 5 are almost completely buried leaving

only the hammerheads above ground level. All girders are supported on steel pin-type

bearings, with and without sliding plates to provide for expansion as necessaiy. Where

sliding plates are installed beneath the pin

assembly, guide bars are also provided to prevent lateral movement and restrain uplift

(Figure 4.2.10). The location of the fixed

and expansion bearings are given in Table

4.2.4.

Longitudinal earthquake couplers were

installed in the bridge between 1985 and

1990 as a retrofit measure to address

inadequate seat widths in the longitudinal

direction. These steel plate restrainers are located at the abutments and connect the

web of each girder directly to the adjacent

back wall of the abutment. They are intended to be effective in the longitudinal

direction only (the unrestrained expansion

direction) and offer no restraint transversely;

the bearing guide bars are expected to resist loads in this direction.

During the earthquake, the bearings at the

west abutment (Al) failed in transverse

loading due to a combination of anchorage

pull-out and guide bar distortion.

Transverse loads were then transferred to the earthquake couplers which also failed,

since they were now loaded in an unintended direction. Several were stripped

from the abutment back wall while at the

same time bending the webs of the deck

girders about their weak vertical axis and

imposing severe plastic distortion in these

sections (Figure 4.2.11).

The loss of restraint at the abutment led to a redistribution of load to the intermediate

piers and the overload of Piers 1 and 3. It was observed that Pier 1 was almost

completely buried over its full height and

this may have been the reason it received a disproportionally high share of the seismic

load after the abutment released its load.

Once excavated, both columns at this location showed flexural distress in the

upper third of their height, which, because

of the taper, is the section of least strength

in flexure and shear (Figure 4.2.12). These

nonductile columns have inadequate

transverse steel for confinement and shear

176
reinforcement to satisfy current performance

criteria. Some damage is therefore to be

expected during strong ground shaking. In

this earthquake, there appeared to be no

residual misalignment in the columns and

thus repair (to the columns) should be a straightforward exercise.

The Hamate Bypass (16) is a two level elevated viaduct carrying Route 2 along the

Kobe waterfront. Longer spans are continuous steel box girders supported on

steel bents constructed from single cell,

internally stiffened, box sections. These

dual-column bents support the upper and

lower decks at about 22 m and 10 m above

the ground respectively. Overall widths at the carriageway levels are about 15 m except

where ramps and emergency stopping

shoulders are accommodated. Column cross

sections are about 2.8 m x 2.2 m. All girders are supported by either fixed or expansion

steel bearings at these bents. Transverse

restraint is provided by the bearings at all locations. Several sections of this elevated

structure were damaged during the

earthquake and the section from Pier 34 to Pier 38 suffered bearing damage with large

lateral offsets at Pier 36 (Figure 4.2.13).

This four span section is comprised of two,

2-span, continuous box girders of

approximately equal length. All bearings at

all five bents under the upper deck appear

to have failed. The lack of transverse

restraint then led to rotation of the upper

level girders about a vertical axis. Both

segments appear to have rotated clockwise

about their respective end supports at Piers

34 and 38. This then imposed a large lateral displacement (estimated to be of the order

of 3 m to 4 m) at the opposite end of each

segment (i.e. at Pier 36). Since these

displacements are of opposite sign, the

relative displacement, parallel to the

expansion joint, at this pier is of the order of

6 m to 8 m. A generous cap width in the

transverse direction prevented collapse and

limited the damage to the bearings,

expansion joints and appurtenances

(guardrails, drain pipes and the like). It is possible that this is an example of Type (c)

bearing behavior, where failure of the

transverse restraints at Piers 34 through 38

has relieved these piers of seismic load,

protecting them from major damage.

4.2.2.2 Damage to Concrete

Substructures

Although several hundred concrete piers were damaged in this earthquake, almost all were designed and constructed in the 1960*s

and early 1970's without the benefit of

modern codes and recent developments in seismology and ductile design. Typical

damage involved shear failures in shorter,

under-reinforced columns. Flexural failures were also evident in taller columns that

lacked adequate confining steel or terminated vertical steel in areas of high

moment. Splice failures in this reinforcement were also common especially

those splices that had been butt welded in

regions of high moment.

Almost all the several hundred

concrete piers damaged in this

earthquake were designed and

constructed in the 1960's and early

1970's without the benefit of modern

codes and recent development in

ductile design.

This section presents examples of these

failures by summarizing the damage

sustained to two sections of the Hanshin

Expressway Route 3 (Higashi-Nada Viaduct

and Pier 240), the Takarazuka Viaduct on

177
the Chugoku Expressway, and the Moribe

Viaduct on the Meishin Expressway.

Reference is also made to the damage

sustained by the Kobe-Oohashi distribution structure and the Route 3 structures at Minatogawa and Takatori (Pier 688).

Constructed in 1969, the Higashi-Nada

Viaduct (3), also known as the Hirata-Fukae

Viaduct, is an 18 span segment of the

Hanshin Expressway on Route 3. It is the

only segment of this Route which has both a concrete superstructure and concrete

substructures. The superstructure is a series

of 35 m prestressed concrete spans with a

total length of 635 m (13 spans are 35 m

long and 5 spans are 36 m long). Each span

consists of two 6.5 m cantilevers that are monolithic with the columns, one at each

end of the span, and a 22 m drop-in girder a form of construction that was popular in

Europe in the 1960's and given the name

"piltz" construction from the German word

for "mushroom." The overall width of the

superstructure is 20.25 m with an effective

carriageway width of 15.5 m.

The substructures are single column bents

that are 3.3 m in diameter and vary in height

from about 10.5 m to 12.5 m, measured

from the top of the piled footings to the

underside of the cap beam. Vertical

reinforcement at the bottom of a typical

column comprises 180 mm x 35 mm

diameter bars arranged in 3 equal concentric

layers. The inner layer is terminated at 3.5 m

above the footing; the remaining two layers

extend over the full height of the column

and into the cap beam. Transverse steel comprises three circular hoops of 16 mm

bars (one around each layer of vertical steel) at a vertical spacing of 300 mm in the

central third of the column height and 200

mm in the end zones.

All foundations are piled footings that vary

in size from 10.5 m x 9.5 m to 13.8 m x 11.5

m with a minimum thickness of 2 m. The

number of 1 m diameter concrete piles

supporting each footing varies from 16 to 20,

with lengths from 11 m to 15.5 m.

All 17 single-column bents of this viaduct,

from Piers 126 to 142, collapsed on their

side during the earthquake (Figures 4.2.14 -

4.2.16). The failure mode appears to have

been a flexural failure at the base of each

column under strong transverse loading.

The termination of one-third of the column

vertical steel at one-third of the column

height meant that this steel was largely

ineffective in the potential plastic hinge zone and the section lacked the capacity (and

probably the confining steel) to develop a

stable plastic hinge. Collapse was due to uncontrolled (irreversible) inelastic rotation

at the base of each column.

It is estimated that about 700 columns along

Route 3 were damaged to some extent and

of these 700 columns, about 200 will need

replacement. Typical of this damage is the

section from Piers 238 to 241 of Route 3 near Uozaki (4). This 3-span segment is a continuous, steel, twin-spine superstructure

supported on single column bents and piled

footings (Figure 4.2.17). Each spine is a 3 m

deep single-cell box girder with spans of

55 m, 87 m and 55 m. All piers have

hammerhead cap beams that measure

16.2 m in overall length. Their width is constant at 3 m, but their depth varies from

1.5 m at the free end to 3.3 m over the

column. Two pairs of steel bearings support

the two box girders over each cap beam.

These restrain lateral movement and uplift

while permitting rotation and longitudinal

movement at all locations except at Pier 240

where the bearings are also fixed against

longitudinal expansion (See Table 4.2.5).

Principal dimensions for the columns,

178
footings and piles are also given in Table

4.2.5.

During the earthquake, Pier 240 failed

catastrophically in longitudinal shear despite

the fact that it was clearly designed to resist large lateral loads (Figures 4.2.18 and

4.2.19). As the only fixed pier in this 3-span

segment, all longitudinal load was attracted

to this pier and it is clear from the relative

sizes of the four substructures supporting

this segment (Table 4.2.5) that this was

anticipated by the designers. Nevertheless

inadequate transverse steel was provided in

this pier to allow ductile flexural hinging to occur before the onset of a brittle failure in shear. Once this column split along a diagonal line from upper right corner to lower left (when looking north at the pier)

the column shortened in height and vertical

support for the box girder was lost. The

girder then sagged over Pier 240 and

attempted to rotate about Pier 239. Since it was held down at Pier 238 by a bearing of

type SO-36 (Table 4.2.5), large compressive

forces were generated in the lower flanges of

the box girders in the end span from Pier

238 to Pier 239. These forces exceeded the

elastic limit and compressive buckling

occurred in the lower flanges and webs of

these girders (Figure 4.2.20). Pier 241 also

sustained structural damage but not as severe or as catastrophic as its neighbor,

Pier 240. The difference in support fixity

between these two piers is probably the reason for this difference in damage level.

The Takarazuka Viaduct (15) is located on

the Chugoku Expressway about 30 km

northeast of Kobe (Figure 4.2.21).

Constructed in 1970, it is a 10 span viaduct

of total length 172 m. Two carriageways are

carried on two independent substructures.

Each superstructure is a continuous hollow

concrete slab and is supported on concrete

multi-column bents. Steel bearings connect

the superstructure to the free-standing

columns; there is no cap beam below the

bearings. The superstructure is comprised

of two 5-span segments from the west

abutment to Pier 5 and from Pier 5 to Pier

* 10. A separate elevated structure extends

east from Pier 10. All spans are 17.2 m in length; support fixity is given in Table 4.2.6.

Each multi-column bent consists of three

rectangular columns, all founded on piled

footings. Piers 2 and 3 are approximately

4.5 m high from top of footing to top of

column, and Piers 7 and 8 are about 9 m

high over the same distance. The footings

under the fixed piers (Piers 2, 3, 7 and 8) are supported on 23 piles of uncertain

diameter and length. Those under the

expansion piers are supported on either six or eight piles depending on location.

Individual columns are about 2.4 m x 1.2 m

in size and oriented so that the strong

direction is transverse to the span. They are

typically reinforced with 36 vertical bars that are 35 mm in diameter. Footings for the

fixed and expansion piers are approximately

9.5 m x 11.5 m and 4.25 m x 10.5 m

respectively.

Damage sustained during the earthquake

implies strong ground shaking in the

longitudinal direction. Piers 2 and 3 failed

catastrophically in longitudinal shear under

both carriageways (Figure 4.2.22). Major

distress to all six columns under the

eastbound carriageway shortened the overall

height of these two piers and allowed this superstructure to sag 300 mm at Pier 2 and

450 mm at Pier 3. Residual longitudinal

displacements of 300 mm and 160 mm at Piers 2 and 3 respectively were also observed

- both in the same easterly direction.

Similar distress was observed for the

westbound carriageway. Since these piers are the fixed piers for this segment of the

bridge, they experienced high longitudinal

179
loads. Judging by the size of the

substructures at these locations, this effect was clearly anticipated by the designers.

However insufficient transverse steel was

provided to force ductile flexural hinging to occur before the onset of a brittle failure in shear. This is a similar situation to that

described above for Pier 240 on the Route 3

Expressway. In this case, however, the

situation was aggravated by the relatively

short height of Piers 2 and 3 which increases

the shear demand in proportion to the

reduction in height.

By contrast, Piers 7 and 8 were relatively

free from damage. These are the fixed piers

for the second segment and it is reasonable

to expect them to have been subjected to the same ground motion as those in the previous

segment. Light flexural cracking was

observed at the bottom of almost all the

columns in these piers but the cracking was

not severe and did not appear to affect the

gravity load capacity in any way. As noted

above, these columns are twice the height of

Piers 2 and 3 and the extra height, for the same transverse reinforcement, favors a

flexural mode of failure.

Piers 6 and 9 in this segment were

significantly damaged and this is a surprise

in view of the expansion bearings carried by

these piers. Flexural cracks were observed

at the base of several columns in these piers

and Pier 9 appeared to be leaning in a westerly direction, which is the opposite

direction to the residual shear displacements

in Piers 2 and 3. It seems likely that the

expansion bearings were not free in the

longitudinal direction as assumed and some

longitudinal shear was transferred to these

piers.

It seems that the two segments are responding as if they were two very different

structures. The columns in the first segment

have an average height of about 5 m; those

in the second segment average about 9 m.

This difference in height leads to an almost

six-fold difference in lateral stiffness, which

in turn means that the fundamental period

of the second segment is about 2.5 times

that of the first segment. This difference in

period means that the seismic response of

the two segments will be unrelated and quite

possibly out-of-phase. Pounding between

the two segments at Pier 5 is quite possible,

but needs to be confirmed.

The Moribe Viaduct (12) on the Meishin

Expressway was completed in 1964 and is located between the Nishinomiya

interchange and the Amagaski interchange.

It carries east- and west-bound traffic on two

independent but parallel concrete bridges

that are supported on concrete pier walls.

The viaduct consists of a series of 5-span

segments; each segment is 85 m long and

comprises a continuous hollow concrete slab

superstructure supported on six piers. All

piers are approximately 5 m long and 7 m

high and are supported on piled footings.

Pier widths vary according to the fixity at the

superstructure level. A single footing is used

to support the two piers at each support

under the parallel structures. Footings that

support fixed piers are about 6 m wide and

18 m long and are founded on a double row

of piles of unknown depth. Footings under

expansion piers are about 3 m wide and use

a single row of piles.

Five segments of this viaduct were damaged

in this earthquake. The most common cause

of distress was shear failures in those wall

piers that were fixed in the longitudinal

direction. Typical of this behavior is the

performance of the segment from Pier 26 to Pier 31. Of the six piers supporting this section, two have fixed bearings and four

have expansion bearings as shown in Table

4.2.7. All bearings permit rotation by using

180
rubber pads. At the fixed connections,

restraint is provided by extending the

vertical reinforcing steel near the neutral

axis of the pier across the joint at 45° and

anchoring it in the superstructure.

In this segment, Pier 30 of the eastbound

bridge and Pier 29 of the westbound bridge

failed catastrophically in shear (Figures

4.2.23 and 4.2.24). Both are fixed piers and

reinforced with 2 layers of 32 mm diameter

bar in the longitudinal direction. Transverse

steel is 16 mm bar at 250 mm spacing and

placed between the two layers of vertical

steel. The width of each pier is about 850

mm. The collapse of Pier 30 reduced the

height of the pier and allowed the

superstructure to sag about 600 mm; Pier 29 was not as severely affected.

Of interest is the fact that Pier 30 of the

westbound bridge and Pier 29 of the

eastbound bridge did not suffer the same

distress. Both are also fixed piers and

detailed in like manner to those piers that

did fail at these locations. This might be

explained if it is assumed that both fixed

piers under the same bridge sustained the

same, or almost the same, elastic shears but one had a slightly lower shear capacity than

the other and failed first (in a brittle manner). This sudden reduction in stiffness

would then have lengthened the natural

period of the segment and perhaps unloaded

the second pier to a safe level for the

remainder of the earthquake. Close

examination of the westbound Pier 30 did

show fine diagonal hairline cracks which

indicate that this pier was indeed heavily

loaded and perhaps on the brink of a massive shear failure when it was saved by

the rupture of the adjacent pier (the

westbound Pier 29).

The Kobe-ohashi (17) near Port Island is a

dual level connector between the Harbor

Highway, the Route 2 Bypass at Kobe, and

Route 3 of the Hanshin Expressway (Figure

4.2.25). The steel superstructure is comprised of a series of simple plate girders

and 2- and 3-span continuous box girders.

* The substructures are concrete and steel,

multi-column, framed bents that support

both the upper and lower carriageways.

These bents differ from pier to pier but in general they are two-column bents of

increasing height from south (Pier 23) to north (Pier 26). However, Pier 23 has three

columns at the lower level and a steel cap

beam at the upper level which is not

monolithic with the concrete columns.

Instead, this cap beam, which is also the

diaphragm for the box girder that is supported at this level, is connected to the

two columns of the bent by fixed bearings.

Support fixity for this section of the

connector is summarized in Table 4.2.8. Spans are approximately 25 m in length.

During the earthquake, Piers 23 to 26 were damaged to varying degrees. Flexural hinges

formed in the columns of all four piers due

to longitudinal loading and bending about

the weak axis (the transverse axis) of each

bent (Figure 4.2.26). These hinges were

well-developed in the shorter bents (Piers 23

and 24) and less well-developed in the taller frames (Piers 25 and 26). For example, the

longitudinal reinforcement was buckled on

both faces of the hinge zones and some

welded splices failed in the inner steel layers

in Pier 23 but only cover concrete was lost

in Pier 26. Hinge locations also varied from

the mid-height of the lower level columns in Pier 23 to just below the lower cap beam in Pier 26. These variations in the extent and

location of the hinging may be due to the

difference in column heights and the

consequential variations in the amount and

detailing of the longitudinal reinforcement.

It is also expected that the shorter columns

attracted a larger share of the base shear

181
than the taller columns because of their

greater stiffness while in the elastic range.

In addition to the column hinging, other

damage sustained by this structure included

several connection failures and pounding

against adjacent ramp structures and

buildings. In particular, the connection

between the steel cap beam at the upper

level of Pier 23 appears to have failed at one

of the columns allowing the girder to slide on that column and develop a permanent

offset of about 150 mm. The resulting

asymmetric load on the bent may have been

sufficient to cause the diagonal cracking that was observed in both the lower cap beam

and adjacent column of this bent.

The Minatogawa interchange (6) comprises

four, highly curved ramp structures that

provide access to Route 3 of the Hanshin

Expressway between Piers 605 and 611.

Each ramp is either a 3- or 4-span structure comprising steel girders on single column

concrete bents with large hammerhead cap

beams. The 90° curvature in each ramp is largely provided by a 2-span curved

continuous box girder which is fixed at its center pier but free to expand tangentially at both ends. The span(s) that makes up the

remaining length of each ramp is a simply

supported span. Since the Expressway is an

east-west route, these ramps connect to a north-south highway and the four ramps can be identified by the compass quadrant, i.e., NE, SE, SW and NW. Two of the four

footings for both the NE and SE ramps are

piled footings whereas all of the bents for

the NW and SW ramps are on spread

footings. Further, both the NE and SE

structures are 4-span ramps whereas the NW

and SW ramps are 3-span ramps. These and

other details are summarized in Table 4.2.9. Table 4.2.9 shows that although the NE and

SE ramps are superficially similar to the NW

and SW ramps, they are in fact different in a

number of important details. In general the

structures are longer, the columns are taller and the foundations are softer in the eastern

half of the interchange compared to the

western half.

During the earthquake, the northern-most

span of the NE ramp and the southern-most

span of the SE ramp collapsed due to loss of

support at the expansion ends of these two

ramps (Figures 4.2.27 - 4.2.29). No span

collapsed in either the NW or SW structure. The most probable explanation for this behavior is the greater flexibility of the

eastern ramps and thus the greater

displacement demands on the available seat width.

In addition to the unseating of these two

spans, the central piers under each of the

curved, 2-span segments suffered damage to varying degrees. These are the fixed piers

for these continuous segments and are required to resist the lateral load from about

80 m of tributary superstructure weight. In

the shorter columns the failure was

principally by shear whereas in the taller columns, shear and flexural distress were

both evident. Of interest in these columns was the flexural cracking directly under the

hammerheads where the bending moments

are expected to be small (Figure 4.2.30).

The distress at these locations implies that

the superstructure provided significant

rotational restraint to these columns which is not unreasonable in view of the high

curvature, the high flexural and torsional

stiffness of the box girders, and the fixity of

the bearings above this pier. Presumably

there was similar distress to the columns just

above the footings but these were below

ground and could not be easily inspected.

At the west end of Route 3, the Hanshin

Expressway crosses the JR Sanyo Line on a

pair of 3-span continuous steel box girders

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-

(Figure 4.2.31). This segment is supported on Piers 687 to 690 near the JR Takatori

railyard (7). These piers are single column

bents with hammerheads, except for Pier 688

which is a 2-column bent with a haunched

cap beam. The bridge has a mild left-hand curve with a radius of 291 m. Two pairs of

steel bearings support the two box girders over each cap beam and hammerhead.

These restrain radial movement and uplift

while permitting rotation and tangential

movement at all locations except Pier 688

where the bearings are also fixed against

tangential expansion - see Table 4.2.10. Principal dimensions for the columns,

footings and piles are also given in Table

4.2.10.

As noted above, Pier 688 is the fixed pier

for this segment of Route 3 and it has

clearly been designed for this purpose.

Substantial additional strength has been

given to this pier, especially when compared

to adjacent substructures - see Table 4.2.10. However, during the earthquake both

columns in this bent failed catastrophically

in shear in the span-wise direction (Figure

4.2.32). It seems likely that the additional

stiffness, which was included with the

additional strength, attracted unexpectedly

high loads to the bent and the shear capacity was quickly exceeded. The fact that the cap

beam was only 2.5 m wide and therefore narrower than the column, meant that not

all of the vertical steel was well confined by

the cap beam. During the failure, much of

the vertical steel on the north face of the

cap pulled out of the cap, further

contributing to severity of the failure. It appears that the gross shear deformation in

i the vertical direction shortened the height of

the bent by about a meter. The

superstructure came to rest on the overhead

electric supply lines for the JR Line causing

closure, not only of the Expressway, but also

of the rail line.

4.2.2.3 Damage to Steel Substructures

Steel substructures for bridges are used

quite frequently in Japan, in contrast to US

practice. Although not as common as concrete columns, circular and boxed steel columns are found throughout Japan and

their performance during this earthquake is of particular interest. Damage was sustained

by both older and newer construction and

included flexural hinging with local buckling

and, in one case, section rupture.

This section presents examples of these

failures by summarizing the damage

sustained by two sections of the Hanshin

Expressway Route 3 (Piers 55 to 58 near

Tateishi and Piers 581 to 586 near Meiji)

and the Route 2 Bypass at Hamate (Piers 41

to 49). Buckling of the cross-bracing in the

Rokko Island tied arch and local buckling in the end piers and approach spans of the

Higashi-Kobe cable-stayed bridge are described in Sections 4.2.2.1 and 4.2.2.4 respectively.

The 2-span section of Route 3 from Pier 54

to Pier 56 near Tateishi (2) varies in width

to accommodate on- and off-ramps that join

the elevated expressway here at Tateishi. Of

the three bents supporting these two spans,

two are steel box columns and one is reinforced concrete. All spans are simply

supported steel girders with spans of 70 m

and 45 m from Piers 54 - 55 and from Piers

55 - 56 respectively. The average clear

height of these columns is about 8 m

measured from the top of the footing to the

bottom of the hammerhead cap beam.

Foundations are piled footings. Principal

dimensions for the columns, footings and

piles are summarized in Table 4.2.11.

The excessive width and unusual shape of

Pier 55 is the result of subsequent widening

to accommodate the later addition of new

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access ramps. Originally 20 m long, the

steel cap beam was doubled in length to 44

m for this purpose. At the same time,

concrete columns were added to support the

free ends of the beam. Both the beam and

central column are constructed from

internally stiffened single cell box sections.

For the beam, the plate thicknesses are 28

mm for the upper and lower flanges and 24

mm for the webs. For the column, the plate

thicknesses are 19 mm. Both the beam and

column were pre-fabricated in sections using

shop welds and assembled on site using

bolted splices. High strength, 20 mm

diameter bolts were generally used for these

connections.

During the earthquake, the steel box column

at Pier 55 split open along the welds that run the full height of the four corners of the

box, allowing the column to collapse in compression, while the concrete outrigger

columns remained upright (Figures 4.2.33

and 4.2.34). Without the support of the

central column, the extended cap beam

failed in flexure on both sides of the main

girder as it attempted to span between the

two external columns. The articulation in

the superstructure allowed this gross

deformation to occur without the

superstructure being unseated. Other steel box columns in adjacent piers also showed

evidence of incipient failures in the corner

welds.

In the Meiji district (5), to the west of

central Kobe, Route 3 separates into two

independent east- and west-bound structures (Figure 4.2.35). These structures are supported on single steel columns that are in

turn supported on hollow concrete shafts. The largest of these circular columns (Piers

583 and 584) have diameters of 2.2 m and

clear heights, from foundation to under side

of hammerhead, of about 14 m. The

foundation shafts under these columns are 4

m in diameter and about 23 m deep. The

superstructure is also steel and includes a

series of simply supported plate girder spans

(35 m to 50 m long) and a 3-span

continuous box girder segment with spans of

55m, 78 m and 55 m respectively. The total length of the 8-span section from Pier 580 to Pier 588, which includes all of the single

steel column bents, is approximately 415 m.

Principal dimensions for these columns and

their foundations on the westbound

structure are given in Table 4.2.12.

During the earthquake many of the columns

in the westbound structure were damaged

but the extent of this damage varied

according to location. All columns appeared

to have been heavily loaded in the transverse

direction and in the cases of Piers 584 and

585, the columns suffered permanent

transverse displacements. In many columns

plastic hinges began to form somewhere in the central one third of the column height,

rather than at the base. Changes in the

plate thickness with column height, probably

accounts for these higher locations.

However, fully developed hinges did not occur due to local buckling, tensile ruptures

and section buckling caused possibly by

column out-of-roundness.

Pier 584 is one of the two largest piers in this section but it failed by section rupture

within a potential plastic hinge zone at about

mid-height (Figure 4.2.36). The hinge began

to form immediately above a change in plate

thickness but the associated weld probably

initiated the crack which propagated around

the circumference of the column during the

reversed loading imposed by the earthquake.

The column was completely fractured at this level and it came to rest with a permanent

lean to the north of about 10° (Figure

4.2.37). Pier 585 also sustained permanent

displacement but in this case the column did

not rupture. Instead a plastic hinge began

184
to develop about 2 m above the ground line

but the section buckled, possibly due to section out-of-roundness, which prevented

the full moment capacity from being

reached. This column also tilted to the

north by rotating about the failed plastic

hinge.

As noted in Table 4.2.12, Pier 586 is almost

two-thirds of the height of Piers 584 and

585. Despite its smaller diameter, this shorter height implies that it is about 25%

stiffer than the adjacent piers. It therefore

attracted a higher share of the lateral loads

during the earthquake and it should have

performed in a similar manner to Piers 584

and 585. In fact, the pier showed no visible

signs of distress and the reason for this behavior appears to be the failed connection

at the top of the pier (Figures 4.2.35 and

4.2.38). Inspection of the bearings at Pier

586 showed that the transverse restraint

provided by these bearings had failed in lateral shear and the girder displaced across

the pier cap a distance of about one meter.

The release of load due to this bearing

failure is another example of fuse-like

behavior in superstructure-to-substructure

connections. The consequential reduction in

column shear almost. certainly protected the

column from the distress suffered by its neighbors. (Tne bearings on Piers 585 and

584 did not fail in transverse shear).

As noted in Section 4.2.2.1 the Hamate

Bypass (16) is a two level elevated viaduct

carrying Route 2 along the Kobe waterfront.

Longer spans are continuous steel box

girders supported on multi-column steel bents constructed from single cell, internally

stiffened, box sections. In all piers the

upper level roadway is supported by two

columns from the lower level cap beam.

This lower cap is then supported from the

ground, in some cases by two columns, as in Pier 41, and in other cases by a single

column (tennis racket-style) as in Pier 49.

In Pier 41, the upper and lower decks are supported at about 22 m and 10 m above

the ground respectively. The overall width

of the pier at the carriageway levels is about

15 m. Column cross sections are 2.2 m x 2.8 m. This is a fixed pier for the superstructure

and it appears that during the earthquake

the longitudinal forces attracted to the pier were sufficient to cause one-half cycle of

inelastic flexure about 3 m up from the base

(Figure 4.2.39). On the compression face,

local buckling occurred between the

stiffened panels of both columns whereas on

the tension side horizontal striations in the

paint were consistent with significant

post-yield tensile strain. However no

obvious offset or misalignment was observed

in the pier and it was assumed to have

returned to its original position. More

detailed surveys may show, however, that

some residual deformation was sustained.

As noted above, Pier 49 has a single column

supporting the first level of traffic from

which a two column bent extends upwards to support the second level. This single column

is 3.2 m in diameter and is supported on a piled concrete footing that measures 10 m

by 12.6 m. The clear height of this column,

from top of footing to bottom of the first cap beam, is 12.1 m. The steel box sections

that comprise the members of the upper

level bent are generally 1.5 m x 1.6 m in

size. Attention has been drawn by others to the distinctive shape of this bent and its striking similarity to a tennis racket that is standing upright.

This pier is another fixed point for both

levels of the superstructure and during the

earthquake, sufficient lateral load was

attracted to this bent to trigger section

buckling (Figure 4.2.40). Section

out-of-roundness and high gravity loads were

185
pre-existing conditions that, when combined

with the seismic overturning moment,

precipitated a uniform buckling

failure across the whole section at the

mid-height of the column.

Factors which tend to confirm a failure in compression rather than one in flexure or shear include the location (unusually high

for a flexural hinge), the uniform

deformation around the circumference and

the absence of residual translation over the

height of the column. Furthermore, an

access ladder runs the full height of this

column and is attached to it at about 1.5 m

intervals. It was also deformed into a bulge

(by bending about its weak axis) but

exhibited no horizontal offset between the

upper and lower sections that might be

indicative of permanent flexural or shear

deformation in the column.

The shape of the buckle in the column may

be compared to an elephant's foot failure,

which occur in large diameter storage tanks

during earthquakes. In this case, however,

the buckle is half way up the leg of the pier

and the damage to Pier 49 might therefore

be likened to an elephant's knee failure in

the handle of a tennis racket.

4.2.2.4 Damage to Structures Due to Special Conditions (Liquefaction,

Skew, Protective Systems)

In addition to the damage already discussed,

which was due to bearing and column

failures, there was also damage due to other

special conditions. These include foundation

failure, adverse effects of skewed geometry,

and failure of special connections associated

with protective systems.

This section presents examples of these

failures by summarizing the damage

sustained by the Shukugawa bridge on the

Hanshin Expressway Route 5, the

Kawaraginishi bridge on the Meishin

Expressway and the Higashi-Kobe bridge,

also on Route 5.

The Shukugawa hridge (9) is a 3-span

continuous box girder bridge carrying Route

5 across the Shukugawa (Figure 4.2.41). It also supports a toll plaza at the west end

(Pier 134) and is therefore about twice the

width here than at the east end (Pier 131).

The girder is supported on concrete

multi-column bents and piled footings.

Expansion bearings are provided at Piers

131 and 134 and fixed bearings located over

Piers 132 and 133.

During the earthquake liquefaction was

widespread in the general area of the bridge

and lateral spreading was evident at many

locations. Both banks of the Shukugawa

were subject to large soil deformations and

moved towards the center of the river

(Figure 4.2.42). Piers 131 and 134 were

displaced with the soil and in the process

dislodged the bearings under the main

girders as well as the approach spans. At

Pier 134, the movement was of the order of one meter to the east, while at Pier 131, the

movement was less (about 0.5m) to the west.

In addition to bearing damage, the

expansion joints were also dislodged and

twisted out of alignment by large vertical (up

to 600 mm) and horizontal offsets imposed

by the piers (Figure 4.2.43).

At Pier 134, the one meter movement of the

pier almost caused the collapse of the

approach span due to insufficient seat width

at the cap. The remaining overlap between

girder and seat, was of the order of 100 mm

or less but collapse was apparently

prevented by the earthquake couplers

(Figure 4.2.44). Preliminary results from

excavations behind the footing under Pier

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134, indicate that some piles failed during

the lateral spreading and that replacements

will be necessary around the perimeter of an expanded footing.

The 3-span Kawaraginishi Bridge (14)

comprises two independent structures that

carry east and westbound traffic on the

Meishin Expressway (Figure 4.2.45). Both

structures have continuous, reinforced

concrete hollow slab superstructures

supported on wall piers at each end (Piers

24 and 27) and by two multi-column bents

(Piers 25 and 26). Two special features are

of interest with this bridge. The first is that

the bridge is skewed 35° to the line of the

support and fixed at the east end only (Pier

27); all other bearings permit longitudinal

movements. The second feature is that each

intermediate bent comprises three pin-ended

columns and therefore has no lateral

stiffness or resistance to lateral load.

During the earthquake, the transverse

restraint at the west end (Pier 24) of the

eastbound bridge failed and in the absence

of any restraint from the intermediate piers,

the superstructure was free to rotate about

the fixed end (Pier 27) in a clockwise

direction. Once support was lost at Pier 24,

collapse of one or more spans and the

associated intermediate bent (Pier 25)

followed almost immediately. In addition,

the high shear forces and twisting moments

placed on Pier 27, as the superstructure

rotated, exceeded the capacity of this wall

and it failed in shear (Figure 4.2.46).

Since the westbound bridge shares the same

features, it is surprising that it did not also

collapse. It is of course possible that the

eastbound bridge prevented the westbound

structure from losing support at Pier 24

moments before the eastbound bridge lost

its own support. It follows that an

earthquake with a longer duration might

have caused the collapse of both bridges.

The Higashi-Kobe bridge (10) is a 3-span

cable-stayed bridge with a total length of

885 m (Figure 4.2.47). The main girder

A weighs 14100 tonnes and is totally supported

by 48 cables arranged in a harp pattern from

the two towers. It is restrained against transverse wind and seismic loads by six wind shoes, one at each tower and one at each of the two piers in both end spans.

These shoes are only effective in the

transverse direction and offer no restraint to the girder against longitudinal loads. A pair

of viscous, vane-type dampers are therefore

provided at both ends of the main girder to control longitudinal seismic loads. These

dampers permit up to 900 mm of

longitudinal movement, and each can

develop a peak force of 108 tonnes at a velocity of 750 mm/sec. In addition, a pair

of vertical eye-bars is provided to counteract

the uplift in the main girder due to an

imbalance in dead load.

During the earthquake the anchor bolts for

the wind shoe at the west end of the main

girder failed and the transverse restraint for

the girder at this end was lost (Figure

4.2.48). The redistribution of load to the

dampers and eye-bars (for which they were

not designed) triggered failure in these

devices also, and the end of the girder,

which was now free of all restraint, rose upwards about one meter (Figures 4.2.49

and 4.2.50). Records from strong motion

instruments in the east tower show that the

input ground accelerations in the transverse

direction were about 0.4 g. These records

also show considerable amplification with

the increasing height of the tower to 0.8 g at deck level and to greater than 1 g at the top

of the tower. These are very high

in-structure accelerations and significantly

larger than those assumed in design (the 2%

damped, design spectrum has a peak value

187
of 0.4 g from 0.6 s to 2.0 s).

It is therefore not surprising that the

structure suffered some distress, including

not only the failure of the protective

systems, but also local buckling in the box

steel bents that support the western end of

the main girder and the adjacent approach

spans.

The above observation, regarding the design

accelerations for the Higashi-Kobe bridge,

also applies to the other structures described

earlier. The design seismic coefficient for

the Hanshin region is 0.3 and the minimum

connection forces are 1.5 times the product

of this coefficient and the tributary weight.

These values were clearly exceeded during

this earthquake and most probably by very

wide margins.

4.2.2.5 Performance of Other Highway

Bridge Structures

When completed in 1997, the Akashi-Kaikyo

suspension bridge will have the world's

longest span at 1990 m. This bridge is currently under construction between the

main island of Honshu and Awaji island

immediately to the west and south of Kobe.

The epicenter for the earthquake was

directly under the bridge and the causative

fault passes obliquely between the two

towers. The right lateral movement on this

strike-slip fault was on the order of a meter

which has lengthened the distance between

the towers by about 0.8 m and created a

lateral offset of about 0.6 m. At the time of

the earthquake, the towers had been

completed and the main cables were in place. Erection of the suspenders and the

stiffening trusses had not begun. No

significant structural damage to the bridge

has been reported but detailed inspection

and redesign of the stiffening trusses to accommodate the new geometry is expected

to add a 10-month delay to the completion

of the structure.

Many bridge spans had been seismically

retrofitted with couplers before the

earthquake and at least two structures on Route 4 are menshin-designed bridges fitted

with seismic isolators. As noted above,

some earthquake couplers failed during the

earthquake, but in many other instances they

performed well and are believed to have

prevented further collapses of simply

supported spans. Furthermore, those few

concrete columns that had been retrofitted

with steel jackets at the west end of Route

3, also appeared to have performed well

during ground motion that caused shear

failures in adjacent (unretrofitted) columns.

There was likewise good performance of the

two menshin bridges. No damage was

sustained in either one but at 45 km from

the epicenter, the input motion was less than

0.15 g and the performance of adjacent

conventional bridges was also damage-free.

Nevertheless, the records obtained from the

Matsunohama bridge confirm the expected

performance of a menshin-designed bridge

during low-to-moderate ground motion i.e., slight amplification in the isolated

(span-wise) direction and strong

amplification in the fixed (transverse)

direction.

4.2.3 Lessons for the United States

To bridge engineers and owners in the

central and eastern United States, this particular earthquake is perhaps of greater

significance than recent earthquakes in

California (e.g., Loma Prieta, 1989 and

Northridge, 1994). One reason for this

opinion is that the predominant type of

bridge in Japan is the steel girder

superstructure (simple and/or continuous

spans) supported by bearings on concrete

columns and foundations. This class of

188
bridge is also found throughout the central

and eastern United States, whereas bridges

in California tend to be concrete box girders

with monolithic bents and integral

abutments, especially in shorter bridges. It follows that bridges in the central and

eastern Umoted States are more like those

in Japan than those in California and the

performance of Japanese bridges is thus of

particular relevance to states east of the

Sierra Nevada mountains "Snowy Range."

A second reason is that an earthquake of

this size was considered to be a rare event

for this part of Japan. Although bridges in

this region are designed for seismic loads,

the design coefficients are considerably

lower than those recorded during this earthquake. The possibility of an

earthquake larger than the design

earthquake was considered to be unlikely

and only nominal attention had been given

to the problem, and then only for structures designed since 1990. This difference,

between the maximum credible earthquake

and the design earthquake, is clearly very

large for this region of Japan - a situation

that is also considered to exist in the United

States, but to a greater degree in the eastern

and central states than in the west.

It follows that the eastern and central US

may have more to learn from this

earthquake than from those in California.

Some of these lessons are as follows:

(a) Large earthquakes can be very

destructive in terms of lives lost,

injuries sustained, business losses,

reconstruction costs and societal

disruption. The closure of arterial

highways and bridges affects

emergency relief and business

recovery and can have a major

economic impact on a region and its

ability to survive such a disaster.

(b) Large damaging earthquakes can

occur in areas that are considered to have, on average, only a moderate

exposure to seismic hazards.

(c) Capacity design procedures, ductile

details and generous seat widths are necessary to prevent catastrophic

collapse during large earthquakes.

(d) Minimum connection forces need to be enforced for all seismic zones

unless such connections can be

shown to be fully protected by

acceptable yielding of the

substructures. Redundancy in connection detailing is particularly

important for essential structures. Alternative load paths are necessary

if the primary load path fails due to unforeseen circumstances.

(e) Critically important structures must

be designed to a higher level of

performance than that provided by

current specifications, if full service is to be maintained after a large

earthquake. Multi-level performance

criteria and corresponding design

strategies are necessary for important

bridges.

(f) Retrofit measures reduce damage

but inappropriate use and/or

installation can defeat their purpose

and perhaps even trigger collapse.

This observation is made with

particular reference to couplers

(restrainers).

(g) Lateral spreading due to liquefaction can lead to span collapse even in

modern structures with massive

foundations (caissons) and

well-engineered fills. (h) Premature failure of some bearings

appear to have reduced the seismic

loads in their supporting

substructures by uncoupling the

superstructure from its supports. This

fuse-like action may have saved a

189
number of spans from collapse and

columns from failure in shear and

flexure.

(i) Accelerations in isolated

superstructures are less than in (d)

conventional structures.

(j) Skewed bridges are susceptible to in-plane rotation leading to large

displacements at their supports and

possible unseating of girders in the

acute corners.

4.2.4 Research Needs and Opportunities (e)

A number of research needs and

opportunities have arisen as a consequence

of this earthquake. These include the

following:

(a) Conduct correlation studies on those

bridges with strong motion records to calibrate theoretical models against

actual behavior. As far as can be

determined at this time, records are

available for two bridges. They are the Higashi-Kobe cable-stayed bridge (f) (with seismic energy dissipators) and

the base-isolated Matsunohama

bridge. Valuable insight into the

performance of these two important

types of bridges would be derived

from such studies.

(b) Develop a detailed database on the

performance of steel bearings and

earthquake couplers (restrainers)

followed by case studies on selected

bridges in which these devices failed.

Results from such a study would help

determine the need for a review of

current U.S. design criteria for

connection forces and restrainers.

(c) Analyze structural response due to large foundation movements during

liquefaction and lateral spreading.

Develop optimum mitigation measures to minimize structural

impacts of such movements. Case

studies could include the

Nishinomiya-ko and Shukugawa

bridges.

Perform case studies on those

bridges that were retrofitted before

the earthquake to determine the

effectiveness of the retrofit measures. Known retrofit measures for which

performance could be evaluated

include earthquake couplers, steel jackets and viscous dampers.

Develop multiple-level performance

criteria which define expected

damage and serviceability states for

various earthquake scenarios and the

corresponding design

strategies/structural options necessary

to satisfy these criteria. Involvement

of social scientists (planners,

economists and experts in public

policy) should be encouraged.

Cooperative U.S. -Japan exchanges on this issue would also be

beneficial.

Study failure mechanisms in large

concrete columns under combined

axial and shear loads. Concrete

columns in single or multi-column

bents in Japanese bridges have very

large cross sections and fall outside

the range of U.S. test data.

Although it is unlikely that U.S.

practice will adopt similar sized

members for short- and

medium-span bridges in the near

future, columns of this size and with

these reinforcement ratios are encountered in some long span

structures. Correlation of

assessment methods and limit states with field data from this earthquake

could give valuable insight into the

lateral load capacity of large concrete

members. It is noted that such field

data are rare and this opportunity is

190
probably unique.

(g) Perform case studies on bridges with

steel substructures. The relatively

large number of damaged steel substructures provides an opportunity

to calibrate proposed new methods

for the seismic design of steel bridge

columns. In particular, their capacity

for ductile actions and the

identification of their limit states should be investigated with the

objective of refining the R-factors in

U.S. bridge codes for these

components.

The poor performance of these older

bridges and elevated expressways

confirms previous lessons in

California and elsewhere, about the

pressing need to retrofit the existing

deficient bridges.

4.2.5 Summary

Damage to highway bridges was both

widespread and catastrophic. Typical

damage included shear and flexural failures

in nonductile concrete columns, flexural and

buckling failures in steel columns, unseated

girders due to bearing failures, and gross

foundation movements due to liquefaction. In addition, pounding between spans

occurred. Some special structures also

suffered atypical damage such as the

excessive rotation of a skew bridge on

pin-ended columns and the loss of seismic

energy dissipators in a cable-stayed bridge

due to the failure of a wind shoe.

Most of this distress was confined to older

structures, built more than 30 years ago

before the introduction of modern seismic

codes. The poor performance of these older

bridges and elevated expressways confirms

previous lessons learned in California and

elsewhere, about the pressing need to

retrofit the existing inventory of deficient

bridges.

However, some new bridges also suffered

serious damage which implies a need to re-evaluate the design loads and procedures

in the current design specifications. As

noted above, the peak ground accelerations

due to this "rare" earthquake were

considerably higher than the seismic

coefficients used in design. This is an example of a low-probability but

high-consequence event causing serious

distress to modern construction. From an

owner's viewpoint, these circumstances might

be best addressed through multiple-level

performance criteria. In the United States,

dual-level criteria have only recently been

developed, and then only for critically

important, long-span structures and a privately-owned transportation corridor.

They should perhaps be extended to a wider

range of bridge types and in doing so clearly

state the expected performance under both

small and large, rare and frequent

earthquakes and identify design strategies

that will satisfy these criteria.

The closure of three major expressways in the Hanshin region has had a major societal

and economic impact on the region. The

estimated total repair cost for one highway

authority alone, the Hanshin Expressway

Public Corporation, is $4.6 billion. Even

though this is only about 2.5% of the total direct costs for the earthquake (estimated at $200 billion), it is still a significant sum.

Furthermore, it does not include the loss of

toll revenue while the network is inoperative

(estimated at $2 million per day) nor does

it include the indirect losses which are

191
expected to exceed the repair costs by the

time the system is fully operational. The

simultaneous closure of the other

transportation routes in the region,

principally the rail lines, further aggravated

the situation and paralyzed the region as emergency access and relief teams were

forced to use surface streets. The

interdependency of these lifelines, especially

when collocated in narrow corridors,

deserves further study.

4.2.6 References

1. Hanshin Expressway Public

Corporation, "Techno Gallery:

Structures and Technologies of the

Hanshin Expressway," 88 pp., 1994.

2. Japan Road Association, "Design

Specifications of Road Bridges; Part

V: Seismic Design," February 1990.

3. Iwasaki,T., Kawashima, K. and

Hasegawa, K., "New Seismic Design

Specifications of Highway Bridges in

Japan," Proc. 22nd Joint Meeting

U.S. -Japan Panel on Wind nd

Seismic Effects, UJNR,

Gaithersburg, MD, May, 1990.

4. Hanshin Expressway Public

Corporation, "Report on Damage to the Hanshin Expressways by the

Great Hanshin Earthquake and its Restoration," Osaka, 1995.

192
Table 4.2.1

Location of Bridges with Major Damage

Route No./ Owner/Agency Number of Bridges (Major Damage)

Expressway

2 (NH) MOC 3

3 (Hanshin) HEPC 11

5 (Hanshin) HEPC 4

43 (NH) MOC 1 171 (NH) MOC 2

Meishin JHPC 4

Chugoku JHPC 2

Notes: MOC Ministry of Construction

HEPC Hanshin Expressway Public Corporation

JHPC Japan Highway Public Corporation

NH National Highway

193
Table 4.2.2

List of Highway Bridges with Major Damage

HIGHWAY

(ROUTE)

Hanshin (3)

Hanshin (5)

Meishin

Chugoku

National Highway

(NH 2)

National Highway

(NH 43)

NAME

Takashio District Overpass

Futaba District Overpass

Tateishi District Overpass

Hirata-Fukae Overpass(U)

Fukae District Overpass

Mikage District Overpass

Uozaki Ramps(1) Kaigan-dori-Benten Overpass

Hyogo-Nagata District Overpass(U)

Minatogawa Ramps(1) Sanyo Rail Line Overpass(1)

Nishinomiya-ko Bridge(1) Shukugawa Bridge(1) Higashi Kobe Bridge(1) Rokko Island Bridge(1)

Moribe Viaduct(1) Mukogawa Bridge(1) Kawaraginishi Bridge(1)

Nishinomiya Interchange

Takarazuka Viaduct(1)

Toyonaka Overpass

Hamate Bypass(1) Kobe-Port Island Ohashi(1)

Shioya Overpass

Iwaya Overpass

TYPE

steel girders/concrete columns

steel box girders/steel columns

steel box girders/steel columns

concrete girders/concrete columns

steel box girders/concrete columns

steel box girders/concrete columns

steel girders/concrete columns

concrete and steel girders/concrete cols, steel girders/steel and concrete columns

steel girders/concrete columns

steel box girders/concrete columns

Nielsen-Lohse tied arch/steel columns

steel box girders/concrete multicol. bent

cable stayed deck/steel columns

Lohse tied arch/steel columns

concrete box girders/concrete pier walls

steel girders/concrete columns

concrete box girders/pin-ended concrete

multi-column bent

concrete box girder/concrete multicolumn bent

steel box girders/steel columns

steel box girders/concrete dual level 2- column bent

concrete girders/concrete columns

National Highway

(NH 171) Mondo Overpass

Ikeda Overpass

concrete girders/concrete columns

Notes: 1. Sites visited by UJNR Reconnaissance Team Feb. 12-17, 1995

2. Includes Higashi-Nada Viaduct

3. Includes Meiji District Ramps

194
Table 4.23

Support Fixity Conditions for the Nishinomiya-ko Bridge

Pier No. 110 Arch Span 111 112 113 114 115 116

Fixity E-F E-F E-E F-E F F E-E

Notes E: Expansion bearing (rotation and longitudinal movement permitted)

F: Fixed bearing (rotation only permitted)

Table 4.2.4

Support Fixity Conditions for the Mukogawa Bridge

Pier Al PI P2 P3 P4 P5 A2

Fixity E-E

Notes A1,A2:

P1-P5:

E:

F:

west and east abutments

intermediate piers

Expansion bearing (rotation and longitudinal movement permitted)

Fixed bearing (rotation permitted)

195
Pier

Table 4.2.5

Substructure Details for Piers 238 - 241, Route 3 near Uozaki

P241 P240 P239 P238

Bearing Fixity

Bearing Type

Column Size

Footing Size

Pile Size (LxD)

No. of Piles

E-E

SO-36

3.3m dia. 11x11x2.5m

14 x lm dia

17

F

SO-37

3.6 x 3.3m

15.5x12x2.5m

15 x lm dia

28

E

SO-38

3.3m sq. 12x12x2.5m

18.5 x lm dia

25

E-F

SO-36

3.3m dia.

10x10x2.5m

14 x lm dia

16

Notes E: Expansion bearing (rotation and longitudinal movement permitted)

F: Fixed bearing (rotation only permitted)

SO-36: Pin and roller bearing with uplift restraint

SO-37: Pin bearing

SO-38: Pin and roller bearing without uplift restraint

Table 4.2.6

Support Fixity Conditions for the Takarazuka Viaduct

Pier Al PI P2 P3 P4 P5 P6 P7 P8 P9 P10

Fixity E E F F E E-E E F F E E-E

Notes E: Expansion bearing (rotation and longitudinal movement permitted)

F: Fixed bearing (rotation only permitted)

196
Table 4.2.7

Support Fixity Conditions for Piers 26 to 31, Moribe Viaduct

Pier 26 27 28 29 30 31

Fixity E-E E E F F E-E

Notes E: Expansion bearing (rotation and longitudinal movement permitted)

F: Fixed bearing (rotation only permitted)

Table 4.2.8

Support Fixity Conditions for Piers 23 to 26, Kobe-ohashi

Pier 23 24 25 26

Fixity F E-F E-F E-E

Notes E: Expansion bearing (rotation and longitudinal movement permitted)

F: Fixed bearing (rotation only permitted)

197
Table 4.2.9

Structure Data for the Minatogawa Ramps, Route 3

Ramp NE SE SW NW

Number of spans 4 4 3 3

Length of curved spans 42.4/44.0m 40.0/42.5m 30.1/29.2m 39.3/40.4m

Column size1 2.5 x 3.75m 2.5 x 3.75m 2.5m dia. 2.5m dia.

oval oval circular circular

Clear Column height1,2 6.1m 8.4m 5.7m 2.6m

Footing size 1 8 x 9.5m 8 x 9.5m 8 x 10m 8 x 10m

Number of piled footings 2 2 0 0

Pile data1 12, lm dia. 12,1m dia N.A. N.A.

16m long3 16m long

Notes 1. Substructure data is given for central pier under curved 2-span segment.

2. Clear height is distance between top of footing and bottom of hammerhead.

3. Estimated.

Table 4.2.10

Substructure Details for Piers 687 - 690, Route 3 near Takatori

Pier P690 P689 P688 P687

Bearing Fixity

Column Size

Clear Column Ht

Footing Size

Pile Size (LxD)

No. of Piles

E-E

3.2m dia.

5.3m

8x9.5x2.5m

21 x lm dia.

11

E

3.6m dia.

4.0m

9.5x12x3.0m

' 22.6 x lm dia. 18

F

2.x 3.5m dia.

6.1m

12.5x17x3.0m

22.6 x lm dia.

28

E-F

3.2m dia.

7.4m

9.5x10x2.5m

12.1 x lm dia.

10

Notes E: Expansion bearing (rotation and longitudinal movement permitted)

F: Fixed bearing (rotation only permitted)

198
Table 4.2.11

Substructure Details for Piers 54 - 56, Route 3 near Tateishi

Pier 56 55 54

Bearing Fixity1 Column Type

Column Size

Clear Column Ht3 Cap Beam Length

Footing Size

Pile Size (LxD)

No. of Piles

E-F

steel box

3.0x3.3m

6.96m

30.8m

12x12x3.5m

12.5 x lm dia.

23

E-F

steel box2 2.8x3.0m2 8.23m

44.3m

12x12x3.5m2

11 x lm dia.2 212

E-F

concrete

3.5m dia.

9.07m

19.5m

10x12x2.7m

16 x lm dia.

17

Notes 1. E: Expansion bearing (rotation and longitudinal movement permitted)

F: Fixed bearing (rotation only permitted)

2. Pier 55 has 2 additional concrete columns that support each end of the cap

beam; these columns are 1.2 x 2.7 m in plan by 9.2 m high; footing sizes are 6.5x13x2.5m and supported by nine 11 x lm dia. piles.

3. Clear height is distance between top of the footing and bottom of cap

beam.

199
Table 4.2.12

Substructure Details for Piers 581 - 586, Westbound Route 3, Meiji

Pier 586 585 584 583 582 581

Bearing Fixity F E-F E-E F-E F-E F-E

Column Size (dia) 1.8m 1.8m 2.2m 2.2m 1.8m 1.8m

Clear Column Ht. 10.3m 12.4m 14.1m 14.1m 13.4m 12.4m

Shaft Size (dia) 3.5m 3.5m 4.0m 4.0m 3.5m 3.5m

Shaft Depth 24.6m 23.8m 23.2m 23.4m 16.2m 17.4m

Notes E: Expansion bearing (rotation and longitudinal movement permitted)

F: Fixed bearing (rotation only permitted)

200
1. Futaba District

2. Tateishi District

3. Hirata-Fukae (Higashl-Nada)

4. Uozaki Ramps

5. Meiji District

6. Minatogawa Interchange

7. Takatorl

8. Nlshlnomiya-ko

9. Shukugawa

10. Higashl-Kobe

11. Rokko Island

1 2. Moribe

1 3. Mukogawa

14. Kawaraginlshl

1 5. Takarazuka

1 6. Hamate

17. Kobe-Ohashl

Figure 4.2.1 Bridge sites visited by the UJNR Reconnaissance Team, February 12-

17, 1995.

201
Figure 4.2.2a General view of Nishinomiya-ko Bridge, Route 5.

Figure 4.2.2b Collapsed approach span between Piers 111 and 112, Nishinomiya-ko

Bridge.

202
Figure 4.2.3 Damaged expansion bearings from under approach spans,

Nishinomiya-ko Bridge, showing nested rollers and guide rails.

203
Figure 4.2.5 General view of Rokko Island Bridge, Route 5.
Figure 4.2.7 Lateral offset at east face of South Pier, Rokko Island Bridge.

205
Figure 4.2.8 Buckled cross-members in Upper Chord, Rokko Island Bridge.
Figure 4.2.10 Bearing and restrainer damage at abutment Al, Mukogawa Bridge,

showing distorted guide rails and uncoupled restrainer from abutment

backwall.

207
Figure 4.2.11 Damaged restrainer at Abutment Al, Mukogawa Bridge, showing

failure of anchor bolts and distortion of web of main girder.

Figure 4.2.12 Failure at top of buried column, Pier PI, Mukogawa Bridge.

208
Lateral offset at Pier 36 in upper level of Hamate By-Pass due

bearing failures at Piers 34 through 38-

View of the collapsed Higashi-Nada Viaduct looking west from

Pier 125.

209
Figure 4.2.16 Higashi-Nada Viaduct, Pier 134.

210
Figure 4.2.17 General view of Hashin Expressway (Route 5) near Uozaki showing

collapse of section over Pier 240 in middle distance.

211
Figure 4.2.19 Shear failure in Pier 240 of Hanshin Expressway showing temporary

repair to column to prevent total collapse.

212
Figure 4.2.20 Compressive failure in lower flange of steel box girder between Piers

238 and 239 of Hanshin Expressway.

Figure 4.2.21 General view of Takarazuka Viaduct, Chugoku Expressway.

213
Figure 4.2.22 Shear failures in 3-column bent at Pier 3, Takarazuka Viaduct.

214
Figure 4.2.23 Shear failure in wall pier (west face), Moribe Viaduct.

215
Figure 4.2.24 Shear failure in wall pier (east face), Moribe Viaduct.

Figure 4.2.25 General view of Kobe-Ohashi Connector near Port Island showing

formation of flexural hinges in lower level columns.

216
Figure 4.2.26 Hinge formation in east column of Pier 23, Kobe-Ohashi.

Figure 4.2.27 Collapse of Southeast Ramp at the Minatogawa Interchange.

217
Figure 4.2.28

Figure 4.2.29 Girder web failure due to unseating of the Southeast Ramp at Minatogawa Interchange.

218
Figure 4.2.30 Column failure in Southwest Ramp at Minatogawa Interchange.

219
General view of Route 3 crossing JR Sanyo Line near Takatori.

220
221
Figure 4.2.33 Pier 55, Route 3 near Tateishi.

Figure 4.2.34 Pier 55, Route 3 near Tateishi showing buckled steel plate on ground

.

222
Figure 4.2.35 General view of westbound elevated section of Route 3 near Meiji

looking from Pier 586 towards Pier 585.

223
Figure 4.2.36 Pier 584 of westbound Route 3 near Meiji

224
225
Figure 4.2.39 Local buckling in steel box columns at Pier 41 of the Hamate By-Pass

Viaduct.

226
227
Figure 4.2.41 General view of the Shukugawa Bridge on Route 5.

Figure 4.2.42 Distant view of the Shukugawa Bridge showing lateral deformation of

the foundation soils and spreading to the right (to the center of the

channel).

228
Figure 4.2.43 Vertical offset in the expansion joints above Pier 134 of the

Shukugawa Bridge due to bearing failure on the best cap below.

Figure 4.2.44 Approach span at edge of seat at Pier 134 of Shukugawa Bridge due

to lateral movement of the pier by about 1 m towards the center of the

channel.

229
Figure 4.2.45 General view of Kawaraginishi Bridge after removal of collapsed

eastbound bridge showing skew and pin-ended columns under

westbound bridge.

230
Figure 4.2.47 General view of the Higashi-Kobe Bridge on Route 5.

231
Figure 4.2.48 Failed wind shoe at Pier 187 of the Higashi-Kobe Bridge.

232
Figure 4.2.49 Failed connection of Vane-type energy dissipator and (at upper right)

part of failed dead load tie-down at Pier 187 of the Higashi-Kobe

Bridge.

233
I

I
4.3 Railways and Rapid Transit System

4.3.1 Overview

There are four electric rail service lines

between Kobe and Osaka (Figure 4.3.1).

Two of the rail lines are operated by

Western Japan Rail and the other two are owned by private companies, Hanshin and

Hankyu. Most of the rail lines that run

through this corridor are on elevated

embankments and on elevated structures. Additionally, there are two guideway systems

in Kobe, the Port Liner from Sannomiya to Port Island and the Rokko Liner from

Sumiyoshi to Rokko Island. The guideway

systems, New Tram Systems, consist of

computerized, automated trains with four to

six medium cars. The Port Liner,

constructed between 1977 and 1980 with a

total length of 6.4 km and nine stations, was

the first such transportation system built in

Japan. It began operation in February,

1981. The Rokko Liner was constructed in

1990 with a total length of 4.5 km and six stations. These trains are the primary

people movers between the islands and the

Kobe area.

There are five other railways and transit

systems in Kobe including the Kobe

Kosotku, Kobe Dentetsu, Kosoku Kobe,

Sanyo Dentetsu, and the Kobe Subway.

The Kobe Rapid Transit Railway, or Kobe

Kosotku, is owned and operated by the

Kobe Rapid Transit Railway Company, Ltd.

As shown in Figure 4.3.2, the Kobe Rapid

Transit Railway (KRTR) provides a rail system which interconnects the Hankyu and

Hansin Railways in the east with the Sanyo

Electric Railway in the west and the Kobe

Electric Railway in the north. The KRTR is owned jointly by the City of Kobe, the four

railway companies whose lines it interconnects, and local business investors.

A schematic of the KRTR is provided in Figure 4.3.3. The east-west routes are 7.2

km long in total, and the north-south line is 0.4 km long. About 6.6 km of the system

are underground, with the remaining

sections at grade or carried by elevated

structures. The system was constructed

between 1962 and 1968. Underground

sections were built by means of

cut-and-cover techniques. Running tunnels

are reinforced concrete box structures with

center column support, generally having

about 4.5 m to 6 m of cover between street surface and top of box. With the exception

of the Shin Kaichi Station, the stations are

reinforced concrete box structures with

center column support. The Shin Kaichi

Station is a steel frame structure with

Vierendeel trusses and a mezzanine level. Depth of cover at the stations is approximately 4 m to 5 m.

The Kobe Municipal Subway, or Metro, is operated by the City of Kobe and is composed of 22.7 km of elevated, surface,

and underground railway. Underground

construction between Shin Nagata and

Sannomiya Stations was performed by

cut-and-cover techniques prior to 1977. Soil

shield tunneling and rock tunneling were

used for portions of the system northwest of

the Shin Nagata Station. Cut-and-cover

sections of the Metro are similar to those of

the KRTR. Both stations and running

tunnels are reinforced concrete box

structures with center columns separating

inbound and outbound tracks. Depth of cover from street surface to top of box is typically 4.5 m to 7.0 m.

4.3.2 What happened

4.3.2.1 Shinkansen - Western JR

The Shinkansen line was built during the

1960s and 1970s. The word "Shinkansen" in

235
Japanese means "the new main line." It is a major line in addition to the original

Japanese National Rail (JNR) main line in

this area. The Tokaido Line, which runs from Tokyo to Shin-Osaka, has been in service since 1964. The Sanyo Line, from

Shin-Osaka to Hakata, was in operation in

1972 from Shin-Osaka to Okayama and was

extended to Hakata in 1975. The train can

reach speeds up to 210 km/h and up to 275

km/h for later models. The rails are continuously welded and mounted on a concrete bed so there is no sway or

clickety-clack noise.

Although damage to the reinforced

concrete structures was extensive, the

major cause of collapsed structures

was the non-ductile detailing of the

steel reinforcement. Structures

designed by current specifications

performed well with minor damage.

The earthquake damage to the Shinkansen was extensive. The Tokaido Line and The

Sanyo Line were both damaged. The Sanyo

Line had several locations with collapsed

structures.

Tokaido Line It has been reported that seven locations along the line have column

damage. Superstructures at two locations near the Shin-Osaka station have deck

offset. This line was put back in service in a

relatively short amount of time.

Sanyo Line In Kobe, the Shinkansen runs through a tunnel under Rokko Sanchi.

Although damage along the tunnel is minor, no detailed information is available. It has

been reported that nine locations between

Shin-Osaka and Shin-Kobe had collapsed

structures including damaged columns at thirteen locations. Superstructures at six locations had deck offsets. One platform at Shin-Kobe station was offset. One elevated

structure collapsed between Shin-Kobe and

Nishi-Akashi. The superstructure at five

locations had deck offsets. From

Nishi-Akashi to Himeji one elevated

structure collapsed, the columns were damaged at 36 locations and decks were

laterally offset at eight places. Strong

motion records along the Shinkansen show

that the highest peak ground acceleration was 0.65 g and the maximum ground

displacement was 42 cm at the Takatori

station. A 5% damping response spectrum

over 2.0 g is observed at this location

(Figure 4.3.4).

At Itami, several elevated structural frames

collapsed in a series. The typical elevated

structure has two columns per bent with a

total of four concrete bents per frame.

Cantilever spans are located at both ends.

Typical column size is 80 cm x 80 cm with

#9 (D28) longitudinal rebars and #2 (D5 @

30 cm) shear reinforcement in the middle

and #2 @ 15 cm at the top and bottom.

Link beams were used in the taller structure frames. The multi-column frames were

severely damaged at the top portion of the

columns and the whole superstructure deck

settled without damage (Figure 4.3.5 and

4.3.6). At the time of the investigation,

workers were removing concrete and cutting

rebars. The superstructure was jacked up to

its original elevation. Columns are being

repaired between the existing deck and

foundation. It is interesting to see that the

cold joint below the top of the deck beam is very smooth which raises the question "did

this type of joint ever initiate a plastic

moment in the column?"

236
4.3.2.2 JR Main Line - Western JR

On the JR main Line, the Tokaido Line

runs from Tokyo to Kobe and the Sanyo

Line from Kobe to Hakata.

Tokaido Line The Tokaido Line between

Osaka and Kobe is sited mostly on an

elevated embankment. The elevated

structure collapsed from the Sumiyoshi

station all the way to the elevated

embankment near Nada 1.25 km to the west. The Rokkomichi station along this stretch

also collapsed. Retaining walls used at an

elevated embankment section between Nada

and Rokkomichi station tilted outward. Soil

anchorages are now being installed to

stabilize the embankment. Near the

Sumiyoshi station, workers are installing

steel jackets around damaged columns. The

jackets have the same shape as the original

columns with a thickness of 10 mm. Two

U-shaped jackets (Figure 4.3.7) are welded

together for the full column height. Welded

joints are staggered (Figure 4.3.8) on

different faces. Damage at this segment of

the JR line is concentrated on the top of the

columns, right below the construction joints.

Less damaged columns show the formation

of a shear crack at this region.

Sanyo Line Damage along the Sanyo line was less than the Tokaido line. It has been

reported that one elevated structure

collapsed, a retaining wall tilted and rail stations damaged. Detailed information is not available.

4.3.2.3 Hanshin Dentetsu

Kobe Line At Higashi-Nada, an elevated

railroad yard collapsed (Figure 4.3.9).

Columns failed in the top region. A small

amount of shear reinforcement was used in these columns. The nearby elevated rail structures also collapsed from a similar

cause. Space under the railroad is used by

either businesses or residences (Figure

4.3.10). Retaining walls near the Mikage

station overturned. Elevated structures from

Iwaya to Mikage were mostly collapsed and

" damaged.

4.3.2.4 Hankyu

Kobe line It has been reported that the

elevated structures between Nishinomiya and

Shykugawa collapsed. The Shykugawa

station also collapsed and the Sannomiya

station was damaged.

Itami Line The Shin-Itami station collapsed

(Figure 4.3.11). The elevated station was at the end of the Itami Line. Railroad tracks

gradually rose through a segment of elevated

embankment and a series of elevated

structures and ended at this station. The

collapse may have been caused by a whipping action.

Takarazuga Line It has been reported that

two overpasses were damaged.

4.3.2.5 Kobe New Tram System

Rokko Liner The train station at Sumiyoshi was seriously damaged when its superstructure collapsed. Columns on the

east side of this station tilted to the north

and one segment of deck was offset. Foundations along the Sumiyoshigawa

moved and several steel columns showed

signs of local buckling. It has been reported

that one long span at Rokko Island lost its support and collapsed.

Port Liner Five of the nine stations along

the line suffered various degrees of damage.

One concrete column near the Sannomiya

station was seriously sheared and dropped

approximately 120 cm. The superstructures

lost their bearings. Restrainers located at

237
the east side of the steel box girder tore off

the web of the girder. Pier 35 tilted to the

north (Figure 4.3.12) and the southern span

dropped off and the superstructure yielded near the bent cap. Piers 56 to 59 tilted to the west (Figure 4.3.13) which may have

been caused by liquefaction in this area. The first span at the south end of the Kobe

bridge offset approximately 15 cm to 20 cm. Although the whole Port Island settled

approximately 0.5 m to 1 m, no columns

supporting the train had suffered any

damage in this area.

4.3.2.6 Underground Rapid Transit

Systems

As shown in Figure 4.3.2, damage was

sustained at the Daikai and Nagata Stations

of the KRTR and at the Sannomiya,

Kamisawa, and Shin Nagata Stations of the

Metro. Damage to the Metro was less severe than that to the KRTR, and was

primarily in the form of cracked and

deformed reinforced concrete center

columns. Metro transit service was restored one month after the earthquake, although

the Sannomiya Station remained closed

because of damage to the center columns.

The KRTR, where more severe damage

occurred, is not expected to resume service

for over a year.

Figure 4.3.3 shows the locations of damage

in the KRTR. Although the most serious

damage in the system was the collapse of the

Daikai Station, significant distress and

failure were in evidence at other locations.

There was structural damage in five reinforced concrete columns at the eastern

end of the Nagata Station. Between the

Daikai and Nagata Stations, 210 reinforced

concrete columns were cracked and

deformed in the running tunnel. Minor to moderate cracking of reinforced concrete

columns and panel walls was observed in an

underground shopping mall adjacent to the

KRTR near Shin Kaichi Station. Figures

4.3.14 and 4.3.15 show typical damage within

the shopping mall. There was severe damage of the elevated rail structure near Sannomiya Station.

The failure of the Daikai Station is

highly significant because it is the

first instance of catastrophic

earthquake damage to a modern

tunnel for reasons other than fault

displacement and instability near the

portal.

Soil conditions adjacent to the Daikai

Station and connecting running tunnels are shown by means of boring records (Figure

4.3.16) obtained by the Kobe Rapid Transit

Railway Company, Ltd. at the eastern and

western ends of the station. The soil profile

consists of relatively loose silty sand to a depth of about 3 m to 4 m, with the water

table at 3 m depth. Fines in the silty sand

layer generally exceeds 20% by weight.

Because the silty and clayey sands and sands

and organic silty clay have relatively high

percentages of fines with considerable

plasticity, they are not considered to be

susceptible to liquefaction. Uncorrected

standard penetration test (SPT or blow

counts) values are plotted for each boring.

The locally high values are associated with

the presence of gravel, and thus do not

provide a reliable representation of in-situ

density.

Using the criteria for liquefaction

susceptibility set forth by Seed, et al., [4] and

assuming a peak acceleration of 0.7 g to 0.8 g, the silty sand and sand between 3.5 m

and 6 m deep appear to be susceptible to

238
liquefaction. The cyclic stress ratios and

corrected blow counts for sands 4.5 m to 6.0

m deep plot very close to the empirical

threshold for liquefaction proposed by Seed,

et al., and thus may be marginal regarding

their tendency to liquefy.

The cut-and-cover construction for Daikai

station involved a braced excavation

supported by steel sheetpiles. The sheetpiles were left in place, and the concrete walls of

the station were cast-in-place. A gap,

approximately 300-mm wide, was left between the reinforced concrete walls and

sheetpiles. Because the narrow separation

did not allow for compaction, sandy fill was

mainly loose-dumped between the station

walls and existing sheetpiles.

Figure 4.3.17 presents plans and profile

views of the collapsed Daikai Station.

Cross-sections at select locations along the

station and running tunnel are shown in Figure 4.3.18.

The station and running tunnel are

reinforced concrete box structures with

4.8 m to 5.2 m of soil cover. The eastern

end of the station contains a second

structural level which apparently provided

sufficient strength and stiffness to restrict roof collapse to the single level box

structure. The collapsed box structure was

approximately 100 m long, 7.2 m high, and

17.0 m wide. The central reinforced

concrete columns of the station failed,

apparently by a combination of shear and

vertical loading. There was only nominal

confining steel (9 mm diameter on 180 mm

spacing) for the 20 mm diameter

longitudinal rebar on 140 mm centers in the

concrete. Collapse of the columns caused

subsidence at the street surface of a maximum 2.5 m, with substantial settlement over an area of 20 m by 100 m. Apart from

the structural collapse-induced movement,

there was no clear evidence of permanent

ground deformation at the site induced by

other causes, such as liquefaction.

Figures 4.3.19 and 4.3.20 show the interior

"portions of the collapsed station.

Compressive failure of the columns in

Figure 4.3.19 occurred in the form of bird

caging of longitudinal steel and shear

rupture of concrete. It appears that

compressive failure occurred at the

mid-height of the columns. Figure 4.3.21

shows subsidence at the street surface over

the station. Many pipelines and conduits in the street failed, although some were able to survive the large deformation. An NTT

fiber optic cable, for example, continued to provide a suitable signal despite the

substantial deformation imposed on it. A

medium pressure A-line operated by Osaka

Gas (see Section 5.3 for Gas System

Description) was deformed severely by the

differential settlement, but did not leak at

this location.

Because of severe distortion in the station

walls, roof, and columns related to the roof

collapse, clear evidence of structural

response at incipient failure could not be

found at the station. Nevertheless,

observations provided by Professor M.

Hamada of Waseda University in the

running tunnel between Daikai and Nagata

Stations provide clues about the seismic

response of the reinforced box at the onset

of structural failure. These observations are shear deformation of the box, with flexural

failure of the reinforced concrete wall at a construction joint connecting the wall and

base slab, bending failure where the center

columns connect with the base slab, and

cracks at the street surface roughly parallel to and directly over the running tunnel walls.

Deformation consistent with observations is illustrated at an exaggerated scale in Figure

239
4.3.22. Shear deformation of the box

structure is the result of transient shear

deformation in the soil. This type of

deformation leads to the formation of plastic

hinges where columns and walls connect

with the roof and base slab. Hinge

formation and associated eccentric loading,

in combination with increased loads from

vertical accelerations and geometric

distortion appear to have caused

compressive failure of the columns at Daikai

Station. The greater width of the station

relative to the running tunnel would have

contributed to higher vertical forces at the

station center columns. Moreover, loose

sandy fill that was placed originally between

the station walls and sheetpiles used for

temporary excavation support would have

been subject to liquefaction and softening

during dynamic loading, thereby reducing

the shear stiffness and lateral support from

adjacent soil.

The deformed shape of the running tunnel is consistent with assumptions about

earthquake-induced deformation which are

part of current design practices. For

example, design criteria for the Southern

California Rapid transit District (SCRTD)

Metro Rail Project [2] call for the evaluation

of structural racking by assuming that shear

deformation in reinforced concrete boxes is equal to shear deformation in the

surrounding soil as determined by

one-dimensional wave propagation analyses

using equivalent linear soil models. If certain joints are strained into the plastic

range, the structure is checked and

redesigned to assure that no plastic hinge

combination capable of leading to a collapse

mechanism can be formed. Using the design

distortions, the effect of seismic racking has

been to increase the reinforcing steel at some joints by 5% to 10% of that required

for static loads. In addition, vertical loads

for maximum earthquake conditions are

taken as 40% larger than gravity loads under

static conditions to account for vertical

accelerations.

Seismic design for underground rapid transit structures was introduced in the United

States during the planning and construction

of the Bay Area Rapid Transit (BART)

system during the 1960s. The design

practices for BART were based on an assumed equivalence of soil and structural

shear deformation and the introduction of

additional reinforcing steel to prevent plastic

hinge formation under the design transient

shear deformation [1]. Construction of the

KRTC and BART occurred during the same

time. It is not clear, however, what

assumptions and structural modifications, if any, were incorporated in the design of the

KRTR to accommodate seismic shear

distortion and vertical loading.

The KRTR followed design procedures

which were derived from those of the Japan

Railway and Tokyo Metropolitan Subway

Corporation. In the KRTR design, dynamic

earth pressures were considered, using the

Mononobe Okabe analysis which has been

discussed extensively in the technical

literature [4,6]. A horizontal seismic

coefficient of 0.1 to 0.15 was taken into

consideration, but vertical acceleration was

not accounted for. When hydrostatic

pressures are included in the analysis, the

increase in total lateral pressure associated

with horizontal seismic coefficients of 0.1 to 0.15 is small, typically less than 5% to 10%

of the lateral forces under static loads.

4.33 Lessons for United States

Rail services suffered more damage along

the elevated structure sections than along

the elevated embankment sections. Most

damage to the elevated structures occurred

at columns either at the bottom of

240
superstructures or at a joint region.

Although shear reinforcement spacing at both ends of the column were reduced by

about one-half, the old non-ductile details were vulnerable to high ductility demands.

The damage was similar to unretrofitted

column damage observed in past California

earthquakes.

Both the Port Liner and the Rokko Liner were built with modern codes. Columns

along the Port Liner are mostly reinforced

concrete whereas columns along the Rokko

Liner were built with steel. It is difficult to conclude which type of substructure

performed better without detailed structural

information. In general, steel columns

suffered minor yielding and local buckling

while concrete columns either yielded or

failed in shear.

Although damage to the reinforced concrete

structures was extensive, the major cause of

collapsed structures was the non-ductile

detailing of the steel reinforcement.

Structures designed by current specifications

performed well with minor damage.

Current retrofit methods can be used for

beams, columns and joints, but with the vast amount of elevated structures in need of

repair and retrofit, a systematic retrofit

technique is needed.

The failure of the Daikai Station is highly

significant because it is the first instance of

catastrophic earthquake damage to a modern cut-and-cover subway station. The

failure appears to have resulted from

earthquake-induced transverse shear

distortion in combination with loads

enhanced by vertical accelerations. Shear

distortion promotes plastic hinge formation

which, in combination with enhanced vertical

loads, can result in a collapse mechanism.

Shear distortion and vertical accelerations

apparently led to collapse of the center

reinforced concrete columns at the Daikai

Station. There was evidence of hinge

formation and associated shear distortion in the running tunnel of the KRTR between

Daikai and Nagata Stations. Elsewhere in "an underground shopping mall near Shin

Kaichi Station and at stations of the Kobe

Municipal Subway, cracking and deformation

of center columns provided evidence of high

vertical loads and shear distortion in the

cut-and-cover structures.

Current design practices, which account for

transient shear deformation and vertical

accelerations, are consistent with the failure

mechanisms inferred from observations of

damaged sections of the Kobe underground

rapid transit systems. Failure of the central

columns at Daikai Station emphasize the

importance of designing to prevent plastic

hinge formation leading to a collapse

mechanism. The lack of significant

confining steel at failed reinforced concrete

columns suggests that attention to confinement and ductility can play an

important role in strengthening underground

structures against earthquake effects.

Attention also needs to be focused on the

density and stiffness of backfill adjacent to structures built by cut-and-cover methods.

For design purpose, large shear distortion

have been considered primarily in deep

deposits of soft clay, where significant

amplification of bedrock ground motion can

occur. Because a rapid transit box structure tends to be relatively rigid with respect to adjacent soft clay, the shear deformation

sustained by the embedded structure is considerably less than that of the

surrounding ground [5]. Strong motion

records from the Kobe and Northridge

earthquakes, however, show that large

transient shear distortions can be generated

in relatively dense and stiff soils at locations

241
close to fault rupture. Because an underground box structure may not be

relatively rigid in a stiff soil, large shear

distortions may be conveyed to the

embedded structure under conditions of near source ground motion. This condition

should be considered for underground

structure located close to a seismic source.

4.3.4 Research Needs

Because of the low redundancy of single

column structures, the structural layout and

substructure performance becomes more

important for those structures than for structures with multiple column bents.

Research is needed to compare the ductility

between reinforced concrete, steel and steel reinforced concrete composite columns. A

damage index should be developed to assess the repairability of columns after an

earthquake. Force levels encountered at collapse sites should be compared to current

U.S. design forces to validate current

designs.

It would be advantageous to investigate the

levels of transient shear distortion which can

occur in soil profiles near a seismic source,

particularly when strong motion is characterized by relatively long pulses of

substantial acceleration, leading to high

velocities and displacements. The severity of

racking in underground structures resulting

from strong motion with high amplitude and

relatively long periods needs to be

understood better, and the combined effects

of racking and high vertical accelerations

needs additional clarification. Site response

needs to be investigated in terms of

differential lateral movements which occur

during earthquake loading at sites with thick

deposits of soft to medium clay and loose

sand. The effects of depth and soil liquefaction on soil shear distortion and

structural racking also need further research.

4.3.5 Summary

All four railways between Kobe and Osaka

and two guideway systems in Kobe were

seriously damaged. Although the death toll caused by elevated structure collapses is not

available, it is believed the number would

have been much higher if the earthquake

had occurred during the day time or rush

hour.

The inability to resist the applied lateral load for the elevated structures which

collapsed can be attributed to a lack of

confining steel within the critical column and

joint regions. The unexpected higher

ground accelerations over a wide area caused damage to miles of elevated

structures. Insufficient seat length caused

the Rokko Liner to lose one span. Modern

steel columns performed well with minor

local buckling.

4.3.6 References

1. Kuesel, T.R., "Earthquake Design

Criteria for Subways," Journal of the

Structural Division, ASCE, Vol. ST6,

June 1969, pp. 1213-1231.

2. Merritt, J.L., J.E. Monsees, and A.J. Hendron, "Seismic Design of

Underground Structures,"

Proceedings, Rapid Excavation and

Tunneling Conference, CD. Mann

and M.N. Kelly, Eds., AIMMPE,

New York, NY, pp. 104-131, June

1985.

3. Seed, H.B. and R.V. Whitman,

"Design of Earth Retaining

Structures for Dynamic Loads,"

Proceedings, Lateral Stresses and

Earth Retaining Structures Specialty

Conference, ASCE, New York, NY,

pp. 103-147, June 1970.

242
Seed, H.B., Tokimatsu, M. Harder, 6. and R.M. Chung, "Influence of SPT

Procedures in Soil Liquefaction

Resistance Evaluations," Journal of

Geotechnical Engineering, Vol. Ill,

No. 12, pp. 1425-1445, 1985.

Wang, Jaw-Nan (Joe), "Seismic

Design of Tunnels: A Simple State- of-the-Art Design Approach." 1991

William Barclay Parsons Fellowship,

Monograph 7, Parsons Brinckerhoff,

Inc., New York, NY, June 1993.

Whitman, R.V., "Seismic Design and

Behavior of Gravity Walls," Design

and Performance of Earth Retaining

Structures, Geotechnical Special

Publication No. 25, P.C. Lambe and

LA. Hansen, Eds., ASCE, New

York, NY, pp. 817-842, June 1970.

243
Figure 4.3.1 Rail lines connecting Kobe and Osaka.

244
Kobe Rapid Transit Railway

Kobe Municipal Subway

Damaged station

Figure 4.3.2 Map of Kobe Underground Rapid Transit Systems showing locations of

earthquake damaged stations.

245
5 columns cracked

and fractured at

east end of station

Nishidai

Collapse of

station o.4km

/ 1.0 km

Daikai

210 columns

damaged over 334 m

Minatogawa

Collapse of

elevated ro

Hanakuma 1.3 km

0.9 km

0.6km

Shinkaichi 0.7km

Kosoku

J Kobe

Underground shopping

mall with minor to moderate cracking of

columns and shear

cracks in panel walls

Nish?'

8km Mo,omochi

Motomachi

Figure 4.3.3 Schematic of the Kobe Rapid Transit Railway showing locations of

earthquake damage.

246
950117 01.17 5.46 34.36 135.00 20.0 7.2 2907 13.8 24.3 TAKATOR1 len = 12000

10000

1000

f3OO 100 <

10000

oo loo <

c/5

DAMPING 2% DAMPING 5% DAMPING 10%

i i i i i i i i i i i i i i i i

10000 :

O0 100

00

-i 1 1—I—

UD Component

i i i

!— DAMPING 2%

!— DAMPING 5% — DAMPING 10%

i i i i i i i i ' I I iiii

1 Period(sec)

Figure 4.3.4 Takatori Station response spectrum.

247
Figure 4.3.5 Damaged concrete frame - Shinkansen.

Figure 4.3.6 Column repair - Shinkansen.

248

250

Figure 4.3.13 Tilted pier - Port Liner.

252

Figure 4.3.15 Cracked reinforced concrete column and concrete panel

wall at underground shopping mall near Shin Kaichi Station.

254
BORING 6

Depth, m

Or

5-

10-

15-

B0R1NG 7

Depth, m

Ot

5-

10-

I5 1

Soil description

Fill

Silty sand and gravel,

some clay

Sand

Sand w/some gravel

Silty and clayey sand

Organic silty clay

Sand, silty sand and

gravel

Soil description

Fill Silty sand and gravel,

some clay

Sand

Sand and gravel

Silty sand and gravel

Organic clay and gravel

Sand and gravel

SPT N-Value

0 20 40

SPT N-Value

0 20 40

i

1 I

' i

1

Locally

Large

N-Values

Large

N-Values

Figure 4.3.16 Soil boring records near Daikai Station.

255
0 SOm

A'<| B'«l

Contour interval: 0.5 m

Plan View

IDOOUUUUUUUUUUULOJJjnnD

Cross- Section

Figure 4.3.17 Plan and profile views of Daikai Station collapse.

256
Cross-Section A-A B-B

0.4 m

Surface settlement

9.0 m 17.0m

Cross-Section A-A Cross-Section B-B'

.1- .1 - c> _ 4.5m 17.0 m 4.5 m

26.0 m

Cross-Section C-C'

Figure 4.3.18 Cross-sections of reinforced concrete station and running

tunnel structures at Daikai Station.

257
Figure 4.3.19 Roof collapse viewed from the station platform at Daikai Station

Figure 4.3.20 Compressive failure of center columns at Daikai Station.

258
Cracks, spoiled

concrete and

deformed rebar

at construction

joint

SOUTH NORTH

Bending fractures

at base of column

Figure 4.3.22 Earthquake deformation of running tunnel at an exaggerated

scale as inferred from reconnaissance observations.

259

4.4 Airports

4.4.1 Overview

The Kansai area is served by three airports:

Kansai International Airport (Kansai

Airport), Osaka International Airport

(Osaka Airport), and Yao Airport. The

Terminal Radar Approach Control

(TRACON), which is located at Kansai

Airport, controls airplanes in the area before

each is turned over to the respective control

towers. Kansai Airport was opened for

service on September 1, 1994, and primarily

serves international flights, although

emergency services, such as police and

rescue and news media, have access. Prior

to the opening of the Kansai Airport, Osaka

Airport served as the area's domestic and

international airport. Osaka Airport now

primarily serves domestic flights and a few

international flights. Neither of these

airports allows general aviation, which is served by Yao Airport. The control towers

and some support facilities at Kansai and

Osaka Airports were inspected.

4.4.1.1 Kansai Airport

supply of fuel. The airport is connected by a bridge to the mainland that carries auto and

train traffic. It is also served by ferry

companies from Kobe and four other cities. There is a pier for off-loading jet fuel.

- Expansion is planned in about 10 years to 15

years and another 700 ha of land will be

reclaimed and two additional runways and a second terminal will be added. Figures 4.4.1 and 4.4.2 show overview of the airport from

the control tower looking east and west,

respectively. Figure 4.4.3 shows a schematic

diagram of the airport, access bridge and the

location of strong-motion instruments

discussed latter.

At the Kansai Airport Control Tower,

it was noted that at one time, Japan

used the same control console system

that is currently used in the U.S., but

Japan is now in the second

generation of equipment that replaced

the original U.S. equipment.

The Kansai airport is built on a 511-hectare island of reclaimed land in Osaka Bay. The bay at the site was about

18 m deep and it took about 5 years to complete the island. It is 28 km southeast,

and across the bay from downtown Kobe

and 38 km southwest of downtown Osaka.

It is located 27 km southeast of the

epicenter. The island has subsided about 2

m since it was completed and currently has

about 5 m freeboard. Recently, subsidence

has slowed and it is anticipated that the

island will subside another 1.5 m in the next

50 years. There is a single runway about

3200 m long. Several tanks store 100000 kl

(kilo liter) of jet fuel. At a typical use of

about 3500 kl/day, there is about a month's

It was noted that in the winter there are normally strong winds. It was fortunate that

at the time of earthquake there was no wind.

Air Traffic Control Tower The Air Traffic

Control Tower (ATCT) at Kansai is a 19

story steel-tubing braced frame. The frame

is comprised of four exterior pipe-columns

outside the building envelope and four

pipe-columns inside the building envelope.

The exterior and interior columns are tied to each other at each floor level by a horizontal

truss, Figure 4.4.4. The lateral force

resisting system is provided by vertical cross bracing between each of the interior

columns (Figure 4.4.5). An interior column,

261
which is about 75 cm in diameter, can be

seen in Figure 4.4.5. Beam/column

connections were made by shop welding

short beam sections to the columns in the

shop and bolting the connecting beam to the

beam stub in the field. Figure 4.4.6 shows

such a detail in the penthouse above the

cab. Based on a brief review of control

tower drawings, the tower and the adjacent

administrative building appears to have a

stiff foundation mat. The drawings did not

show any piles. The tower is connected to the administration building by two catwalks, on the fifth and seventh floors (Figure

4.4.4). The control tower contained an

active control system to reduce wind induced

vibration.

The vibration control system consists of two

systems located on opposite sides of the

control tower on an upper floor. Each

system has a mass consisting of metal blocks

filling a 1.2 m by 1.2 m by .3 m box. The

mass is suspended on an arm that has a universal joint at its top, which is supported

by a box shaped frame. The frame is connected to the floor. There are two

actuators, which lie in a horizontal plane,

connected to the arm. The angle between

the actuators is 90 degrees (Figure 4.4.7).

Rubber snubbers are connected to the frame

to limit the motion of the suspended mass. The strategy for the operation of the

vibration control system is not known.

As noted above, Kansai Airport is built on

reclaimed land which has experienced

significant subsidence prior to airport

construction, so that ground settlement is a

serious concern. If settlement occurs the

building can be leveled by using two

hydraulic rams at each of the eight columns

located on the foundation slab (Figure

4.4.8). The columns are held against the

action of the hydraulic rams by about twelve

10-cm studs. The shear capacity of the

columns is not known, but there are two

shear keys on each side of the tower (Figure

4.4.9). These shear keys are detailed to carry lateral load parallel to the foundation

wall, including torsion of the building, but no vertical axial load (Figure 4.4.10). The

lower end of each ram is supported by the

foundation pad and the upper end is connected to a stiff diaphragm, consisting of

the deep beams shown in Figure 4.4.11. The

shear keys are configured so that they stay

engaged when the rams are used to relevel

the structure. It is not known if the leveling

mechanism is used to compensate for

differential settlement of the tower to prevent leaning, or if it is also used to maintain the level between the structure and

the surrounding ground. This may be

needed to prevent damage to utility lines

that enter the building.

The terminal building columns are also

supported so that they can be adjusted for

settlement at the site. Unlike the control

tower columns, the terminal building

columns do not have permanently installed

hydraulic cylinders to adjust column length.

Instead, there is a position that can accommodate a portable hydraulic cylinder

that can be used to raise the column.

Anchor bolts would have to be loosened and

shims inserted to reposition the column.

This control tower cab is constructed

differently than those found in the United

States, in that the cab roof is supported by

four columns in the interior of the cab

(Figure 4.4.12). The column cross-section

decreases in the cab, just above the floor

and below the ceiling. In the United States

the cab roof is supported only by the

window mullions, in order to allow a 360

degree view from anywhere in the cab with

the only obstruction being the narrow

mullions. In the United States the failure of

control tower windows, which is generally

attributed to the flexibility of the cab roof

262
relative to its floor, is relatively common.

The columns at Kansai should provide the

cab with much larger lateral stiffness.

The cab is octagonal in plan, with four wide

sides and four more narrow sides. The

windows are supported with twenty

structural tubing mullions, with three larger

members (20 cm x 10 cm) along the interior

of the wide window face and two smaller

members (15 cm x 7.5 cm) at the corners of

the narrow sides. The window panes

inserted in slots in the mullions with an engagement of about 2.5 cm on the sides

and about 3.5 cm at top and bottom. An

outside view of the cab is shown in Figure

4.4.13.

Operationally the control towers are

different from the United States. Communication control consoles and

monitoring oscilloscopes form controller

positions around the periphery of the cab, as

is done in the United States. However, near

the center of the control tower is a master

monitor for a supervisor (Figures 4.4.14 and

4.4.15). These appear to be used when

there is more traffic than was the case during the visit. It is interesting to note that

the monitors in Japan were much smaller

than those used in the United States and are incorporated into the control console. In the United States they are often suspended

from the ceiling. The computers that

control the displays were not visited, as they were located in another building. It was

noted that at one time, Japan used the same

system that is currently used in the United

States, but Japan is now in the second

generation of equipment that replaced the

original U.S. equipment.

Support Facilities A small room above the

control tower cab contained communication

transmission equipment, heat exchanger and

cable trays. The communication equipment

was well anchored. The cable trays used for

communication lines resemble those used by

the power industry for control cables in the

United States, in that sections are bolted

together (Figure 4.4.16). Cable trays were

* typically supported by trapezes suspended by

threaded rod. At some locations they were

restrained by friction clips (Figure 4.4.17).

A heat exchanger on the roof was well

anchored, as was most equipment observed

(Figure 4.4.18).

A battery plant provided an uninterruptable

power supply. Battery support structures observed in Japan tended to be short and

close to the ground, well braced, and

provided with rubber spacers between the

batteries and their restraints and between

cells (Figure 4.4.19). Because of the high

operating voltage, very long battery strings were used.

A large diesel-generator that supplied

emergency power was supported on

vibration mounts typical of those seen at other Japanese facilities (Figure 4.4.20).

Utilities connected to the diesel-generator were provided with flexible connections to accommodate the motion of the vibration

isolation system. Large diameter pipes, such

as those used for cooling water had flexible

couplings (Figure 4.4.21). The diesel engine

used compressed air for starting, typical of

larger engines. The compressor and air storage tanks were well anchored.

The cooling system for the diesel used a

small cooling tower adjacent to the building.

The cooling tower was supported on a large

concrete water storage tank that measured

about 6 m by 15 m by 2 m (Figure 4.4.22), so that emergency power could continue to operate for a long time even if the external

water supply was disrupted.

263
4.4.1.2 Osaka Airport

Osaka Airport is located 28 km

east-northeast of Kobe Japan Railroad

Station and 12 km north-northwest of

downtown Osaka. It is located about 43 km

east-northeast of the epicenter. The control

tower was the only part of the airport that was visited.

The leveling system provided in the

basement of the Kansai Airport

Control Tower appears to be an

innovative approach to provide for

the possible uneven ground settlement

that may be caused by liquefaction or

consolidation.

The control tower at the Osaka Airport was

constructed in 1969. It is on the top of an

eight story reinforced concrete

administration building. The concrete frame

includes shear walls in the short direction.

The cab is octagonal in plan and the roof

and windows are supported by 16 window

mullions. Equipment was generally well

anchored, although there were some heat

exchangers on the roof that were supported on unsecured concrete blocks (Figure

4.4.23), or had anchorage of questionable

strength.

The window size is 2 m wide and 2.25 m

high. They are rectangular except for the corner panes. What appeared to be double

paned glass was secured in the mullions by

inserting its sides about 2 cm, the bottom

about 2.5 cm and top about 2 cm, but it is difficult to make these estimates accurately.

The emergency power was located in a separate building that was closed on the

weekend, and the communications facility was off the airport site and was not visited.

4.4.2 What Happened

4.4.2.1 Kansai Airport

An array of 19 strong-motion instruments

recorded the earthquake at Kansai Airport

facilities [1]. Figure 4.4.3 gives a schematic

layout of airport facilities, and a section view

of the access bridge. It also indicates the

location of four instruments on runways with

letters W, C, SI and S2. The location of

instruments on the access bridge are also

indicated. Figure 4.4.24 indicates the

location of strong motion instruments in the

main terminal building - 10 instruments at the first, forth and roof levels, 1 instrument

at the Automated Guideway Transit System

Control Center, 1 down-hole instrument, 2

instruments on the access bridge, and 1 instrument at the ground surface in the

railway station. Table 4.4.1 lists the peak

acceleration, in gals, recorded by each

instrument. Figure 4.4.25 shows the largest

horizontal component recorded at location

W on one of the runways. The duration of

strong shaking is about 12 seconds and with

most of the peaks below 110 gal. Thus, the

ground motion at the site, even though it was recorded on land fill, was very low. The

records give no indication of liquefaction.

An air traffic controller in the Kansai tower

at the time of the earthquake said it "shook

like a snake," however, it was dark at the

time of the earthquake and from the control

tower, the deformation of the tower could

not be observed. It is assumed that this refers to vibration rather than mode shape.

No damage was reported to the tower or its contents. The connections of the cross walks that span the control tower and the

264
administrative building, which are locations

of potential damage due to interaction

between the buildings, were inspected for

signs of damage from within the crosswalk,

and none was observed. The area around

column footings that support roadways was

carefully inspected for signs of differential

settlement and none was found. The only

indication of damage was to a walkway in front of the main terminal building between

the roadway and building foundation.

Repairs were being made, but there

appeared to be a strip about 3 m wide

running the length of the terminal that

subsided about 7 cm (Figure 4.4.26). This was the only observed settlement and the

strip, which lies between the terminal

foundation and roadway, may have not been

adequately compacted. It was reported that

there was no subsidence or lateral spreading

around the boundaries of the island. Small

cracks across the runway were observed,

primarily at construction joints, about every

100 m that were attributed to the

earthquake.

Impact on Operations At the time of the

earthquake, there was a flight on approach.

The captain was told to hold until runways

could be checked, and then cleared for

landing. There are normally about 240

operations per day. Note that a landing and

departure are two operations. At the time

of the earthquake a maximum of 23

operations per hour were possible, but this was about to increase to 26 per hour. As a

result of the earthquake, there was a drop in tourist traffic, but since east-west road and

rail links were blocked at Kobe, there was

an increase in domestic flights to and from

western Japan. These flights were routed

through Kansai because of the difficulty in

getting to Osaka Airport and to reduce its load, as most relief traffic went to Osaka.

As a result, there was little net change in

traffic at Kansai Airport. The small cracks

observed in the runway had no effect on

operation.

4.4.2.2 Osaka Airport

The ground motion at the airport is not

known, but an air traffic controller on duty

at the time of the earthquake indicated that

the shaking was very severe, that it was

difficult to stand, that things fell off of

desks, and that it seemed to last one or two

minutes. Damage in the area and at the

nearby power substation indicates that the

shaking at the site was severe. Numerous

diagonal shear cracks were found in shear

walls in the stair well and above windows.

The largest crack was about 6 mm wide and

located at the floor level just above the roof

of the main building that adjoins the control

tower. Other cracks were about 3 mm wide

or less and decreased in size with the height

at higher floor levels. The abrupt change in lateral stiffness at the floor above the roof of

the main building and the reduction of shear

loads with elevation explains the

observations. The stairwell shear walls may

have attracted large lateral loads because of

relatively high stiffness in the short direction

of the building. Figure 4.4.27 shows an example of this damage.

As noted above, this tower, like those in the

United States, has its roof supported by the

mullions. One window had a crack

emanating from a lower corner that

continued to lengthen as the days passed.

Both elevators serving the control tower were damaged and out of service following

the earthquake. One elevator was restored

to service in just one day, the other was out

for 4 or 5 days.

The earthquake caused a crack

perpendicular to and through the runway at the airport, but it did not disrupt operations.

265
Impact on Operations Osaka Airport is a

restricted airport, that is, there is no general

aviation; however, police, fire, rescue, and

press use of helicopters is allowed.

Normally there are about 20 Visual Flight

Rule (VRF) operations per day. But after

the earthquake, the Japan Self Defense

Force and the U.S. forces had helicopters

and there were about 300 operations a day.

These operations were used to deliver

emergency supplies and to move emergency

personnel in and out of the earthquake

affected region.

4.4.3 Lessons for United States

The braced frame structural system in the

Kansai control tower appears to have an

effective seismic design, but it has not yet

been put to a severe test. The leveling

system provided in the basement of this

building appears to be an innovative

approach to provide for the possible uneven

ground settlement that may be caused by

liquefaction or consolidation. The use of

interior columns to support the roof of the

cab in the Kansai control tower did not

appear to be a significant visual impediment

and should reduce earthquake window

damage frequently observed in the United

States. Future construction in the United

States should consider this design feature in structures that might be subjected to seismic

loads.

4.4.4 Research Needs

The earthquake performance of control

tower windows in the United States has been

poor and similar performance was observed

at Osaka Airport. The loss of these

windows can be very disruptive to operations; therefore improved performance

is desirable. The Kansai Airport control

tower had columns incorporated into its design that did not appear to adversely

affect the functionality of the tower.

Practical methods are needed to upgrade

control towers in a way that will not

interfere with their function.

4.4.5 Summary

Two members of the reconnaissance team

inspected the control towers at the Kansai

and Osaka Airports. They found the Kansai

tower to be well constructed with an

innovative method of leveling the tower

should it be subjected to differential

settlement. This tower also had columns in the interior of the cab to support the roof

and resist lateral motion of the cab, thus

protecting the windows. The columns

appeared to cause little visual interference.

The cooling system for the emergency

generator was provided with a large local

water supply. This tower sustained no damage from the low level ground motion in this earthquake.

Both administration building and control

tower at the Osaka Airport sustained some

damage. Damage included a crack in a window in the cab of the tower, minor

damage to shear walls in the administration

building and temporary loss of use of the

elevators.

4.4.6 Acknowledgment

Strong-Motion data was provided by Stu

Werner, Dames and Moore, San Francisco,

1995.

266
Table 4.4.1

Peak Accelerations Recorded at Kansai Airport

(> indicates input exceeds instrument range)

Airport Facilities

Heasumsent Maximum Acceleration(gal

)

Position (D Component © Component © Component — Horizontal(X) Horizon tal(Y) Vertical(Z)

A Common duct W 16 8. 5 10 3.9 2 4 7. 1

Runway Northern end of Runway p 14 7. 4 1 1 8. 0 2 0 4. 5

B Common duct c;o i1 9 7.1 1 0 5. 9 1 5 4. 5

Southern end of Runway 8 8.4 7 0.7 14 2. 9

Access

Bridge

Horizontal(X) Horizontal(Y) VerticaL(Z)

Top k base of pier

Top 2 7 2. 4 17 8. 7 8 3.6

Base 13 3. 8 9 3.9 7 0.6

Horizontal (N-S)r~

Horizontal(E-W) Vertical

Outside of Building

(50a under ground) G-l 74. 8 10 1.1 103. 5

South Side of B1F B-l 3 6. 4 3 6. 0 >1 0 2. 4

North Side of B1F B-2 37. 8 32. 4 >1 0 2. 4

P

South Side of B1F B-3 *? 35. 1 >102. 4

Main

Terminal

Building

North Side of B1F B-4 33. 5 3 1. 8 >102.-4

T

South Side of 4F 4-1 95. 8 9 5. 8

North Side of 4F 4-2 93. 9 79. 0

B

South Side of 4F 4-3 96. 3 8 2. 7

North Side of 4F 4-4 86. 7 8 0. 1

South Side of Roof R-l 3 4 7. 6 276. 1 534. 6

North Side of Roof R-2 3 10. 6 321. 9 4 5 1.2

A.G.T Control Center 3 1. 0 (Horizontal)

Railway Substation 131. 0

267
Figure 4.4.1 Overview of airport looking east from control tower.

Figure 4.4.2 Overview of airport looking west from control tower.

268
International Cargo Terminal

aySubstation

hFuel Tanker Berth

^Access Bridg

Schematic Diagram of Kansai Airport

(Instrument Locations: SW, C, SI, S2)

Airport Island Mainland

A! Pt P2 PJ PJ P5 PS P7 Rj pg p^ Pu - P1:> p, 3 p u p , 5 p , e P|7 p,j p, 9 m R| p.„ p.^ p-^fiJp^KJpM

Profile of Kansai Access Bridge

Figure 4.4.3 Schematic diagram of airport, access bridge and strong-motion instrument

locations.

269
Figure 4.4.4 Kansai Airport Air Traffic Control Tower.

270
Figure 4.4.6 Beam/column connection in the penthouse above the cab.

271

Figure 4.4.9 Basement of the tower showing system for leveling the building and shear keys.

273
Figure 4.4.10 One of two shear keys parallel to each side of the control tower.

274
Figure 4.4.11 Deep girders of the rigid diaphragm above a column.

275
Figure 4.4.12 Column supporting the cab roof in Kansai Control Tower.

276
Figure 4.4.14 Supervisor control position located in center of control tower Cab.

277
Figure 4.4.15 Supervisor control position communication council.

Figure 4.4.16 Communications cable tray with bolted connections above cab.

278
Figure 4.4.17 Communications cable tray secured with friction clips.

279
Figure 4.4.18 Roof-mounted heat exchanger braced with cables.

280
Figure 4.4.19 Very long battery string on low slung battery racks provides emergency

powerFigure 4.4.20 Large diesel engine-generator on vibration isolators typically found in

Japan.

281
Figure 4.4.21 Flexible coupling in water cooling line to diesel engine-generator.

282
Figure 4.4.22 Cooling tower and water tank for emergency engine-generator.
r

r

i

B-3 8-4 o o -i

1 J a-S A-A 1 O U

i

i j B-l B-2 1 4-1 o o o o La La

First Floor Plan View Fourth Floor Plan View

R-l R-2

La

Roof Plan View

P2 P3

Roof truss

! i iffTO

I rr^fat Mil i j)rnb^;

improved soil area I

-H

j

Reclamed laver

Alluvial clay layer (improved bv

Diluvial clay layer _ , 5rl

(Under ground) 3 component

Profile of Terminal Building (Section A-A)

Airport Terminal Building

Top of Pier.

» 111 91 B 71

Base of pier/ fS4

Access Bridge - Profile Detail Instrument Location

Access Bridge

Figure 4.4.24 Strong-motion instrument locations at Kansai Airport.

284
200.0gal

H1

-200.0gal

1

10 40 60 ,80 ,100 ,120 140 ,160 ISO sec

i i ii 1 1 ii i 1 1 It M 1 II 1 1 1 1 1 1 1 1 1 1 1 1 ii 1

1 1 II 1 1 1 1 II 1 M 1 1 1 1 1 1 II 1 1 1 1

1 1 1 1 1 1 1

i 1 1 i 1 1 i ii ii 1 ii i 11 1 1 1 1 1 1 1 1 1 1 ii

Figure 4.4.25 Strong-motion record from Kansai Airport runway - Position W.

285
Figure 4.4.26 Subsidence in sidewalk and repaired sidewalk outside the Kansai Terminal

Building.
4.5 Ports and Harbors

4.5.1 Overview

Kobe has been a prominent port city since

the formal opening of its harbor to the West

on January 1, 1868. It is the largest foreign

trade port in Japan and the third busiest

port in the world. It has also been one of

the world's most expensive ports to

construct. Two major manmade islands,

Port and Rokko Islands, cost about $2

billion dollars to create. The port contains

152 berths with an aggregate wharf length of

27 km [1]. The Port operates 400 dockside

gantry cranes and derricks to load and

unload cargo.

In addition to the port facilities on Port and

Rokko Island, there is extensive commercial,

recreational, and residential development,

particularly in the central part of each

island. Many high-rise buildings have been

constructed.

The Kobe port facilities are built on ground

reclaimed from Osaka Bay (Figure 4.5.1).

The source of the fill is obtained from

outcrops of the Kobe and Osaka Groups

and weathered granite from the adjacent

Rokko Mountains. The fill was excavated

from several large scrapping areas east and

west of Kobe. The first reclamation efforts

filled 529 hectares along the Kobe City

shoreline from 1953 to 1970. Port and

Rokko Island were created following these

reclamation efforts. Reclamation of Port

Island, which is west of Rokko Island,

started first and was done in two phases.

The first phase, which filled 436 ha, was

from 1966 to 1980. The second phase

started in 1986, and increased the size of the

island by 390 ha Rokko Island, which is 580

ha, was reclaimed from 1973 to 1992.

Construction of Port Island is described by

Nakakita and Watanabe [2]. Silty sand fill was placed in standing water with an average

water depth of 12 m and continues to an

elevation of about 4 m above water level. The upper and lower parts of the fill were

placed using different techniques. The lower

part of the fill to within 2 m of high water

level was dumped into standing water from a trap-based barge with no compaction effort. The lower part of fill was created in 2-m to 4-m-thick layers. The upper part of the fill was accomplished by scooping from barges

that were moored to the quay wall,

transporting to the interior of the island by a movable conveyor, and spreading with

modest compaction by rolling. No

significant effort was made during

reclamation to compact the sandy fill to increase its liquefaction resistance.

Preearthquake field blow counts typically

ranged from 5 to 10.

The extensive damage to the port of

Kobe highlights the seismic hazard to

port facilities posed by sandy fills.

Such materials have been widely used

in both United States and worldwide

to reclaim ground for port

development and expansion.

A typical soil profile in the reclaimed area is shown in Figure 4.5.2. Immediately

underlying the fill is an approximately 13-m

thick layer of marine clayey silt with water

contents that ranged from 7 to 100 percent. In addition, soft compressible clays were

encountered over a 20-m interval beneath a depth of 50 m. Intercalated between these

two marine clays is a 30-m thick sequence of

alternating sand and clay. Consolidation of

the naturally occurring soft clayey silt

287
beneath the fill was a major geotechnical concern during the reclamation and post

reclamation construction of wharf structures and buildings. Large settlements caused by

the weight of the fill are documented.

Most of the quay walls forming the wharfs

are sand-filled caisson structures, although a few consist of cellular steel sheet piles. A

design drawing of the caisson-type

construction is shown in Figure 4.5.3. The

foundation for each caisson was prepared by

excavating the natural silt layer on the sea

floor and replacing it with sand fill. A

gravel pad was placed on the fill and then

the 10-m-tall concrete caisson was lowered

into place and filled with local sandy

material. The waterside crane rail rests on

the caisson. Most of the gantry cranes have

rail spans of 30.5 m, but a few of the older cranes at Port Island and Maya Wharf have

rail spans of 16 m. The 30.5-m rail girders are supported either by a concrete slab

placed on engineered fill or a concrete pile

supported wall and the 16-m rail girders rest on a concrete pile supported wall.

4.5.2 What happened

Liquefaction was widespread along the

shoreline and on the islands in the port area

(Figure 4.5.4). Evidence for liquefaction

included areally extensive blankets of ejected

sand and water and ground cracking parallel to the shoreline. Most of the ejected

materials consisted of silty sands. Locally,

however, 10-cm diameter granite fragments were ejected. Damage to quay walls in the

harbor area from liquefaction and lateral spreading was extensive. For example, aerial

photography and on-site inspection indicate

that 11.5 km and 12.5 km of quay wall along

Port and Rokko Island, respectively, were

seriously damaged by permanent ground

displacement. Laterally spreading typically

displaced walls seaward about 1 m to 2 m.

Downdropped blocks formed on the

landward side within 20 m of the wall

(Figure 4.5.5). The land surface of the

downdropped block was commonly lowered

as much as 3 m. Ground cracking

associated with the lateral spreading along

the shoreline extended landward from quay

walls for distances of about 100 m.

A variety of ground improvement

techniques are available, but they are

costly. The localization of lateral

spreading near the quay walls

suggests that only portions of the fill

need to be improved. The

development of such guidelines would

facilitate remedial efforts at other

ports with similar exposure.

Loading and unloading of cargo from ships was essentially brought to a standstill by

damage to dockside gantry cranes associated

with permanent ground displacements that

damaged wharf areas and affected the crane

rail systems that run along the quay walls.

Differential horizontal displacements

between the crane rails associated with

lateral spreading distorted and damaged the

steel moment frames of many cranes along

the waterfront (Fig. 4.5.6). The primary

damage to cranes was structural. There was

little damage to the mechanical components.

Despite the distortion of the framing of the

cranes, most remained upright. Frames with

weak portal beams, lacking ductile moment

frames, incurred leg buckling above the

portal beams. Cranes with strong portal

beams and ductile moment frames were damaged less severely.

288
The large lateral displacements of the quay

walls undoubtedly were caused by the

increase in lateral pressure on the wall from

the liquefied soil mass retained behind the

wall. Because of the large settlements of the

caissons themselves, it is suspected that the

sandy fill beneath the caissons liquefied as

well. Figure 4.5.7 is a hypothetical cross

section illustrating the interpretation of the

failure mode of caisson-type quay walls.

Note that the lateral spreading also

displaced the landside pile-supported crane

rail.

Permanent horizontal ground deformation

from lateral spreading did not appear to extend inland more than about 100 m from

the sea walls. Liquefaction settlements

inland from the quay walls, however, were

dramatic and areally extensive on both Port

and Rokko Islands. Settlements ranged

from 30 cm to 50 cm throughout the harbor

area, but locally exceeded 100 cm.

Most buildings and elevated transportation

corridors on the islands are pile supported.

Settlements were easy to detect because

piles extend through the liquefied zone. Damage from settlements was primarily

limited to underground utility connections to structures.

Damage from ground shaking was modest

relative to damage caused by permanent

ground deformation associated with

liquefaction. For example, only a few

straddle carriers, used to transport cargo

containers, were toppled by the ground

shaking. A recording of ground shaking on

reclaimed ground in Kobe north of Port

Island is shown in Figure 4.5.8. The station

is located at the Port of Kobe Construction

Office near the shoreline and is free field. No evidence of liquefaction was reported at

this station. The peak horizontal

acceleration was 502 gals (0.51 g).

Liquefaction reduced the strength of shaking

at the land surface on Port Island. At a Port Island station which is 1860 m south of

the Construction Office station, the peak

horizontal acceleration at the land surface

" was only 341 gals (0.35 g) despite a peak

acceleration of 565 gals (0.58 g) at the base

of the fill.

4.53 Lessons for United States

The extensive damage to the port of Kobe

highlights the seismic risk to port facilities posed by loose sandy fills. Such materials

have been widely used in both the United

States and worldwide to reclaim ground for

port development and expansion. The 1995

Hyogoken-Nanbu earthquake illustrates once

again the potential for these fills to liquefy

and generate large permanent ground

displacements when shaken by earthquakes.

The 1995 earthquake furthermore illustrates

the ability of such liquefaction to totally

disable a port.

Stabilization of loose sandy fills by ground

improvement is generally a costly endeavor

because of the volume of material that must

be improved. For regions with low to modest earthquake hazard, the cost/benefit

ratio may be too high to warrant ground

improvement efforts. The localization of

lateral spreading around the margin of the

Port and Rokko Islands suggests that the

hazard of permanent horizontal ground

deformation can be substantially reduced by

improving only the outer margins of these

loose fills. While large vertical settlements

may still occur, particularly in inland areas of unimproved ground, damage may be

tolerable. Modern pile-supported structures on Port and Rokko Islands performed well

in locations where they were subjected only

to ground settlement.

289
Another important engineering lesson from

the Kobe port experience is the vulnerability

from using one style of design for a key part

of an important facility. Clearly liquefaction was not considered to be a significant

possibility during the design of port quay

walls. By repeatedly using quay wall designs

that were vulnerable to lateral spreading,

operation of the entire port was left vulnerable to this hazard.

4.5.4 Research

The extensive damage to the quay walls that

disabled the port operations indicates that

the failure mechanism of these structures needs to be understood from the perspective

of being able to design against such failures.

A variety of ground improvement techniques

are available, but in general they are costly.

The localization of lateral spreading near the

quay walls suggests that only portions of the

fill need to be improved. The development

of such guidelines would facilitate remedial

efforts at other ports with similar exposure.

The large vertical settlements observed in sandy fill during the earthquake also provide an excellent opportunity to develop a case

history of ground deformation associated

with liquefaction. There are very few well

documented examples of post-liquefaction

consolidation. The numerous pile-supported

structures and bench marks provide an

opportunity to systematically document the

regional nature of the soil consolidation.

The high level of ground shaking,

approximately 0.5 g, and the large

volumetric strains, greater than 10%, should

permit rigorous evaluations of existing

methods for predicting settlement.

4.5.5 Summary

Liquefaction during the 1995 HyogokenNanbu earthquake disabled the port of

Kobe, the third largest port in the world.

Permanent ground deformation caused

failure of quay walls and differential

displacements of crane rails causing crane

operations to stop. Lateral spreading was

restricted to the margins of the port

facilities, usually extending less than 100 m

from quay walls. Vertical settlements of

30 cm to 50 cm were widespread inland, but

did not do great damage because of their

uniform character. Port facilities were built on ground reclaimed from Osaka Bay. The

land was reclaimed by loosely dumping silty

sand into about 12 m of standing water.

Liquefaction of the fill was not a geotechnical concern during construction.

Because loose sandy fill is commonly used

for ground reclamation in many ports, it is important that the failure mechanisms of the

quay wall be studied in order to develop

cost- effective remedial methods for these

other ports.

4.5.6 References

1. Fairplay, World Ports Directory,

Pairplay Information Systems, Ltd.,

Surrey, United Kingdom, pp. 407-408,

1994

2. Nakakita, U., and Watanabe, Y., Soil

stabilization by preloading in Kobe

Port Island, in Proceedings of the 9th

International Conference on Soil

Mechanics and Foundation

Engineering, Tokyo, Case History

Volume, pp.61 1-622, 1977.

290
Figure 4.5.1 Map of Kobe area with reclaimed ground boundary.

291
Land Surface

Reclaimed Ground

K.P. +4-+7.5

K.P. ±0

-12

-25

-55

H.W.L -1.7 L.W.L -0

Fill N=5-10

Marine Clay

q u =0~10

kgf/cm z

-75

Interlayered

Sand and

Clay

N=10~50

Marine Clay

q u =1.5-5.5

kgf/cm^

Interlayered

Sand and

Clay

K.P.±0

-10

-20 -

-30

-40

-50

-60

-70

-80 hN-Value

0 20 40 60

s.

q u (kgf /cm'

q u lkgf/cm'

Figure 4.5.2 Typical soil profile at Port island (from Nakakita and Wantanabe, 1977).

292
CRANE RAIL [O O

LOW WATER LEVEL

CAISSON

^00 V AG

~RAVE

"

L bed, 0

SANDY FILL

SAND LAYER

10 m

I* «

// ^ II

II * ft ^

// // * /,

'/ CLAY* '/

II w^^

j

SAND LAYER

NO VERTICAL EXAGGERATION

Figure 4.5.3 Construction drawing of wharf on Port Island (From Port and Harbor Research

Institute).

293
LIQUEFACTION AREAS

DAMAGED WHARFS

and QUAY WALLS

I | RECLAIMED GROUND

• STRONG MOTION RECORDING

Kobe

KOBE-JI SM

Ashiya

Nishinomiya

Port Rokko is/and

Island

I

S

0

0)o

3

PORT ISLAND SM

Osaka Bay 5 km

Figure 4.5.4 Areas of liquefaction and damaged quay walls in the Port of Kobe. Areas are generalized from aerial photography and unpublished maps by the Geographical

Survey of Japan.

294
Figure 4.5.5 Damaged to Maya Wharf caused by liquefaction-induced lateral spreading.

Downdropped block has formed behind quay wall where land has settled and

moved outward. Landward side of block is the pile-supported rear crane rail. Photograph taken February 15, 1995.

295
Figure 4.5.6 Collapsed crane caused by permanent differential horizontal displacement

between crane rails on Rokko Island. Lateral spreading caused permanent

seaward displacement of quay wall and crane rails to pull apart. This caused the

legs of the crane to pull apart and crane to topple. Photograph taken February

15, 1995.

296
Figure 4.5.7 Hypothetical failure mechanism of caisson quay wall.

297
500

0

-500

500

-500

500

0

-500

0 10 20

Time (s)

30

Figure 4.5.8 Kobe-ji strong ground motion record at Port of Kobe Construction Office from

January 17, 1995, Hyogoken-Nanbu earthquake

298
CHAPTER 5

PERFORMANCE OF LIFELINE SYSTEMS

5.1 Introduction

Lifelines are public works and utilities systems including telecommunications,

electrical power, gas and liquid fuels,

transportation, and water supply and sewage

treatment. They are vulnerable to natural

and man-made hazards such as earthquake,

extreme wind, flood, accident, and terrorism.

Proper performance of lifelines is important

to assure public safety, vitality of economic

activity, and quality of life. However,

lifelines and their importance to our way of

life generally are not recognized until their

failure causes deaths and destruction,

impedes emergency response following a major disaster, hinders post-disaster

recovery, or paralyses a community.

Disruption of regional lifeline systems as the

result of a major natural disaster such as this

earthquake in Kobe, can have a profound

effect on the entire nation because of the

economic interdependence of lifeline systems

and the functions they support.

The Kobe earthquake is expected to be the

costliest natural disaster in recent human

history and a significant portion of those

losses is due to the loss of function of

lifeline systems immediately after the

earthquake, the cost of their repair and

replacement, and the related near- and longterm indirect economic losses.

This chapter gives a brief overview of the

performance of lifeline systems; water and

wastewater systems, gas delivery systems,

electric power, telecommunications, and

hospitals. Observations of lifelines related

to expressways, highway, railways and rapid

transit systems, airports, and ports and

harbors are given in Chapter 4. Post- earthquake fires issues are presented in Chapter 6.

299

5.2 Water and Wastewater Systems

This section describes the City of Kobe's

water system, as well as the Hanshin Water

Authority Water Purification Plant that is jointly owned and provides water to the

cities of Kobe, Ashiya, Nishinomiya, and

Amagasaki. Damage to the Kobe's

wastewater system is also described.

No information has been gathered for the

other cities east of Kobe. The City of

Kyoto's water system had no pipeline

damage, and suffered only minor window

glass damage and damage to a small

diameter buried pipeline at one of its purification plants.

5.2.1 Overview of Water System

5.2.1.1 System General Overview

The City of Kobe water system serves 608844 households including 1.5 million

people. The system was started in 1900 as the 7th modern water system in Japan. The

Water Department began actively using

computers in 1987, inputting water pipe

drawings and boring log data for 4000

borings in 1988.

The city area is 547 km2 of which 251 km2

has water service. The balance of the city is underdeveloped, and has no water service.

The Kobe Water Department has over 1000

employees. Its system includes the following

inventory:

- 3963 km pipe

- 239 reservoirs at 119 sites

- 43 pump stations with 231 pumps

- 64 km transmission tunnels

Figure 5.2.1 shows a schematic of the system

and Figure 5.2.2 shows a more detailed map

of the system serving the urban area.

The U.S. lifeline earthquake

community should learn from both

the successes and failures observed in

Kobe. Successes include the

monitoring and control system,

performance of water treatment

plants (except geotechnical) and

tankage, and possibly seismic joint

pipe. Failures include lack of

adequate water supply for fire

suppression and inadequate focus on

geotechnical failure.

The system is divided by Mt. Rokko into two

service areas, Hokushin and Shigaichi. The

Hokushin area is served by Sengari

Reservoir located in the north. This

mountainous area makes up less than 10%

of the water demand, and has been

developed primarily since the 1960's.

The Shigaichi area, the Kobe urban and

western parts, is served by the Yodogawa

River. The area is approximately 30 km

long, east to west, and 1.5 km to 6 km wide,

running between the shoreline and the

mountains. Over 90% of the water demand

is from this region. Water to this area is supplied from the east; it takes up to 12

hours for the water to traverse the distance

from east to west.

Water is pumped to the water purification

plants, and runs by gravity to the west at an

elevation starting at 90 m above sea level through Kobe's tunnel system. The tunnel

301
system operates in the open channel flow or low pressure regime. The first tunnel, 1.8-m

diameter and built in the 1930's, is constructed in rock with an unreinforced

concrete lining. The second tunnel, 2.5-m

diameter, was built in the 1950's and lined

with reinforced concrete. There is apparently no concern about water quality

degradation in the tunnel even though it is open channel flow. Water used at an

elevation above 90 m (apparently 15% of

the demand) is pumped from the tunnel

system. Refer to Figure 5.2.3 for a schematic

of the system profile.

The Kobe water system is designed to provide both water for drinking and fire protection. There is no dedicated water

system for fire suppression, although one was under consideration in 1993. Fire

fighting is the responsibility of the fire department.

There are a number of cisterns (Photo 1)

located throughout the City for use for fire suppression. The urban area is laid out on a 400 m by 400 m grid. Three quadrants of

the grid each has a fire hydrant, and the

four quadrant has a cistern. There is one

special radio system for communication

between the water and fire departments

during emergency response situation.

5.2.1.2 Supplies

Nearly all of Kobe's water comes from

surface water supplies. Nearly three

quarters of Kobe's water comes from the

east with primary sources including Lake

Biwa and the Yodogawa River. Table 5.2.1 summaries these sources. Figure 5.2.1 shows

where many of these sources are located.

5.2.1.3 Water Treatment Plants

All of Kobe's water is treated before it is distributed. There are eight water

purification plants treating potable water for

Kobe, and one treating water for industrial use The three largest plants are Uegahara,

Hanshin (Kabutoyama), and Sengari. The

Uegahara and Hanshin (Kabutoyama) plants are immediately adjacent to one another,

and are located to the east of the City. The

Sengari plant is located north-northeast of

the City. Table 5.2.2 summarizes the water

treatment plants information. Figures 5.2.4

and 5.2.5 show schematics of two of the

purification plants that were damaged in the

earthquake, Uegahara and Motoyama.

5.2.1.4 Distribution

Kobe has an aggressive pipeline replacement

program that has resulted in 90% of their

system being constructed of steel or ductile

iron pipe. Their pipe inventory is summarized in Table 5.2.3.

Approximately 6% of that pipe employs

special seismic joints as depicted in Figure

5.2.6 and Photo 2. These joints, Standard

G113 and 114, Japan Water Works

Association (JWWA), are specially designed

to allow longitudinal extension and

compression but are restrained before they

separate. The ductile iron pipe with S joints

is manufactured by both Kubota and

Kurimoto, and is estimated to cost 30%

more than pipe without seismic joints. All

new pipelines greater than 400 mm in diameter and all pipelines in reclaimed and

landslide-prone areas are required to be

constructed with this seismic resistant pipe.

For example, all major pipelines on Rokko

Island are constructed with this special

seismic resistant joint.

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The steel pipe Kobe uses employs butt

welded joints. Pipe larger than 600 mm

diameter is welded from both interior and

exterior, smaller diameter pipe only from the

exterior.

Kobe Water uses polyethylene encasement,

commonly referred to as baggies, for

external corrosion control for their ductile

iron pipe. They line larger diameter pipe

with cement mortar, and smaller diameter

pipe with epoxy. For new service

connections, they use High Impact Vinyl

Pipe, thought to be similar to PVC used in

the United States.

Kobe has an aggressive pipeline replacement

program which began in 1964. Tables 5.2.4

and 5.2.5 summarize this program covering

both general renewal and earthquake

specific upgrade.

The results of Kobe's aggressive pipeline

replacement program were evident in a leakage survey of its system undertaken in 1990. The Kobe system had a 93.5%

effective use of its water compared to Tokyo

which had 87.8% and Osaka 92.7%.

Effective use is calculated by dividing the

amount of water delivered to customers

(through meters) divided by the amount of

water taken from the source. Meter

accuracy and system leakage are the two

elements that can dramatically affect the

j results.

In addition to potable water pipelines, Kobe

has an industrial water pipeline system.

Water is treated at Uegahara Water

Purification Plant in a separate treatment

system delivering a lower grade water

quality, and distributed to Rokko and Port

Islands, and other industrial areas along the

shoreline. That system includes the

following pipelines: conveyance, 21 km;

transmission, 13 km; and distribution, 62 km.

5.2.1.5 Distribution Reservoir and Pump

Stations

The Kobe Water Department has an

inventory of 239 service reservoirs at 119

sites. These include cast-in-place concrete

reservoirs (approximately 80%), and precast

concrete reservoirs and welded steel reservoirs (approximately 20% combined),

which range in capacity from 40 m

3 to 20000 m

3

. Table 5.2.6 summarizes the

location of these reservoirs by elevation, and

Table 5.2.7 by area.

Nearly all of the reservoirs are constructed

with two at each site. This provides

redundancy for pOst-earthquake function

and allows the removal of one from service

for cleaning.

Kobe does not use pressure reducing valves

between pressure zones as is commonly

done in the United States. Rather, control

tanks are used, with flow from the upper

pressure zone into the tank controlled by an

altitude valve.

Kobe Water has a program to advance the

design of reservoirs to meet a wide range of

requirements including general structural

performance, earthquake performance, and

corrosion resistance. At the Okuhirano

Water Purification Plant, Kobe constructed

two reservoirs at about the same time, one

using welded steel and the other

precast/post-tensioned (prestressed) concrete. The objective was to be able to evaluate the relative long-term performance

of both designs. Figure 5.2.7 shows a

section of the steel reservoir. It is specially

designed to accommodate radial expansion

during filling, similar to the U.S.

precast/post-tensioned concrete tank design.

Inherent in the design is damping of

compressive earthquake loading on the steel

shell.

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5.2.1.6 Control System

The Kobe Water Control Center, built in 1977, is located at the Okuhirano

Purification Plant. It is a Fujitsu 400 MHz

UHF-multi-directional multiplex

broadcasting system. It monitors over 2000

sets of information including reservoir level; tunnel level; tunnel, transmission, and

distribution flow; pump status; and access

alarms. It controls 469 components

including pump on/off, rate-of-flow

controllers, valve controls, and control

selection.

The Control Center communicates with

distributed facilities through a repeater

station on the International Trade Center

Building. That repeater serves much of the

urban area and the Uegahara Water

Purification Plant directly and also transmits

secondary repeaters at Mt. Rokko, which

serves the northern service area and Sengari

Water Purification Plant; and Mt. Takao

which serves the western area. Figure 5.2.8

presents a schematic of the

communication/repeater system.

5.2.1.7 Earthquake Monitoring and

Control

Kobe Water has an earthquake monitoring

and control system in place to isolate water

from the system and to maintain it in selected reservoirs for drinking following an

earthquake. Without this system in place,

pipe damage in the system would result in a quick drainage of the service reservoirs. The

system is also designed to maintain water for

fire suppression. There is no capability

however, to isolate major lines crossing

vulnerable areas, such as lines to the

reclaimed land areas.

The system consists of ground motion

monitoring at the Okuhirano Control

Center, a control panel, telemetry (as

described above), and reservoirs with

earthquake isolation valves at 21 locations,

with plans for a total of 29 locations. The

earthquake valves are motor operated with

backup batteries.

The seismograph at the Control Center measures ground motion and provides input

into the earthquake control system. The

earthquake control system allows both

automated and manual control of isolation

valves on service reservoirs. The decision

logic is given below:

- Level 1: 40 gal--manual alarm

- Level 2: 80 gal--automatic shut down

when combined with

excessive rate of change of

flow

- Level 3: 250 gal-automatic shut down

Figure 5.2.9 shows a schematic of the

control system.

There are dual reservoirs at each of the 21

sites, one has an isolation valve to be

controlled following an earthquake and the

other does not. This concept allows

shutdown of one reservoir while maintaining

service should an inadvertent shutdown

signal be received. If the system can keep

up with system leakage, the isolated

reservoir can be put back on line from the

Control Center. If the system can not keep

up with the demand, the reservoir remains

isolated.

Emergency planners based the number of

locations of isolated reservoirs on serving

the population 3 liters per day for drinking

for 7 days. They estimated that it would

take up to 7 days to repair the system.

Figure 5.2.10 shows the locations of the

reservoirs within the system. Isolated tanks were selected so that each would serve an

304
area approximately 4 km in diameter.

Figure 5.2.11 shows a schematic of the local

post-earthquake water distribution system at each reservoir.

5.2.2 What Happened to the Water

System

5.2.2.1 Conditions Following the

Earthquake

Earthquake valves closed on 18 out of 21

service reservoirs following the earthquake

storing 33800 m

3 of water. Total storage

before the earthquake (5:05 a.m., January

17) was 338455 m

3

. Minimum storage after

the earthquake (6:01 a.m., January 18) was

94906 m

3

. The 86 distribution reservoirs

serving the urban area without earthquake

valves quickly emptied as shown in Figure

5.2.12. This resulted in inadequate water

available for fire suppression.

Water carried by the Hanshin system

dropped from 6000 m

3/hr to 1000 m

3/hr

immediately following the earthquake. This was caused by loss of power to Yodogawa

River Pump Stations for 15 hours following

the earthquake as well as transmission main

breaks.

Water restoration work began on January

18. Leaks were identified and repaired with

the following priorities:

(a) damaged areas, medical facilities, areas with populations

(b) broken pipes, minor leakage areas

(i.e., fix areas first that could be

easily restored)

(c) broken pipes, major leakage areas

(d) shelters and areas in danger of

landslides

Mutual aid was provided by estimated 1000

people from 37 agencies.

U.S. utility decision makers need to

be thinking in terms of consequences

similar in magnitude to the Kobe

event. For example, what happens

when you have no records because all

utility buildings are destroyed? Wliat

happens...?

Emergency supply using water tank trucks was initiated on the evening of January 17. Later, water supply aid came from other

cities and from the Self Defense Forces.

Regular water supply points were established

and increased in numbers as time went on. Figure 5.2.13 shows the status of emergency

water supply in the days following the

earthquake in terms of truck loads of water,

distribution points, and relief workers

working on water distribution. It is not clear

what the correlation is between trucking in water and use of service reservoirs that had

been isolated for local distribution for

drinking. When service was resumed, the

chlorine feed rate at the purification plant was increased but no boil water notice was

issued. When leaks were repaired, lines were flushed, but not disinfected.

Figure 5.2.14 shows the percent of people

receiving water after the earthquake.

Figures 5.2.15 and 5.2.16 show the number

of emergency response workers from other

cities assisting in restoration of the

distribution system and purification and

pump station equipment, respectively.

Based on the information provided by the

Kobe Water Department in these figures, it appears that it took approximately one week

to muster mutual aid.

305
Figure 5.2.17 shows the status of water

system restoration by ward, through

February 13. Based on the information in the figure, approximately three quarters of

this system was initially without service. The

western area of the system was the most

severely impacted, while the northern part of

the system had the least damage. Other

parts of the system appear to be equally

hard hit. Water was restored to 99% of

customers by March 29. It took 35 days to restore water to Port Island.

5.2.2.2 Damage to Water Facilities

This section describes damage to specific

system components.

Supply Reservoirs A cracked handrail along

a walkway on the dike was noticed at the

Nunobiki Reservoir. Also, at the same site,

the service bridge required major repairs.

At the Karasuhara Reservoir site, vertical

cracks occurred at one location on the back

of the dike.

Water Purification Plants Uegahara,

Hanshin (Kabutoyama), and Motoyama

water purification plants were damaged by

the earthquake. The Sengari, Okuhirano,

and Sumiyoshi water purification plants had

little damage. Information is not available on the other two small plants, Arima and

Mt. Rokko.

Uegahara Water Purification Plant The

plant was rendered inoperable following the

earthquake. On the west side of the plant,

fill behind a retaining wall subsided when

the retaining wall moved outward. This

resulted in the separation of pipeline joints on three treated water lines, each 1.2 m

diameter reinforced concrete. The lines were (a) Uegahara potable water, (b)

Uegahara industrial water, and (c) Hanshin

potable pipeline. The Hanshin line was

operating as of February 11.

Some subsidence occurred under the sludge

thickener building. The floor settled

differentially. There was subsidence around

the pile supported foundation of the sludge

hoppers. Unanchored electrical equipment

toppled in the sludge thickener building.

The building and adjacent sludge hoppers were both pile-supported. The cross section

of the slope, retaining wall, and fill is unclear.

This same subsidence also probably led to the following damage: muddy water and

increased water volume in water passages

(pipe galleries); clarifiers (damage to expansion joints, water leakage); process

tanks (some leakage); sludge thickening

equipment (extensive damage to piping and

equipment); high rate filter piping (bent and

disconnected); and other damage to pipe,

mechanical, and electrical equipment. Steel

baffles in the clarifiers were damaged from

impulsive hydraulic forces.

Hanshin Water Authority (Kabutoyama)

Water Purification Plant The plant was not

damaged and was operating at 3000 m

3/hr as of February 12. There was a major landslide

in back (northeast) of the treatment plant,

undercutting the wastewater treatment

building which was pile supported, and

taking out a tennis court and a sludge drying

bed. The slide killed 36 people in a housing

development below, and dammed the

Nigawa River. The original slope was 18°

,

much less than the 30° where the code

requires mitigation. After the slide

occurred, workers placed a plastic cover to cover the area above slide to keep rain off,

installed slope monitoring instruments, and

began to do borings to further investigate

the slide. This was the largest slide in the

urban area. Damage to buildings appeared

to be light with occasional roof damage.

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Motoyama Water Purification Plant The

Motoyama Plant had damage to two

segments of pipelines and minor cracking in a process tank. Pipelines to and from the

backwash water tank failed as a result of

slope failure.

The retaining wall along the side of the

Simiyoshi River moved, breaking the intake

box overflow line. Water is fed to the intake

box through a pipeline connected to a small

diversion structure in the river bed. This

facility is located upstream of the plant.

There was a concern that the cast iron raw

water line running from the intake box to the treatment plant may have been damaged

as a result of the retaining wall movement,

and should be checked before it is put into

operation. The property owners living just

above the suspect raw water line were

uneasy because they did not want a break to undermine their houses.

Intake, Pump Stations, and Transmission

Pipelines The intakes and pump stations near the Yodogawa River were not

damaged. The two major lines from the

Yodogawa River were broken at 10

locations. One ductile iron line had a split

30 cm long and 5 cm wide. One 100 meter

section had to be replaced. One pipe failure

had an opening 30 cm long by 4 cm to 5 cm

wide. It took 12 days to repair the raw

water lines serving the plant. Transmission

pipe materials may have included both

ductile iron and/or prestressed concrete.

The Mt. Rokko Tunnels, carrying water

from the Uegahara and Hanshin plants west

to be distributed, had not been inspected on

the interior when information was collected

for this report. However, no major leakage was occurring and only minor damage was

expected.

Pumps in Karasuhara mine (spring) were

destroyed and out of service. The spring

only provides a minor supply to the Kobe

water supply system. Other pump stations were undamaged. Damage to air release

valves was reported.

Distribution Reservoirs (Tanks) Of the 119

reservoirs throughout the City, there was

only minor damage to one pre- World War II cast-in-place partially buried concrete tank.

At the Egeyama Reservoir, there was

leakage in the pipe connecting the reservoir

and the adjoining well, and a vertical crack

in the expansion joint. A 500 mm diameter

transmission main to Egeyama Reservoir, 10

m long, was replaced.

Distribution Pipes Distribution pipeline

damage was reported as follows:

- distribution pipes 1,800

(75-300 mm)

- service lines (<75 mm) 10,000

Total 11,800

An early survey of the 328 distribution pipe

failures is shown below:

Failure Percent

- Pipe breaks 54 16

- Pipe joint 136 41

damage (ramming

and pull out)

- Equipment 69 21

(fire hydrants, air release valves, etc)

- Other 70 21

Total 328 100

Table 5.2.8 shows Kobe Water pipeline

damage data as of March 29 including the

type of damage. Only 964 of the 1800

repairs identified at that time are shown in the table. Pipe material is not identified.

307
Approximately 80% of the pipe in the

system was ductile iron. Ductile iron pipe

has performed well in previous earthquakes.

It would make sense that the primary failure

mode was pulled joints.

The three predominant types of service line

failures were (a) house collapse, (b) joint

separation, and (c) failure where the line

passed below the concrete stormwater

gutter. Service line repairs were

accomplished at a rate of two per day with a crew of 5 to 6.

It is estimated that indoor and outdoor

supply pipe leakage sites will number 50000,

out of a total city water supply region of

650000 homes.

There was significant pipeline damage on

Kobe's Port Island where Tyton-type and/or

mechanical joints were deployed. In

contrast, there was very little water pipeline

damage on Rokko Island where the great

majority of mains were ductile iron pipe with

S-type joints.

Pipelines hung on the Kobe, Rokko, Mikage,

and Fukae bridges were damaged, and in some cases disrupted service to these islands.

As the distribution system repair was nearing

completion, water demand was more than

30% greater than pre-earthquake use. This

raised concern that there were still many

leaks that had not been identified.

There were two major issues identified that

delayed system restoration: (a) no water

pressure was available to check the repairs

as the tunnels were drained, and (b) access was limited by collapsed buildings and traffic congestion. However, there were adequate

repair materials.

Water Department Buildings The Water

Department Main Office, including

administration and engineering, was located on the 6th floor of the Old City Hall

Building (City Hall Annex). The 6th floor

of this eight story concrete frame building

pancaked. Because of the early morning

hour, only one employee was killed.

Distribution system maps, facility drawings,

etc., were not available during the initial restoration phase. Later in the restoration,

some records were being pulled out of the

collapsed floor.

The Water Department maintained a

distribution and maintenance building in five areas throughout the City. The upper three

floors of the eight story Water Department

Eastern Center partially collapsed. The

Western Center partially burned. The

combined damage of these three facilities made emergency response and restoration

very difficult. The Central, North, and

Tarumi Centers were not damaged.

Monitoring and Control System The

control system designed to isolate reservoirs

for drinking worked in 18 out of 21 sites,

and water was saved for drinking. Two of

the failures were electrical or mechanical

related, and one hydraulic. Three repeater

stations and telemetry systems were undamaged.

5.23 Wastewater System Overview and

Damage

This section describes the Kobe wastewater

system. An overview of the system and

associated damage will be described first. Second, damage to the Higashinada

Wastewater Treatment Plant, where the

most extensive damage took place, will be

described.

308
5.2.3.1 System and Damage Overview

The Kobe sewer system serves 1.46 million

people. The collection area of 157 km2 is 97.4% sewered. Kobe has eight wastewater

treatment plants, three of which were damaged by the earthquake, as shown in

Table 5.2.9. The sludge is barged to Rokko

Island where it is incinerated. The

remaining 15 tons of ash are landfilled.

There are 23 pump stations; 20 were damaged or inoperable from power loss,

building damage, or caisson damage. Most

were operable when power was restored.

Collection system pipe is 70% concrete, 20%

PVC, and 10% VCP. Kobe uses Fiber

Reinforced Plastic for large diameter pipe

and PVC for smaller diameter pipe in liquefaction areas. The length of sewers by

sewage treatment plant service area is shown

in Table 5.2.10. While we were informed

that some of the sewers are combined

sewers, it is unclear whether the storm

sewers shown in Table 5.2.10 drain into the

respective treatment plant.

In the future, Kobe is considering

constructing a transmission line between the

Higashinada and Tarumi WWTP to provide

operational flexibility.

Three pipelines were relocated in the Daikai

area where the subway station collapsed and

as a result were heavily damaged. At the

time of the team's visit, the crew was

checking flows in manholes, and inspecting

60 km of sewers with 30 to 40 TV crews. There was only one public health incident

where sewerage was backed up. Photos 25

and 26 show a manhole that floated due to liquefaction near the Higashinada Plant.

Photo 27 shows a sewer that was buoyed as a result of liquefaction on Port Island. The

estimated cost of sewer repair is 12 billion

yen ($120 million). Fifty people were

involved in the planning and design of the

restoration phase and an estimated 400

people were assisting in the restoration

effort.

5.2.3.2 Higashinada Wastewater

Treatment Plant

The Higashinada Wastewater Treatment

Plant is the City of Kobe's largest plant

providing one third of the city's treatment

capacity. It is an activated sludge plant,

located on Uozaki Hama Machi (island),

immediately east of the bridge to Rokko

Island as shown in Figure 5.2.18.

The plant has an average daily flow of

162000 m

3 /day of which 23% is industrial.

Some sewage is from a combined

sanitary/storm collection system. The plant

capacity is 225000 m

3 /day, and is being

expanded to 350000 m

3 /day. The oldest

portion of the plant was constructed starting

in 1962, shortly after placement of the fill for the island was completed.

The facility was heavily damaged when the

seawall along the north side of the plant

adjacent to the channel moved as much as

3 m towards the water as a result of

liquefaction (Photos 29, 30). As a result, the

entire site settled an average of one meter.

Liquefaction-induced lateral spread and

settlement were most severe within a distance of 100 m south of the seawall along

the southern margin of the channel.

Horizontal displacements of 3 m and

settlements as large as 2 m were observed

within the plant site. Figure 5.2.19 shows

the plant layout and notes damage locations.

Lateral displacement and settlement

ruptured the inverted siphon at the plant

through which raw sewage was conveyed to the plant on the other side of the channel

for treatment. Because of the loss of the

309
siphon, sewage was being dumped directly

into the channel.

Figure 5.2.20 presents a soil profile for the

borings located in Figure 5.2.19. The soils consist of about 6 m to 8 m of artificial fill, primarily granitic sands and gravels,

underlain by approximately 3 m to 5 m of

alluvial sand. The fill and alluvial sands are

loose, as evidenced by the low uncorrected

blow counts between 5 and 15. The sands

are underlain by soft to medium soft alluvial

clay approximately 8 m thick, which overlie

deep deposits of dense granular soils and

still clays. The water table is about 2 m

below ground surface.

Lateral deformation caused severe damage

to underground structures and facilities founded on spread footings. The effluent

channel separated in 4 places (Photo 31).

The pipe rack distorted from foundation

settlement (Photo 32).

Primary and secondary clarifiers and

aeration basins were pile supported. The

primary clarifiers were 8 m deep so the pile

length subjected to liquefied sand was

relatively small. Secondary clarifiers and

aeration basins were only 4 m deep which

subjected a longer pile length to liquefaction

and lateral movement and resulted in some

pile damage. Aeration tank joint separation

is shown in Photos 33 and 34. Photo 35

shows scrapper chains which came off of

sprockets. Concrete piles supporting

digester tanks closest to the channel cracked

at their tops. Photos 36 and 37 show broken

sludge digester connecting piping.

Differential settlement and lateral spreading

of approximately 600 mm occurred at the

filter building, as shown in Photos 38 and 39

resulting in some pile damage. The control

building and the sludge thickener room

moved north 60 cm (Photos 40, 41). The

return activated sludge pump and backup

blower room flooded. Equipment and

piping on mat foundations near the south

edge of the channel was damaged due to ground movement (Photos 42-46).

It is expected to take 2 years to 3 years to repair the plant at a cost of 25 billion yen

($250 million). This estimate seems low for

the extensive damage observed.

Recent earthquakes have shown that

there is a low probability of

maintaining a water system following

an earthquake. Consideration

should be given to identifying and

developing alternate supplies.

As of February 10 the Higashinada Plant was providing primary treatment with

chlorination. This was accomplished by an

innovative but necessary use of the channel

between the mainland and island. The

channel was blocked off at either end with a row of piles and covered with a filter membrane making a temporary

sedimentation basin. Temporary baffles are placed in the sedimentation basin to keep

solids away from the membrane filter, and to keep sewage from short circuiting to the

filter membranes on each end. As raw

sewage enters the pump station, chlorine

and a chemical coagulant are added. The

sewage enters into the temporary

sedimentation basin. The sewage solids

settle to the bottom of the basin, and the

liquid passes through the filter membrane.

The solids area dredged from the bottom

and pumped to a barge located outside the

sedimentation basin where they are thickened. Solids are then dewatered and

taken to a landfill.

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5.2.4 Lessons for United States and

Research Needs

There do not appear to be any significant

technical surprises from this earthquake

which are applicable to the United States,

but there are a number of reoccurrences of

many situations that should help clarify

earthquake planning and earthquake

resistant design.

5.2.4.1 Overwhelming Conditions

We need to always be aware of the potential

magnitude of earthquake consequences.

This earthquake was the largest earthquake

in recent years to directly impact an urban

area in a country with facilities comparable

to the United States. The results were

overwhelming in terms of loss of life and

property damage, as well as poor

performance of utility systems.

From an emergency response perspective,

there is always discussion about what might

occur following a large earthquake located

in a densely populated area. It is beyond

comprehension for most people outside of

California that such an event will happen,

and therefore they do not truly consider the

consequences. One of the biggest issues in the Kobe event was the loss of all transportation. Every major mass

transportation route failed, and surface

roads were blocked by fallen buildings. The

resulting congestion made walking the

fastest form of transportation. This caused

emergency response to slow to a crawl.

The same situation was true for the response

of utility personnel. For moderate

earthquakes, there is an emergency response

plan to enable effective data acquisition and

response. However, utility decision makers

need to be thinking in terms of

consequences similar to the Kobe event.

For example, what happens when you have no records because all utility buildings are destroyed? What happens if the plan is to dispatch crew to isolate critical pipelines to save water or shut off natural gas, but the

fastest way to get there is by walking?

5.2.4.2 Fire Following

We need to examine the issue of fire following earthquakes. While there was no

fire storm, there were over 100 ignitions,

and in many cases no water to suppress

them. Water purveyors and fire departments should relook at the

vulnerability of water supplies. Recent

earthquakes have shown that there is a low

probability of maintaining a water system

following an earthquake. Consideration

should be given to identifying and

developing alternate supplies.

Similarly, the use of monitoring and control

systems should be considered and/or

reconsidered to enable the timely control of

a water system following an earthquake to increase the probability of delivering water

to suppress fires. Water purveyors and fire departments should use permanent ground

deformation mapping to identify areas where

pipelines will likely fail so that plans can be

made to isolate damaged areas and/or use

alternate water supplies.

5.2.4.3 Geotechnical Issues

We need to refocus on the potential

consequences of geotechnical failures. Many

lifeline system owners are lulled into an earthquake program that includes nonstructural upgrades, and minor building

strengthening. Geotechnical hazards are often considered and potentially dramatic

consequences identified; however, efforts to remediate these consequences are dropped

when mitigation costs are developed.

311
In Kobe, geotechnical failures governed the

poor performance of the water system.

Landslides, consolidation, and liquefaction or lateral spread stopped the flow of water

from the source: damaged two major and

one small water treatment plants; and tore the distribution system apart. In general,

the structural aspects of the "steel" transmission pipelines matched current

design used in the United States. The

treatment plant structures performed

reasonably well except that they were on

soils that failed. An aggressive pipeline

replacement program apparently only

marginally helped mitigate geotechnical

failure-related damage to the pipeline

distribution system.

5.2.4.4 Design

In general, water treatment plants and

service reservoirs performed well. The

United States should study Japanese design

approaches for these facilities. As discussed

above, their tank designs are somewhat

different from those used in the United

States and apparently had no damage when

subjected to high peak ground acceleration.

Pipelines were heavily damaged, except that

preliminary information on performance of

the S joint pipe appears that it had no or few failures. If it is confirmed that it performed well in areas of significant

permanent ground deformation, such as what was observed at Rokko Island, we

should introduce it to the United States. If

it did not perform well, we should find out

why, and improve U.S. pipe design based on

those findings.

An estimated 65% of the pipeline failures were pulled joints. As 80% of the pipe

inventory in Kobe was ductile iron pipe with

Tyton or mechanical joints without restraint,

we should not become complacent with use

of non-restrained joints in areas expecting

significant permanent ground deformation.

5.2.4.5 Recovery

The three Kobe Water Department

buildings storing records were destroyed.

The probability of this occurring is very low. In the United States, we should make sure

that our resources are distributed so that the

loss of any one facility will not substantially

impact our ability to respond to an

earthquake.

5.2.5 Summary

The Hyogoken-Nanbu earthquake left one

million households without water following

the event, with only 70% restoration in three

weeks. Water for fire suppression was

substantially exhausted after six hours.

The two large diameter transmission lines

carrying water from the Yodogawa River to the Uegahara and Hanshin (Kabutoyama)

water purification plants failed in ten

locations. This source constitutes nearly

three quarters of Kobe's supply. The

Uegahara and Hanshin (Kabutoyama) plants are Kobe's largest. In addition to their

supplies being disrupted, soil failures at the

plants resulted in failure of the major

treated water lines, as well as moderate

damage to the plants themselves. The

tunnels carrying water from the plants west

to Kobe remained intact.

Kobe Water had an aggressive earthquake

design program for some of their service

reservoirs. There were no tank failures

reported for the 239 tanks located at 119

sites. There was some connecting piping

failure at one tank. However, it should be

noted that these tanks were in the hills surrounding the city and in areas of

relatively low ground motion.

312
Nearly 90% of Kobe's water distribution

system was made of either welded steel or

ductile iron pipe, both thought to be

resistant to earthquakes. This unusually

high percentage of earthquake-resistant pipe

resulted from an aggressive pipeline

replacement program initiated in the mid1960's. Even with this in place, an estimated

1800 pipeline failures occurred in distribution piping. It is speculated that

much of this damage is associated with joint

separation from liquefaction-induced lateral

spread. This should be verified through

followup studies.

Kobe had implemented a monitoring and

control system designed to isolate reservoirs

to be used for drinking following an

earthquake. The system worked as designed. It should be determined whether

this effort would have been better focused on water for fire suppression. In other

words, was the water saved for drinking

critical in meeting that demand, or was

drinking water available from other sources?

There was no system focused on postearthquake performance of the water system

to provide water for fire suppression. There

was no water available to put out many of

the 100 plus ignitions.

The Higashinada Wastewater Treatment

Plant provides one-third of Kobe's treatment

capacity. Liquefaction or lateral spreading

failures resulting in movement of a retaining

wall 2 m to 3 m towards a waterway

dropping the entire site an average of one

meter. The result was devastating. A 2 m x 2 m effluent channel separated in four

places. The control and filter buildings

moved, and equipment and piping settled as the soil moved away from under them.

More attention should be paid to geotechnical failures.

The lifeline earthquake community in the

United States should learn from both the

successes and failures observed in Kobe.

Successes include the monitoring and control

system, performance of water treatment

plants (except geotechnical) and tankage,

and possibly seismic joint pipe. Failures

include a lack of adequate water supply for

fire suppression (including alternate

supplies) and inadequate focus on

geotechnical failure.

5.2.6 Acknowledgments

The authors would like to thank Professor

Takada at Kobe University and Mr.

Matsushita at the Kobe Water Department

for providing information on the Kobe water

system both before the earthquake (October

1993) and following the earthquake. Input

and review is also gratefully acknowledged

from Messrs John Eidinger and LeVal Lund

who provided information gathered in a followup ASCE/TCLEE study trip to Kobe.

Dr. Ian Austin, Mr. Fumihiro Kujihara, and

Mr. Ken Sasaki, all from Chiyoda-Dames &

Moore in Tokyo, made local arrangements,

provided translation, and travelled with Mr.

Don Ballantyne in Kobe. Their assistance is greatly appreciated.

313
Table 5.2.1

Kobe Water Supplies

Source and Comments Percent of

Total Supply

Supply in 1000 m

3/day

Lake Biwa/Yodogawa River - includes Hanshin Water Supply

Authority (Yodogawa River 30 km east ofKobe).

73.9% 606

Sengari Reservoir (constructed in 1919) 13.8 113

Karasuhara Reservoir (constructed in 1905) 4.4 36

Rivers in City - Sumiyoshi, Sanyo Shinkansen Tunnel 3.8 31

Nunobiki Reservoir, 420,000 m

3 capacity constructed in

1900; oldest gravity concrete dam in Japan)

2.4 20

Dondo Dam 1.7 14

Total 100 820

314
Table 5.2.2

Water Treatment Plants Serving Kobe

Filter Plant Hanshin Water

Co. (1)

Urban Area Hokushin

District

Mt. Rokko

Uegahara

(potable)

(2)

Uegahara

(indus.)

Okuhirano (3)MotoyamaSumiyoshiSengariAri- ma

Mt. Rokko

Date Constructed 1917 1964 1900 1967

Source Yodogawa

River

Sengari

Reserv.

Yodogawa

River

Nonobiki,

Karasuhara

Reservoirs

Sumiyoshi

River

Sengari Reser

Number

of Filter Basins

slow 8 1

rapid 8 4 4 5 8(4) 1

Capacity per day

(1000 m

3

)

144 128 150 60 8(5) 6 108 0.3 1

Note:

1. Municipal corporation including Kobe, Ashiya, Nishinomiya, and Amagasaki, and

has three water treatment plants (a) Kabutoyama, (b) Inagawa, and (c)

Amagasaki.

2. The Hanshin Water Authority Water Treatment Plant (Kabutoyama) is immediately adjacent to the Uegahara Water Purification Plant. Uegahara uses sodium hypochlorite for disinfection.

3. Control center adjacent to treatment plant.

4. Granular activated carbon media.

5. Usually runs at 6,000 m

3

, including 1,000 m

3 to Sake plant in summer and 2,000

m

3 in winter.

315
Table 5.2.3

Pipe in Place as of April 1994

Pipe Material Joint Type Length (km) Remarks

Ductile Iron Pipe Earthquake Resistant

Joint (S, SII)

237.3 (6.0%) All trunk mains >400 mm diameter;

=>300 mm for reclaimed land and

landslide areas.

Mechanical Joint 3,180.2 (80.2%) 300 mm (sub main)

Tyton Joint 75 mm-200 mm (distribution pipe)

Steel Pipe Welded Joint 103.3 (2.6%) high pressure pipe (>100psi)

Cast Iron Pipe Mechanical Joint 308.9 (7.7%) Replacement in progress

Leaded Joint 7.0 (0.2%)

Polyvinyl Chloride Pipe Bell & Spigot Joint 126.4 (3:4%) Replacement in progress

Asbestos Cement Pipe 0 Replacement completed in 1987

Total 3963.1 (100%)

316
Table 5.2.4

Rehabilitation and Renewal Project - 1978

Year Cost (million yen) Diameter (mm) Length Replaced (km)

1982-86 10,480 700-100 139

86-88 4000 800-150 20

89-91 4000 800-150 27

Table 5.2.5

Strengthening/Earthquake Proofing Pipelines - 1991

Cast Iron

Pipe

Polyvinyl

Chloride Pipe

High-Pressure

Pipe Network

Total

Length Replaced (km) 84 3 20 107

Cost (billion yen) 9.1 0.2 2.2 11.5

317
Table 5.2.6

Summary of Service Reservoirs by Elevation

Layer

ill Altitude IX IUUW pHhvp dUU V w Sea Level Blocks

Water TV Cllw Consumption (%) Reservoir Sites

1 0-30 m 10 53 10

2 3 1-60 m 10 20 13

3 61-90 m 14 13 19

4 91-180 m 31 11 77 (includes layers 5,6)

5 181-280 8 3 included in layer 4

6 Over 280 1 < 1 included in layer 4

Total 74 100 119

Table 5.2.7

Reservoir Distribution by Area

Block Name Urban Western Northern Total

Distribution Reservoirs Sites 71 8 30 109(1)

Reservoirs 147 14 54 215(1)

Pumps Sites 25 5 12 42

Pumps 132 18 50 200

Discharge

Lines

50 9 17 76

Population (1,000's) 1117 103 174 1394

Population Served

(1,000)

1116 86 174 1377

1 . Total numbers of distribution reservoirs differ from Table 6. Information source is different

and presumed to be from several years earlier.

318
Table 5.2.8

Kobe Water Pipeline Damage

(As of March 29, 1995)

Diameter

(mm)

Inventory

(m)

Repairs Repairs/

km

Broken

Pipe

Pulled

Joint

Damaged

Fitting

50 63,143 15 0.24 6 9 0

75 165,051 40 0.24 7 30 3

100 790,329 197 0.25 43 127 27

150 1,455,137 301 0.21 55 206 40

200 744,689 138 0.19 23 104 11

250 39,706 6 0.15 3 3 0

300 386,606 139 0.36 20 96 23

350 18,195 5 0.27 0 4 1

400 79,700 30 0.38 4 17 9

450 3,082 0 0 0 0 0

500 88,450 24 0.27 2 7 15

600 45,224 13 0.29 2 3 8

700 46,857 24 0.51 1 7 16

800 10,264 9 0.88 3 5 1

900 26,131 21 0.80 1 6 14

1,000 498 2 4.02 0 0 2

Total 3,963,062 964 0.24 170 624 170

319
Table 5.2.9

Kobe Wastewater Treatment Plants

Wastewater

Treatment Plant

Capacity

(1000 m

3/dayL

Location Post-Earthquake Status

Higashinada 225.0 Shoreline Heavily damaged; detailed damage description in

LCA.L.

Seibu 10 1.5 Shoreline Secondary plant with 2 process trains. Concrete

yard piping was damaged; pump station settled and flooded. Repaired within one week.

Tarumi 133.9 Shoreline No damage

Chubu 77.9 Shoreline Plant suffered cracks in the sedimentation tank

and the dislodged chain drive. Operating within

1 day.

Tamatsu 75.0 1 km inland No damage

Suzurandi 43.8 10 km inland No damage

Port Island 20.3 Port Island No damage

Myodani 12.0 10 km inland No damage

Total 749.4

Tobu Sludge Center 1 50 tons/day Rokko Island Damaged

320
Table 5.2.10

Kobe Wastewater "System Piping

Treatment Plant Area Sanitary Sewer

Length (km)

Storm Sewer

Length (km)

Chubu + Seibu 790 109

Higashinada 719 76

Tarumi 619 108

Tamatsu 570 103

Inland Areas 406 49

Suzurandi 186 33

Port Island 28 4

Total 3318 482

321
Figure 5.2.1 Kobe water system schematic.

322

m

300

200

o 90

c

o 60

30

0

Parliculary

high layer

High layer

Medium layer

Low

layer

Mountains

0 Water

transmission

tunnel

[_| Distribution reservoir A Pump station

Figure 5.2.3 Schematic profile of Kobe water delivery system.

Backwash

Water

Solids Handling

Susidence

Area

Flash Mix/

Flacculator

From

Sengari

Reservoir

Pump Station

From Yodogawa

River

Clean/veil

Filters

Legend:

[ | High Rate Treatment (Potable) HHH Low Rate Treatment (Potable)

Wastewater

Industrial Water Treatment

Filters/Clearwell

Figure 5.2.4 Uegahara Water Purification Plant schematic.

324
I

Figure 5.2.5 Motoyama Water Purification Plant schematic.

325
Lock

Rubber Ring

Gasket

Maximum Expansion/Contraction

77 - 85 mm

Depending on Diameter

3E

"S" Joint (500 - 2600 mm Diameter)

Gland Rubber r— Lock

Gasket / Ring

Maximum Expansion/Contraction

45 - 75 mm

Depending on Diameter

"Sll" Joint (100 - 450 mm Diameter)

Figure 5.2.6 Seismic joints, S and SII

326
327
Figure 5.2.8 Schematic of communication/repeater system.

328
Figure 5.2.9 Schematic of typical communication from ground motion instrument,

through radio communication, to the earthquake valve.

329
10km

o

Worked successfully

Did not secure water

Under construction or planning at time of earthquake

Figure 5.2.10 Map of Kobe water service area showing reservoirs with earthquake valves

and their respective service area.

Spigot Assembly for Emergency Distribution

Water Level

Maintained at a Minimum

Elevation

Earthquake

Valve

Figure 5.2.11 Schematic of water distribution from tank with earthquake valve.

330

o till I i ll I I I I

'

I I '1 I I I I 1 1 1 It I M l I 1 M M ' I I HH II III

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48

Days Following Earthquake

Figure 5.2.13 Status of emergency water supply.

332
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59

Days Following Earthquake

Figure 5.2.14 Percent of people in Kobe receiving water following earthquake.

333
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47

Days Following Earthquake

Figure 5.2.15 Mutual aid from other cities repairing the water distribution system.

334
Days Following Earthquake

Figure 5.2.16 Mutual aid from other cities repairing the water supply system

(purification plants, pump stations, and tanks).

335
Figure 5.2.17 Restoration of distribution reservoirs and water mains.

336
Figure 5.2.18 Location map for Higashinada Wastewater Treatment Plant.

337
Differential Settlement Between Digesters/Gas Holders and Pipinc

Sedimentation Tanks- Chains Off Sprockets

Boring 1 Separated

Pedestrian/Pipe Bridge- Support Damaged on

South End

Influent

Retaining Wall/Building Foundation Moved 0.5-1 Meter Towards Water Damaged Inverted Siphon

Retaining Wall Moved 2-3 Meters Towards Waterway Between

Mainland and Island

Temporary Sedimentation Basin

Damaged Effluent Channel

Damaged Filter Building

Primary Clarifiers

Sheet Pile Wall with Filter Membrane

(Typical of one at each end)

50 100

Scale in Meters

Figure 5.2.19 Higashinada Wastewater Treatment Plant site plan showing damage

locations.

338
Elevation (m) 10 -i

-10-

-20-

-30-

-40-

-50-

No.2 N Value

0 50

No. 4 N Value 0 50

30m

Diluvial ClayDiluvial Gravel

Notes:

No. 1 N Value

0 50

Alluvial: Holocene deposit

Diluvial: Pleistocene deposit

Figure 5.2.20 Soil profile at Higashinada Wastewater Treatment Plant.

339

Photo 3 Steel water storage tank at Okuhirano Purification Plant, less than 7 years old.

341
Photo 4 Concrete water storage tank at Okuhirano Purification Plant,

less than 7 years old.

Photo 5 Seismograph at Okuhirano Control Center used for control of earthquake valves on reservoirs.

342
Photo 6 Control Panel for earthquake valves to provide flexibility to control automatically or by operations staff in Okuhirano Control Center.

Photo 7 Person collecting water from central water distribution point near the collapsed

Daikai Subway Station.

343
Photo 8 Emergency water supply delivered in tank trailer.

Photo 9 Aerial view of Kobe's Uegahara Water Purification Plant (lower left) with the

Hanshin (Kabutoyama) Water Purification Plant immediately adjacent (upper

right). The landslide that undercut the Hanshin (Kabutoyama) Plant's solids

handling building is evident. The area at about 10:00 O'clock outside the circular

basin settled approximately 30 cm, separating joints on three 1.2 m diameter

pipelines over a length of approximately 100 m, and damaging the solids handling

building.

344
345
Photo 11 Subsidence (approximately 30 cm) around pile-supported sludge hoppers at Uegahara Plant.

346
Photo 12 Landslide undermined solids handling building at the Hanshin (Kabutoyama)

Plant.

347
Photo 13 Broken lines to/from backwash tank at the Motoyama Water Purification Plant

.

348

Photo 16 Repair of 700-mm welded steel pipeline which ruptured at a weld on the north

side of Port Island in an area affected by liquefaction induced lateral spread. This

line carries the entire potable water supply for the island.

Photo 17 Ground cracking from lateral spread in fill area along a water way. Immediately

behind the crack, a pipeline emerges out of the ground to be supported on the

bridge.

350

Photo 19 Pipe repair on approach to bridge to island where the wastewater plant was

located. Settlement and slight lateral movement (see concrete wall on right) likely

caused the pipe failure.

352
Photo 20 Kyoto Water Department truck and crew was making repair shown in Photo 19. The crew was directed to make the repair as quickly as possible, even though the

repair might be temporary. The crew also indicated that the materials they used

in Kyoto were completely different from those used by Kobe Water.

Photo 21 Differential settlement at building in mid-Rokko Island. Most modern buildings on the island were pile supported and were note damaged. Differential

settlement required repair of utility connections as shown in Photo 22.

353
Photo 22 Repair of utility connections in mid-Rokko Island.

354
Photo 23 Differential settlement of approximately one meter along the front of pile

supported ferry terminal on Port Island connecting Kobe to Kansai Airport.

Utility connections were left hanging.

355
Photo 24 Pancaked sixth floor of City Hall Annex.

Photo 25 Manhole floated as a result of liquefaction near the wastewater treatment plant.

356
Photo 26 Same as Photo 25.

357
;

r

I

Photo 27 A 500 mm diameter sewer floated upward on Port Island, resulting i upheaval of ground.

358
359
Retaining wall along the inlet between the island and mainland moved towards

the water (north) 2 to 3 meters, resulting in the entire site subsiding an average of one meter.

Ground cracking behind the retaining wall (which is off to the left)

.

360

Photo 32 Pipe rack foundations adjacent to channel settled approximately one meter,

distorting piping.

362
Photo 33 Aeration tanks construction joint separated down the entire bank of tankage as a

result of settlement.

363
Photo 34 Close up of torn dumbbell rubber water stop in aeration tank.

Photo 35 Sludge scraper chain came off sprockets in sedimentation tanks.

364
365
Photo 37

Photo 38 Filter building support pipes failed allowing the building to move and settle

differentially.

366
Photo 39 Piping distorted as a result of the building movement.

367
Photo 40 Control building (upper right), which is pile supported, moved towards inlet

approximately 30 cm, moving away from adjacent building which had a basement.

368
Photo 41 Shows the gap between the two buildings in Photo 40.

369
Photo 42 Piping distorted as a result of the movement.

370
Photo 43 Piping and equipment distorted as a result of subsidence of the structures' foundation.

371
Photo 45 Same as Photo 43.

372
Welded steel pipe, approximately 200 mm in diameter folded when the foot/pipe

bridge support was distorted from lateral spread.

373

53 Gas Delivery System

53.1 System Description

Natural gas for the areas most severely

affected by the earthquake, including Kobe

City, Ashiya, Amagasaki, and Nishinomiya,

is supplied by the Osaka Gas Company, Ltd.

The company provides gas to more than 5.6

million metered customers, accounting for

30% of the total gas sales volume in Japan.

Major trunk lines, pipelines, and distribution

mains total 49430 km. The Osaka Gas

system is comparable in size to the gas

delivery network operated by the Southern

California Gas Company, which is the

largest U.S. gas supplier with approximately

4.6 million metered customers and nearly

74000 km of transmission, distribution

supply, and distribution pipelines. Liquefied

natural gas (LNG) accounts for about 94%

of the Osaka Gas system feedstock. Most of

the supply is imported by means of tankers

from Brunei, Australia, and Indonesia.

Residential gas operations accounted for

nearly 40% of total volume sales in 1994 and

about 95% of the customer base. Industrial

gas sales accounted for nearly 42% of total volume in 1994, compared to only 30% in 1989. The rapid increase in industrial supply

shows the increasing dependency of

industrial heat energy demand on gas. At

the time of the Hyogoken-Nanbu

earthquake, about 41% of the industrial heat

energy demand in the Osaka Bay region was

being met with natural gas to fuel heating

units, such as furnaces and boilers.

Figure 5.3.1 is a map of the main facilities and pipelines of the Osaka Gas system.

Three LNG terminals provide the primary

sources for distribution. The two Senboku

terminals have a combined capacity of 25.6

million m

3

, and the Himeji terminal has a capacity of 8.1 million m

3

. Gas is conveyed

regionally through a system of major trunk

lines, which operate at internal pressures of

4 MPa. Transportation of gas also is accomplished through what is termed a "medium pressure" system of A lines, at internal pressures of 0.3 MPa to 1.0 MPa,

and B lines at internal pressures of 0.1 MPa

to 0.3 MPa. There are 19 gas distribution

stations where 37 gas holders are located for a nominal overall capacity of 4.15 million

m

3

. Only the major trunk lines, medium

pressure A lines, and distribution stations in Kobe and Nishinomiya are shown on the

map.

Emergency plans should be

developed; and formal and specific

communication procedures should be

established between gas, electric

power, water supply, and fire

department personnel.

The Osaka Gas system is divided into what

company personnel call "super blocks." The

eight super blocks of the network are large areas which can be isolated through

telemeter control by closing valves activated

by compressed carbon dioxide. Closing

valves with carbon dioxide allows for control

independent of electric power supply. The

system can be subdivided further into about

55 "middle blocks," each of which may

provide service to hundreds of thousands of

customers. The middle blocks must be

isolated by means of manually operated

valves. The low pressure pipeline system

within the middle blocks can be subdivided

again into sectors, each provides service to between 3000 and 4000 customers.

375
From 1976 to 1991, Osaka Gas was involved

in a conversion program in which artificial gas plants, producing methane from coal and

petroleum sources, were decommissioned

and replaced with supply from LNG

terminals. As a consequence of these

changes and other operational

considerations, the distribution network was

divided into the aforementioned sectors,

each of which could be isolated and

converted to natural gas. This partitioning

of the system is typical of the way in which

gas delivery systems are organized and can be used for system restoration in the event

of major supply disruption.

5.3.2 Observations

5.3.2.1 LNG Facilities and Trunk lines

There was no significant damage reported at the Senboku and Himeji LNG terminals,

and at the gas distribution stations. As

shown in Figure 5.3.1, there were three

distribution stations with gas holders at Kobe, Fukiai, and Nishinomiya. No

significant damage was reported at these

structures even though they were subjected

to high levels of acceleration. Peak

accelerations at the Fukiai and Nishinomiya

stations of 0.85 g and 0.81 g, respectively, were recorded.

At the time of the earthquake, there were

490 km of transmission or major trunk lines

in the system. The trunk lines are composed

of X-42 or X-52 steel pipe with full penetration, electric arc, girth welds.

Typical wall thickness for a 600-mm

diameter pipe is 12 mm. There was no damage reported in the trunk lines.

5.3.2.2 Medium Pressure Lines

The medium pressure A lines are composed

principally of steel pipe with full penetration,

electric arc, girth welds. The oldest

pipelines in this system were constructed in

1952. The medium pressure B lines were composed either of electric arc welded steel pipe or ductile iron pipe with restrained

mechanical joints on 5 m spacings. The

mechanical joints are similar to the S-type

joints deployed in the water supply system.

The joints are equipped with a locking

mechanism, and are installed to allow 6 cm

of extension and 2 cm of compression.

There were 1245 km and 3800 km of A and

B lines, respectively, at the time of the

earthquake.

Restoration of gas can be especially

critical in winter, as it was in Kobe.

The situation in Kobe can be

replayed if a major earthquake

happens in central and eastern

United States during the winter

season.

Table 5.3.1 summarizes the number of

repairs and principal types of damage

sustained by the medium pressure pipelines,

based on data reported by Oka [2]. There

were a total of 35 and 61 repairs to medium

pressure A and B lines, respectively. The

damage was concentrated at Dresser

couplings and bolted flange joints. The

Dresser couplings were typically 600-mm

long sleeve joints with compression gaskets

and restraining devices against pullout.

Damage was predominantly in the form of

leakage where compression gaskets had

loosened. A total of 14 low grade girth

welds were damaged on steel pipelines. The

low grade welds were installed after 1962

and were characterized by poor root

penetration of the welds. Steel pipelines

installed after 1962 were constructed in

376
accordance with modern welding practices

and did sustain weld damage.

At several locations medium pressure steel pipelines were subjected to large permanent

ground deformation. Even though the steel pipelines were deformed at these locations, no leakage was observed. For example, the

collapse of the Daikai Station (see Section

4.3.2.6 on Underground Rapid Transit

Systems) imposed 2.5 m of settlement over a

length of about 25 m to 50 m on a 400-mm

diameter A-line. No leakage was reported

at this location. Oka [2] cites other

examples of substantial steel pipeline

distortion with no gas leakage at a landslide

site and a location of liquefaction-induced

bridge abutment deformation. These

pipelines, which were composed of X-grade

steel with full penetration electric-arc, girth

welds, provides field evidence for the high

degree of ductility and resistance to rupture

of this type of modern steel pipeline.

5.3.2.3 Low Pressure Distribution

System

The low pressure distribution system

operating at internal pressures equivalent to 150 mm to 210 mm of water column, or about 1.8 kPa, sustained the greatest

damage. There were 43895 km of low

pressure lines at the time of the earthquake.

In Kobe and adjacent communities, the low

pressure system is composed predominantly

of steel pipe with threaded steel couplings, or screw joints. A small portion of the low

pressure system, approximately 5%, is composed of polyethylene mains and

services. Some steel piping with restrained

mechanical joints and polyethylene linings was deployed in areas of artificial fill as a seismic countermeasures.

Table 5.3.2 summarizes damage reported by

Oka [2] in the low pressure distribution

system. There was no observed failure in the bodies of steel pipe segments, and only

36 locations of ruptured cast iron pipe walls. The predominant type of damage was failure

at the threaded, or screw, joints of steel piping and leakage and cracking at the joints

of cast and ductile iron pipelines. There was

a total of 5190 repairs to distribution mains

and branches within city streets, compared

with 10161 damaged service lines and 11108

locations of damage at piping attached to buildings. Over 80% of the low pressure

system damage was sustained by services.

There were no repairs in polyethylene

piping.

5.3.2.4 Seismic Monitoring and Control

System

The Osaka Gas Company operates a system

of seismic sensors throughout its service area

to provide rapid feedback about the

likelihood of earthquake damage to pipelines and associated facilities. The

theoretical aspects of seismic monitoring and

control and the application of such measures

to the gas system in the Osaka area have

been described by Takada, et al., [4]. The

monitoring system works by telemetering

data from an array of seismic sensors, which

are deployed throughout the service area, to the company control center in Osaka. Data

from the sensors, which includes acceleration

and velocity, provide information about the

severity of ground motion. In combination

with the appropriate algorithms, these data can be used to estimate levels of damage.

With these preliminary damage assessments,

field crews are directed to confirm or modify

the estimates and proceed with emergency

operations.

At the time of the earthquake, 34 sensors had been installed throughout the service

area, and company plans had been

implemented to install an additional 30

377
sensors by the end of March 1995. Strong

motion data were acquired from the seismic sensor array, and additional information was

obtained through emergency calls from

customers and reports from field personnel

during the morning of January 17.

Figure 5.3.2 is a map showing the 8 super

blocks and middle blocks of the Osaka Gas

system. The gas supply was shut down in the 5 middle blocks shaded in the figure.

Osaka gas personnel report that by 11:30

a.m. on January 17, gas supply was

suspended to 386000 customers in Blocks 2

and 3. Blocks 7 (102000 customers), 1 (221000 customers), and 4 (124000

customers) were shut down by 4:15 p.m., 5:10 p.m., and 9:00 p.m., respectively,

suspending gas supply to a total of 836000

customers. By January 23, gas supply had

been discontinued to 857400 customers, or 15% of the total in Osaka Gas' service area. Venting from gas pipelines was

accomplished by radio-controlled venting

regulators on major trunk lines and

manually operated valves on medium

pressure lines. In areas of the system

outside the five shaded blocks in Figure

5.3.2, there were 24844 reports of gas

leakage.

5.3.2.5 Repair and Restoration

Approximately 6000 employees of Osaka

Gas and 2300 personnel from 86 other

utility companies were engaged in the repair

and restoration shortly after the earthquake.

The outside work force from other utilities was increased to approximately 3700 by early

March.

Restoration was performed on a sector-by- sector basis. After a sector was isolated,

each customer meter box was closed and air

pressure tests were performed on mains and

services. Leaks were repaired and additional

air pressure tests were performed. After

repairs to mains and services, leakage tests and repairs, if needed, were performed in

each customer building. Restoration

progress was hampered by the need to clean

water and debris which had washed into

broken gas lines from adjacent soil and

ruptured water mains. Restoration also was

restricted by blocked and damaged roads

and traffic congestion. Full restoration of a

single sector often required 4 to 5 days.

By February 13, all medium pressure A lines

had been put back into service, and the B

lines were almost completely restored. By

February 13 and 22, gas service had been

restored to 32% and 46% of the customers,

respectively. It was not until mid-April,

however, that gas service had been restored

throughout the system, excepting severely

damaged structures. Figure 5.3.3 shows

both the number of customers restored per

day and the cumulative percentage of the

damaged system that was restored as a function of time [2]. As of April 11, gas had

been restored to 700000 customers. Because

of structural collapse, fire, and associated

damage, service could not be restored to roughly 160000 customers.

The total expense of restoration is estimated

at 190 billion yen, or approximately $2.3

billion. This cost covers network repair,

replacement, administration, and related

activities.

5.3.2.6 Intelligent Meters

Approximately 74% of customers were

equipped with intelligent meters according

to Osaka Gas personnel. The meter is equipped with a seismic sensor triggered by

acceleration exceeding 0.2 g, a pressure

sensor, and a flow rate transducer. The

pressure and flow rate sensors detect

abnormal drops in pressure and increases in

378
flow, respectively, which are indicative of

broken and disengaged piping and gas

appliances. A microcomputer monitors the

incoming signals and shuts off flow, if required. A lithium battery is used as a power supply for the microcomputer and gas

shut-off valve.

Gas company personnel report that the

intelligent meters appear to have functioned

as intended. Data were not available,

however, at the time of writing this report

from which to assemble statistics about

meter performance or to assess the extent to which the meters reduced fire initiation.

5.3 J Lesions for the United States

One of the most important lessons

associated with gas system performance

during the Hyogoken-Nanbu earthquake is the need to coordinate the restoration of

electric power with an assessment of the

state of gas system repair. In the first day

after the earthquake, electric power was

restored to 60% of customers at the same

time that shutting down and venting of

middle blocks were being performed and

appraisals were being made of gas system

damage. It appears that there was no prearranged coordination between gas and

electric company personnel to restore

electric service in concert with shutting off

and venting gas in areas severely damaged

by the earthquake. Although the

consequences of restoring electricity in areas of gas leakage have not been fully evaluated,

it appears that early restoration of electric

power in some areas of Kobe with leaking

gas may have contributed to additional fires.

Emergency plans should be drawn up and

specific, formal communication procedures

should be established between gas, electric

power, water supply, and fire department

personnel. Specific checking mechanisms

should be embodied in emergency response

and restoration procedures so that gas and

electric power personnel cannot proceed

beyond a certain recovery level until there

has been formal confirmation by their

• counterparts that gas systems are secure.

The difficulty and substantial time required

for restoration of gas service in Kobe is an

important reminder of the complexities and

resources required for the resumption of gas

supply after large areal shutdowns.

Restoration of gas can be especially critical in winter, as it was in Kobe. It may be

advantageous, therefore, to provide for

remote control and other rapid means of

isolation of smaller, more manageable areas of the gas system. Strategies of this type

require microzonation techniques which are capable of identifying areas with the

potential for locally severe site response and

soil liquefaction. Hazard mapping and

scenario earthquake planning can be

especially valuable to identify and isolate

troublesome areas.

Although the widespread damage to steel pipe with threaded steel couplings occurred

at an unprecedented scale, the vulnerability

of this type of piping has been long

recognized and reported in the technical

literature [1,3]. Threaded steel sections are not only vulnerable to earthquake effects

because of reduced cross-sectional area, but

because threaded sections tend to be

locations of corrosion concentration. A

threaded coupling provides for a rigid

connection, and thus lacks the longitudinal

flexibility inherent in a pipeline with

mechanical couplings that maintain a seal

with compression gaskets.

The extensive damage to vulnerable piping is a very important lesson and a sobering

reminder of potential earthquake effects in weak systems. Although threaded steel

379
piping is used rarely in U.S. gas systems,

many U.S. systems do use cast iron mains

for low pressure distribution. Several of

these systems are located in midwestern,

eastern, and west coast portions of the

United States which are susceptible to serious earthquakes, albeit with various

return intervals. Although cast iron

pipelines have provided generally long and

reliable service, they nonetheless are composed of brittle material that does not

possess sufficient ductility to accommodate

large ground deformation caused by

liquefaction or locally high transient motion.

Given the vulnerable nature of cast iron

pipelines to large differential movement, it is especially important to identify portions of

cast iron systems in liquefiable soils as the

basis for network isolation, replacement, and

special emergency response planning.

5.3.4 Research Needs

The performance of the gas system

reinforces the need to understand better the

interactions among different lifelines. Recent earthquakes, such as the 1989 Loma

Prieta, 1994 Northridge, and 1995

Hyogoken-Nanbu earthquakes, provide

excellent vehicles for exploring these

interactions. Of special importance is the

relationship between gas system disruption

as a potential source of flammable

substances and the damage to and

restoration of electric power as a potential source of ignition. There is a need to evaluate and optimize the use of water and

fire protection relative to gas and electric

system vulnerabilities and operational

characteristics.

The Hyogoken-Nanbu earthquake provides an excellent opportunity to study the seismic

behavior of a particular class of pipelines,

such as threaded steel piping, at locations of

permanent ground deformation caused by

liquefaction and at locations where transient

ground deformation was the principal source of pipeline distortion. Comparison and

contrast of pipeline performance for these

two conditions will help quantify seismic risk

and improve system planning, retrofitting

and design. The earthquake also provides an opportunity to evaluate the response of

several different types of pipelines to similar

levels of seismic intensity so that appropriate

levels of vulnerability can be established for

risk assessment.

The performance of the intelligent gas meter

should be investigated to provide a more

complete database with respect to the

earthquake operation and effectiveness of

seismic gas shutoff valves. The HyogokenNanbu earthquake provides an opportunity

to assemble statistics on triggering, fire initiation relative to locations of shutoff

meters, and overall reliability and

effectiveness of the devices.

5.3.5 References

1. Katayama, T. and R. Isoyama,

"Damage to Buried Distribution

Pipelines during the 1971 San

Fernando Earthquake," Earthquake

Behavior and Safety of Oil and Gas

Storage Facilities, Buried Pipelines

and Equipment, PVP-Vol. 77,

American Society of Mechanical

Engineers, pp. 124-132, 1983.

2. Oka, S., "Damages of Gas Facilities

by Great Hanshin Earthquake and

Restoration Process," Proceedings,

6th U.S. -Japan Workshop on Earthquake Disaster Prevention for

Lifeline Systems, Osaka, Japan,

Public Works Research Institute,

Tsukuba, Japan, July 1995.

380
O'Rourke, T.D., M.D. Grigoriu, and

M.M. Khater, "Seismic Response of

Buried Pipes," Pressure Vessel and

Piping Technology - A Decade of

Progress, C. Sundararajan, Ed.,

ASME, New York, NY, pp. 281-323,

1985.

4. Takada, S., T. Fuke, and J. Ueno,

"Seismic Monitoring and System

Control for Lifelines," Technical

% Memorandum No. 3198, Proceedings

of the Fifth U.S.-Japan Workshop on

Earthquake Disaster Prevention for

Lifeline Systems, Tsukuba Science

City, Japan, pp. 481-502, October

1992.

381
Table 5.3.1

Summary of Repairs of Medium-Pressure Gas Pipelines [Oka (2)]

Steel Pipe

Pipe

Body

Ductile Iron Pipe

Pipe

Body

Total

for

Joints

Total

for Pipe Bodies

Grand

Total

Welded

Joint

Flange

Joint Mechanical Joint (Dresser)

Subtotal Mechanical Joint Subtotal

GM

II

Bell-and- Spigot

Medium-A

pressure

8 5 22 35 0 NA NA NA NA 35 0 35

Medium-B

pressure

6 17 38 61 0 3 7 10 0 71 0 71

Total 14 22 60 96 0 3 7 10 0 106 0 106 NA - not applicable GMII - gas mechanical joint with a compression gasket

382
Table 5.3.2

Summary of Repairs of Low-Pressure Gas Distribution Pipelines [Oka (2)]

Steel Pipe Ductile and Cast Iron Pipe PE Steel Pipe Total

for Joints

Total

for Pipe Bodies

Grand

Total

Welded Flanged SGM Screw Subtotal

Pipe Body GMII Bell-and

Spigot Type

Socket Type

Subtotal

Pipe BodyJoint Pipe Body

Main 0 NA NA NA 0 0 76 439 34 549 34 0 NA NA 549 34 583

Branch NA NA 156 4451 4607 0 NA NA NA NA NA 0 NA NA 4607 0 4607

Service Pipe NA NA 106 6045 6151 0 5 28 NA 33 0 0 NA NA 6184 0 6184

Service Pipe on

Customer's

Property

0 0 59 3906 3965 0 3 7 0 10 2 0 NA NA 3975 2 3977

House Pipe Between

Meter and Cock

0 0 13 11085 11098 0 1 1 0 2 0 0 8 0 11108 0 11108

Total 0 0 334 25487 25821 0 85 475 34 594 36 0 8 0 26423 36 26459 NA - not applicable SGM - steel gas mechanical joint: special polyethylene-coated steel joint for mechanical joint connections GMII - gas mechanical joint with a compression gasket

Bell-and-Spigot Type - joint with lead caulking and jute packing and a compression gasket Socket Type - conventional lead caulked joint with jute packing in cast iron pipelines PE - polyethylene

383
Figure 5.3.1 Map of principal facilities, trunk lines, and major pipelines operated by the Osaka

Gas Company.

384
re 5.3.2 Map of super blocks and middle blocks in the Osaka Gas system showing areas where gas flow was shut off after the earthquake.

385
Figure 5.3.3 Graph showing rate of gas system restoration after the earthquake [Oka (2)].

386
5.4 Electric Power

5.4.1 Overview

5.4.1.1 Kansai Electric Company

The Kansai Electric Power Company is one

of the nine major investor-owned electric

utilities in Japan. It was established in 1951

as a result of a nationwide reorganization of

the electric power industry. The service area

of the company is located in the central part

of the main island in the Japanese

archipelago, and covers about 28500 km2

, or about 8% of Japans total land area. The

area has a population of about 20 million

people and the company supplies about 12

million customers (meter connections). The

Kansai area ranks second after the Tokyo

metropolitan area in economic importance

to Japan. The company serves four major

cities: Osaka with 2.5 million, Kyoto with

1.39 million, Kobe with 1.47 million, and

Nara with 0.35 million people [1]. A

summary of vital statistics is given in Table

5.4.1.

While the Kansai District accounts for only

8% of the land, it consumes 18 percent of

the nation's power. The break down of

power sales is given in Table 5.4.2.

5.4.1.2 System Description

In the earthquake impacted area the

transmission and sub-transmission voltages

are 500 kV, 275 kV, 154 kV, and 77 kV.

The 500 kV system lies primarily to the

north, northeast, and east of the earthquake

impacted area. These lines carry power

from major nuclear generating stations on

the Japan Sea, and large pumped storage

facilities. There are eight fossil-fuel

generating facilities on Osaka Bay east of

the epicenter with a total capacity of 5912

MW. The 500 kV substations use

gas-insulated circuit breakers and in some

cases gas-insulated bus. Breaker-and-a-half

bus configuration is used at most 500 kV

substations. Most 500 kV substations in

other parts of Japan use double bus-single

- breaker bus configurations. The lower

voltage substations are configured as double

bus-single breaker with a tie breaker

between the busses. Figure 5.4.1 shows a simplified schematic diagram of the service area with major facilities and transmission

lines. The primary distribution voltage is 6.6

kV, although there are some 22 kV and 33

kV distribution lines.

Aerial lines and towers are used for most

high voltage lines, although there are more

275 kV cables in urban areas than is typical

for 230 kV in California. Distribution is primarily aerial on concrete poles, with

cables in steel conduit in central business

areas like Kobe.

5.4.1.3 Differences in Equipment,

Facilities, and Practices

Between Kobe and the United

States

There are notable differences between the

facilities observed in the Kobe area and

those found in California. It should be

noted that these observations are based on

visits to only three substations, two operating

at 275 kV and one at 77 kV. No 500 kV

facilities were visited.

The transmission towers tend to have

heavier construction than in the United

States, probably due to large wind loading

associated with typhoons, and the fact that

they typically carry more circuits than in the

U.S. (Figure 5.4.2). The distribution system

uses spun-concrete poles that were typically

more heavily loaded than in the United

States (Figure 5.4.3).

387
The three substations that were visited, all in urban areas in which residential and light

industrial areas were adjacent to the

substation, had acoustical enclosures around

all transformers. High voltage transformers

often had a separate, smaller line reactor

nearby, but outside the acoustical enclosure.

The units resemble power transformers with

a 10 MVA rating. Under light load these

units are used to control system voltage.

Transformers tended to be larger than in the

United States, with weights of about 800000

pounds, not including radiators. All

transformers were bolted to cast-in-place

plates in foundation pads as compared to welding to embedments, which is common in the United States. Different reports were

given on transformer bushings. One

description was that porcelain is grouted

into pockets in flanges, and the other

indicated that they are the same as those

used in the United States, that is, post-tension is used to hold the upper

porcelain to the flange. Circuit breakers use

post-tension connections of the porcelain to

their flanges, as is common for transformers

in the United States. The radiators on some

77 kV transformers have substantial

structural supports and piping connections to the transformer body included a flexible

coupling (Figure 5.4.4). The transformers at a distribution substation operating between

77 kV and 6.6 kV were designed differently

than those observed in the United States in that they had a large metal box supported on a large porcelain insulator on top of the

transformer (Figure 5.4.5). Japan also uses

a frail plate (busting plate) on top of

transforms that can quickly release over

pressures. In the United States, pressure

release valves are used. The valves are

self-closing but have a more limited flow

capacity and release pressure slower. On an

earthquake investigation after the

Off-Miyagi earthquake in 1978, thin (about

1-1/2 cm) rubber pads under the

transformers were thought to contribute to extensive bushing damage. None of these

pads were observed in this earthquake.

Much of the equipment, such as potential

transformers (Figure 5.4.6) and bulk-oil

circuit breakers (Figure 5.4.7), appeared to be much larger than one would expect based on 230 kV equipment found in the United

States (Figure 5.4.8). All capacitors are enclosed in large tanks and have

transformers installed on the isolated rack

(Figure 5.4.9). A typical U.S. installation is shown in Figure 5.4.10. Flexible conductors were used to interconnect all equipment and

in busses, however, liberal slack was not

always provided. It was reported that

Kansai Power uses flexible conductors,

including their 500 kV switchyards, with the

exception of some operating at 77 kV.

Some equipment installations were designed

to conform to seismic design practices that were instituted in 1980, although most

substation equipment observed was installed

prior to this date. The support structures

for some of these newer installations were

very massive and stiff (Figure 5.4.11).

Ground resistors are used, but they do not

appear in this form in the U.S. Lightning

arrester are frequently supported on short

concrete pads just above the ground and

surrounded by a railing to keep electrical

clearances (Figure 5.4.12). Wave traps

which are suspended from overhead bus

supports (Figure 5.4.13), use a current-voltage transformer as a lower

restraint rather than a separate insulator

string that are attached to a structure or the

ground as is done in the United States

(Figure 5.4.14). The two high voltage sites had large water tanks to store water for

cleaning salt deposits off of porcelain after

typhoons. There were also water spray

nozzles distributed in the high voltage

switchyard that are activated under certain

wind conditions to add water to the

388
atmosphere to reduce the salt concentration

as there is a concern with flash-over. Many

bushings are covered with a thin, green

colored silicone rubber to improve surface

properties of the porcelain. The

transformers that provided station power

were much larger than those found in the

United States, even at much larger

substations. Their system uses a grounded

neutral, as it is thought to reduce the

chances of fire.

In general, Kansai Electric does not store any spare parts at substation. In the United

States, some spares, such as bushings, post

insulators, and lightning arresters are

distributed throughout the system at major

transmission substations. As in Japan, small

parts, hardware, and electronic parts used in

control rooms, such as protective relays, are stored at service centers.

5.4.1.4 Seismic Design Criteria

During the visit to Kansai Power, a copy of

the "Guide for Seismic Design of Substation

Equipment," developed by the Japan Electric

Association [2] was provided (English

translation) and represented the current

practice for the seismic design of high

voltage substations. It was developed after

the Off-Miyagiken (Sendai) earthquake of

1978 and represents a consensus document

of a committee representing the Ministry of

International Trade and Industry (MITI),

the Society of Electrical Cooperative

Research, the Central Research Institute of

Electric Power Industry (CRIEPI) (This is the Japanese counterpart to the Electric

Power Research Institute in the U.S.),

electric power companies and the equipment

manufacturers. It was to serve as a

"tentative substitute of Japanese standard..."

Only the key points of this 42 page

document are discussed here. The guide was to provide a design procedure to avoid

serious problems in the supply of power

resulting from earthquakes. It was limited

to main circuit apparatuses and auxiliary

equipment rated above 170 kV. Its criteria were to be used for new construction and

when equipment had major renovation.

There was no retrofit requirement.

The document, through a review of existing

strong motion data in Japan (549 records

including those from the Off-Miyagi

earthquake of 1978) and a few U.S. records

and past earthquake performance, sets forth a basic seismic design. Figure 5.4.15

reproduces a map of the expected

distribution of horizontal accelerations with

a 75 year return interval. Based on this plot,

the maximum horizontal acceleration is set

at 0.3 g to be applied at the ground surface.

Vertical accelerations, typically only used for

wall bushings, are to be one half horizontal

values. Analysis and testing are to be done

at resonant frequencies between 0.5 Hz and

10 Hz. The provisions of the guide were to be applied uniformly throughout Japan, for

sites that met a minimum requirement for

soil properties. (The velocity of the

secondary wave is higher than 150 m/s or the

blow count value of the soil is higher than 5.

It is not known if this test is consistent with

those used in the United States) For sites that do not meet this requirement, special

design should be applied to the equipment.

Additional requirements are to be applied to outdoor porcelain type apparatus and

outdoor type transformers. For porcelain

type apparatus, equipment shall be designed

to withstand a quasi-resonant three cycle

sinusoidal wave at its lowest support. For

outdoor transformers, the tentative

provisions call for bushings to be designed to withstand a quasi-resonant horizontal

acceleration of a 0.5 g three cycle sinusoidal wave to be applied to the bottom of the

bushing turret. The main body of the

389
transformer is to be designed for a 0.5 g

static acceleration. A provision is made that a user of the equipment can stipulate a 2

cycle sinusoidal, 0.3 g test or actual

earthquake waves may be used. Provisions

for indoor equipment are covered in the

document, but will not be discussed here.

The design practice used prior to the issuing

of the document was to be applied to most

other equipment, based on its good

earthquake performance. It is noted that

the use of aluminum pipe busbars is under

investigation and is to be covered in a supplemental report.

5.4.2 What Happened

5.4.2.1 Seismic Environment at Power

Facilities

Figure 5.4.1 shows a rendering of a map

provided by Kansai Electric showing the

peak horizontal and vertical accelerations at 11 strong motion instruments located at power facilities. Instruments on the Japan

Sea coast are located at a gas turbine and

three nuclear generating stations and had

peak horizontal accelerations between 13 gal

and 70 gal and peak vertical accelerations

ranging between 6 gal and 56 gal. The

accelerations of 547 gal horizontal and 478

gal vertical were recorded at the Shin-Kobe

substation located about 24 km

east-northeast of the epicenter. The

Amagasaki-Higashi and the Nanko

generating stations had 279 gal and 126 gal

horizontal, and 331 gal and 199 gal vertical,

respectively. The three sites with the largest

accelerations had high vertical acceleration

relative to their horizontal accelerations. It

is noted that the record obtained at the

Shin-Kobe substation and many others

recorded in this earthquake significantly

exceed the 1980 design guide criteria. Table

5.4.3 provides information about the

characteristics of strong-motion instruments

at Kansai Power facilities. Note that these

are digital instruments with 16 bit resolution,

sample rates between 100 to 1000 samples

per second, a bandwidth from 1 hz to between 30 hz and 60 hz, and full scale

ranging from 300 gal to 2000 gal. It is interesting to note that these bandwidths are comparable to instruments used in the

United States. It has been reported that

most Japanese instruments have an upper

cutoff frequency of about 10 hz.

5.4.2.2 Restoration of Service

The overall performance of the power

system, as measured by the restoration of

power to substations and to areas that were

not severely damaged, was very good. It should be noted that power could not be

restored to some areas as this presented

life-safety hazards until some damage could

be cleared. Figure 5.4.16 shows the number

of customers (meters - not individuals)

without service as a function of time. The

initial estimate of one million customers is very rough. It is interesting to note the

slight increase in the number of customers

without power during the 17th, as was

believed due to loss of service associated

with the spread of fire. The disruption after

the 18th is primarily due to the slow process

of restoring the massive damage to the

distribution system. It should be noted that

some of the restoration was of a temporary

nature to get power to customers, and

substantial rework was required. Figure

5.4.16 also shows the recovery of load

following the earthquake.

Extensive mutual aid was provided, primarily

to restore the distribution system. Work

crews totaling 295 individuals, 46 high

voltage generating vehicles (6.6 kV) with a

total capacity of 16 MW, 74 vehicles with

materials to support the crews, water trucks,

390
substation and transmission line hardware,

and 2 earth station vehicles for

communication were provided. Figure

5.4.17 shows the sources and types of mutual

aid provided by utilities within Japan. The

mobile generating units were distributed to

critical facilities, such as hospitals. Table

5.4.4 shows the number and work

assignment distribution of restoration

personnel. The average length of stay of

mutual aid personnel was about 10 days.

It is interesting to note that some pictures

contained in picture books published by

newspapers show massive destruction to the

power distribution system but a working

traffic light (Figure 5.4.18). To help control

traffic, special power lines were set up for

traffic signals. U.S. delegates who were

attending a meeting in Osaka at the time of

the earthquake observed special power

distribution lines being strung to establish

power outlets at residences. It is not known

how widespread this practice was.

5.4.2.3 Overview of Damage

A summary of damage to power system

facilities is given in Table 5.4.5. There were

four 500 kV substations just outside of the

damage area. Figure 5.4.19 is a composite

of several figures provided by Kansai

Electric Co. This figure shows transmission

lines and substations that were damaged,

substations that were blacked out as a result

of damage, the times that power was

restored to major substation, and the

approximate time that power was restored to various service areas. There are five 275 kV

substations that were de-energized as a

result of damage at the substation, four that were damaged but did not lose power

because of the damage, and two substations

and one switching station that were undamaged. Six 154 kV substations were damaged but did not lose power because of

the damage and six were undamaged. Of

the forty 77 kV (and below) substations near

the epicenter, four were de-energized as a

result of damage, 28 were damaged, but did

not lose power as a result of the damage,

and eight were undamaged. It is interesting

to note that the Awaji Island did not lose

power (Figure 5.4.19). The disruption in a

large part of the west end of the disrupted area was due to damage to one of the 275

kV substations. It was reported [3] that

nearly all problems that caused disruption

could be attributed to transformer bushings

at five 275 kV substations and one at 187

kV substation and four at 77 kV substations.

As a result of the damage from this

earthquake and the large amplitude of the

recorded ground motions, the power

industry is reviewing seismic design criteria.

It is anticipated that this study will be

competed in about 2 years.

The total cost of damage and some

upgrading to the electrical system was

reported by Kansai Electric as about $2.3

billion. About $1 billion was attributed to the distribution system and the remainder to transmission, generation and possibly the

loss of the Kobe office building. In the

review of damage to the distribution system,

it was impossible to get a feeling of the

losses, but as discussed below, extensive

damage was done in the Kobe business

district to buried conduit and surface

facilities were damaged over a much broader

area. Damaged generating facilities were

not visited, but most were generally put back

into service quickly. Three generating

stations experienced soil subsidence and the

Higashinada generating station (120 MW)

was going to require substantial restoration

time.

391
5.4.2.4 Itami Control Center and

Substation

The Itami substation was reported to be the

most severely damaged substation. The

substation is located approximately 39 km

East-Northeast of the epicenter on what was

wetlands adjacent to the Mukogawa river. The substation was originally built in 1941

and the 275 kV switchyard was added in 1960. The age of specific banks or bus

positions is not known, but much of the

equipment in the switchyard is over 20 years

old. The control house is 3 years old and it was built on a specially prepared foundation,

but piles were not used. The 275 kV

switchyard has a double-bus single-breaker

configuration with 11 positions. There are

four 275 kV lines supplying the bus, six transformer banks (three 275 kV to 154 kV

and three 275 kV to 77 kV), and one tie breaker. The 275 kV and 154 kV busses

have bulk-oil circuit breakers. Figure 5.4.20

shows a modified schematic one-line

diagram for the 275 kV and 154 kV

switchyards that is approximately configured

with the same physical layout at the site. Note that for a few items of equipment,

individual phases are shown. The control

house, two water tanks, transmission and

microwave towers, and two large fissures in the ground are also shown.

The review of seismic response of the

equipment at the facility will start where the

high voltage lines enter the switchyard and

work through to the lower voltage

switchyards, the control house and its equipment, and then the transmission-line

towers.

The four 275 kV circuits enter the

substation from drops from dead-end

structures. Two phases of each circuit have wave traps (Figure 5.4.13). Note that there

is relatively little slack between the wave

trap and the adjacent disconnect switch.

Several failures were observed. In two

cases, one of the four cast iron legs on the

lower flange of the current-voltage

transformer failed. One unit was observed

in the graveyard (Figure 5.4.21), and one

unit was still in service with a cracked base

support (Figure 5.4.22). One current-voltage

transformer had a porcelain failure at the

base just above its lower flange (Figure

5.4.23). Several other current-voltage

transformers developed leaks at "O" rings

used to seal the units, but these were

repaired and put back into service. Two

damaged wave traps were also observed in the graveyard. Notation on an operating

diagram indicated that disconnect switches on each circuit were damaged, but the

number of phases or type of damage is not

known. These were the units adjacent to the wave traps and vibration of the wave trap

could generate interaction loads.

In the United States, the lower wave trap

restraint of suspended wave traps is typically

configured like the phase without a current-voltage transformer (CVT) or wave

trap. That is, the wave trap restraint is connected to a structure or to the ground

with an insulator string. The CVT would

have its own support adjacent to the wave

trap restraint. In the configuration shown,

the lower support is provided by the CVT,

so that it must withstand its own inertial

loads and the wave trap restraint loads. In the United States, CVTs and similar devices,

such as potential transformers, have been

very seismically vulnerable, even without

interaction loads. As noted earlier, the

CVTs appear to be large for their operating

voltage as compared to the United States. In Japan, all of the CVTs were supported on

lattice-types structures that were probably

relatively stiff. In the United States most

CVTs are supported on a tubular steel column that is probably relatively flexible.

392
CVTs in the United States with stiffer supports appear to perform better.

One bulk-oil circuit breaker was used in each of the 275 kV circuits that fed into the

bus (Figure 5.4.24). Two of these units were marked as damaged and one had a slipped

bushing (Figure 5.4.25). The damage

patterns in the United States and Japan

appear to be reversed. That is, in the U.S.

transformer bushings tend to slip, with over 50 examples in the Northridge earthquake,

and circuit breaker bushings do not. The

opposite is true in Japan. There were two

spare bushings at the site, an unusual

occurrence since most spares are stored at service centers in Japan. Twelve bushings

from two circuit breakers were removed to replace damaged units at other sites (Figure

5.4.26).

A double-bus single break configuration is used on the 275 kV bus. The potential

transformers on the bus were much larger

that those typically found in the United

States (Figure 5.4.6). These units were

installed after 1980, when more stringent

design standards were used and the support

structure and anchorage details reflects this

(Figure 5.4.27). These units were not

damaged. Twelve of the thirty disconnect

switches in or adjacent to the double bus were indicated as being damaged. A picture

of one unit (Figure 5.4.28) shows that the

post insulator failed at its base. Note that

this is an isolated failure and that there is relatively little slack between the drop and

the disconnect switch. In the Northridge

earthquake several switches were damaged

due to the dynamics of the switch and

probably interaction loads associated with

the insulator string used in the drop.

However, in Northridge the metal supports

below the post insulators of the switch were

deformed, while in Japan the post insulators

failed. Since the insulator string is relatively

light weight, nonlinear effects due to the

interaction of the string, slack in the

connections, and vertical motions of the

conductor support tower may cause larger

than expected loads. The post insulators in the graveyard, which had solid cores, had an

unusual failure mode, as they appeared to

split in half longitudinally (Figure 5.4.29).

In the position shown in Figure 5.4.12,

adjacent to the circuit breaker is a pot-head of a cable to Bank 6, a disconnect

switch and a lightning arrester. The pothead design is different from that used in

the United States in that there are standoffs

between the bottom flange of the pot-head

porcelain and its support structure, similar

to lightning arresters. The disconnect switch

is similar to the center break disconnect

switches used in the United States, except arms are fabricated from copper rather than

aluminum. The three lightning arresters in

this position failed (Figure 5.4.30), and

probably damaged the B-phase disconnect

switch in the background. The lightning

arrester is supported from a short concrete

pedestal. This configuration avoids the

expense of a support structure and the

dynamic amplification that it contributes to the response of the lightning arrester. Note

that there is a small fence around the

lightning arrester to maintain adequate

clearance. Under U.S. rules, a tall fence

would probably be required to prevent

access. The lightning arrester has a standoff

that is the same diameter as the lighting

arrester. This type of design is occasionally

used in the United States, but small

insulators are much more common. Seven

of the fifteen lightning arresters failed in this elements, as indicated by items in the

graveyard (Figure 5.4.31). The lightning

arresters were also positioned much further

from transformer bushings than in the

United States. Many of the porcelain

members were a bright green color, which

393
was from a thin silicon rubber coating

applied to the porcelain (Figure 5.4.32).

The site has six transformer banks, each

bank consisting of a three-phase

transformer. Some units weighed about

800000 pounds and were anchored by eight

3.75 cm to 4.5 cm diameter bolts. All units were bolted to nuts or plates embedded in the transformer pad. Three of the banks

had anchorage failures, with one unit moving

about 45 cm (Figure 5.4.33). As a result of

the displacement, flexible covers on tertiary

bus were severely stressed (Figure 5.4.34),

control cables that entered the transformer

junction box through a hole in the concrete

pad were almost sheared off (Figure 5.4.35), a low voltage bushing failed at its top due to interaction load with the adjacent item of

equipment, and the case of the transformer

hit and shorted out connections in a cabinet

that contained tertiary circuits (Figure

5.4.36). A decision was made to replace

some of these transformers and a soil investigation was underway to determine the

requirements for the foundation of the new

transformers. Because of the proximity of

residential and light industry to the

substation, transformers have acoustical

enclosures. In one case the enclosure

supports were damaged and the enclosure

had shifted (Figure 5.4.37). A small line

reactor, which looks like a transformer and

controls line voltage under light loads, was

connected to the main banks and also had

damaged or failed anchorage. One units

sheared its anchor bolts and slid about 25

cm in the opposite direction form that of the

main transformer (Figure 5.4.38),

aggravating the interaction problems with

the transformer bushings.

Capacitor banks observed at several sites have a different form than those typically

found in the United States. The capacitors are enclosed in relatively large tanks and

have small transformers located on the

electrically isolated rack (Figure 5.4.9).

Note that the post insulators that form

diagonal braces are mounted so that they can take tensile and compressive loads.

Station batteries were secured to well-braced

and anchored battery racks (Figure 5.4.39).

A rack of a different design, positioned close

to the floor, reduces the need for bracing

(Figure 5.4.40). A common detail found at several Japanese facilities is the use of stiff rubber spacers between the cells and

between the cells and their restraints (Figure

5.4.41). Cabinets associated with the

batteries were well-anchored. Just outside

of the battery room there was a relay

cabinet that was unanchored at the time of

the earthquake and it fell over and relays

had to be replaced. The cabinet is now

anchored at its base and brace at the top.

The cable trays were similar to those used

by the power industry in the United States,

except that they have rungs rather than solid

bottoms (Figure 5.4.42).

Several soil effects were observed at the site. As noted above, the site was constructed on

wetlands adjacent to a river. Figure 5.4.20

shows two large cracks in the surface of the

site. Figure 5.4.43 shows one of the large

cracks that opened about 25 cm in the

switchyard. Where these cracks crossed

concrete cable trenches the trenches were

fractured or deformed (Figure 5.4.44). The

crack which crossed the site diagonally

opened between 20 cm and 30 cm. Because

of the potential of control cable damage

(Figure 5.4.45), all transformers were

operated manually rather than by using the

controls until the cables could be checked.

None of the cables were damaged, but a pipe for a system of compressed air in one

of the trenched failed. Bus support

structures and equipment foundation pads were also disturbed. The footings on a bus

394
support structure rotated and there was a

crack in the soil about a foot deep (Figure

5.4.46). A lightning arrester support

structure tipped over about 2-1/2 degrees

(Figure 5.4.47), which probably contributed

to the failure of the lightning arrester. The

diagonal crack also passed though the six separate footings of a 275 kV disconnect

switch. This switch had been removed and a monolithic pad of reinforced concrete about

1-1/4 m thick was being installed (Figure

5.4.48). At the time of the visit, work was in

progress to repair water pipes near the

control house. This did not have any effect on equipment or technical operations, but it did make it difficult for operating personnel

as sanitary facilities were not available.

Water stored in two 100000 liter tanks was

used to clean porcelain after typhoons.

These were old installations and their

response was somewhat puzzling. Each tank was surrounded by a 10 cm thick concrete

ring about 45 cm outside of the outer

diameter of the tank. The annular ring

between the tank and the concrete was

covered with asphalt. It has been suggested

that these rings were to retain the soil that was compacted below the tanks. Each tank was secured by about eight bolts on chairs.

The details of the anchorage of the bolts is not known, but it was reported that they were not secured to the concrete ring. The

bolts on the southern tank were stretched or

pulled out, the asphalt strip between the

tank and the concrete ring was broken and

deformed, and some of the chairs were deformed indicating that there was a large

force between the anchor bolt and the chair

(Figure 5.4.49). On the north tank, the bolts

appeared similar to those on the south tank,

and some chairs were deformed, but there was no disturbance to the asphalt at the

bottom of the tank or by the concrete ring.

There was no indication that the tank had

rocked, other than the bolt position. The

good detailing in the flexible pipe

connection provided to this old installation

(Figure 5.4.50) is rarely seen in the United

States. Other soil effects are discussed

below relative to a transmission-line tower.

A transmission tower adjacent to the control

house had the ground around the tower

footings settled about 15 cm (Figure 5.4.51).

Conduit attached to the tower by a "U" bolt was pulled down with the soil about 8 cm

(Figure 5.4.52), and there was damage to concrete cable trenches near the base of the

tower. Relative movement of the soil and

the tower could damage signal lines coming

off of the tower, such as optical fibers, if adequate slack is not provided.

The transmission tower adjacent to the one shown above also carried two 275 kV

circuits and two 154 kV circuits. These are dead-end types structures (Figure 5.4.53).

That is, the insulator string is in the load

path of the line to the tower, rather than the

line being supported by a string hanging

from the arm. Note that the lines on the

left side of the tower are supported by post

insulators below the tower arm. On those

and several other transmission lines the post

insulators failed at the sand ring and were

hanging from the line. This did not put the

line out of service, but did require repair.

Some towers carry optical fiber

communication cables in their transmission

tower ground wire that are used for

protective relay signaling. This provides a redundant path with the microwave system,

but there are no plans to eliminate carrier

signals and wave traps, as has been done by

some utilities in the United States. A microwave tower at the site had two

members that were bent or had minor

buckling (Figure 5.4.54), which did not effect

operations. While this damage was minor, it

is very unusual for earthquakes to damage

395
communication towers. The foundation did

not appear to be disturbed. Communication

equipment and an engine-generator at the

site were not visited because of a lack of

time.

5.4.2.5 Shin-Kobe Substation

The Shin-Kobe substation is located about

30 km Northeast of the epicenter on a

hillside on at least three man-made terraces. The back of each cut was faced with a concrete wall. While grading diagrams were

not seen, it appears that the back part of the

terraces were on cut and the front part were

on fill. This appears to be born out by

cracks and separation in a wall at one side

of the site and subsidence and cracks at other locations. Circuit breakers were

frequently located on the fill part of the

terrace.

Damage to equipment at the site was similar

to that at Itami. Lightning arresters failed

and damaged disconnect switches when they

fell (Figure 5.4.55). Bulk-oil circuit breaker

bushings slipped on their lower flange

(Figure 5.4.56), probably due to inertial

rather than interaction loads because of the

configuration of the conductors. Post

insulators on disconnect switches failed

(Figure 5.4.57). The failures could have

been from combined effects of interaction

and inertial loads. Insulators in general did

not fail at the base of the insulator stack,

but in the body of the porcelain, and in some cases fractured the porcelain

longitudinally. The three insulators in the

stack were graded, that is, successive

segments from the bottom were thinner.

The vast majority of post insulator failures

in the United States are at the sand ring

rather than in the body of the insulator.

There were several differences in the

damage between this substation and Itami

substation. Transformer anchorage did not

fail. Post insulators supporting neutral

resistors failed (Figure 5.4.58). Of particular

interest, a 77 kV, three-phase, gas-insulated

circuit breaker lost three bushings (Figure

5.4.59) . In the United States, the failure of

any equipment at this voltage is unusual, and

a dead-tank circuit breaker has never failed.

One possible cause of the failure was that

the ground settled and the bus support

structure did not because of its better

foundation. If the vertical drop to the

circuit breaker did not have slack, as is often

the case, the relative displacement could

have pulled the internal conductor from the

bushing.

Another feature not observed in the United

States was fresh water spray heads that were

used during certain wind and atmospheric

conditions to lower the concentration of salt in the air to reduce the potential for

flash-over in the 275 kV switchyard (Figure

5.4.60) .

5.4.2.6 Fukiai Control Center and

Substation

The Fukiai substation is a distribution

substation operating between 77 kV and 6.6

kV, the primary distribution voltage of

Kansai Power Co. The substation has three,

three-phase transformer banks and the 77

kV switchyard is gas insulated. A control

center is located in a building adjacent to the substation.

Transformer Bank 1 failed its anchorage,

slid into an acoustical or fire wall, and

caused it to lean (Figure 5.4.61). A pot

head connected to one phase of the

transformer primary failed (Figure 5.4.62),

probably when the bushing hit the pot head.

The radiators are supported by structural

members at the top and bottom, and the

piping connections at the top and bottom

396
incorporate flexible couplings (Figure

5.4.63) . This design feature would eliminate

a common seismic problem in the United

States of leaking radiator connections on

transmission transformers. Relative motion

between the control cable support structure and the radiators was sufficient to overcome

the current 60 cm gap and cause the

radiators the be crushed and leak (Figure

5.4.64) .

The anchorage on transformer Bank 2

apparently failed, but some bolts were still in their holes, suggesting that the transformer

may have rocked back and forth. Diagonal

rods bracing the fire walls all failed,

indicating that there had been significant

motion of the wall. Conductors, supported

from post insulators connected to the fire wall structure appear to have loaded the

bushings and caused leaks. The design and

damage to Bank 3 was similar to that on Bank 2. Three mobile transformers

temporarily replaced the damaged units.

Due to severe traffic congestion, the first transformer arrived from Osaka about 3 PM.

The second unit arrived in the afternoon of

the next day, the delay again due to very

heavy traffic. Each unit has a 10 MVA

rating.

The site had 77 kV and 6.6 kV gas insulated

switchyards which were undamaged (Figure

5.4.65) .

In a building adjacent to the switchyard

there is a small control center. The

earthquake caused computer monitors to fall to the floor, but there was little significant

damage. Station batteries associated with

the control center and substation were

well-restrained in battery racks that were

well-braced and anchored similar to those

shown in Figure 5.4.39.

5.4.2.7 Performance of Generating

Facilities

Prior to the earthquake, 35 generating units were operating or in a startup process.

However, of these 35 units, 12 units (8 units

that were operating and 4 units that were in startup process) stopped due to excessive

turbine shaft vibrations and other causes

triggered by the earthquake. Among those

units which automatically stopped, no damage was found to the facilities of 4 units,

and these units were started up the same

day. The remaining 8 units, however, had

leakage at boiler tubes and other problems

and temporary repairs were completed by

January 27, 1995. Figure 5.4.66 shows the

location of generating station in the

earthquake impacted area. Table 5.4.6

summarizes damage reported to thermal

power generating units that shut down as a

result of the earthquake. Table 5.4.7

summarizes damage to generating units that

continued to operate during and after the

earthquake. No damaged generating station

sites was visited. There were no leaks in fuel oil tanks at generating sites, but one

tank was emptied as there was concern that

it would leak due to a nearby soil failure.

Soil deformation and liquefaction at generating stations, which were located

adjacent to Osaka Bay, had the largest

impact on generation facilities.

5.4.2.8 Performance of High Voltage

Transmission Lines

Problems with transmission towers were

discussed in the section on the Itami

substation. The damage did not disrupt the

operation of the lines and was of a character

described above. It was reported (Electric

Utility Week, 1995) that ten transmission

lines suffered damage, three 154 kV and

seven 77 kV. In addition, two 275 kV

towers, one 154 kV tower, sixteen 77 kV

towers, and one 22 kV tower suffered slight

397
damage, but did not affect service.

Conductors opened on one 77 kV line and

two 22 kV lines. There were broken

insulators on thirteen 275 kV towers, twenty

six 154 kV towers, and three 77 kV towers.

One tower had problems with its footings.

All lines were temporarily restored within

two days.

5.4.2.9 Performance of the Distribution

System

Because of the pervasiveness of the

distribution system, only an extremely

limited assessment of the damage is possible.

Summary statistics for the distribution

system are given in Table 5.4.5 and are taken from a Kansai Electric report dated

March 7, 1995. Based on pictures that

appeared in publications (Figure 5.4.67 and

5.4.18), much of the damage to the aerial

system had been cleared and many repairs

had been made at the time of the site visit,

almost one month after the earthquake.

Several types of damage were observed from

the visit and a review of pictures in publications. In the Kobe business district,

where the distribution system is underground

in steel conduits, relatively little had been

done to the system, and major demolition

activities were underway to remove damaged

buildings, many in excess of eight stories. It was reported [3] that there were 446 circuits

damaged along the Kobe district's 57614000

miles of distribution lines. Restoration

required 900 poles and 300 transformers be

replaced, although the data in (Kansai

Electric Company, 1995) has much higher

numbers.

The limited observations of the aerial system

used outside of the central business district shows extensive damage to spun concrete

utility poles. Clearly many poles were

pushed over when nearby houses fell into

the street (Figure 5.4.68). Other poles

appeared to fail as a result of severe

shaking, although some may have been

pulled over by power lines connected to nearby poles that were knocked down by

falling houses (Figure 5.4.69). Downed

poles were also a serious impediment to foot

traffic (Figure 5.4.70), as well as the passage

of vehicles. There were many cases where

poles settled when the ground liquefied

(Figure 5.4.71). In this case, one of the

most extreme examples, the stirrup

protruding from the pole at a level just

below the knee of the individual in the

picture, was originally about 2 m above the

ground, thus, this pole settled about 1.5 m. To a casual observer, this damage is not

obvious. It is not clear how extensive this type of damage is. There were many areas with liquefaction, particularly on Rokko and

Port Islands.

The damage to underground facilities in the

central Kobe business district is indicated by

the distortion of some of the above ground

transformers and disconnect switched

(Figure 5.4.72), and the distortion in pavements. In the business district, steel conduit, rather than plastic, is used. To the

extent that the system has been inspected,

there appears to be very little damage to the

electrical cables, not withstanding the

deformations experienced by the conduit. In a few locations, rather unconventional

temporary repairs were made to restore

service (Figure 5.4.73). Here, a 6.6 kV

primary distribution line has been connected

to a conduit below grade and strung on

existing poles to a third floor window in a building across the street. The line is then

brought to the units substation in the

basement of the building so that power can be temporarily restored.

398
5.43 Implications of Observations

to the United States

(a) Leaks and porcelain failure of

transformer and circuit breaker

bushings has contributed to the poor

seismic performance of high voltage

substation equipment in the United

States and Japan.

(b) The use of flexible couplings in

piping connections of the

transformer radiator to the

transformer body may reduce

problems with leaks observed in the

United States.

(c) The performance of instrumentation

transformers in Japan appears to be

better than in the United States. Some units acted as lower restraints to suspended wave traps, and still performed better than in the United

States.

(d) At potentially liquefiable sites, the

need for adequate slack was

demonstrated.

(e) The use of concrete poles appears to increase the vulnerability of the

aerial distribution system. In the

1992 Cape Mendocino earthquake

over 600 wooden poles were about to be replaced because they were weakened due to dry rot, and none

of these failed.

5.4.4 Research Needs

(a) The performance of transformers

and circuit breaker bushings in the

United States and Japan is just the

opposite of each other. That is, in Japan circuit breaker bushings failed

due to slipping and transformer

bushings did not. Why is the

performance in the two countries so

different?

(b) Several bolted transformers moved

even though they appeared to have

substantial anchorage. While new

transformers are typically welded to embedments in the United States,

bolts are often used for retrofits. What were the design and actual

loads on the equipment that failed

and what was the cause of the

anchorage failures?

(c) It would be useful to evaluate the

performance of seismic design

practices that were formulated in 1980 in Japan. Only two high

voltage substations were visited and

it appeared that most of the

equipment predated the new criteria. There may have been other

substation with equipment that met

the new criteria and the evaluation

of the relative performance of the

new and old criteria may be possible.

(d) It would be interesting to explore the reasons for the relatively good

performance of instrumentation

transformers (PTs, CVTs, CCPD,

etc.) in Japan as compared to that in

the United States. While these

components appear to be larger in Japan, they also appear to be

supported on more rigid structures. The differences in design and

installation should be explored.

(e) There have been failures of

equipment adjacent to line drops.

The drops, which use insulator

strings to restrain the lower end of

the line, have very little weight

associated with them but there

appears to be interaction problems.

The nature of these problems should

be explored.

(f) At least one substation and one power station that suffered damage

had strong motion instruments that

recorded the earthquake. It would

399
be very beneficial to review the

performance of equipment at these

sites using the response spectra for

the site and more detailed

information that could be derived

from site conditions.

(g) There is a need to weigh the

advantages, disadvantages and the

risks associated with rigid and

flexible bus and evaluate their

performance in the United States

and Japan.

(h) The relative performance of spun

concrete and wooden poles should be

evaluated. When a house falls on a

pole, it can be expected to fail, but

there appeared to be many concrete

pole failures that are not observed in the United States with wooden poles.

It would be useful to evaluate the

relative performance of the systems,

their advantages and disadvantages

and if the use of the poles is different in the two countries.

(i) The large differences in the design of

capacitors in the United States and

Japan from a seismic performance

point of view should be explored.

5.4.5 Summary

The overall performance of power systems,

as measured by the extent and duration of

disruption, was very good. The seismic

performance of high voltage equipment was

different than that observed in the United

States. In Japan, dead-tank circuit breakers were damaged and transformers failed their

anchorage which contributed to bushing

damage. In the United States, more damage

appears to be associated with transformer

bushings, the failure of current-voltage

transformers, potential transformers, and

disconnect switches. If sites are subject to liquefaction, it is important that flexible bus

be used with liberal, but manageable slack.

Transformer anchorage frequently failed.

There was relatively little damage to high

voltage substations as compared to what was

observed in the Loma Prieta and Northridge

earthquakes. The subsidence at substations

appears to have contributed to the failure of

bushings connected to vertical conductor

drops, as little slack is typically provided.

There was uniformly high quality use of

good design and installation details in

station batteries. The bushing performance

of transformer and circuit breaker bushings

in the United States and Japan are very

different and unexplained. Discounting the

direct damage to poles from falling houses,

there appeared to be very high damage to the aerial system resulting from the failure

of concrete poles.

5.4.6 Acknowledgments

The help of Mr. O. Usuda and Mr. K.

Matsuno in visiting Itami substation is gratefully acknowledged as well as the

assistance of many other Kansai Electric

Power Co. personnel who provided

information on the earthquake response of

their facilities. The help provided by Jim

Stoner, Duke Power, in interpreting one-line

drawings is also acknowledged.

5.4.7 References

1. Current Information on Kansai

Electric Company, March 1994.

2. "Guide for Seismic Design of

Substation Equipment," Japan

Electric Association Guide: JEAG

5003-1980, 1980.

3. Electric Utility Week, January 30,

1995.

400
Table 5.4.1

Summary of Vital Statistic of the Kansai Electric Company

(as of March 31, 1994 )

Installed Generation MW 35,035

Nuclear MW 9,768

Fossil Fuel MW 18,581

Hydro MW 6686

Energy Sales Millions of KWH 123,300

Number of customers Thousands 11,730

System Peak Demand MW 28,411

Electric Operating Revenues Millions of Yen 2,371,828

Assets Millions of Yen 6,204,016

Number of Employees 26,205

Table 5.4.2

Breakdown of Kansai Power Electricity Sales

Lighting (mosdy residential) 28.4%

Light and Power (office buildings, and hospitals) 19.7

Small Power (small- and medium-sized factories, shops) 13.6

Steel Industry 7.8

Chemical Industry 3.9

Machinery Manufacturing 5 .

Cement, Glass, and Ceramics 2.4

Textile Industry 1.0

Other Manufacturers 8 .

Transportation, Communications Electrical, Gas, Water

Construction businesses etc. 7.1

Others (water heaters, etc.) 1-7

401
Table 5.4.3

Specification of Kansai Power Strong-Motion Instruments

Location Year Sensitivity

Gal

Frequency

Range, Hz

Number

of Bits

0 i Sample

Rate

Components

Mihama PS 1 A~7 C 1976 0.1-600 A 1 O A

0.1-30 16 1 AA 100 3

-7-11 7-0 Takasago PS 1 A O O 1983 A ^> 0 f\(\(\ 0.2-2000 A 1 /I A 0.1-40 16 A AA 400 3

Ohi PS 1 (\(\ 1 1991 A AO 1 AAA

0. 03-1000 A 1 OA 0.1-30 16 1 AA100 3

\ a ' no Miyazu PS 1 a 0 a 1989 A 1 C AA 0.1-500 A 1 r

1 A

0.1-50 16

r AA 500 Vertical

Yamazaki 1 no/ 1986 A 1 1 AAAO.l- 1000 A 1 C A

0.1-50 16 O AA 200 3

Nishikyoto SS 1 AO"! 1987 A 1 1 AAA 0.1- 1000 A 1 £ A

0.1-50 12

a AA 400 Vertical

Kobe SS 1988 a 1 1 aaa 0.1-1000 A 1 OA 0.1-30 1 AAA 1000 3

lakasago PS 1 hot * 198 / r\n oaa .03-300 A 1 OA 0. 1-30 12 /I AA 4UU 3

A UoKa DC 1 7 0 / U. 1- 1UUU u. 1 -ou ZUU vertical

Research Center 1988 0.3-300 0.1-30 12 400 3

Ahagasaki No 3 1987 0.1-1000 0.1-70 12 200 Vertical

Nanko PS ? 0.1-1000 0.1-20 16 100 Vertical

YaoSS ? .0021-69kine

Shigi SS 1987 1-320 0.3-30 12 400 3

Minami-Osaka SS ? .0021-69kine 0.25-70 16 100 3

Kainanko SS 1981 0.03-300 0.1-30 12 400 3

Gobo PS 1984 0.1-1000 0.1-60 12 200 Vertical

Tuzaki SS ? .0012-40kine 0.025-70 16 100 3

Table 5.4.4

Distribution of Workers During Restoration

Day 17 18 19 20 22 23 24

Distribution

System

KEPCO 371 657 788 765 794 794 709

Other Utilities 0 260 284 287 291 283 219

Contractors 639 2,070 2,895 2,963 3,616 3,616 3,032

Total 1,101 2,987 3,967 4,015 4,701 4,693 3,960

Power

Transmission

Communications

KEPCO 1,169 947 722 657 334 290 464

Contractors 1,168 1,582 1,448 1,467 1,113 743 1,316

Total 2,336 2,529 2,170 2,124 1,447 1,033 1,780

| Grand Total 3,346 5,515 b,i3/ 6,139 6,148 5,726 5,740

402
Table 5.4.5

Summary of Damage to Power Facilities

Damaged Slightly Damaged Total Main Facilities Main Facilities and

Damaged Other Facilities

Fossil Power Stations 5 4 9

Boiler, Gas Turbine 8 12 20

Substations 17 30 47

Transformers 23 29 52

Circuit Breakers 9 1 10

Power Capacitors 4 4

Shunt Reactors 5 5 Disconnect Switches 41 41

Lightning Arresters 15 15 Busses 7 points 7 Buildings 12 points 12

Neutral Grounding Devices, etc. 32 32

Overhead Transmission Lines 11 12 **23

Wire 3 spans 3 Supporting Structures 11 9 20

Insulator Assemblies 3 36 39

Grounds, etc. 1 1

Underground Transmission Lines 3 92 **95

Cables 20 *384 404

Ducts *183 183

Manholes *257 257

Bridge Section of Line *14 14 Support for Cable Termination *4 4

Oil Feeding Equipment *2 2

Distribution Lines (22 kV, 33 kV) 1 1 11 Overhead - Wire 1 span 1 Overhead - Insulator 1 1 Underground - Cable 11 11 Underground - Duct 8 spans 8 Underground Manholes 125 125

Distribution Lines (6.6 kV) 649 649

Overhead - Wire *6,188 spans 6,188

Supporting Structures *7,869 7,869

Transformers *4,512 4,512

Underground - Cables 185 *1,317 1,322

Underground - Ducts *247 spans 247

Underground - Manholes *125 125

Communication Circuits 76 76

Cable 171 spans 171

* Verified before February 24

** 1 12 lines were damaged - 6 lines consist of overhead lines and underground lines.

403
Table 5.4.6

Power Stations Sustaining Damage to Main Facilities

and Experiencing Trouble in Power Generation

Power Station Unit No. Restoration DateEquipment Damage

Higashi Nada

gas turbine

1.2 June 1996 o Land subsidence spread across the entire yard (fissures and liquefaction occurred) o Uneven settling of buildings and

equipment foundations (gas turbine foundations and the like) o\j Fxnosed i^Apuowu fiifl luifi tan kail foundation luuuuaiiuii nilc^ uuwj (ThpI \i uwi tank does not appear to be leaning) o Cracked, leaning time embankments

Amagasaki

Higashi

1, 2 Jan. 19,18 o Land subsidence and fissures (areas

surrounding the main building, on-site roads,

and the like) Distilled water tank leaning, purified water

tank has settled, drainage gutter damage, and

partial cracking of oil retention embankment)

o Steel frame damage to turbine building

(braced portions and the like)

• Pipe support damage (main steam pipes,

high temperature reheating steam pipes, and

the like) Osaka PS 1, 2, 4 Jan.

22, 27, 23

• Boiler tube damage (cooling spacer tubes bent and fractured; wall tubes partially

deformed from impacts)

Sakaiko PS 2 Jan. 20 o Boiler tubes bent (bending of cooling spacer

tubes)

• Economizer header drain tube nozzle

fractured Sanpo PS 1 Jan. 23 • Economizer element damage (cracks

developed on welded portions of attached metal fixture)

Himeji No. 2

Takasago

Himeji LNG

Terminal, etc.

2 Jan. 18 • Thermal insulation dropped off (high

temperature reheating steam pipes and the

like) o Building structure damage (cracks developed on the main building and service building) o Partial cave-in of soil bank

Legend: • Repaired o To be repaired

Unit numbers in bold face type automatically stopped. The following units stopped, but were not damaged and were re-started - Himeji No. 2(1,3, 5), Takasago (2).

404
Table 5.4.7

Power Stations Sustaining Damage to Facilities

Power Station Unit No. Restoration

Date

Equipment Damage

Amagasaki No 3 1 -3 Summer '95 Damage to boiler seismic-tie

Deformed boiler frame

Kasugade 1.2 Summer '95 o Superheater and reheater spacers became

detached from boiler

Nanko 1 February 2 • Boiler tubes bent (cooling spacer tubes bent)

Osaka 2 February 3 Bent boiler tube

Sakaiko 14

7

April 26

May 11 June 10

Bent boiler tube

Takaigo End Sept. Cracked road on premises

405
Figure 5.4.1 Schematic diagram of Kansai service area and peak acceleration at

utility instruments.

406
407
Figure 5.4.3 Spun-concrete distribution pole used in Kobe.

408
Distribution transformer (77 kV to 6.6 kV) have radiators with

structural supports independent of the piping system and flexible

couplings in connections.

409
Figure 5.4.5 The box with porcelain support is a design feature on a distribution

transformer not seen in the U.S.

410

Figure 5.4.7 A 275 kV bulk-oil circuit breaks which is very large compared to

230 kV units in the U.S.

412
Figure 5.4.8 Typical 230 kV bulk-oil circuit breaker

413

415
Figure 5.4.11 Very stiff support structure for a potential transformer installed

after the more stringent seismic design practices were adopted in

1980.

416
A 275 kV circuit breaker, disconnect switch, pot head and lightning

arrester. Lightning arrester installed on short pedestal reduces cost

and amplification of a taller support structure.

417
Figure 5.4.13 A current-voltage transformer are used as the lower restraint for a suspended wave trap.

418
Figure 5.4.14 In the U.S. suspended wave traps usually have independent lower

restraints

Figure 5.4.15 The Kawasumi map showing the distribution of horizontal

accelerations on the ground surface expected one at the interval of

75 years. (From Ref. 2).

419
Number of Customers Without Power

•10,000 260(5:46 The earthquake occurred.

100(7:30)

50(20:00)

40(8:00) 21(7:00) 32(14:00)

11(6:00) 16(14:00) / All tentative restoration work was completed: 12(19:00)/ 9(13:00) 5(9: oo) 2(9:00) 0.2(9:00)

I / I 8(18:00)1 . . 1 / I \ \ 4(15:00) j i.5(i3:30)\ 0(15:00)

-ntm 1

I

1/17 1/18 1/19 1/20

Month/Day

Load Losses Following the Earthquake

1/21 1/22 1/23

(MW)

3000

2500

2000

3

t 1500

1000

Total Loss of Load

Loss of Load by T-Line & Substation Damage

I \ Substations were restored at 8am of Jan. 18.

T—Lines were restored at 2am of Jan. 21. 500

1/17 1/18 5:46 The earthquake occurred.

All tentative restoration work

was completed at 3pm of Jan.23

1/19 1/20 1/21 Day/Month

1/22 1/23

Figure 5.4.16 Number of customers and loss of power vs time.

420
Aid of Other Electric Utilities

TOTAL

Distribution 319 Workers, 52 High Voltage Power Generating Vehicles (17,890kVA)

77 Vehicles, Commodities of living, Water Wagons, etc. Substation and T-Line

Disconnecting Switches, Hardware for Insulator Assembly, etc. Communication

2 Earth Stations on Vehicles

HOKUR1KU

Distribution 56 Worken, 9 High Voltage Power Generating Vehicles (2.70t)kVA)

9 Vehicles Substation sod T-Une

Electric Wife, clc.

CHUOOKU

Distribution 77 Worsen, 6 High Voltage Power Generating VehkHes (4,O0OkVA)

14 Vehicles, Cora moji lies of IMng. Wilet Wagotnt Subsutloa and T-Une

Hardware foe Iaauiatof Assembly, etc.

KYUSHU

Dbuibulkas

102 Workers. 24 High Voltage Power Generating Vehlclea (7 JOOkVA)

24 Vehicles . . Substation and T-Une O *

lrrsulalors

ollcretl help.

TOIIOKIJ

Dlatribulioa

15 Workers. 3 High Vohage Powei Generating Vehicles (8U0kVA)

6 Vehicles

TOKYO

Distribution SO Temporary Tofte! Facilities, Commoullles ol living, Water Wagons

Subslatloa and T-Une

Disconnecting Switches. Hardware (or Insulator Assembly, etc. Communlcalion

2 Earth Stations on Vehklca

CHUBU

Dhuributton 39 Workers. 6 High Voltage Power Generating Vehicles (l,29nkVA)

II Vehlclea Subslatloa and T-Une

Hardware for Insulator Assembly, etc.

SHIKOKU

DrstributkM X Workers. 4 High Voltage Power Generating Vehicles (1.900kVA)

13 Vehicles eA also onered help. ELECTRIC POWER DEVELOPMENT COMPANY also offered help.

Fossil power production sections of other electric utilities also offered help.

Figure 5.4.17 Sources and types of mutual aid from other utilities.

421
Figure 5.4.18 Damage to the distribution system was massive, but a traffic light in

the background is the result of special restoration of the traffic

control system.

422
SOOkV Substation 275kV Substation 154kV Substation 77kV(or below) Substation 500k V T-Linc

;275kV T-Line

154kV T-Line

: 77kV(or below) T-Line

Blackout Substation by Damage

Damaged Substation D: Damaged Transmission Line Number of Damaged Facilities Verified before Feb.24

Facilities Damaged Damaged and Restored

Substation 9 4

7 3 34 14

275kV

187 & 154kV

77k V or below

Transmission Line 275k V

187 & 154kV 77kV or below

3

1198

2

6

4

.4.19 Schematic diagram showing the damage to substations and

transmission lines.

423
Figure 5.4.20 A modified one-line diagram for the 275 kV and 154 kV switchyard.

424
Figure 5.4.21 Failure of a current-voltage transformer base flange.

425
Figure 5.4.23 Porcelain failed at the base plate of this current-voltage transformer,

426

Figure 5.4.25 The porcelain slipped on its lower flange on a 275 kV bulk-oil

Circuit breaker.

Figure 5.4.26 Bulk-oil circuit breakers with the bushings removed to replace

damaged units at other sites.

428
Very strong and stiff anchorage detailed used on a large potential

transformer to meet more stringent 1980 seismic design criteria.

429
Figure 5.4.28 Isolated failure of disconnect switch may be due to interaction with

the bus drop and insulator string.

430
Figure 5.4.29 Damaged post insulators in the grave yard exhibit unusual

longitudinal cracks.
Figure 5.4.31 Damaged 275 kV lightning arrester in the grave yard.

Figure 5.4.32 Silicon rubber used to improve contamination problems has peels

from this damaged equipment in the grave yard.

432
Figure 5.4.33 Bolts anchoring a transformer failed allowing the unit to slide 45 cm

and causing damage to bushings.

Figure 5.4.34 Offset in bus covers caused by the failure of transformer anchorage

and its movement.

433
Figure 5.4.35 Transformer control cables were almost sheared off due to

movement of the transformer.

Figure 5.4.36 Movement of transformer damaged cabinet and shorted transformer

case the tertiary output.

434
Figure 5.4.37 Transformer acoustical enclosure support was damaged and the

enclosure shifted.

435
Figure 5.4.38 Small transformer sheared its anchor bolts and moved 25 cm

increasing the load on bushings.

436
Figure 5.4.39 Batteries are secured to a well braced and anchored battery rack.

437
Figure 5.4.40 A low slung battery rack configuration not found in the U.S.

reduces bracing requirements of the rack.

438

Figure 5.4.43 A long crack in the ground surface opened about 25 cm and

damaged cable trenches.

440

Large soil deformations at equipment and pedestal foundations did

not damage control cables.

442

Figure 5.4.47 A lightning arrester support structure tipped about 2-1/2 degrees

and probably contributed to the failure of the lighting arrester.

444
445
Figure 5.4.49 The asphalt surface between the tank and the concrete ring was

broken and the bolts stretched or were pulled out due to rocking of

the tank.

446
Figure 5.4.50 While these were old installations, the tanks were provided with

flexible coupling at pipe connections.

Figure 5.4.51 Soil around footing subsided about 15 cm.

447
Figure 5.4.52 Conduit attached to the tower and buried in the ground was

displaced about 8 cm and has the potential of damaging internal

signal cables is they are not provided with adequate slack

.

448
Figure 5.4.53 Post insulators that restrain the lines as they pass under the support

arm failed on several towers, but did not cause disruption.

449
Figure 5.4.54 The bent member in a microwave tower is very unusual, but it did

not effect operations.

Figure 5.4.55 Lightning arresters failed and probably pulled down adjacent

disconnect switched.

450
Figure 5.4.56 All three bushings shifted on this 275 kV bulk-oil circuit breaker.

Figure 5.4.57 The failure pattern of splits in the post insulators of these

disconnect switches is unusual.

451
Figure 5.4.58 Neutral resistors failed, a device not used in this configuration in

the U.S.

Figure 5.4.59 A 77 kV three-phase, dead-tank gas insulated circuit breaker failed

it bushings, probably due to inadequate slack to accommodate soil

settlement at the site.

452
The water spray heads near the fence are used to reduce salt

concentration and the potential of flash-over under certain

atmospheric conditions.

453
Figure 5.4.61 A transformer pushed over the fire wall after it failed its anchorage.

454
455
Figure 5.4.63 The radiator on this distribution transformer has a structural

support and the piping connections have flexible couplings.

456
Figure 5.4.64 Movement of the transformer after its anchorage failed allowed the

radiators to hit a nearby structural support causing a leak.
Himeji 0

: Power stations sustaining damage to equipment, facilities, etc. O: Seismic intensity as per announcement by the Meteorological Agency

tft? I

Himeji No. 2 U

(

Power Station Takasago

Power Station

tp Kobe©

Nada Gas Station Osaka

Turbine ^ _sr~] A—i Power

Nanko Power [_K?LJ Station

Station q~~)Sanpo Power

n^j lT Station /Qsakaiko Power

(/) Station

. ^ /£1

Figure 5.4.66 Location of Generating Stations in the Earthquake Impacted Area.

Figure 5,4.67 Damage to the aerial distribution system was severe in many regions.

458
Figure 5.4.68 Fallen housed pushed over some distribution poles
Figure 5.4.70 Fallen poles contributed to the disruption of traffic.

460

Figure 5.4.72 The conduit and the foundation pad under this transformer pad was

disrupted in down town Kobe due to soil liquefaction.

462
Figure 5.4.73 A primary distribution line of 6.6 kV was temporarily installed to

restore power to a building.

463

5.5 Telecommunications

5.5.1 Nippon Telegraph and Telephone

(NTT) Corporation

The telephone communication system is dominated by NTT, although independent

companies are now providing long-distance

services. The large metropolitan areas of

Tokyo, Nagoya, and Osaka have diverse

communication routing systems installed [1]. The Osaka regional center has connections

to five district centers, and there is a loop

connecting the district centers providing

multiple redundant transmission routes. There are also priority service line in Japan

that are available to customers at additional

charges that connect the customer to two

central offices, although diverse routes from

the customer may not be used. It appears

that this option is available at lower cost in

Japan than in the United States as it is used

more frequently. In addition, special

provisions have been made to new conduit

installations to improve their earthquake

resistance.

Table 5.5.1 shows current measures used to improve the earthquake resistance of

conduit joints. It was reported that welded

steel conduit is exclusively used. This is in contrast to the United States, where plastic

conduit is used. Central offices are connected by optical fiber, copper cable and

microwave trunks. Tunnels are used to carry communication trunk lines. NTT has

two types of tunnels: bored or shielded

tunnels make up 60% of the tunnel system,

and cut-and-cover tunnels make up the

other 40%. The shield tunnels are from 7 m

to 20 m deep and are about 4.5 m in diameter. The cut and cover tunnels are from 2 m to 4 m deep, and their cross

sections are 2 m to 3 m square. In addition,

there are joint utility tunnels made by the

government that have separate sections for

communication, power, and gas lines that are paid for by a utility tax. These tunnels

tend to be very costly, but are encouraged by

the government because they reduce the

impact of surface transportation cause by the

installation of tunnels or repair of buried

lines. Tunnels have sumps or pumps to remove water that leaks into the tunnel.

The loss of water to communication

facilities and its effect on emergency

power in this earthquake further

substantiates this vulnerability to

U.S. facilities.

The annual capital expenditures of NTT are about $200 billion; annual revenues are about $400 billion.

5.5.2 What Happened

A briefing was held at an NTT facility at which system damage was described and

pictures of damage were distributed. An

NTT news release was also distributed [2]. The earthquake reconnaissance team of the

Technical Council on Lifeline Earthquake

Engineering (TCLEE), ASCE, also provided

information on system response. No

damaged central offices were visited in Kobe. The total loss was estimated by NTT

to be ¥300 billion (over $3.6 billion). It is understood that NTT is not insured for

earthquake damage to network facilities. It

is unknown whether this cost will be

recovered through rates.

5.5.2.1 Central Offices

Three central office buildings sustained

damage, but the damage had no effect on

operations except for one office. The three

465
damaged central offices at Kobe, Kobe Sai,

and Saiku were restored by January 29.

Three building-mounted towers were

damaged. One, which was removed later, is shown in Figure 5.5.1. A buckled member

can be seen on the inner cord on the right

leg. Because of the concern that the tower

may collapse, the building was evacuated

until the tower was removed. The tower on

the Daikai-building was back to normal on

January 21 and the one on the

Kobe-Port-building was back to normal by

January 24. They both have been

reinforced.

There was a loss of commercial power in most of the earthquake impacted area (see

Section 5.4). Of the 1440000 lines in the

Kobe area, 285000 had problems related to power failures. By noon on January 18,

electrical problems were solved by the

restoration of commercial power or the use of mobile emergency generators. As in the

United States, central offices have large

battery power plants that can provide power

for several hours and there is an

engine-generator to recharge the batteries to provide long-term emergency power. There was no battery damage. It was reported that

at one central office, the engine-generator

would not operate because there was a loss of municipal water needed for cooling. The

central offices do not appear to have

provisions for a quick electrical hookup

when a generator fails, as are now being

added by some California utilities. It is not

clear why only one central office was

impacted by water disruption, as most of the area was without water. It was also not

clear why the loss of air conditioning, which

also requires water, did not impact

operations, as switches usually require

cooling, even in winter.

5.5.2.2 Outside Plant

There was extensive damage to conduit at manholes and at locations where it entered

central offices. The information received at the briefing indicated that there were no

failures to optical fiber trucks and only a few

to copper trunks. Reliable, independent

sources indicate that there was damage to optical fiber trunks. The news release

(NTT, 1990) notes that the earthquake

caused damage to 193000 lines, and

approximately 100000 were restored by

January 31. The remaining lines that were

out of service were due to collapsed or fire destroyed buildings. There was also damage

to 3170 special service lines, and

approximately 2730 were restored by

January 31. There were 440 of these lines

that could not be restored and temporary

lines were laid.

There were varying degrees of damage to tunnels. A superimposed seismic intensity

map on the NTT tunnel network indicated

that about 6 km were in JMA 7+ zone, 2

km in JMA 6 zone, and 4 km in JMA 5 zone. After the earthquake, 10 sump pumps

were used to remove water that collected in

the tunnels due to leaks and seepage. They

had to be operated using mobile generators

due to the loss of commercial power. These

generators were obtained through contract.

It was noted that waterproofing specialists were in short supply after the earthquake to make tunnel repairs, and were thus critical in terms of making timely repairs.

The shield tunnels had no damage. There

were problems with some of the cut and

cover tunnels. A manager and three

supervisors checked out the 12 km of buried

tunnel in the Kobe area, and the damage

was repaired by March 26. At the Mindato

Central Office, which is located about 200 m

from Kobe Bay just north of Highway 43,

466
the tunnel settled about 7 cm relative to the

building and shifted about 7 cm laterally;

however, there was no damage to trunk

lines. Figure 5.5.2 shows a schematic

diagram of the tunnel-building connection

and a post-earthquake repair used to stop

water leaks. This detail was used

throughout Japan. There was minor damage

to the Joint Utility Tunnels, primarily slight

movement at construction joints resulting in

leaks (Figure 5.5.3). Communication cables

in the Joint Utility Tunnel had fire resistant covers near entrances and staircases, but were generally unprotected (Figure 5.5.4).

At many manholes, the conduits were

pushed into the manhole boxes by up to 30

cm. This can exceed the available cable

slack and cause a cable failure (Figure

5.5.5). The relative motion also can damage

the manhole-conduit seal, and water seepage

can also damage the cables. In older

conduits, cable slack was 2 cm at the

manholes, and some of these broke. At new

conduits, cable slack was up to 15 cm, and

these did not break. It appears that there can be large variations in slack provided to cables at manholes. In an earlier visit to Tsukuba City, an NTT Outside Plant

research group proposed service loops of

about 8 cm diameter before each splice

joint. However, a tie-wrap to secure the

loop to a tray or shelf was also

recommended, so that the deployment of the

slack may be impeded. Liquefaction and

soil movement also moved junction boxes

(Figure 5.5.6). Figure 5.5.7 shows a schematic diagram of a 4 cm offset of plates

used to form the manhole entry. Subsidence

of soil around manholes also caused conduit

failures (Figure 5.5.8). Conduit carried on

bridges were also damaged due to motion of

the bridge deck (Figure 5.5.9). Subsidence

in roadways caused extensive damage

(Figures 5.5.10 and 5.5.11). Telephone

booths were also severely damaged by soil

failures (Figure 5.5.12).

At a stream crossing the telephone conduits were supported on their own bridge. The

slope on one side slumped into the water,

imposing large deformations on the bridge

and conduits, and causing the failure of the

conduits. Visually, the displaced conduits

appeared to have moved up to 1 m. At

another location, the walls of a canal moved

towards each other causing conduit spanning

the canal to buckle (Figure 5.5.13).

The extensive damage to concrete poles

used to carry aerial lines is discussed in Section 5.4.2. In addition to the failure of

poles due to liquefaction, inertial loads,

interaction with fallen houses and other

poles, some lines were damaged due to fire (Figure 5.5.14).

5.5.2.3 Network Operations

There were significant problems with

congestion, that is, attempts to place more

calls than the system can accommodate, a

situation common in the United States from

even minor earthquakes. On January 17,

call volume from other parts of Japan to Kobe increased by a factor of 50 over normal traffic. This dropped to 20 times

normal traffic on January 18. There were

reports that it would typically take ten

attempts to complete a call. At the same

time, it may only take three attempts to complete a call using the cellular system.

During a visit of an ASCEATCLEE

reconnaissance teams at the end of March,

some areas required as many as five attempts to complete a call using a pay

telephone.

To prevent switch saturation, line control was implemented. Restrictions on calling were removed on January 22, when call volume was about twice normal levels. Due

467
to load control efforts by NTT, some areas away from the earthquake, for example in area code 0742 south of Osaka, could not

call other parts of 07 areas, even though

those areas had no telephone system

damage. About 50000 extra lines were

installed to the Hyogo area by using mobile

switching units and mobile satellite transmission units. Telephones were

connected directly to mobile switching units.

5.5.2.4 Restoration

Initially 7000 NTT personnel, many from

other parts of Japan, were working on

restoration. During the ASCE/TCLEE visit at the end of March, there were still 3000

personnel working on locating damage and

restoring outside plant.

Six mobile satellite units were used after the

earthquake to provide transmission capacity

due to damaged towers. In addition, 11

diesel-generators were used to provide

power where commercial power was

disrupted and emergency power was not

provided or had failed.

On Port Island, television inspection of a 7.5 cm steel conduit had just been started at the

time of the visit. Two out of five steel conduits that had been inspected failed due

to differential settlement, but the cables were not damaged.

It was reported (NTT, 1990) that NTT will examine the current disaster management

program based on Japanese intensity 6 by

organizing a Large Scale Disaster

Management Committee to review the

impact of the earthquake and submit a report with recommendations by July, 1995.

5.5.2.5 Special Post-Earthquake Services

NTT provided free telephone service,

including long distance, with 2700 phone

sets, including 350 fax machines at 760

locations in the disaster area.

Telegram service was provided for the

people who evacuated Kobe. E-mail

providers also established a database of the

displaced, injured and diseased persons so

that relatives could obtain information

quickly.

5.5.3 Lessons for the United States

Three building-mounted microwave towers were damaged, one of which was removed.

One of the striking features about

communications towers in Japan, where

there are large wind loads associated with

typhoons, is their massive construction as compared to those found in the United

States. The damage to Japanese towers

suggests that those in the United States may

also be vulnerable, particularly where central

offices are built on poor soil.

The loss of water to communication facilities and its effect on emergency power further

substantiates this vulnerability to U.S.

facilities.

5.5.4 Research Needs

There is a need to get a better

understanding of practices used for outside

plant in Japan and to review in detail, their

earthquake performance. The collection and

analysis of this data on outside plant damage

can provide insight into the outside plant in the United States, particularly in the

Midwest where liquefaction is expected to be

a serious problem.

468
5.5.5 Summary 5.5.6 Acknowledgments

There was relatively little service-disrupting

damage to central offices. Emergency power

was disrupted due to the loss of water at central offices, which caused the loss of

service to 285000 lines. There was extensive

damage to outside plant. A massive

restoration effort was required to restore

service and the restoration of conduit and

other facilities continues, two months after

the earthquake. Total cost of damage from

the earthquake is estimated by NTT at $3

billion. NTT has established a committee to review the impacts of the earthquake and

will make recommendations for changes.

The translation of the news release (NTT,

1995) by Alex Tang, Nortel, and Satoshi

Tanaka, Princeton University, is gratefully

acknowledged.

5.5.7 References

1. "Disaster Prevention Measures of

NTT for Telecommunications

Network Systems," IEEE

Communications Magazine, pp.

18-24, June 1990.

2. A news release in Japanese, dated

February 1, 1995, "Damage and

Restoration of Hyogo-Nanbu

Earthquake," was distributed at the

NTT briefing, 1995.

469
Table 5.5.1

Current Measures Used to Improve Earthquake Resistance of Conduit Joints

Name Structure (Unit : mm) Application

Duct sleeve

-330-

JUL

Expansion Rubber

corilracilon ring pari

PVC-pipe

PS*pipe

concrete

Duct

sleeve

Manhole

At manhole duct

Expansion Joint

^Casing ^Scre\

m

Screw ring Rubber

ring At end of protection concrete

-330- PS-pip«

PSj plpe

Casing .Metal ring ^Rubber ring PS-pipe

Stopper Joint On the side of the bridge abutment

Expansion Joint

for Pipe Installed

in a Bridge

z_

^--Rubber ring

PVC-pipe

At movable

pier

.370- PVC-pipe

Expansion Joint

for Tunnel

Cut off plate <L

Socket

5i 3

Cut off <L plate

On the side

of telephone

office and in places where

topographical

changes are extreme

(a) Collar type expansion joint(b) Socket type expansion joint

470
/

Figure 5.5.1 Microwave tower on top of a central office which was damaged and later

removed.

Building

Concrete

Waterstop

Packing

Post-Earthquake

New Waterstop 20 mm

Tunnel

Concrete

Figure 5.5.2 Schematic diagram of tunnel-building connection detail and

post-earthquake repair.

471
Figure 5.5.3 Slight movement at a construction joint caused a small water leak in a

joint utility tunnel.

472
473
Figure 5.5.5 Cables were pushed into manhole boxed breaking water seals and in some

cases damaging cables.

Figure 5.5.6 Movement of manhole box can damage conduits and trunk lines.

474
manhole entry

{///////

ground

E2222222L off-set

V//////A rings

manhole space

Figure 5.5.7 The entry of a manhole built by stacking rings were offset by 4 cm due to

soil failure.

475
Figure 5.5.8 Subsidence around manhole can damage conduit and trunk lines.

Figure 5.5.9 Conduits carried on bridges were damaged when bridge deck moved.

476
Figure 5.5.10 Large differential settlements in roadways can damage conduit and trunk

lines.
Figure 5.5.12 Soil instability damaged telephone booths.

Figure 5.5.13 Walls of a canal moved causing conduit bridge and conduit to buckle.

478
Figure 5.5.14 Fire damaged aerial lines and cables along the pole.

479

5.6 Hospitals

5.6.1 Overview

5.6.1.1 Scope of Investigations

The investigations of hospitals focused on

the impact of lifeline disruption on hospital

operations. Some additional information was gathered, but issues related to the

medical response and patient treatment were

not investigated. The Kobe Medical College

of the University of Kobe was visited [1]. A

limited amount of information about the

Hyogo Medical Center was also obtained

through a brief interview [2].

5.6.1.2 Kobe Medical College of the

University of Kobe

The Kobe Medical College is located about

10 km east-northeast of the epicenter. It is about 1 km north of the Japan Railroad

Kobe station and up a slight hill from the

shore. Thus, the buildings on the campus

are not on reclaimed land adjacent to the

Osaka Bay. There are several buildings

associated with the college including a new

hospital building, built about 1985, an old

hospital building, built about 1967 and at least one large classroom and laboratory

building. The two hospital buildings are about 10 stories high. They were joined by a narrow section that contained corridors

connecting the two buildings. The old

hospital building did have cracks in a first floor wall between windows that was being

repaired with injected epoxy (Figure 5.6.1).

This damage indicates that there was

significant ground motion at the site.

The hospital appears to be similar in some

respects to teaching hospitals in the United

Sttes. It is a critical care facility and obtains

its patients primarily by reference of

physicians of patients that have special

needs. The earthquake did not have a

significant impact on admissions to the

pediatric section of the hospital.

* We need to review lifeline needs in

critical facilities, such as hospitals,

and establish guidelines for

minimum levels of service for each

lifeline.

5.6.2 What Happened

5.6.2.1 Kobe Medical College of the

University of Kobe

There appeared to be relatively little structural damage to the hospital, except as noted above. In the new wing of the

hospital a section of a wall that joins the

new and old wings had severe local damage

due to interaction of the two buildings

where the corridor connects the two

buildings (Figure 5.6.2). There was some

spalling of concrete adjacent to at least one

seismic joint observed during the short visit to the hospital.

There were reports that equipment in a ward on the tenth floor moved and some

items fell from work tables to the floor. There apparently was some damage to the

oxygen distribution system causing a drop in pressure in the system. The hospital has a

centralized oxygen source that distributes

oxygen throughout the hospital. One patient

in the pediatric ward, who was dependent on

oxygen, was transferred to another hospital.

The cause of the problem could not be

explored because of a lack of time.

The hospital has two emergency generators, one each in the old and new wings of the

481
hospital. The unit in the new wing, which is assumed to be 10 years old - the same age

as the wing - is a large diesel generator. It

is designed to start automatically when there

is a loss of commercial power and provides

emergency power to the hospital complex.

It is installed on elastomer vibration mounts

(Figure 5.6.3). This type of mount was

observed on all emergency generators in

Japan, including some units that were about

30 years old (Figure 5.6.4). This type of

engine mount has not been observed in the

United States, although it would appear to have some advantages over mounts used in the United States. The elastomer has good

damping characteristics and the mount does

not need a snubber to limit motion. This is an advantage because when

vibration-isolated equipment hits snubbers,

large accelerations can result. All utility

connections to the engine-generator were

provided with flexible couplings. The

engine-generator, like many large units, uses compressed air to start the generator. The

air tanks and compressor were well

anchored (Figure 5.6.5). The day tank was

supported on a well-braced and anchored

structure (Figure 5.6.6). There was a 3000

liter water storage tank used for engine

cooling water that was well anchored and

provided with flexible couplings. The

cooling system for the diesel engine uses a

single pass system. That is, water from the

water tank passes through and cools the

engine, and then is dumped into the sewer

system. Water to refill the tank is provided

from the municipal water supply.

The engine-generator in the old wing of the

hospital was a smaller unit and was a quality

installation similar to the unit in the new

wing (Figure 5.6.7). This unit is started

manually and serves as a back up to the new

unit. This engine has a closed loop cooling

system that includes a cooling tower on the

roof of the hospital. This type of system

makes much better use of the available

water, but still requires that evaporative

losses, which take place in the cooling tower,

be made up. The make up water for the

engine cooling system comes from the

building water supply, which will be

discussed below.

The engine in the new wing started when

commercial power was lost. However, due

to the loss of the municipal water supply,

when the small tank near the engine was

empty, there was a loss of cooling water and

the unit shut down due to overheating. The

old generator, with the closed loop water

cooling system, was switched manually to pick up the load in the new wing, and this appeared to meet the emergency needs of

the hospital.

There were no provisions to connect an

external generator to the facility should both

generators have failed to operate.

Commercial power was restored to the

hospital at 8:40 am on January 17, and the

generator was shut off 2 hours later after

commercial power continued without

interruption.

Three large buildings in the hospital

complex have an integrated water system

depicted in Figure 5.6.8. The system

consists of a tank on top of each building

and a common large water storage tank with

a capacity of 400 tons (400000 liters). It should be noted that very few hospitals in the United States have the water storage

capacity of the Kobe facility. This tank,

which is supplied with water by the

municipal water supply, has four pumps

associated with it. Three of the four pumps

supply the tanks on the roof of each of the

buildings. A fourth pump supplies water to the fire suppression system in the three

buildings. This pump also supplies water to

482
two of the building tanks. There was a pipe

failure in the line connecting the fire suppression system to the tank in the old

hospital, Building No. 1. This system also

supplied make up water to the emergency

engine in the old hospital wing.

There was a break in the pipe connecting

the fire suppression system to the tank in Building 1. The pump that feeds this tank

and the fire suppression system were shut

off after the danger of fire had passed. It is not known if Building 1 lost all of its water

supply. The extent of flooding that may

have occurred due to the pipe failure is also

unknown. The water contained in the roof

tanks and the main storage tank lasted 6

hours. Provision was made for a tanker

truck to deliver water to the hospital - 20

tons every 2 hours. However, there was no

simple way of getting the water from the

tanker truck into the hospital system.

Initially, this water was carried to the top of

the building manually, as none of the

elevators were operating. By the second day one of the elevators was operating; but other

than the elevator ride to the roof, it was a manual operation. This operation continued

until the municipal supply was restored after

4 or 5 days.

The telephone system within the hospital

consisted of a main distribution frame

(Figure 5.6.9), Private Branch Exchange

(PBX), an uninterruptable power supply

(UPS), cable trays, and a remote switch.

The Private Branch Exchange was connected

to Nippon Telephone and Telegraph (NTT)

trunks through the main distribution frame.

The uninterruptable power supply (batteries) was charged by commercial power or the

emergency generator in the complex, if commercial power was lost. In addition,

there were a few telephones connected to NTT through the main distribution frame

without going through the Private Branch

Exchange (Figure 5.6.10). These were to provide communications in the event that

there was a failure in the Private Branch

Exchange. The communication equipment was well anchored to a regular building floor

- (raised floors were not used in the

communications room). The batteries for

the uninterruptable power supply were mounted in a cabinet, and restrained by

brackets attached to the shelves (Figure

5.6.11). The restraints were not snug at the

ends and they were made of relatively

lightweight metal. It is interesting to note

that the cells and bus straps connecting the

cells are constructed so that the top edges of

the cells butt against each other, thus, there

is no need for spacers between the cells. The battery cabinet was well anchored. The

communication cable tray sections were

bolted together (Figure 5.6.12), so that they

formed a structural system. The

communication cable trays typically used in the US are fabricated with friction clips, so

that units cannot withstand tensile loads

(Figure 5.6.13). The trays were bolted to

structural walls (Figure 5.6.14). This is a more reliable method of anchoring the cable

trays than the J bolts that are often used in the United States (Figure 5.6.15). The main

distribution frame was bolted to the cable

tray to provide bracing at the top of the

frame to limit the motion of the frame

(Figure 5.6.16). There were no problems

with the main communication facilities. The

remote system had unspecified problems,

however, there was insufficient time to explore the difficulties. The impact of

congestion on the NTT telephone system on

hospital operations is not known.

The loss of the gas supply also had a large

impact on hospital operations, as gas was

used for preparing patient food.

It might be interesting to briefly compare

some of the lifelines at Kobe Medical

College with a university teaching hospital in

483
California, namely Stanford University

Hospital (SUH). It should be noted that no

comparison is made between the relative

size or special roles that the respective

institutions may have in their unique

environments. Water is supplied to SUH

from the municipal system. There are no

storage facilities for raw water, however, a well at the university can also be connected

to supply the hospital. There are three

tanks (23000 1, 6000 1, and 2300 1) that store water treated by reverse osmosis that can be

interconnected. The water used for dialysis

is treated by a special processing units and

there is no storage capability. There is a 23000-liter liquid oxygen tank that supplies

the hospital's needs and a distribution

system. There are also many small portable

units that can meet the needs of individual

patients. The main oxygen distribution

system has many sectionalizing valves, but it would be very time consuming to isolate

sections to find a leak, as all patients would

have to be transferred to portable tanks

before a section could be isolated. The

reduction in overall flow would have to be

compared with the use in the isolated

section to determine if there was a leak.

There are shut off valves for gas within the

hospital. Research labs and the kitchens use

gas. The kitchens also have electric stoves. Emergency power for the main hospital

complex is provided by a large co-generating

unit located on campus. It is interesting to note that if there is a loss of the municipal

water supply, the co-generating plant will have to shut down.

5.6.2.2. Hyogo Medical Center

As a result of the earthquake, a water tank on the roof of the hospital collapsed,

flooding part of the hospital. As was true in

many parts of Kobe, there was a loss of

water and power. Because of the loss of

water, the emergency generator would not

operate so that the hospital lost all power

and it had to be evacuated. The water to the hospital was disrupted for about two

weeks.

5.63 Lessons for the United States

The loss of water supply at Kobe Medical

College indicates that hospitals need to establish an emergency water use policy.

Normal water use is well beyond what one

could expect in resupply after a major

earthquake. There is also a need to

facilitate the delivery of water into the

hospital water system. This requires that

there be appropriate water hookups and

pumps. The hookups do exist for fire service on some facilities. That is, there is an

external access to a stand pipe that is fitted

with a valve or check valve so that an

external source can be attached to the

system when the system is pressurized. As

in the Loma Prieta and Northridge

earthquakes, it appears that some critical

facilities, such as hospitals, should have a method for quickly hooking up an external

generator should the emergency power fail. The impact of the loss of gas on food

preparation was also significant, as many

patients requires special meal. As in the

United States, the loss of elevators in a

hospital is a common problem.

5.6.4 Research Needs

There is a need to review lifeline needs at

critical facilities, such as hospitals, and

establish guidelines for minimum levels of

service for each lifeline. Alternative

facilities and equipment that can mitigate

the effect of the loss of lifeline service

should be evaluated and guidance provided

to facility designers. There is a need for

guidelines for the distribution of special

lifelines within hospitals, such as oxygen.

484
There is a need to review different classes of

water needs in hospitals and establish

guidelines for technical and administrative

procedures for controlling and reducing

water use in emergency situations.

5.6.5 Summary

The quality of lifeline facilities and their

installation, from an earthquake engineering

perspective, observed in the hospital visited was very high as compared to U.S.

installations. Few U.S. hospital would have

a large emergency water supply as existed at Kobe Medical College. The loss of water

still had a large impact on hospital

operations. The loss of water disabled one

generator at the hospital and also caused the

loss of all emergency power at another

medical facility. The 400 ton capacity water

storage tank lasted only 6 hours which

implies that almost 70000 tons were used

per hour immediately after the earthquake.

Some of this usage may have been due to a

water line break shown in Figure 5.6.8. The

resupply by tanker truck was at a rate of

10000 tons an hour, so that water

consumption had to be significantly reduced.

The dependence on gas for food preparation was disruptive to hospital operations. The

distribution of lifelines within a hospital

needs review. Special services, such as the

distribution of oxygen, can be disrupted,

particularly when lines pass through seismic

joints.

5.6.6 Acknowledgments

The authors wish to thank Dr. David

Stevenson, Department of Pediatrics,

Stanford University Hospital; Dr. Nakamura,

Head Pediatrics, Medical College of

University of Kobe; and Dr. Tanaka,

Department of Pediatrics, for their

assistance in arranging interviews with

hospital personnel during the course of this study.

485
Figure 5.6.1 Column on the first floor of the old hospital being repaired with epoxy

injection.

486
Figure 5.6.2 Beam shattered due to interaction between the two wings of the hospital

at cross walks connecting the buildings.

Figure 5.6.3 Engine-Generator in the new hospital wing, which has vibration isolators

and flexible connections on utilities.

487
Figure 5.6.4 Detailed view of vibration isolators used on emergency power engines.

488
489
490
Figure 5.6.7 Diesel engine used for emergency power in the old wing of the hospital.

T3

1

12

Distribution

to building

services

I

Disttt

T1

Distribution

to building

services

~i—

A Distribution

to building

services

P - Pump

FSP - Fire Suppression

Pump

T - Tank

X - Damged Pipe

Figure 5.6.8 Schematic diagram for the Kobe Medical College water system.

491
Figure 5.6.9 Main distribution frame for the hospital communication system.

492

Figure 5.6.11 Battery within UPS used by the PBX. Note that cells fit snugly together,

that there is a gap between the end restraint and the cell, and that the end

restrain is light weight494
Figure 5.6.13 Typical, low tensile strength, friction-clip type communication cable tray

hardware used to join tray sections in the U.S.
Figure 5.6.15 J bolts are often used to secure cable trays to walls. These type of

connections have not been reliable.

496
CHAPTER 6

POST EARTHQUAKE FIRES

6.1 Introduction

As a result of the 1995 Hyogoken-Nanbu

earthquake, 148 fires [1] occurred in the

Kobe city area, between January 17 and 20.

Approximately 660000 m

2

, occupied by more

than 6900 buildings, were damaged by fire. Due to the large number of simultaneous

fires, disrupted water supplies and blocked

roads, fire fighting efforts were largely

ineffective. The fire spread was limited

primarily by wide roads, open spaces, noncombustible walls, fire resistive building

construction and favorable weather

conditions.

This chapter examines the fire events,

factors contributing to the cause and spread

of the fires, the performance of fire protection systems including the response of

the fire department, lessons to be learned

from this disaster, and research needs. The

information in this chapter is based on

observations, news media coverage, and

preliminary reports from the Building

Research Institute of Japan [1] and the Fire

Research Institute of Japan [2].

6.2 Fire Events Following the

Earthquake

The earthquake occurred at 5:46 am on

January 17, 1995. Based on the "119" (fire

department) calls for January 17, 53

separate fires were reported between the

time of the earthquake, 5:46 am, and 7 a.m. Between 7 a.m. and 9 a.m. 13 additional

fires were reported, bringing the total to 66.

Before midnight, 42 more fires had been

reported. An additional 40 fires were

reported during the next 3 days, bringing the

total number fires attributed to the

earthquake to 148 [3]. To provide a point

of reference, the Kobe City fire department

responded to 812 reported fires in 1992 [4]. Therefore over a typical four day period, the

Kobe City Fire Department would expect to respond to nine reported fires or approximately two per day.

Alternative water delivery systems

need to be developed and utilized in

large urban areas for fire

suppression after an earthquake.

Typically a reported fire involves a single

building or building complex. However,

following the earthquake, many of the

reported fires involved a large contiguous

group of buildings. Figure 6.2.1 shows the

number of fires reported during the 10 days

after the earthquake. Only the fires from

the first four days have been considered as

direct results from the earthquake by the

Japanese research organizations investigating

the fires. The 148 fires reported over that

four day period occurred in 6 of Kobe City's

9 wards (Suma, Nagata, Hyogo, Chuo, Nada

and Higashinada) and in Ashiya City,

Nishinomiya City, and Amagasaki City

(Figure 6.2.2). Preliminary reports [1,2]

indicate that approximately 660000 m

2

, and

more than 6900 buildings, were damaged by

fire. Approximately 500 deaths were caused

by fire. Figure 6.2.3 is a photograph

representative of post earthquake fire damage in Kobe.

497
The area which received the heaviest

damage from fire was the Nagata Ward on

west side of Kobe City. The fire area in Nagata accounted for almost 50% of the

total area damaged by fire. Buildings in the

Nagata Ward were predominantly 2 story

wooden structures approximately 50 years

old. The buildings were of wooden post and

beam construction with wooden lathe, a thin veneer of exterior stucco and thin wood

interior panels. The structures had heavy

tile roofs seated on a layer of dirt. This roof

design was used to resist damage by

typhoons. The heavy roof along with

insufficient lateral support allowed the

buildings to collapse easily, resulting in a

debris pile that included thin dry wood with

a large exposed surface area. In addition,

the Nagata area had residential, commercial,

and industrial facilities, frequently

intermixed in the same building. Many of

the industrial occupancies were synthetic

shoe factories which had highly flammable

solvents and plastics. The Nagata Ward is also the most densely populated ward in Kobe City having 10985 people per square

kilometer [2].

As addressed in Chapter 5, disruptions of

water, gas, and electrical service proved

disastrous. No water was available from the

fire hydrants for fire fighting due to a

severely damaged water system. Damage to the natural gas lines and damaged but

energized electric lines provided fuel and

ignition sources, respectively, for the fires. Kobe City's transportation network was also

severely damaged by the earthquake. Many

roads were damaged or blocked by debris

from collapsed buildings.

Given the multiple simultaneous fires that

occurred, lack of a reliable source of fire fighting water, and the difficultly in accessing

the fire areas, many of the fires burned

unabated until they reached a fire barrier.

Most of the Study Team's investigation

focused on the perimeters of the fire areas, examining the conditions that halted the

progress of the fires.

The fire investigation involved a preliminary

visit, during the week of January 23, to one

of the larger fire sites south of Shin Nagata

Station and three smaller sites (less than one

block in size) north east of Shin Nagata

Station. A detailed investigation of eight of

the largest fire sites took place during the

week of February 13 (Table 6.2.1).

6.2.1 Fire Causes

Based on our observations there were

several combinations of fuels and ignition sources which most likely caused the fires. Broken natural gas pipes (Figure 6.2.4) were

evident at many of the fire sites. Kerosene

heaters were present in the ruins of most of

the buildings (Figures 6.2.5 and 6.2.6). The

temperature in Kobe was 3 °C the morning

of the earthquake, so it is likely that early

risers had turned on the heaters to warm

their homes. Customarily heaters would not

be used during the night while people are

sleeping. Electric power lines were

Locations where the fire spread

stopped were clear demonstrations of

the effectiveness ofpassive fire

protection systems.

knocked down by the earthquake or torn

from collapsed buildings creating potential

arcing situations. Some electric lines were

still connected to partially collapsed

buildings (Figure 6.2.7). These lines may

have stretched, creating a reduced cross

sectional area of the wire, which could cause

498
ignition of a fire due to overheating.

Insulation may have pulled away from the

wires making short circuits or ground faults more likely. The majority of the fire damage occurred in areas of predominantly

wooden construction which provided fuels to sustain and spread fires which ignited.

Of the 148 fires, 88 fires were reported more

than 3 hours after the earthquake occurred.

Although there may have been some slow

growing fires that initially were not reported,

a significant number of fires started well

after the initial shock. These may have been

fires associated with aftershocks, fires resulting from restoration of electrical

power, fires associated with recovery

activities, and the spread of the initial fires to create additional separate fires. Fire

spread will be covered in more detail in the next section, however it should be noted that

fire spread was slow due to favorable

weather conditions. According to Dr.

Murosaki of Kobe University, ignitions due

to power restoration were prevalent [5]. Many damaged homes had a serviceable

electric power connection following the

earthquake. When electric power was

restored, damaged appliances, wiring, and

light fixtures ignited combustibles. This is supported in part by data from the Kansai

Electric Power Company [6]. The power

company had reduced the number of

customers without electricity from 1 million

just after the earthquake to 420000 by the

evening of the 17th (Figure 6.2.8). Then

there was an increase in the number of

customers without electric power from

420000 to 500000 during the evening of the

17th. The rate at which the customers'

service was restored occurred at a much

reduced rate until most of the fires were out on the 18th. The reason for the increase in the number of customers without power has

been attributed to the fires that developed

during the evening of the 17th. Dr.

Murosaki and his students had examined 69

of the 148 fire sites at the time of our

investigation. At that time, Dr. Murosaki

indicated that about 25% of those fires were

caused by restoration of electricity.

Other potential sources of the fires which

occurred later in the day on the 17th and

during the 18th and 19th could have been

candles used in search and rescue efforts or

in shrines to commemorate people who had

been lost to the earthquake; fires for

warming displaced survivors, which had

gotten out of control; and suspected arson.

Table 6.2.2 provides a breakdown of the

number and the size of the fire sites for the

day of the earthquake [3]. The number of

fires shown in the table is the total number

of fires in a given size range from the time

of the earthquake until the time shown in the upper column. Note that the majority of

the fires that occurred after 7 a.m. were

relatively small fires. In other words, fires no larger than the size of a small apartment

building.

6.2.2 Fire Spread

Three primary means of fire spread in conflagrations are (a) flame spread over a continuous fuel surface or array, i.e., direct

flame impingement on the fuel, (b) ignition

of adjacent fuel by thermal radiation from

flames and (c) spot ignitions started down

wind of the main fire by burning brands and

embers. In this disaster, the primary

mechanism of fire spread was direct flame

impingement.

For fire to spread by flame impingement,

the flames must be in contact with unburned

fuel, i.e, the fire can only spread along a continuous fuel chain. In the earthquake

damaged areas continuous fuel chains were

prevalent. Rubblized structures are a good

499
example (Figure 6.2.9). The structures collapsed leaving combustible debris next to adjacent structures. In some cases the

structures collapsed across streets providing

a path for the fire spread from one block to another (Figure 6.2.10). In several of the

fire areas, markings and residue could be

seen across streets where the fire had spread

from one side to another.

Wire glass exterior windows appeared

to be effective in reducing the fire

spread. These windows with small

gauge wire are common in Japan but

are rare in the United States.

For fire to spread solely due to thermal

radiation, the "source fire" must be intense

enough to heat the target fuel, which is remote from the fire, to its spontaneous

ignition temperature. The spontaneous

ignition temperature for many organic

materials is approximately 600 °C [7]. In laboratory tests with arrays of wooden sticks,

it has been demonstrated that reducing the

open area between sticks can reduce the

heat release rate significantly [8]. Similarly

due to under-ventilated conditions, the heat

release rate of a collapsed wooden structure

is less than that of the structure prior to collapse due to under ventilated conditions.

The reduced "source fire" intensities of the

collapsed structures minimized the flame

spread by radiation and by fire brands.

For fire to spread due to burning brands or embers, brands must be lofted into the air by the fire, blown by the wind, and land on

unburned fuel. If the brands or embers are hot enough when they land on the fuel to provide ignition, the fire spreads. The

average wind velocity during the 3 days

following the earthquake was low; 2.6 m/s on

the 17th, 3.6 m/s on the 18th and 3 m/s on

the 19th [3,9]. Experience and predictions

of fire conflagrations indicate that at wind

speeds above 9 m/s the fire spread and

associated loss will increase dramatically

[10]. This is due primarily to flame

extension, increased burning rate, and wind

aided transport of burning brands. The

temperature ranged from a low of 0 °C to a high of 8 °C over the 3 day period. The

relative humidity stayed between 45% and

70% between the 17th and the 19th. The

calm, cool and relatively moist conditions

are not as conducive to fire spread as windy,

hot and dry conditions.

Automobiles were identified by Murosaki [5] as a mechanism for fire spread. Burnt

automobiles were seen in narrow alleys

between burnt structures. The automobiles,

serving as a source of fuel, spread fire from one building to the other. Parking areas with burnt cars were also observed (Figure

6.2.11). Without the fuel provided by the

autos, the parking areas would have acted as

fire breaks (Figure 6.2.12).

In summary, the intensity of the fires was

reduced since a large number of the

combustible buildings in the fire area were

collapsed and the flame spread was not wind

driven due to favorable weather conditions.

Since direct flame impingement was the

primary source of flame spread, with minor

contributions from the other flame spread

mechanisms, the spread of the fires was

relatively slow.

6.23 Performance of Fire Protection

Systems

There are two basic categories of fire protection systems for buildings; active and

passive. Examples of active systems are automatic sprinkler systems and hose

500
stations. Passive systems are features of the

design of the building, such as fire resistive or noncombustible construction,

compartmentation, and protection of

openings.

Fire departments could be thought of as an

active fire protection system for a city.

Wide roadways and city blocks with only

noncombustible construction acting as fire breaks could be thought of as a macro-scale

passive fire protection system.

6.2.3.1 Active Systems

Active building systems were not a factor in mitigating the fires during this disaster. No

active systems were present in the residential

fire areas and only hose stations and stand

pipes were observed in the burned out

industrial/commercial areas. A few hose

station systems had self contained water

supplies, however the majority of

suppression systems were rendered useless

by a lack of water due to the broken supply

piping. Even if the fire department could

have supplied water to the standpipe systems

of a building, many standpipe connections

which had broken free of the building

system were observed (Figure 6.2.12).

6.2.3.2 Passive Systems

Most of the structures involved in the postearthquake fires were old (greater than 50

years), 2-story, wooden framed, structures with a mortar exterior similar to stucco. The mortar was held in place by thin brads

and the brads were widely spaced. This

construction style is known as Ohkabe.

While the exterior mortar covering is noncombustible, very little of it stayed in place

after the earthquake. As a result, Ohkabe

buildings, which did not collapse, had their

wooden structure exposed (Figures 6.2.13

and 5.2.14). Solid wooden walls are difficult

to ignite, however, the wood lattice and

bamboo construction of these walls provided an optimized burning configuration. The

exposed wood construction was well

ventilated, with extensive surface area, and

layered to allow re-radiation.

Some passive systems were effective in stopping the fire's spread or limiting fire damage to the exterior of the building.

Gasoline stations, electric power sub stations

and schools survived the earthquake and the

ensuing fires quite well. The buildings all used a combination of passive fire protection

systems.

Gasoline stations are required to have

concrete block perimeter walls,

approximately 2 m tall. In addition, noncombustible shielding is installed on top of

the block walls. These walls are intended to protect adjacent structures from a fire at the

gasoline station. In this disaster, the walls

protected the gasoline stations from the

adjacent buildings which were on fire. In one case, an entire city block was destroyed

with the exception of the corner gasoline

station (Figures 6.2.15 and 6.2.16).

Electric power substations also had

perimeter walls which served to prevent fire from encroaching on the building. Typically

the walls were 2 m or less in height. In some cases, there was very little space (1 m

or less) between the walls and the buildings

and the fire impinged on the side of the

building burning the paint. However, the

buildings' exterior walls were made of

concrete and had no windows, so even though flame impinged on the exterior walls,

the buildings did not ignite (Figure 6.2.17).

School buildings also had perimeter walls. But unlike the "bunker style" construction of

the power stations, the schools had many

unprotected openings, such as large windows

501
and doorways. The schools, however, had

open spaces around the buildings serving as playgrounds, soccer fields, etc. These spaces

in conjunction with the perimeter walls

served to prevent fire spread.

Many buildings with non-combustible

exteriors were destroyed by fire because they were surrounded by burning buildings and

the flames penetrated openings such as windows (Figure 6.2.18). Other buildings

with noncombustible exteriors had burn

patterns from flame impingement on them

but the buildings were saved because they

had windows that remained in place (Figures

6.2.19 and 6.2.20). The difference was wired

glass in the windows. The wired glass would

crack from the heat of the flame but the

wire would keep the glass in place and not

allow the flame to penetrate to the inside of

the building. Steel shutters were another

example of successful window and door

protection which was observed.

On a larger scale, clusters or groups of fire resistive buildings, with noncombustible

exteriors, served to prevent the spread of

fire. If the fire resistive buildings were

surrounded by combustible structures, a fire starting in the combustible structures would

burn around and in some cases through the

fire resistive building. In areas where there were adjacent fire resistive buildings, only

those buildings next to the burning

combustible structures were effected. Fire

spread from one fire resistive building to another was not evident.

6.2.4 Fire Service

The Kobe City Fire Bureau has 27 stations

with approximately 1300 personnel. The

department is well equipped with more than

200 vehicles, including pumper/rescue trucks,

aerial ladder trucks, lighting trucks, rescue

trucks, ambulances, fire boats and

helicopters. The department also has a volunteer corp with approximately 4000

members [4]. Kobe City had made

significant preparation for a loss of their fire hydrant system by constructing 971 water

cisterns across Kobe City for fire fighting use, of which 628 of the cisterns were

reinforced to withstand earthquakes. The

cisterns ranged in size from 10000 to 40000

liters. A photograph of a modern,

conspicuous, seismically reinforced fire fighting water cistern connection is shown in

Figure 6.2.21.

The damage caused by the earthquake alone

would have overwhelmed the rescue capacity

of any modern, well equipped and well

trained fire department. The outbreak of

fires across the city compounded this

problem. As a result, the fire service had

very limited success in containing or suppressing the fires. The difficulties the

Kobe Fire City Fire Bureau faced were: (a)

multiple fires at one time, (b) limited water

supply, (c) limited access to fire sites, (d)

priority on rescue efforts and (e) earthquake

damage affecting the fire stations and fire fighters.

Immediately following the earthquake, 53

fires were reported. On average this was

almost two fires per fire station.

Unfortunately, the fires were not uniformly

distributed across the city. The fires were

concentrated on the east and west sides of

Kobe City. Many of these initial fires were

fed by natural gas and they grew quickly.

No fire department is prepared to immediately handle that number of major

fire incidents simultaneously.

After arriving at the fire scene, fire fighters

found the pressure from many of the fire hydrants to be inadequate. In some cases, the fire fighting cisterns were utilized. In the older sections of town, where the fire

502
damage was the most severe, most of the

cisterns were of the old design (unreinforced

masonry) and were not designed to withstand an earthquake (Figure 6.2.22).

For example, of the 92 fire fighting water

cisterns in the Nagata Ward only 23 were

seismically reinforced. Given the extent of

the ground motion, it is likely that many of

the older cisterns were damaged and lost their water.

Many fire fighters had difficulty reaching the

fire sites due to collapsed buildings and

debris blocking the roadways (Figure 6.2.23

to 6.2.25). With the main highways through

Kobe City heavily damaged, traffic jammed

the remaining roads and pedestrians looking

for refuge or searching for relatives added to the congested streets. Given that many of

the fire hydrant connections and cisterns are accessed via metal plates in the streets (Figure 6.2.26) and sidewalks it is likely that

many of the cisterns were inaccessible due to collapsed structures and debris. The city is divided into north and south portions by the

JR rail line. Several of the train line

overpasses collapsed, thus limiting

movement north and south (Figure 6.2.24).

The fire apparatus in Japan are small in order to navigate the narrow streets. This

limits the amount of water the trucks can

carry. Based on conversations with fire

fighters, the pumpers only carry

approximately 800 1 of water. Since Kobe

City had no water tankers, pumpers had to be used to transport water. Given the

congestion and debris on the roads this was

an extremely slow and difficult process.

Scawthorn [11] indicates that during a fly over of the fire areas, on the 17th at approximately 5 p.m., "No fire streams were

observed, and all the fires were burning

freely..."

With many people trapped in buildings,

rescue had priority over fire suppression

efforts. Experience has shown that the

chances of surviving are highest during the

first 24 hours (Figure 6.2.27) [12]. Many of

the collapsed building which were occupied

at the time of the earthquake were two story

wood frame homes with heavy tile roofs.

Rescues from this type of structure did not

require the use of specialized tools or

extrication equipment to reach many of the

people trapped in their homes. These types

of buildings are often the most "survivable"

type since they have a large number of void

spaces where victims can be trapped, yet still be viable. These are rescue situations where

the general public could be effective in providing rescues since heavy equipment is not required. While some rescues were

performed by untrained residents, some level of information and training could make

rescues by the general public more effective

and wide spread.

The Kobe City Fire Bureau was affected by

the earthquake, as was everyone within the

impacted area. At one of the fire stations

we observed that the building had been

damaged by the earthquake and that the

metal doors for the two apparatus bays were

cut out with a welding torch (Figure 6.2.28).

It is not known to what extent this affected

that station's response but there was clearly a delay. Fire service personnel who were

not at the stations at the time of the

earthquake may have suffered losses at their

homes and disruptions in public

transportation which may have prevented

them from responding to the emergency.

Researchers have developed models [13,14]

which can be used to optimize post

earthquake fire fighting efforts. The models

predict simultaneous ignitions and the rate

at which the fires are spreading and

compare them with fire department response

times and suppression effectiveness. These

models are beneficial for pre-planning

503
exercises. They were not applicable to this

incident, because they assume that the fire department can access the fire site and that

water for fire fighting will be available. In Kobe, accessibility and water were the

exception.

6.2.5 Resident Self-help

Disasters of the magnitude of a major

earthquake followed by large fires overwhelm the capabilities of fire departments and public service rescue

organizations. In cases such as these

resident self-help needs to be part of the

disaster response. After the earthquake,

there were many cases where residents were

quite effective in stopping the spread of fire. The residents formed bucket brigades

bringing water from rivers and school

swimming pools. In one incident, residents

protected a kerosene storage facility in their

neighborhood by removing debris which fell next to the kerosene warehouse and holding

a fire line with buckets of water.

In another instance, a father and son

protected their house while the collapsed

structure next to their home burned to the

ground. The fire in their neighborhood

started mid afternoon on the day of the

earthquake. The fire continued to burn for

the next 3 days damaging several city blocks.

The house which was saved had a perimeter

wall, but it was less than 1 m from the house on the side exposed to the fire. The father

and son kept dumping water, from buckets

filled in the river two blocks away, on the

fire side of the wall to keep the fire from

spreading to their home. It appeared the

fire would overrun the families efforts, when

flame impinged on the second story of the

home cracking the wired glass windows and

burning the plastic eave troughs and down

spouts. Fortunately, the wind shifted the

fire away from the house allowing the

residents to apply more water to the

boundary area near the house and save their

home from destruction.

Information necessary for residents

to prepare for post-earthquake fires

needs to be developed and

disseminated to the public.

While these efforts were heroic and

effective, they appeared to have little overall

impact on the fires. They were only possible

since the flame spread occurred at a

relatively slow rate due to light winds. If the

wind speed was 9 m/s or higher, fighting the

fires with buckets of water would not have

been effective.

6.3 Lessons for the United States

Locations where the fire spread stopped were clear demonstrations of the

effectiveness of passive fire protection

systems. For maximum effect, the systems

need to be designed on a city wide basis. A

network of wide roadways would serve as

fire breaks and provide ample egress and

emergency access. Consideration must be

given to buildings which border the egress

routes and the components of the egress

routes, such as bridges. The buildings

should be designed to withstand earthquake

forces and should be built of noncombustible materials. This concept can be

thought of as creating fire resistive egress

corridors for cities, with performance goals

similar to those desired for means of egress

in buildings.

Wired glass exterior windows appeared to be

effective in reducing the fire spread. These

windows with small gauge wire are common

504
in Japan but are rare in the United States.

Alternative water delivery systems need to be developed and utilized. One such system

might consist of caches of high volume,

diesel powered (or other independent power

supply), portable pumps located near natural sources of water around the city. From the

pumps, networks of large diameter hose line

could distribute water to portable drafting

tanks or to pumpers.

Fire fighting with aircraft dropping water or

Class A foam should be examined. For

areas near bodies of water where scooper

aircraft or helicopter buckets can be used,

fast turn around time would make this option attractive. Although aircraft dropped

water cannot attack interior fires it may be

effective on fires in rubblized buildings. Fire

fighting from the air may be a method of

overcoming the problem of accessing the

fires due to blocked roads.

Information necessary for residents to prepare for post-earthquake fires needs to be further developed and disseminated to the general public. Technologies to assist residents in protecting themselves and their

property need to be developed and

evaluated.

6.4 Research Needs

The following have been identified as areas

for possible improvement in reducing the

loss of post-earthquake fires.

(a) Limit Ignitions-Re-energization of an earthquake damaged area needs

to be coordinated between the

different utilities and the emergency

rescue and recovery services. Work

needs to be conducted on the impact

of earthquakes on gas service to

buildings and appliances. Prior to restoration of electrical service,

techniques or instrumentation needs

to be developed to assure that

electricity is not restored to damaged

structures or areas with natural gas

leaks.

(b) Passive Fire Protection SystemsExamine current construction

requirements for fire resistive

buildings, especially the protection of

openings such as windows and

doorways. Special efforts should be

taken toward materials or systems

which could be retrofit to existing

structures. The concepts of fire resistive egress corridors for cities should continue to be investigated.

(c) Alternative Water Supplies and

Delivery Systems- Wildland fire agencies utilize a wide variety of

methods to move water to the fire location. Their methods should be

examined for applicability to an urban conflagration.

(d) Predictions of post-earthquake fire losses-Case studies of the fire propagation and the fire suppression

activities from this earthquake could

provide a basis for further post

earthquake fire model development.

6.5 Summary

The 1995 Hyogoken-Nanbu Earthquake

demonstrated the potential for significant

fire damage following an earthquake even though favorable weather conditions kept

fire intensities relatively low and helped to

limit fire spread. New fire ignitions and

spread continued for days after the

505
earthquake as a result of electric power

restoration and the need for open fires by

earthquake survivors. The large number of

simultaneous fires, disrupted water supply, rescue operations, and limited access to fire

sites rendered the fire suppression activities

by the fire department ineffective. City and

building design, zoning, home owner self- help and alternative water delivery systems

need to be reevaluated in areas prone to earthquakes.

6.6 Acknowledements

Many Japanese researchers provided us with

the logistical support and guidance that

enabled us to conduct this investigation. For

their efforts, appreciation is extended to Dr.

Hiroaki Suzuki and Mr. Ichiro Nakaya of

the Building Research Institute in Tsukuba,

Mr. Masatomo Yoshida of the Japan

Building Laboratory in Osaka, Dr. Koichi

Yokoyama and Dr. Hiroshi Sata of the

Public Works Research Institute in Tsukuba

and Professor Murosaki of Kobe University.

We would also like to thank Dr. Takashi

Kashiwagi of the Building and Fire Research

Laboratory at NIST and Mr. Takashio Noto

a guest researcher at NIST for their

assistance in interpreting the preliminary

data received from Japan.

6.7 References

1. Heisei 7 Hyogoken-Nanbu

Earthquake Disaster Investigation

Report (Preliminary Report).

Ministry of Construction, Building

Research Institute (Japan), February

1995

2. Urban Area Fire Investigation

Report of Kobe City as a Result of

the Hyogo Ken Nambu Earthquake

(Draft Report). Fire Defense

Agency, Fire Research Institute

(Japan), March 1995.

3. Urban Area Fire Investigation

Report of Kobe City as a Result of

the Hyogo Ken Nambu Earthquake

(Draft Report), Appendix 7 Kobe

City Fire Department Official

Report. Fire Defense Agency, Fire

Research Institute (Japan), March

1995.

4. Statistical Data of the Kobe City Fire

Bureau. Kobe City Fire Bureau,

Kobe, Japan, April 1993.

5. Personal Communication with Dr.

Suzuki of FRI and Dr. Murosaki of

Kobe University, 1995.

6. Earthquake Impact on Electric

Facilities of the Kansai Electric

Power Co., Inc. The Kansai Electric

Power Co., Inc., February 2, 1995.

7. Drysdale, D.D., An Introduction to Fire Dynamics, John Wiley and Sons,

New York, 1985.

8. Bryner, N.P. and Mulholland, G.W.

Smoke Emissions and Burning Rates

for Urban Structures. Atmospheric

Environment Vol 25A, No 11. Pergamon Press, Great Britian.

pp2553-2562, 1991.

9. Kobe Weather Data for January 17

and 18, 1995. Meteorological

Research Institute (Japan), January,

1995.

10. "1994 Northridge Earthquake,

Performance of Structures, Lifelines,

and Fire Protection Systems."

National Institute of Standards &

506
Technology, NIST SP862,

Gaithersburg, MD, May, 1994.

The Hyogoken-Nanbu Earthquake,

Preliminary Reconnaissance Report,

Earthquake Engineering Research

Institute, February 1995.

Risk Factors for Injuries Due to the

1990 Earthquake in Luzon,

Philippines. Bulletin of the World

Health Organization, Vol 70, 1992.

13. Sekizawa, A., Sagae, K., and Sasaki,

H. A Systematic Approach for the

Optimum Firefighting Operation

against Multiple Fire Following a Big

Earthquake. Fire Safety Science - Proceeding of the Second

International Symposium, pp 423-

432.

14. Eidinger, J.M., Dong, W., Fire

Following Earthquake in Development of a Standardized

Earthquake Loss Estimation

Methodology, prepared for National

Institute of Building Sciences by

RMS Inc., February 1995.

507
Table 6.2.1

Fire Sites Investigated by the UJNR Fire Team

Site

No.

2

3

City

Kobe, Nagata

Ward

Kobe, Nagata

Ward

Kobe,

Nagata/Suma

Wards

Kobe, Suma

Ward

Kobe, Nagata

Ward

Kobe, Nada

Ward

Kobe, Nada

Ward

Kobe, Nada

Ward

Location

Sugawara Market Area

Shin Nagata Station,

South

Mizukasa West Park

Chitose Small Park

Shikanashita, Block 3

Rkko, Block 1&2

Burned

Area

(m2

)

74,043

39,570

106,241

15,542

Takahashi Hospital Area 68,850

Oishiminami, Block 2 & 3 2,456

2,398

19,940

Number of

Burned

Buildings

927

434

1164

179

825

24

41

221

508
Table $.2.2

Number and Size of Fires on the Day of the Earthquake.

Fire Area January 17th, 7 am January 17th, midnight

Less than 1,000 m

2 23 60

Greater than 1,000 m

2

, 20 31

Less than 10,000 m

2

Greater than 10,000 m

2 10 14

509
17 18 19 20 21 22 23 24 25 26

Date

Figure 6.2.1 Post-earthquake fire occurrences

(January 17 through January 26, 1995).

510
Figure 6.2.2 Kobe City map showing UJNR fire investigation sites.

511
512
Figure 6.2.5 Kerosene heater representative of those found in and around many of the

businesses and residences.

Figure 6.2.6 Kerosene heater representative of those found at many of the fire sites.

513
Figure 6.2.7 Example of electric power lines connected to a damaged house.

6

CO

o

<DCO

o

E3

5:46am

Figure 6.2.8 Number of households without electric service.

514
Figure 6.2.9 Collapsed houses. Notice that the pile of debris is in contact with

the adjacent houses, forming a continuous fuel chain.

515
Figure 6.2.11 Parking area where automobiles contributed to fire spread between buildings.

Figure 6.2.12 Standpipe connection severed at street level.

516
Figure 6.2.13 Example of okabe construction with portions of the fire resistive mortar displaced

by the earthquake.

Figure 6.2.14 Example of a structure with mortar exterior after earthquake.

517
Figure 6.2.15 Gasoline Filling Station on the SW corner of the Sugawara Market Fire Area

(Site No. 1).

t I

Figure 6.2.16 Gasoline Filling Station Perimeter Wall and Non-Combustible Shielding.

518
Figure 6.2.17 Electric Power Sub-Station.

519

Figure 6.2.21 Seismically reinforced fire fighting water cistern.

Figure 6.2.22 Access cover to unreinforced fire fighting water cistern

Figure 6.2.25 Road blocked by collapsed structure.

Figure 6.2.26 Collapsed train overpasses such as this one divided Kobe north and south

523
Rescues vs. Time

100

gQ I • i I , i i i i I i i i i i I—i—i—i—i—i—I—

I

0 12 24 36 48

Time, hours

Figure 6.2.27 Time history of rescues made after the 1990 earthquake in Luzon, Philippines.

Figure 6.2.28 Fire station damaged by the earthquake

.

524
CHAPTER 7

OBSERVATIONS, CONCLUSIONS, AND RECOMMENDATIONS FOR RESEARCH

7.1 Introduction

The January 17, 1995 Hyogoken-Nanbu

(Kobe) earthquake was the first earthquake

in recent history that had a direct hit on a modern urban region and resulted in

unprecedented damage and economic loss. Many U.S. cities have similar geographic

settings as the City of Kobe, i.e., narrow

strip of coastal land, soft soils along the

shore, and congested urban buildup and

transportation systems. Examples of these

cities include Seattle, Washington, and Long

Beach and San Diego, California along the

west coast; New York City, Boston,

Charleston, South Carolina, and Memphis,

Tennessee, all located in the eastern and

central regions. In many respects, the

nature of devastation of Kobe by this earthquake is most relevant to the cities in the eastern and central United States.

Urban areas in eastern and central United

States are much older than the region in Japan where this earthquake hit-Kobe was

rebuilt after World War II. However, many

of the Japanese buildings were constructed

without the benefit of modern seismic

design, likewise their lifeline systems. The

Kobe earthquake therefore provided an unprecedented opportunity to learn many

valuable lessons that can help prepare us to reduce the devastating effect from future

earthquakes.

7.2 Observations and Conclusions

Some key observations and conclusions

which resulted from the visits of the team

members are summarized below.

7.2.1 Seismology, Geology, and

Geotechnology

The earthquake reemphasized that moderate

to large earthquakes directly beneath

densely urbanized areas can cause

catastrophic loss of life and property.

1. Proximity to the earthquake crustalrupture zone Strong-motion recordings

show that peak acceleration values

attenuated from values greater than

0.8 g near the source zone to values less than 0.25 g at some sites at distances near

20 km on firm soils. This rapid attenuation

of strong shaking appears to have been an important factor influencing the confinement

of damage primarily to the Awaji Island,

Kobe City and Nishnomiya areas.

2. Amplification effects of soft-soil deposits

The amplification effects of Holocene soil deposits appear to have contributed to increased peak amplitudes and duration of

strong shaking at many sites. The increased

levels of shaking contributed to direct

structural failures and liquefaction induced

ground failures. The amplification effects of

the Holocene soil deposits are consistent

with those inferred empirically from the

Loma Prieta earthquake.

3. Liquefaction susceptibilities of reclaimed

land and soft soil deposits

From the geotechnical viewpoint, the

liquefaction of about 17 km2 of land

underlain by artificial fill highlights the

seismic hazard of loose sandy soils. The

experience during the 1995 earthquake

reaffirmed the proclivity of areas built on

these fills for large permanent ground

525
deformations when they are strongly shaken.

Many artificial fills in coastal and river areas of the United States are similar to the loose

sandy fills in Kobe, which performed so

poorly. Much artificial land has been

created in the United States by dredging or dumping sand into open water without

compaction. These older fill areas in ports

and harbors, both in seismically active areas and areas of low seismicity, are vulnerable to earthquakes. As the 1995 earthquake

demonstrated, this vulnerability can extract a steep price when these areas are strongly

shaken.

7.2.2 Buildings

With the exception of the unique SRC

construction type, the construction and

detailing practices of Japanese buildings

have generally evolved in a manner that

closely parallels U.S. practice. Code

improvements, while not identical, have

occurred at the same general pace in both

countries. This tragic earthquake therefore

offers an excellent opportunity to reflect on

several general issues.

1. Poor performance of traditional wood

houses The majority of the casualties in this

earthquake were caused by the collapse of

old Shinkabe and Ohkabe houses made of

wood. They were built primarily to support

gravity loads. In more recent Ohkabe

design, lightweight cross braces were

introduced to provide better lateral resistance. There were no indications of

plywood or particle-board shearwalls being

used in these constructions, as is common

practice in the United States. Many severely

damaged houses had heavy ceramic roof

tiles set on soil as bedding, which

contributed a great deal to their collapse.

2. Damages to older reinforced concrete

buildings Many older reinforced concrete

(RC) moment frame buildings experienced

full or partial floor collapses. The damaged

low to mid-rise RC buildings that were

observed could easily have been U.S.

buildings that were constructed in the 1950's

and 1960's, particularly in zones of low to moderate seismicity. The large amount of

damage that occurred in Kobe points out

the high vulnerability of these older, poorly

detailed structures. This problem is not only one of concern for the zones of higher

seismicity in the western United States, but

it is also a concern for the lower seismicity zones in the central and eastern United

States, where detailing practices in many

cases have not kept pace with Western U.S.

practice. These older and less ductile RC

structures will require significant

rehabilitation to be made less vulnerable.

3. Good performance in new RC buildings

No evidence of collapse in any of the newer

(post-1981) engineered RC structures was

evident. The 1981 Japanese code

improvements, which added the second

phase of seismic design that addresses

ultimate capacity, is quite similar to the

intent of current U.S. building codes that

focus on life safety, or collapse prevention,

in the one-time severe seismic event. In this

light, this earthquake is a vindication of the

current code philosophies in both countries

and the technical changes that have occurred

in those codes as a result of the RC research

that has been carried out since the early

1970's in both the United States and Japan.

4. Performance-based design philosophy A

somewhat more subtle issue regarding new

construction is whether there should be

standards that provide better building

envelope integrity than the basic one-event

life safety standard that we have today. It was clear from the external envelope surveys

that racking had caused many windows in newer structures to crack or pop out of their

526
frames. Also, facade cracking and other

minor damages were present. These less severe damages represent costs to the

building owners, and in many circumstances can also pose life safety dangers from falling

debris. The event should fuel further debate

in both the United States and Japan about

weighing initial construction costs against

potential future earthquake losses.

5. Avoiding stiffness or mass irregularities

The earthquake again pointed out the need

for avoiding the use of "soft" stories and

stiffness or mass irregularities either in plan or elevation. Many of the older building

collapses could be at least partially

attributed to the presence of such weak

links.

6. Eliminating pounding between buildings

The need to eliminate pounding of adjacent

buildings was evident. Building separation is the obvious solution. When it is not

provided, the interactions of adjoining

buildings must be considered.

7. Performance of steel frame structures The performance of steel frame structures was generally encouraging. Although there was extensive damage in many of these

structures, particularly low- to mid-rise

apartments and offices, few collapsed and

egress means were maintained. The nature

of the damage also indicates that extensive

monetary damage can be inflicted on a

structure in the form of cladding failures. The extensive base metal and weld failures

observed at the AHST complex in Ashiya

City echo problems first observed in steel structures in the United States following the

January 17, 1994 Northridge earthquake.

7.23 Highways and Bridges

1. Lessons for bridge design in central and

eastern United States To bridge engineers

and owners in the central and eastern

United States, this earthquake is perhaps of

greater significance than recent earthquakes

in California. One reason is that the

predominant type of bridge in Japan is the

steel girder superstructure supported by

bearings on concrete columns and

foundations. This class of bridge is also

found throughout the central and eastern

United States. Bridges in California tend to be concrete box girders with monolithic

bents and integral abutments especially in shorter bridges. The performance of

Japanese bridges is thus of particular

relevance to states east of the Sierra Nevada

"Snowy Range."

A second reason is that the difference

between the maximum credible earthquake

and the design earthquake is clearly very

large for this region of Japan, which is a situation that is also considered to exist in the United States, but to a greater degree in the eastern and central United States than in the west.

(a) The closure of arterial highways and

bridges affects emergency relief and

business recovery and can have a major economic impact on a region

and its ability to survive such a

disaster.

(b) Large damaging earthquakes can

occur in areas that are considered to have, on average, only a moderate

exposure to seismic hazards.

(c) Capacity design procedures, ductile

details and generous seat widths are necessary to prevent catastrophic

collapse during large earthquakes.

(d) Minimum connection forces need to be enforced for all seismic zones

unless such connections can be

shown to be fully protected by

acceptable yielding of the

substructures. Redundancy in

527
connection detailing is particularly

important for essential structures.

(e) Critically important structures must

be designed to a higher level of

performance than that provided by

current specifications, if full service is to be maintained after a large

earthquake. Multi-level performance

criteria and corresponding design

strategies are necessary for important

bridges.

(f) Retrofit measures reduce damage

but inappropriate use and/or

installation can defeat their purpose

and perhaps even trigger collapse.

(g) Lateral spreading due to liquefaction can lead to span collapse even in modern structures with massive

foundations (caissons) and

well-engineered fills. (h) Premature failure of some bearings

appear to have reduced the seismic

loads in their supporting

substructures by uncoupling the

superstructure from its supports.

(i) Skewed bridges are susceptible to in-plane rotation leading to large

displacements at their supports and

possible unseating of girders in the

acute corners.

7.2.4 Railways and Rapid Transit

System

1. Damage to elevated structure sections

Rail services suffered more damage along

the elevated structure sections than along

the elevated embankment sections. Most

damage to the elevated structures occurred

at columns either at the bottom of

superstructures or at a joint region.

Although shear reinforcement spacing at both ends of the column were reduced by

about one-half, the old non-ductile details were vulnerable to high ductility demands.

The damage was similar to unretrofitted

column damage observed in past California

earthquakes.

2. Better performance of Port and Rokko

Liners Both the Port Liner and the Rokko

Liner were built with modern codes.

Columns along the Port Liner are mostly

reinforced concrete whereas columns along

the Rokko Liner were built with steel. It is difficult to conclude which type of

substructure performed better without

detailed structural information. In general,

steel columns suffered minor yielding and

local buckling while concrete columns either

yielded or failed in shear.

3. Need for a systematic retrofit technique

for RC structures Although damage to the

reinforced concrete structures was extensive,

the major cause of collapsed structures was

the nonductile detailing of the steel reinforcement. Structures designed by

current specifications performed well with

minor damage. With the vast amount of

elevated structures in need of repair and

retrofit, a systematic retrofit technique is needed.

4. Collapse at the Daikai Station The

failure of the Daikai Station is highly

significant because it is the first instance of

catastrophic earthquake damage to a modern cut-and-cover subway station. The

failure appears to have resulted from

earthquake-induced transverse shear

distortion in combination with loads

enhanced by vertical accelerations. Shear

distortion promotes plastic hinge formation

which, in combination with enhanced vertical

loads, can result in a collapse mechanism.

Shear distortion and vertical accelerations

apparently led to collapse of the center

reinforced concrete columns at the Daikai

Station.

528
Current design practices, which account for

transient shear deformation and vertical

accelerations, are consistent with the failure

mechanisms inferred from observations of

damaged sections of the Kobe underground

rapid transit systems. Failure of the central

columns at Daikai Station emphasize the

importance of designing to prevent plastic

hinge formation leading to a collapse

mechanism. The lack of significant

confining steel at failed reinforced concrete

columns suggests that attention to confinement and ductility can play an important role in strengthening underground

structures against earthquake effects. Attention also needs to be focused on the

density and stiffness of backfill adjacent to structures built by cut-and-cover methods.

7.2.5 Airports

1. Good performance of airport facilities at Kaisai Airport The braced frame structural

system in the recently completed Kansai

control tower appears to have an effective

seismic design; but it has not yet been put in a severe test. The leveling system provided

in the basement of this building is an

innovative approach to provide for the

possible uneven ground settlement that may

be caused by liquefaction or consolidation.

The use of interior columns to support the

roof of the cab in the Kansai control tower

did not appear to be a significant visual

impediment. Its use in the United States should be explored to reduce earthquake

window damage frequently observed in this country.

7.2.6 Ports and Harbors

1. Severity of damage The extensive

damage to the port of Kobe highlights the

seismic hazard to port facilities posed by

loose sandy fills. Such materials have been

widely used in both the United States and

worldwide to reclaim ground for port

development and expansion. The

earthquake illustrates once again the

potential for these fills to liquefy and

generate large permanent ground

displacements when shaken by earthquakes.

It further illustrates the ability of such

liquefaction to totally disable a port.

2. Ground improvement of loose sandy fills Stabilization of loose sandy fills by ground

improvement is generally cost prohibitive

because of the volume of material that must

be improved. The localization of lateral spreading around the margin of the Port and

Rokko Islands suggests that the hazard of

permanent horizontal ground deformation

can be substantially reduced by improving

only the outer margins of these loose fills. Modern pile-supported structures on Port

and Rokko Islands performed well in locations where they were subjected only to ground settlement.

3. Consideration of multi-style of design

Another important engineering lesson from

the Kobe port experience is the vulnerability

from using one style of design for a key part

of an important facility. Possibly

liquefaction was not considered to be a

significant possibility during the design of

port quay walls. By repeatedly using quay

wall designs that were vulnerable to lateral spreading, operation of the entire port was

left vulnerable to this hazard.

7.2.7 Water and Wastewater Systems

There are reoccurrences of many situations

that should help clarify earthquake planning

and earthquake resistant design.

1. Overwhelming Conditions From an emergency response perspective, there is always discussion about what might occur

following a large earthquake located in a

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densely populated area. One of the biggest

issues in the Kobe event was the loss of all transportation. Every major mass

transportation route failed, and surface

roads were blocked by fallen buildings. The

resulting congestion made walking the

fastest form of transportation. This caused

emergency response to slow to a crawl.

Utility decision makers need to be thinking

in terms of consequences similar to the

Kobe event. For example, what happens

when you have no records because all utility

buildings are destroyed or become

inaccessible? What happens if the plan is to dispatch crew to isolate critical pipelines to save water or shut off natural gas, but the

fastest way to get there is by walking?

2. Fire Following Recent earthquakes have

shown that there is a low probability of

maintaining a water system following an

earthquake. Consideration should be given

to identifying and developing alternate

supplies.

Similarly, the use of monitoring and control

systems should be considered to enable the

timely control of a water system following an earthquake to increase the probability of

delivering water to suppress fires. Water

purveyors and fire departments should use permanent ground deformation mapping to identify areas where pipelines will likely fail so that plans can be made to isolate

damaged areas and/or use alternate water

supplies.

3. Geotechnical Issues In Kobe,

geotechnical failures governed the poor

performance of the water system.

Landslides, consolidation, and liquefaction or lateral spread stopped the flow of water

from the source; damaged two major and one small water treatment plants; and tore the distribution system apart. In general,

the structural aspects of the "steel" transmission pipelines matched current

design used in the United States. The

treatment plant structures performed

reasonably well except that they were on

soils that failed. An aggressive pipeline

replacement program apparently only

marginally helped mitigate geotechnical

failure-related damage to the pipeline

distribution system.

4. Recovery The three Kobe Water

Department buildings storing records were

destroyed. The probability of this occurring

is very low. In the United States, we should

make sure that our resources are distributed so that the loss of any one facility will not

substantially impact our ability to respond to an earthquake.

7.2.8 Gas Delivery System

1. Coordination in restoration process A

most important lesson associated with gas

system performance during the earthquake is the need to coordinate the restoration of

electric power with an assessment of the

state of gas system repair. In Kobe, it appears that there was no pre-arranged

coordination between gas and electric

company personnel to restore electric service

in concert with shutting off and venting gas

in areas severely damaged by the

earthquake. It appears that early restoration

of electric power in some areas of Kobe with

leaking gas may have contributed to additional fires.

Emergency plans should be developed and

specific, formal communication procedures

should be established between gas, electric

power, water supply, and tire department

personnel. Specific checking mechanisms

should be embodied in emergency response

and restoration procedures so that gas and

electric power personnel cannot proceed

530
beyond a certain recovery level until there

has been formal confirmation by their

counterparts that gas systems are secure.

2. Gas Service restoration can be a timeconsuming process The difficulty and

substantial time required for restoration of

gas service in Kobe is an important reminder

of the complexities and resources required

for the resumption of gas supply after large

areal shutdowns. Restoration of gas can be

especially critical in winter, as it was in

Kobe. It may be advantageous, therefore, to provide for remote control and other rapid

means of isolation of smaller, more

manageable areas of the gas system.

Strategies of this type require microzonation

techniques which are capable of identifying areas with the potential for locally severe

site response and soil liquefaction. Hazard

mapping and scenario earthquake planning can be especially valuable to identify and

isolate troublesome areas.

3. Poor performance of steel pipe with

threaded steel couplings Widespread

damage to steel pipe with threaded steel couplings occurred at an unprecedented

scale. Threaded steel sections are not only

vulnerable to earthquake effects because of

reduced cross-sectional area, but because

threaded sections tend to be locations of

corrosion concentration. Further, a threaded coupling provides for a rigid

connection, and thus lacks the longitudinal

flexibility inherent in a pipeline with

mechanical couplings that maintains a seal

with compression gaskets.

Although threaded steel piping is used rarely

in U.S. gas systems, many U.S. systems do

use cast iron mains for low pressure

distribution. Several of these systems are located in midwestern, eastern, and west

coast portions of the United States which

are susceptible to serious earthquakes, albeit

with various return intervals. Although cast iron pipelines have provided generally long

and reliable service, they nonetheless are composed of brittle material that does not

possess sufficient ductility to accommodate

large ground deformations caused by

liquefaction. Given the vulnerable nature of

cast iron pipelines to large differential

movement, it is especially important to identify portions of cast iron systems in liquefiable soils as the basis for network

isolation, replacement, and special

emergency response planning.

7.2.9 Electric Power

1. Poor performance of high voltage

bushings Leaks and porcelain failure of

transformer and circuit breaker bushings has

contributed to the poor seismic performance

of high voltage substation equipment in the

United States.

2. Flexible couplings for transformer

radiators The use of flexible couplings in piping connections of the transformer

radiator to the transformer body may reduce

problems with leaks observed in the United

States.

3. Better performance of instrumentation

transformers The performance of

instrumentation transformers in Japan

appears to be better than in the United

States. Some units acted as lower restraints

to suspended wave traps, and still performed

better than those in the United States.

4. Need for adequate slack At potentially

liquefiable sites, the need for adequate slack was demonstrated. Slack needs to be

provided in vertical drops at sites that are vulnerable to subsidence.

5. Performance of concrete poles The use of concrete poles appear to increase the

531
vulnerability of the aerial distribution

system. In the 1992 Cape Mendocino

earthquake over 600 wooden poles were

about to be replaced because they were weakened due to dry rot, and none of these

failed.

7.2.10 Telecommunications

1. Performance of microwave towers Three

building-mounted microwave towers were damaged, one of which was removed. One

of the striking features about

communications towers in Japan, where

there are large wind loads associated with

typhoons, is their massive construction as compared to those found in the United

States. The damage to Japanese towers

suggests that those in the United States may

also be vulnerable, particularly where central

offices are built on poor soil.

2. Effect of loss of water The loss of water

to communication facilities and its effect on emergency power further substantiates this vulnerability of U.S. facilities.

7.2.11 Hospitals

1. Need for emergency water supply The

loss of water supply at Kobe Medical

College indicates that hospitals need to establish an emergency water use policy and

normal water use in hospitals is well beyond

what one could expect in resupply after a major earthquake. There is also a need to

facilitate getting delivered water into the

hospital water system.

7.2.12 Post Earthquake Fires

1. Effectiveness of passive fire protection

Locations where the fire spread stopped were clear demonstrations of the

effectiveness of passive fire protection

systems. The systems need to be designed

on a city wide basis. A network of wide

roadways would serve as fire breaks and

provide ample egress and emergency access. Consideration must be given to buildings

which border the egress routes and the

components of the egress routes, such as

bridges. The buildings should be designed

to withstand earthquake forces and should

be built of noncombustible materials. This

concept can be thought of as creating fire resistive egress corridors for cities, with

performance goals similar to those desired

for means of egress in buildings.

2. Effectiveness in using wire glass exterior

windows Wired glass exterior windows

appeared to be effective in reducing the fire spread. These windows with small gauge

wire are common in Japan but are rare in

the United States.

3. Alternative water delivery systems

Alternative water delivery systems need to be developed and utilized. One such system

might consist of caches of high volume,

diesel powered (or other independent power

supply), portable pumps located near natural sources of water around the city. From the

pumps, networks of large diameter hose line

could distribute water to portable drafting

tanks or to pumpers.

4. Fire fighting with aircraft Fire fighting

with aircraft dropping water or Class A foam

should be examined. For areas near bodies

of water where scooper aircraft or helicopter

buckets can be used, fast turn around time

would make this option attractive. Although

aircraft dropped water cannot attack interior

fires it may be effective on fires in rubblized

buildings. Fire fighting from the air may be

a method of overcoming the problem of

accessing the fires due to blocked roads.

5. Information regarding preparation for

post earthquake fires Information necessary

532
for residents to prepare for post-earthquake

fires needs to be further developed and

disseminated to the general public.

Technologies to assist residents in protecting

themselves and their property need to be

developed and evaluated.

7.3 Recommendations for Research

Research needs in each of the technical areas covered during the team's

reconnaissance visits are summarized in the

following:

7.3.1 Seismology, Geology, and

Geotechnology

1. Availability of strong-motion data set in

soft-soil deposits The large set of

recordings on Holocene soil deposits within

5 km to 20 km of the crustal rupture

provides a unique set of in-situ measurements of the response of soft-soil

deposits at high input ground motion levels. These data provide a potentially important

data set for research on: (a) the location and

nature of the crustal-rupture process as it can be inferred from augmentations to the

seismological and strong-motion data sets, (b) compilation, analyses, and distribution of

the strong-motion recordings obtained by all contributing agencies, (c) compilation of

detailed seismic and geotechnical logs at as many of the strong-motion stations as resources permit, (d) thorough analyses of

surface and borehole strong motion

recordings to develop an improved

understanding of the response of soft-soil deposits at high input ground motion levels,

and (e) interpret improved estimates of the

response of soft-soil deposits for purposes of

code revisions and site-specific design

analyses.

The extensive lateral spreading around the

margins of the artificial fills placed in Osaka

Bay provides an opportunity to clarify the

mechanism of horizontal ground

displacements associated with soil liquefaction. The widespread damage to engineered works should permit

documentation of details of deformation

fields associated with lateral spreading. This

understanding should improve the design of

countermeasures to minimize the impact of

liquefaction on engineered works. Areas of

ground improvement need to be

documented. Evaluation of the performance

of these areas should increase confidence in our ability to reduce the hazard from

liquefaction of sandy soils.

7.3.2 Buildings

1. Improvement of performance of existing

RC buildings The most urgent research

need for RC buildings is the extensive

research on seismic vulnerability assessment,

rehabilitation, and retrofit for older,

nonductile RC moment frame and shear

wall buildings in the three to ten story range.

These buildings are numerous both in Japan

and the United States, so they represent a substantial area of risk and potential damage

cost. More accurate models of existing

nonductile structures are needed,

necessitating research on older member and

system capacities. Rehabilitation techniques

need to be cost effective and nonintrusive

for building owners and users. Continued

focus on improving the deformation

capacities of columns, girders, and joints in

moment frames is needed. Beyond this,

continued research into less traditional

techniques for rehabilitation, such as supplemental energy dissipation and the use of newer structural composites, should be

conducted.

533
2. Difference in design philosophies

Current Japanese design techniques result in

stiffer but less ductile RC structures than in the United States. A study of these two

differing approaches would seem to be

appropriate.

3. Study of Steel-Reinforced Concrete

(SRC) buildings The distinctive Japanese

practice of SRC construction should be

studied. Disregarding the apparent

problems that existed with discontinuities in these systems, it is important to examine

whether the use of such composite

construction does enhance ductility in RC

beyond that provided by current U.S. RC

detailing techniques, and if so, to determine

its cost-effectiveness with respect to current

detailing techniques.

4. Steel frame structures The behavior of

heavy steel frame highrise structures under

strong low cycle lateral loading should be

examined. Given the wealth of data

concerning the design procedures, weldment

details, and material specifications for the

AHST complex in Ashiya City, research

should be conducted into the behavior of

built-up steel column sections and truss weldments under very low cycle fatigue.

This would augment research programs

already underway in the United States

following the Northridge earthquake.

7.3.3 Highways and Bridges

1. Study of bridges with strong-motion

records Conduct correlation studies on

those bridges with strong motion records to calibrate theoretical models against actual

behavior. Valuable insight into the

performance of these two important types of

bridges would be derived from such studies.

2. Case studies of steel bearings and

earthquake couplers Develop a detailed

database on the performance of steel bearings and earthquake couplers

(restrainers) followed by case studies on

selected bridges in which these devices

failed. Results from such a study would help

determine the need for a review of current

U.S. design criteria for connection forces

and restrainers.

3. Study of superstructure-foundation

interaction Analyze structural response due

to large foundation movements during

liquefaction and lateral spreading and the

development of optimum mitigation measures to minimize structural impacts.

4. Performance of retrofitted bridges

Perform case studies on those bridges that

had been retrofitted before the earthquake

to determine the effectiveness of the retrofit measures. Known measures for which

performance could be evaluated include

earthquake couplers, steel jackets and

viscous dampers.

5. Development of performance-based

design approach Develop multiple-level

performance criteria which define expected

damage and serviceability states for various

earthquake scenarios and the corresponding

design strategies/structural options necessary

to satisfy these criteria. Involvement of

social scientists (planners, economists and

experts in public policy) should be

encouraged in this study.

6. Study failure mechanisms in large

concrete columns under combined axial and

shear loads Concrete columns in single or multi-column bents in Japanese bridges have

very large cross sections and fall outside the

range of U.S. test data. Although it is unlikely that U.S. practice will adopt similar

sized members for short- and medium-span

bridges in the near future, columns of this size and with these reinforcement ratios are

534
encountered in some long span structures. Correlation of assessment methods and limit states with field data from this earthquake

could give valuable insight into the lateral load capacity of large concrete members. It

is noted that such field data are rare and

this opportunity is probably unique.

7. Study of bridges with steel substructures

The relatively large number of damaged

steel substructures provides an opportunity

to calibrate proposed new methods for the

seismic design of steel bridge columns. In

particular, their capacity for ductile actions

and the identification of their limit states should be investigated with the objective of

refining the R-factors in the U.S. bridge

codes for these components.

7.3.4 Railways and Rapid Transit System

1. Ductility study between RC, Steel, and

SRC columns Because of the low

redundancy of single column structures, the

structural layout and substructure

performance becomes more important for

those structures than for structures with

multiple column bents. Research is needed

to compare the ductility between reinforced

concrete, steel and steel reinforced concrete

composite columns. A damage index should

be developed to assess the repairability of

columns after an earthquake. Force levels encountered at collapse sites should be

compared to current U.S. design forces to validate current designs.

2. Study of transient shear distortion It would be advantageous to investigate the

levels of transient shear distortion which can

occur in soil profiles near a seismic source,

particularly when strong motion is characterized by relatively long pulses of

substantial acceleration, leading to high

velocities and displacements. The severity of

racking in underground structures resulting

from strong motion with high amplitude and

relatively long periods needs to be

understood better, and the combined effects

of racking and high vertical accelerations

needs additional clarification.

3. Study of differential lateral movements

Site response needs to be investigated in terms of differential lateral movements

which occur during earthquake loading at

sites with thick deposits of soft to medium

clay and loose sand. The effects of depth

and soil liquefaction on soil shear distortion

and structural racking also need further

research.

7.3.5 Airports

1. Development of methods for improving

the performance of control towers The

earthquake performance of control tower

windows in the United States has been poor

and similar performance was observed at Osaka Airport. The loss of these windows

can be very disruptive to operations so improved performance is desirable. The

Kansai Airport control tower incorporated

columns in their design that did not appear

to significantly adversely effect the

functionality of the tower. Practical

methods are needed to upgrade these towers

in a way that will not interfere with the

function of the towers.

7.3.6 Ports and Harbors

1. Better design and construction of quay

walls The extensive damage to the quay

walls that disabled the port operations

indicates that the failure mechanism of these

structures needs to be understood from the

perspective of being able to design against

such failures. A variety of ground

improvement techniques are available, but in general they are costly. The localization of

lateral spreading near the quay walls

535
suggests that only portions of the fill need to be improved. The development of such

guidelines would facilitate remedial efforts

at other ports with similar exposure.

2. Study of ground deformation due to liquefaction The large vertical settlements

observed in sandy fill during the earthquake

also provide an excellent opportunity to develop a case history of ground

deformation associated with liquefaction.

The numerous pile-supported structures and

bench marks provide an opportunity to systematically document the regional nature

of the soil consolidation.

7.3.7 Water and Wastewater Systems

1. Study of water treatment plant design In

general, water treatment plants and service

reservoirs performed well. We should study

Japanese design approaches for these

facilities. Their tank designs are somewhat

different from those used in the United

States and apparently had no damage when

subject to high peak ground acceleration.

2. Study of the performance of S-joint pipe

Pipelines were heavily damaged, except that

preliminary information on performance of

the S joint pipe indicates that it had no or few failures. If it is confirmed that it performed well in areas of significant

permanent ground deformation, such as what was observed at Rokko Island where

such pipe was placed, we should introduce it to the United States. If it did not perform

well, we should find out why, and improve

U.S. pipe design based on those findings.

7.3.8 Gas Delivery System

1. Study of interaction among lifelines The

performance of the gas system reinforces the

need to understand better the interactions

among different lifelines. Recent

earthquakes provide excellent vehicles for

exploring these interactions. Of special

importance is the relationship between gas

system disruption as a potential source of

flammable substances and the damage to and restoration of electric power as a potential source of ignition. There is a need

to evaluate and optimize the use of water

and fire protection relative to gas and

electric system vulnerabilities and

operational characteristics.

2. Study of seismic performance of several

types of pipelines The earthquake provides an excellent opportunity to study the seismic

behavior of a particular class of pipelines,

such as threaded steel piping, at locations of

permanent ground deformation caused by

liquefaction and at locations where transient

ground deformation was the principal source of pipeline distortion. Comparison and

contrast of pipeline performance for these

two conditions will help quantify seismic risk

and improve system planning, retrofitting

and design. The earthquake also provides an opportunity to evaluate the response of

several different types of pipelines to similar

levels of seismic intensity so that appropriate

levels of vulnerability can be established for

risk assessment.

3. Performance of intelligent gas meter

The performance of the intelligent gas meter

should be investigated to provide a more

complete database with respect to the

earthquake operation and effectiveness of

seismic gas shutoff valves. The earthquake

provides an opportunity to assemble

statistics on triggering, fire initiation relative to locations of shutoff meters, and overall

reliability and effectiveness of the devices.

536
7.3.9 Electric Power

1. Study of the performance of

transformers and circuit breaker bushings

The performance of transformers and circuit

breaker bushings in the United States and

Japan is just the opposite of each other.

That is, in Japan circuit breaker bushings

failed due to slipping and transformer

bushings did not. Study should be

conducted to find out whether there is a difference in design and installation

procedures in the two countries.

2. Study of failure mechanism of bolted

transformers Several bolted transformers

moved, even though they appeared to have

substantial anchorage. While new

transformers are typically welded to embedments in the United States, bolts are often used for retrofits. The design and

actual loads on the equipment that failed

and the cause of the anchorage failures

should be evaluated.

3. Study of the performance of

instrumentation transformers It would be

interesting to explore the reasons for the

relatively good performance of

instrumentation transformers (PTs, CVTs,

CCPD, etc.) in Japan as compared to those

in the United States. While these

components appear to be larger in Japan,

they also appear to be supported on more

rigid structures. The differences in design

and installation should be explored.

4. Study of equipment failure next to line

drops There have been failures of

equipment adjacent to line drops. The

drops, which use insulator strings to restrain

the lower end of the line, have very little weight associated with them but there

appears to be interaction problems. The

nature of these problems should be

explored.

5. Study of substation performance with

respect to strong-motion records At least one substation and one power station that

did suffer damage had strong motion

instruments that recorded the earthquake.

It would be very beneficial to review the

performance of equipment at these sites using the response spectra for the site and

more detailed information that could be

derived from site conditions.

6. Study of the relative performance of

spun concrete and wooden poles When a house falls on a pole, it can be expected to

fail, but there appeared to be many concrete

pole failures that are not observed in the

United States with wooden poles. It would

be useful to evaluate the relative

performance of the systems, their advantages

and disadvantages and if the use of the poles

is different in the two counties.

7.3.10 Telecommunications

1. Study of the performance of outside

plant There is a need to get a better

understanding of practices used for outside

plant in Japan and to review in detail, their

earthquake performance. The collection and

analysis of this data on outside plant damage

can provide insight into the outside plant in the United States, particularly in the

Midwest where liquefaction is expected to be

a serious problem.

7.3.11 Hospitals

1. Review to establish guidelines for

minimum levels of service for each lifeline There is a need to review lifeline needs at

critical facilities, such as hospitals, and

establish guidelines for minimum levels of

service for each lifeline. Alternative

facilities and equipment that can mitigate

the effect of the loss of lifeline service

should be evaluated and guidance provided

537
to facility designers. There is a need for

guidelines for the distribution of special

lifelines within hospitals, such as oxygen.

2. Need for different classes of water supply

There is a need to review different classes of

water needs in hospitals and establish

guidelines for technical and administrative

procedures for controlling and reducing

water use in emergency situations.

7.3.12 Post Earthquake Fires

1. Limit ignitions Re-energization of an earthquake damaged area needs to be

coordinated between the different utilities and the emergency rescue and recovery

services. Work needs to be conducted on

the impact of earthquakes on gas service to buildings and appliances. Prior to restoration of electrical service, techniques

or instrumentation needs to be developed to assure that electricity is not restored to damaged structures or areas with natural gas

leaks.

2. Passive fire protection systems There is a need to examine current construction

requirements for fire resistive buildings,

especially the protection of openings such as windows and doorways. Special efforts

should be taken toward materials or systems

which could be retrofit to existing structures. The concepts of fire resistive egress

corridors for cities should continue to be

investigated.

3. Alternative water supplies and delivery

systems Wildland fire agencies utilize a wide variety of methods to move water to the fire location. Their methods should be

examined for applicability to an urban

conflagration.

4. Predictions of post-earthquake fire losses

Case studies of the fire propagation and the

fire suppression activities from this

earthquake could provide a basis for further

post earthquake fire model development.

& U.S. GOVERNMENT PRINTING OFFICE : 1996 0 - 413-662 (QL 2)

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Technical Publications

Periodical

Journal of Research of the National Institute of Standards and Technology—Reports NIST research and development in those disciplines of the physical and engineering sciences in which the Institute is active. These include physics, chemistry, engineering, mathematics, and computer sciences. Papers cover a broad range of subjects, with major emphasis on measurement methodology and the basic technology

underlying standardization. Also included from time to time are survey articles on topics closely related to the Institute's technical and scientific programs. Issued six times a year.

Nonperiodicals

Monographs—Major contributions to the technical literature on various subjects related to the

Institute's scientific and technical activities. Handbooks—Recommended codes of engineering and industrial practice (including safety codes) devel- oped in cooperation with interested industries, professional organizations, and regulatory bodies. Special Publications—Include proceedings of conferences sponsored by NIST, NIST annual reports, and

other special publications appropriate to this grouping such as wall charts, pocket cards, and bibliographies.

National Standard Reference Data Series—Provides quantitative data on the physical and chemical

properties of materials, compiled from the world's literature and critically evaluated. Developed under a worldwide program coordinated by NIST under the authority of the National Standard Data Act (Public

Law 90-396). NOTE: The Journal of Physical and Chemical Reference Data (JPCRD) is published

bimonthly for NIST by the American Chemical Society (ACS) and the American Institute of Physics (AIP).

Subscriptions, reprints, and supplements are available from ACS, 1155 Sixteenth St., NW, Washington, DC

20056.

Building Science Series—Disseminates technical information developed at the Institute on building

materials, components, systems, and whole structures. The series presents research results, test methods, and

performance criteria related to the structural and environmental functions and the durability and safety characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of

a subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often serve as a vehicle for final reports of work performed at NIST under the sponsorship of

other government agencies.

Voluntary Product Standards—Developed under procedures published by the Department of Commerce

in Part 10, Title 15, of the Code of Federal Regulations. The standards establish nationally recognized

requirements for products, and provide all concerned interests with a basis for common understanding of

the characteristics of the products. NIST administers this program in support of the efforts of private-sector

standardizing organizations.

Order the following NIST publications—FIPS and NISTlRs—from the National Technical Information

Service, Springfield, VA 22161.

Federal Information Processing Standards Publications (FIPS PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register. The Register serves as the

official source of information in the Federal Government regarding standards issued by NIST pursuant to the Federal Property and Administrative Services Act of 1949 as amended, Public Law 89-306 (79 Stat.

1 127), and as implemented by Executive Order 1 1717 (38 FR 12315, dated May 11, 1973) and Part 6 of

Title 15 CFR (Code of Federal Regulations).

NIST Interagency Reports (NISTIR)—A special series of interim or final reports on work performed by

NIST for outside sponsors (both government and nongovernment). In general, initial distribution is handled

by the sponsor; public distribution is by the National Technical Information Service, Springfield, VA 22161,

in paper copy or microfiche form.
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