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U.S. Geological Survey

Prepared in cooperation with the National Science Foundation

The Loma Prieta, California,

Earthquake of October 17,1989

Highway Systems

science 

USGS

fora chanoino wnrlH
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The Loma Prieta, California, Earthquake of 

October 17, 1989—Highway Systems

By MARK YASHINSKY

PERFORMANCE OF THE BUILT ENVIRONMENT 

THOMAS L. HOLZER, Coordinator

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1552-B

Prepared in cooperation with the National Science Foundation

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1998
DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

MARK SCHAFER, Acting Director

Any use of trade, product, or firm names in this publication

is for descriptive purposes only and does not imply endorsement

by the U.S. Government

Manuscript approved for publication, 

January 28,1998

Library of Congress catalog-card No. 92-32287

For sale by the

U.S. Geological Survey

Information Services

Box 25286

Federal Center

Denver, CO 80225
CONTENTS

Page

Abstract————————————————————————— 1

Introduction—————————————————————— 1

References———————————————————— 6

Bridge damage—-——————————————————— 6

References———————————————————— 10

Major damage in the city of Oakland—————— 13

San Francisco-Oakland Bay Bridge:

East Bay Crossing———————————— 13

Description of bridge————————— 13

Bridge damage———————————— 14

Analysis of damage—————————— 14

Bridge repair————————————— 16

References——————————————— 17

Cypress Street Viaduct——————————— 19

Description of bridge————————— 19

Bridge damage———————————— 19

Rescue efforts————————————— 19

Testing and demolition———————— 22

New bridge construction——————— 26

References——————————————— 26

Route 980 Southbound Connector-————- 29

Description of bridge————————— 29

Bridge damage———————————— 29

Bridge repair————————————— 31

References——————————————— 32

Port of Oakland Overcrossing——————— 32

Description of bridge————————— 32

Bridge damage————————————— 35

Bridge repair————————————— 35

References——————————————— 35

Distribution structure———————————— 37

Description of bridge————————— 37

Bridge damage———————————— 39

Bridge repair————————————— 39

References——————————————— 39

Fifth Avenue Overhead——————————— 42

Description of bridge————————— 42

Bridge damage———————————— 42

Bridge repair and replacement———— 42

Major damage in the city of San Francisco——— 48

San Francisco viaducts——————————— 48

Southern Freeway Viaduct————————— 48

Description of bridge————————— 48

Bridge damage———————————— 49

Repair and retrofit——————————— 49

References——————————————— 49

China Basin Viaduct———————————— 54

Description of bridge————————— 54

Bridge damage———————————— 56

Repair and retrofit——————————— 57

References——————————————— 57

Page

Embarcadero Viaduct————————— 59

Description of bridge—————— 59

Bridge damage—————————— 59

Description of repairs—————— 59

Terminal Separation ————————— 70

Description of bridge—————— 70

Bridge damage—————————— 71

Testing and removal—————— 71

Central Freeway Viaduct——————— 78

Description of bridge—————— 78

Bridge damage-————————— 78

Alemany Interchange————————— 86

Description of bridge—————— 86

Bridge damage—————————— 86

Work recommended——————— 86

Repair and retrofit——————— 86

Summary of damage to San Francisco

viaducts———————————— 88

Other bridges with major damage————— 88

Route 92/101 Separation—————— 88

Description of bridge—————— 88 

Bridge damage————————— 88 

Damage and repair to the

Northwest Connector——— 89 

Damage to the

Southeast Connector——— 95 

Damage to the

Northeast Connector——— 95

Conclusion———————— 95

Struve Slough Bridges——————— 99

Description of bridge—————— 99

Bridge damage—————————— 99

Bridge replacement——————— 100

References———————————— 102

Grant Undercrossing————————— 105

Description of bridge—————— 105

Bridge damage————————— 105

Mococo Overhead——————————— 107

Description of bridge —————— 107

Bridge damage—————————— 107

Repair and retrofit——————— 110

Napa River Bridge—————————— 112

Description of bridge—————— 112

Bridge damage—————————— 112

Diaphragm damage————— 113

Girder damage———————— 113

Other damage———————— 113

Bridge repairs—————————— 114

Richardson Bay Bridge and Separation— 116

Description of bridge —————— 116

Bridge damage————————— 116

Repair and retrofit——————— 118

III
Page Page

San Mateo-Hayward Bridge———— 123 Damage to culverts—————————————— 180

Description of bridge————— 123 Jetty Road at Moss Landing state beach— 182

Bridge damage———————— 123 Elkhorn Road culverts——————————— 183

Bridge repair and retrofit—— 124 Spanish Ranch Road culverts——————— 183

References—————————— 124 Summit and Morrill Road culverts————— 183

Mora Drive Overcrossing————— 130 Temescal Creek culvert—————————— 183

Description of bridge————— 130 Damage to earth-retaining structures————— 185

Bridge damage———————— 130 Crib wall at Highland Road in Santa Cruz

Bridge testing and repair——— 131 County—————————————————— 185

Bridge motion——————————————————— 135 Soil-nail wall at the University of

Sierra Point Overhead———————————— 136 California at Santa Cruz————————— 185

Description of bridge—————————— 136 Damage to local highway systems—————— 186

Bridge motion—————————————— 137 References—————————————————— 186

Dumbarton Bridge—————————————— 143 Changes to engineering practice—————————— 187

Description of bridge—————————— 143 References——————————————————— 190

Bridge motion—————————————— 146 Conclusion————————————————————— 191

HaywardBayAreaRapidTransitelevatedstructure- 154

Description of bridge—————————— 154

Bridge motion—————————————— 154

San Juan Bautista Route 156/101 Separation— 159

Description of bridge—————————— 159

Bridge motion—————————————— 159

Route 280-680/101 Separation—————— 161

Description of bridge—————————— 161

Bridge motion—————————————— 161

Golden Gate Bridge—————————— 163

References——————————————————— 164 

Highway damage—————————————————— 165 

Damage to roads——————————————— 167 

Damage on State Highway 17————— 167 

Lone Tree landslide on Route 1————— 168 

Eastern approach to the San FranciscoOakland Bay Bridge——————— 170

San Francisco city streets———————— 171

Jetty Road at Moss Landing state beach- 172

Treasure Island————————————— 173 

Sand Hill Road at Interstate 280 near

PaloAlto———————-——-—— 174

Morrill Road at the San Andreas fault— 175

Damage to tunnels—————————————— 176

Webster and Posey Street Tube Crossings- 176

Fort Cronkite Tunnel—————————— 177

Presidio Park Tunnel——-—————— 177

Caldecott tunnel—————————— 177

Tunnel at Geary and Avenue in

San Francisco————————————— 177 

Stockton Street Tunnel (between 

Sacramento and Bush Streets in San

Francisco)——————————————— 177 

Broadway Street Tunnel (between Mason

and Hyde Streets in San Francisco)— 177

IV
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17,1989: 

PERFORMANCE OF THE BUILT ENVIRONMENT

HIGHWAY SYSTEMS

By Mark Yashinsky, 

California Department of Transportation (Caltrans)

ABSTRACT

This paper summarizes the impact of the Loma Prieta 

earthquake on highway systems. City streets, urban freeways, 

county roads, state routes, and the national highway system 

were all affected. There was damage to bridges, roads, tunnels, and other highway structures. The most serious damage occurred in the cities of San Francisco and Oakland, 60 

miles from the fault rupture. The cost to repair and replace 

highways damaged by this earthquake was $2 billion. About 

half of this cost was to replace the Cypress Viaduct, a long, 

elevated double-deck expressway that had a devastating collapse which resulted in 42 deaths and 108 injuries.

The earthquake also resulted in some positive changes 

for highway systems. Research on bridges and earthquakes 

began to be funded at a much higher level. Retrofit programs 

were started to upgrade the seismic performance of the 

nation's highways. The Loma Prieta earthquake changed 

earthquake policy and engineering practice for highway departments not only in California, but all over the world.

INTRODUCTION

The Loma Prieta earthquake occurred on the San Andreas 

fault in the Santa Cruz Mountains of Northern California. 

The earthquake caused damage to roads and bridges within 

about 100 miles of the epicenter including major damage to 

bridges in the cities of San Francisco and Oakland. On two 

bridges, this damage resulted in a tragic loss of life. On the 

Cypress Viaduct in the City of Oakland, 42 people died and 

108 people were injured. One person died and 13 people were 

injured on the nearby East Bay Crossing of the San Francisco-Oakland Bay Bridge. Approximately 100 bridges suffered some damage from the earthquake. Eleven bridges and 

several roads were closed, resulting in traffic problems in 

the weeks and years following the quake.

This report is a summary of how roads and bridges were 

impacted by the earthquake. The main impact was damage 

to roads and bridges. However, there were other effects to 

bridges as well. These include changes to bridge seismic 

design codes, acceleration of California's bridge retrofit program, initiation of bridge retrofit programs in other states 

and countries, changes to emergency response procedures, 

improved methods of analysis, higher levels of bridge research funding, legislation affecting bridges, and changes to 

society's attitudes concerning bridges and earthquakes.

The Loma Prieta earthquake occurred in a remote location and was much smaller than a maximum credible event 

for the area. However, because it interrupted a World Series 

baseball game being played in San Francisco, it caught the 

world's attention. Moreover, although overall damage to the 

state highway system was minimal, there was major damage 

to some important bridges. These facts, as well as the unfortunate loss of life on two bridges, made the California Department of Transportation (Caltrans) a target for criticism 

after the earthquake. Some felt that Caltrans was negligent 

in allowing seismically deficient state bridges to be used by 

the public. Should Caltrans have been aware of any bridges 

that couldn't withstand a large earthquake? Should Caltrans 

have replaced all bridges that were seismically deficient? 

These questions led Governor Deukmejian to create a Board 

of Inquiry to determine why the bridge damage occurred. 

The board spent several months holding hearings to determine what Caltrans' seismic policies were before the earthquake. On May 31, 1990, the board published its report 

"Competing Against Time" (Thiel, 1990). They found that 

Caltrans had been doing a good job of improving their seismic design procedures for new bridges. They felt that the 

major cause of the bridge damage was the low level of funding for Caltrans' seismic retrofit program. They recommended 

that Caltrans increase funding for the seismic retrofit program, fund additional seismic research, utilize more stateof-the-art solutions to protect bridges from future earthquakes, 

and open Caltrans up to external review of its seismic policies.

The State of California has about 24,000 state and local 

bridges, many of which were designed before a rigorous seismic design code was developed. Before the 1971 San 

Fernando earthquake, there was minimal seismic criteria for 

bridges. The San Fernando earthquake was the genesis of 

Caltrans' education into the effects of earthquakes on bridges. 

One of the lessons from that earthquake was that bridge superstructures could fall off hinge and abutment seats. Thus 

Caltrans began the first seismic retrofit program to provide

1
HIGHWAY SYSTEMS

DATE

cable restrainers and shear 

keys on existing bridges to 

prevent them from separating 

at the thermal expansion joints 

during earthquakes. This program cost $54 million and resulted in retrofits to about 

1,265 bridges. The earthquake 

also showed that columns with 

#4 ties at 12 inches were incapable of handling the large displacements that occurred. 

Caltrans changed its design 

criteria to include more tightly 

spaced transverse reinforcement and better reinforcing details between columns and 

footings and bent caps. The 

Whittier-Narrows earthquake 

of 1987 again pointed out the 

need to retrofit older unconfined columns. Caltrans began 

a testing program at the University of California at San 

Diego to evaluate the effectiveness of encasing columns in 

steel shells. Caltrans learns 

from every earthquake and 

uses that knowledge to improve design procedures.

The seismic criteria for 

bridge design in place at the 

time of the Loma Prieta earthquake was far in advance of 

that bejng used by the rest of 

the country. However, the

speed at which Caltrans retrofits older bridges as new 

knowledge revealed their vulnerability is highly dependent on budgetary constraints. Before Loma Prieta, it was 

hard to justify spending a great deal on seismic retrofits 

when there were so many other pressing problems. Before the San Fernando earthquake, there was very little 

bridge damage from any California earthquake. Until 

Loma Prieta, only two people had ever died in California 

from bridge damage during earthquakes. Many more 

people die every year from traffic accidents on the highway system than from bridges collapsing during earthquakes and yet both of these problems are competing for 

the same scarce tax dollars. Since Loma Prieta and the 

recommendations of the Governor's Board of Inquiry, 

Caltrans has made protecting bridges from earthquakes a 

high priority. Before Loma Prieta such a commitment was 

almost impossible in spite of the fact that living where 

earthquakes occur is dangerous. The people of California 

do not have enough money to remove all dangers to sociTable 1.—Chronology of significant events related to the Loma Prieta earthquake

EVENT

9 February 1971

1 October 1987 

17 October 1989

21 October 1989 

23 October 1989

2 November 1989

3 November 1989 

6 November 1989

17 November 1989

18 November 1989 

25 November 1989 

28 November 1989

30 November 1989

13 December 19S9

14 December 1989 

4 January- 1990 

17-18 January 1990 

26 January 1990

8 February 1990 

10 February 1990 

1-2 March 1990 

15 March 1990 

31 May 1990 

17 January 1994 

17 December 1995

15 November 1996

15 November 1998 

31 December 2000

6.6 magnitude San Fernando earthquake occurs (major bridge damage).

Causes major changes to Caltrans' seismic design procedures.

Initiates Phase 1 retrofit program (providing restraint at hinges). 

6.1 magnitude Whittier Narrows earthquake occurs (minor bridge damage).

Initiates Phase 2 retrofit program (providing confinement for single column bents). 

7.1 magnitude Loma Prieta earthquake occurs at 5:04 P.M. (P.S.T.).

(12 state bridges and several highways closed ). 

Rescue effort ends on the Cypress Viaduct.

California Legislature holds special session to address Loma Prieta. 

Route 92/101 Interchange reopens.

Mora Drive Overcrossing reopens (10 state bridges still closed). 

State Route 129 reopens in Watsonville. 

State Legislature appropriates $1 million for seismic engineering research.

State Bill 36X and Assembly Bill 36X signed into law mandating a seismic retrofit

program for all publicly owned bridges. 

East Bay Bridge reopens.

West Grand Avenue Viaduct reopens.

The Distribution Structure reopens (7 state bridges still closed). 

Highway 17 landslide cleared and the road is reopened to traffic. 

China Basin Viaduct reopens (6 state bridges still closed). 

Testimony begins before the Governor's Board of Inquiry (first of seven public

hearings).

Full scale test of portion of Cypress Street Viaduct begins. 

Governor's Board of Inquiry tours damage.

Testimony continues before the Governor's Board of Inquiry (second public hearing). 

Testimony continues before the Governor's Board of Inquiry (third public hearing). 

Testimony continues before the Governor's Board of Inquiry (fourth public hearing). 

Struve Slough Bridge reopens to traffic. 5 state bridges remain closed - Cypress

Viaduct, Central Viaduct (partial), Embarcadero Viaduct, Terminal Separation, and

the Southern Viaduct.

Testimony continues before the Governors Board of Inquiry (fifth public hearing). 

Cypress demolition completed

Testimony continues before the Governors Board of Inquiry (sixth public hearing). 

Testimony concludes before the Governors Board of Inquiry (seventh public hearing). 

Governor's Board of Inquiry publishes its report, "Competing Against Time." 

6.7 magnitude Northridge earthquake occurs at 4:30 A.M. (P.S.T.). 

Southern Freeway Viaduct completely reopened to traffic, however retrofit is still

continuing.

Top deck for Central Viaduct removed. No decision made for retrofit or replacement 

of northern (concrete) portion of structure. 

Rte 880 (Cypress) Viaduct replacement completed (anticipated). 

Anticipated completion of Phase II bridge retrofit program including San Francisco

Bay Toll Bridges.

ety. However, Caltrans is working to reduce the risk of 

bridges collapsing during earthquakes.

The California State Legislature also played an active role after the earthquake. They wanted to ensure that 

the public would be adequately protected against a recurrence of events like the Cypress Viaduct collapse. A special 2-week session was called by the Governor beginning 

on October 23, 1989, to write specific legislation to address seismic safety issues. Simultaneously, the Senate 

Transportation Committee held a hearing in San Francisco 

to gather facts about the bridge damage. Burch Bachtold, 

Director of District 4 (where most of the damage occurred) 

and James Roberts, Chief of the Division of Structures 

testified at the hearing. At the end of the 2-week session, 

on Wednesday, November 6, 1989, the Governor signed 

24 bills that made seismic safety a much higher priority 

in California. The Senate and Assembly passed identical 

bills to speed the legislative process. The most significant 

legislation for highways was Assembly Bill 36X. It ex-
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT

empted earthquake repair work from having to meet the usual 

time-consuming permit processes. This enabled repairs of 

the damage to begin quickly. It also allocated a quarter-cent 

sales tax that helped raise money to seismically retrofit vulnerable bridges. The most significant events related to highway systems after the earthquake are listed in table 1.

After the earthquake, Caltrans' first task was to identify 

the damaged state and local bridges and to determine what 

repairs were needed before they could be reopened. To understand how Caltrans' emergency response worked after 

Loma Prieta requires an explanation of how Caltrans is organized. Caltrans divides the State of California into 12 Transportation Districts. Most of the earthquake damage occurred 

in District 4 (fig. 1). District transportation engineers work 

out of an office located in each District. District 4's office 

was located in San Francisco at the time of the earthquake. 

The District Director is in charge of district personnel and 

signs all the contracts for work done in their District.

Bridge maintenance engineers have three offices. Bridge 

Maintenance South is located in Los Angeles, Bridge Maintenance North is located in Sacramento, and Toll Bridge 

Maintenance is located at the Bay Bridge Toll Plaza. Bridge 

maintenance engineers are responsible for the inspection and 

evaluation of all state and local bridges, and the maintenance 

of state bridges once construction is completed. Each bridge 

maintenance engineer is assigned responsibility for the 

bridges in their transportation district. If the maintenance 

engineer requires traffic control or a manlift, the engineer 

will usually ask a district maintenance crew for help.

Bridge construction engineers have a main office in Sacramento; however, they typically work from a field office 

next to their construction site. They are responsible for overseeing the work of contractors on bridge projects. If the work 

involves roads and bridges, a district construction engineer 

will have overall responsibility for the project and the bridge 

construction engineer will be responsible for any structures 

on the project. Bridge design engineers work from an office 

in Sacramento and design structural facilities on state roads. 

All bridge maintenance engineers, bridge construction engineers, and bridge design engineers work for the Division of 

Structures. The Chief of the Division of Structures at the time 

of the earthquake was James E. Roberts.

District transportation engineers have general responsibility to ensure that all transportation systems are functioning in their district. Most of the responsibility for bridges 

comes from the Division of Structures in Sacramento. Consequently, coordination between District and Headquarters 

staff was required after the earthquake. This coordination 

required good communication, especially between field and 

office personnel. Immediately after the earthquake, most of 

the damaged bridges were identified by District maintenance 

crews, California Highway Patrol officers, and bridge construction engineers. This was because they were in the area 

and could quickly examine the bridges nearby. They closed 

the structure if it was deemed hazardous and contacted DisEPICENTER

Figure 1.—Map of state highway districts (numbered) impacted 

by the earthquake.

trict office personnel who would then contact bridge maintenance. Most field personnel were equipped with mobile twoway radios.

Immediately after the earthquake, electricity, phone service, and the radio transmitter were all inoperative at District 4's office. One of the lessons learned from the earthquake 

was how effective cellular phones and pagers were for communication with field personnel. Unfortunately, they were a 

scarce commodity in the days immediately following the 

earthquake. To improve communication, an emergency command center was set up in the office at the Caldecott Tunnel. 

This center had superior radio equipment for communicating with field personnel. Even so, the mobile radio band was 

so jammed after the earthquake that a new band had to be 

found for Caltrans' staff. After a few days, bridge maintenance set up headquarters at the Cypress Viaduct to manage 

the inspection and repair effort. However, due to the distractions imposed by the rescue effort at Cypress, the bridge 

maintenance command center eventually moved to the Bay 

Bridge Toll Plaza. All of the staff from bridge maintenance 

north as well as six engineers from bridge maintenance south 

participated in the inspection effort. Every morning all bridge 

maintenance engineers were given state routes to inspect. They drove along the route with a log book and 

checked off each bridge as they completed an inspection report. They also inspected all county and city
HIGHWAY SYSTEMS

bridges. Maintenance engineers also completed inspections for all of the Bay Toll Bridge Crossings.

After the bridge maintenance engineer determined 

what was needed to temporarily or permanently repair 

a damaged bridge, an emergency contract would be 

created by the District Director. The ability to quickly 

write contracts and obtain money to pay contractors 

was essential to expedite bridge repair and reopen damaged bridges after the earthquake. California's legislature passed a bill to allow Caltrans to forego (for a 

limited time) the lengthy process of obtaining environmental documents so they could quickly make repairs 

and reopen bridges. Moreover, the District Director 

could hire contractors and write emergency force account contracts that would bypass the process of advertising contracts and evaluating bids, which can take 

many weeks. A force account pays a contractor for labor, equipment, and materials at the direction of a 

Caltrans' engineer, usually at a higher rate than would 

normally be allowed. The repair of most bridges immediately after the earthquake was made with force account contracts. The Bay Bridge was repaired in 30 

days with a force account contract. A special contract 

with an incentive clause for early completion was written to replace the Struve Slough Bridges in Watsonville. 

Contractors from the Bay Area immediately began shoring damaged bridges, on occasion, even before an inspector had a chance to examine the bridge. Hard work 

on the part of many individuals helped the Bay Area 

recover so quickly. Several interesting reports describe 

how the Bay Area turned to trains, ferries, and other 

forms of mass transit after the earthquake (Bennett, 

1991; Fahey, 1991).

Money for emergency repairs was available on federal aid roads from the Federal Highway Administration (FHWA) (table 2). The United States Congress 

appropriated $1.37 billion of emergency relief funds 

for the repair of roads and bridges. On those roads not 

eligible for FHWA funding, the State Office for Emergency Services (OES) and the Federal Emergency Management Agency (FEMA) provided funds for 

earthquake repairs. These funds are appropriated by the 

Congress of the United States after an emergency and

are used not only for road repairs but also to repair 

public buildings and other public facilities. FEMA and 

FHWA money was available to both state and local 

bridges. However, the vast majority of state roads and 

bridges are repaired with FHWA funds, while the majority of local agency repairs are made with FEMA 

money. The cost to repair or replace damaged bridge 

structures after the earthquake was about $1.7 billion. 

However, the replacement of the Embarcadero Viaduct, 

Terminal Separation, and a portion of the Central Viaduct may never occur due to opposition from the city 

of San Francisco. The cost to repair roads was an additional $0.3 billion. Table 2 shows how the federal emergency relief funds were allocated to repair the damage. 

An additional $0.33 billion came from the state of California. These costs do not include retrofitting or replacing seismically deficient structures in the Bay Area 

after the earthquake. To put these costs in perspective, 

we can compare the costs to the highway system from 

other recent earthquakes as shown in table 3. What is 

particularly worrisome about the Loma Prieta earthquake is that most of the highway damage occurred so 

far from the fault rupture.

Most of the bridges with major damage were closed 

at least temporarily after the earthquake. All of the 

double-deck viaducts in San Francisco with the exception of the Alemany Interchange were closed due to 

column cracks. Some bridges, like the eastern portion 

of the San Francisco-Oakland Bay Bridge and the 

Struve Slough Bridge were reopened in record time. 

Other bridges, like the Cypress Street Viaduct and the 

Southern Freeway Viaduct, were still undergoing repair or replacement 6 years after the earthquake. Finally, structures such as the Embarcadero Viaduct and 

Terminal Separation were demolished with little chance 

of ever being rebuilt. A combination of politics, economics, and the state of bridge research were powerful 

forces affecting the fate of each damaged bridge.

After any earthquake, two groups from Caltrans 

are responsible for making a thorough investigation of 

bridge damage. Bridge maintenance engineers record 

the damage so that they can maintain their bridges and 

finance repairs. Caltrans' Post Earthquake InvestigaTable 2.—Cost to the Federal government of repair to highway system

Type of Repair Federal Highway Administration 

funds, in millions of dollars

Replace Embarcadero and Terminal Separation.

Replace Central Viaduct.

Other Bridge Repair and Replacement.

State Highway Repair.

City and County Roads and Bridges.

120

40

910

280

21
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 

Table 3.—Bridge repair costs after recent earthquakes

Earthquake

1989LomaPrieta 

1994Northridge 

1995 Kobe, Japan

Cost

$1.7 billion 

$0.3 billion 

$6.5 billion

tion Team (PEQIT) records bridge damage as a way of 

evaluating current seismic design procedures and as a 

record for future research. A report of the PEQIT investigation after the Loma Prieta earthquake is available in Zelinski (1994). A third group, from the Federal 

Highway Administration (FHWA), accompanies bridge 

maintenance engineers and writes their own report to 

justify federal emergency funding.

Other groups from around the world rushed to California to make a record of earthquake damage. The National Institute of Standards and Testing (NIST) 

produced an excellent report on bridge damage (Lew, 

1990). The Earthquake Engineering Research Institute 

(EERI) also has an excellent report (Benuska, 1990). 

Countries from Asia and Europe also recorded the damage (Kawashima, 1990).

Another interesting report, put together by Caltrans 

Transportation District 4, was an oral history of the 

earthquake. This report is the transcribed record of 

hundreds of recorded interviews taken in the days following the earthquake. The interviews offer a look at 

the experiences of many of the people involved in the 

emergency response after the earthquake. Secretaries 

and district directors, maintenance workers, and ferry 

boat operators are all included. The transcribed record, 

many thousands of pages long, is currently being summarized under a contract with the University of California and will be a great resource for a variety of 

researchers.

Not only was Caltrans busy repairing damaged 

bridges after the earthquake, but the seismic retrofit of 

existing bridges became Caltrans' number one priority. In fact, the line between repair and retrofit became 

somewhat vague. For instance, Caltrans expedited the 

retrofit and repair of several of the double-deck bridges 

in San Francisco in an attempt to get these structures 

back into operation as soon as possible. Several contracts were written for consultants to make Plans, 

Specifications, and Estimates (PS&E) to retrofit China 

Basin, Southern Freeway, and others. However, those 

retrofits were eventually rejected by a special Peer 

Review Panel chosen to review retrofits to the doubledeck bridges in San Francisco. The cost to the state of 

California was several million dollars. Robert Cassano 

of the Peer Review Board and former Chief of the Division of Structures writes (Cassano, personal 

commun., 1993):

Although it is very understandable, considering the transportation crises created by the loss of these viaducts, it is none-theless unfortunate that considerable money was spent developing 

detailed plans and performing construction work that was subsequently discarded. This happened because of concerns that 

performance objectives would not be met using the original retrofit schemes or because of political factors. (I consider the 

demolition of the Embarcadero Viaduct and portions of the Central Viaduct to be political decisions.) With the perfect vision 

afforded by hindsight, it seems that more time should have been 

spent on conceptual studies and in building a consensus with 

local jurisdictions rather than rushing headlong into the final 

design phase.

The politics that Mr. Cassano refers to was the opposition to elevated expressways in the city of San Francisco. 

Caltrans spent much time and effort redesigning the Terminal Separation, now with little chance for its reconstruction. Thus, Mr. Cassano felt that more time should have 

been spent testing the political waters before proceeding 

with design.

James Roberts, Chief of the Division of Structures at 

Caltrans along with Deputy Director William Schaefer and 

Public Affairs Officer James Drago became spokespersons 

for Caltrans after the earthquake. In the weeks and months 

that followed the earthquake, they presented to reporters, 

state legislators, and the Governor's Board of Inquiry how 

Caltrans had been in the forefront of seismic related research and design since the 1971 San Fernando earthquake 

had shown the damage a large earthquake could inflict on 

transportation facilities. It soon became apparent that 

Caltrans' seismic design code was more than adequate and 

that the major problem had been a low level of funding 

for seismic retrofits of older bridges. However, that situation soon changed, as the State Legislature held hearings, 

passed laws, and appropriated funds to retrofit bridges 

deemed vulnerable to collapse or major damage from a 

large earthquake.

The Loma Prieta earthquake alerted the world to the 

effects a large earthquake can have on a modern metropolitan area. It changed seismic policy for cities, states, 

and countries around the world. The Federal Highway Administration made changes to its bridge specifications that 

all states would follow. Many countries sent investigation 

teams to write reports and make recommendations based on 

what they learned. Cities examined their emergency procedures, retrofitted vulnerable structures, and changed their design codes. Caltrans began an ambitious research program
HIGHWAY SYSTEMS

that has advanced the state of knowledge of earthquake engineering.

REFERENCES

Bennett, A. K., 1991, The Loma Prieta 

earthquake and employer-based 

transportation programs: Institute of 

Transportation Studies (ITS) Review, 

v.l 4, no. 2, p. 4-6.

Benuska, Lee, 1990, Loma Prieta earthquake reconnaissance report: Earthquake Spectra, v. 6 (suppl.), no. 

90-01,448 p.

Fahey, M.R., and Gray, G., 1991, Bay Area 

emergency ferry service: transportation relief after the October 17,1989 

earthquake: National Research Council, Washington D.C., Transportation 

Research Board Paper 910782, 27 p.

Kawashima, K, 1990, Damage of bridges 

and overcrossings by the 1989 Loma 

Prieta, California earthquake: 

Tsuchi-to-kiso, v. 38, no. 11, p. 25- 

32.

Lew, H.S., 1990, Performance of structures 

during the Loma Prieta earthquake of 

October 17,1989: NIST Special Publication 778, 201 p.

Thiel, Charles, 1990, Competing against 

time: State of California, Office of 

Planning and Research, 264 p.

Zelinski, Ray, 1994, Loma Prieta Earthquake PEQIT Report: California Department of Transportation.

Figure 2.—Thickness of San Francisco Bay mud in feet (Goldman, 1969).

BRIDGE DAMAGE

Bridge damage from the Loma Prieta earthquake occurred over a large area and more than 100 miles from the 

earthquake epicenter. Some of the contributing factors to 

this damage were as follows:

Most of the Bridge Damage Occurred Where There Was Soft Soil

The Cypress Viaduct collapse occurred where the structure was supported on loose fill over Bay mud (fig. 2). There 

was no damage to portions of the freeway on firmer material. The damage to the San Francisco-Oakland Bay Bridge

was a result of a combination of soft soil and flexible piles. 

All of the doubled-deck viaducts (fig. 3) except for the Central Freeway Viaduct were on soft soil. This includes the 

Embarcadero, Terminal Separation, China Basin, and Southern Freeway Viaducts, all of which suffered major damage 

during Loma Prieta. These bridges were over 60 miles from 

the epicenter, but the soft soils amplified the earthquake 

motions causing damage to these long, flexible structures.

The collapse of Struve Slough, near Watsonville, occurred in what is essentially a swamp. The deep soft soil 

pushed the pile extensions away from the bent caps. The 

Napa River Bridge, although over 100 miles from the epi-
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 7

SAN FRANCISCO 

DOUBLE DECK SITES

EMBARCADERO 

VIADUCT

TERMINAL 

SEPARATION

SOUTHERN FREEWAY 

VIADUCT

Figure 3.—Location of San Francisco double-deck viaducts.
HIGHWAY SYSTEMS

center, sustained substantial damage due to the long-period motion which was amplified by soft soil. Of the 2,000 

state bridges affected by the earthquake, only 20 suffered 

significant damage and 17 of those were on poor soils. 

This means that 85 percent of the heavily damaged bridges 

were on poor soils.

Most of the Damage Occurred to Bridges Built Before 

the 1971 San Fernando Earthquake

With the exception of the Route 980 Southbound Connector OC and the Route 92/101 Interchange, all of the 

state bridges with over $100,000 in damage as a result of 

the Loma Prieta earthquake were older bridges, without 

post-San Fernando seismic details. The San FranciscoOakland Bay Bridge sustained its most devastating damage when the portion of the bridge east of Pier E-9 moved 

away from the pier, shearing all the bolts connecting it to 

the pier and dropping the top and bottom spans onto a 

platform on Pier E-9. Almost all the other major damage 

was the result of insufficient concrete reinforcement (particularly confinement reinforcement) that allowed columns, joints, and pins to suffer damage, pile extensions 

and precast girders to pull out of bent caps, and shear keys 

and hinge diaphragms to shatter. Research and new concrete details were developed in the 1970's that prevented 

serious damage to newer bridges.

Most of the Serious Bridge Damage Occurred in the Cities 

of San Francisco and Oakland

Of the 20 bridges that suffered major damage, six were 

in Oakland and six were in San Francisco, both 60 miles 

from the rupture, illustrating how site amplification and focusing of ground motion can damage bridges far from the 

earthquake hypocenter. Because cities are often the location

of elevated freeways, complicated interchanges, and 

unengineered fills, urban areas are particularly vulnerable to 

highway damage during large earthquakes.

Most of the Damage Was the Result of Inadequately Designed Connection Details

Almost all of the serious bridge damage was the result 

of problems in transferring forces between vertical and horizontal elements. This was a problem for both steel and reinforced concrete members. Outrigger joints cracked, pinned 

connections shattered, moment connections sheared, bolted 

connections broke, and development rebar pulled out (fig.

Figure 4.—Damage to outrigger knee-joint on Route 980 Southbound Connector. Figure 5.—Location of bridges with over $ 100,000 in damage.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT

4). Much of the research after the earthquake focused on 

improving these connections.

There were 20 state-owned bridges that suffered over 

$100,000 in damage during the Loma Prieta earthquake. This 

damage varied from complete collapse to cracks and spalls 

that were expensive to repair but had no impact on system 

performance. Table 4 and figure 5 provide geographical and 

other information about these bridges.

There were 40 state-owned bridges that suffered between 

$5,000 and $ 100,000 in damage during the earthquake. Table

Table 4.—State bridges with over $100,000 of damage

5 and figure 6 provide details on these bridges. A few of 

these bridges had serious enough damage to require temporary closure.

There were also many state-owned bridges that had damage of less than $5,000 to repair. Most of this minor damage 

was a result of bridge movement, particularly at expansion 

joints and bridge approaches that resulted in bearing damage 

and minor spalls. The occurrence of minor bridge damage was 

more general and covered a wider area than major bridge damage. Although most of the damage was confined to older bridges,

BRIDGE COUNTY 

LOCATION # 

(see fig. 5)

ROUTE POST BRIDGE NAME 

MILE

STATE 

BRIDGE

#

EPICENTRAL SOIL 

DISTANCE 

(miles)

YEAR 

BUILT

DAMAGE

15

16

17

SOL 037 R07.39

MRN 101

CC

ALA

ALA 580

SF

04.03

680 24.26

080 01.15

30.38

46.09

7

8

9

10

11

ALA

ALA

ALA

SF

SF

080

880

980

280

480

02.41

32.39

00.01

R04.40

L00.01

Port of Oakland OC 33-1261 60.0

Cypress Street Viaduct 33-178 58.9

Route 980 South Connector 33-483f 57.6

Southern Freeway Viaduct 34-046 56.9

Terminal Separation 34-054 59.0

480 00.54

SCR 001 17.19

SCR 001 R01.59 

SCL 280 13.12

Napa River Bridge 23-064 78.6 Poor 66 Superstructure shifted

longitudinally. Restrainers 

damaged. 

Richardson Bay Bridge 27-010 68.7 Poor 57 Bearings, restrainers, bent caps,

and columns damaged. 

MococoOH 28-171 70.0 Poor 62 Hinges and earthquake

restrainers damaged. Cracks in 

piles.

East Bay Bridge 33-025 60.0 Poor 36 Top and bottom decks fell at pier

e9. Anchor bolt and bearing 

damage. Large bridge movement. 

Fifth Avenue OH 33-027 56.4 Poor 48 Columns, bent caps, bearings,

and substructure damaged. 

Distribution Structure 33-0611 58.1 Poor 35 Bent caps and columns

damaged.

Poor 66 Bents and columns damaged. 

Poor 57 Upper deck collapsed. 

Good 85 Two outrigger bents damaged. 

Poor 64 Bent and column damage. 

Poor 55 Bearings on steel spans

damaged. Bridge shored and 

closed. 

Embarcadero Viaduct 34-055 59.4 Poor 55 Column damage to bents 72

through 74. Bridge shored and 

closed.

Alemany Interchange 34-070 56.6 Poor 60 Minor cracks. 

Central Viaduct 34-077 59.0 Good 55 Bent and column damage. Bridge

closed. 

China Basin Viaduct 34-0100 57.7 Poor 71 Bent and column damage. Bridge

closed. 

Poor 67 Spalls on concrete trestle and

misc. Steel damage. 

Poor 86 Bearing and expansion joint

damage.

36-075! 8.1 Poor 56 Damage to bearings and curtain

walls.

36-088! 10.8 Poor 65 Complete collapse.

37-235 23.9 good 67 Superstructure moved 4 inches

longitudinally. Restrainers 

damaged. Column cracked.

SF 280 R04.07 

SF 101 R04.2S

SF 280 R06.61

SM 092 R14.44 San Mateo-Hayward Bndge 35-054 43.2

SM 092 R11.78 Route 92/101 Separation 35-252! 42.8

Grant UC

Struve Slough 

Mora Drive OC
10 HIGHWAY SYSTEMS

Figure 6.—Location of state bridges with between $5,000 and $10,000 in 

damage.

several newer bridges also sustained minor damage. This type 

of damage is considered inevitable for bridges in seismic areas 

as expansion joints bang together and approach fills settle. There 

was also some damage to city, county, and privately owned 

bridges. Table 6 and figure 7 provide details on these bridges. 

This was generally minor damage with the exception of a few 

bridges near the epicenter.

In addition, railroad bridges owned by the Southern Pacific 

Transportation Company and by the Atchison, Topeka, and Santa 

Fe Railway Company sustained some minor damage (fig. 8). 

Three timber pedestrian bridges owned by the city of Palo Alto 

were damaged and closed after the earthquake. There was even 

some bridge damage in state parks and recreation areas. The 

San Lorenzo River Bridge (Big Tree Bridge) in Henry Cowell 

State Park sustained some minor damage. Abutment #4 moved 

backward several inches and had some spalls. The Forest of 

Nisene Marks and Mt. Diablo State Park had some minor damage to trail bridges. Surprisingly, there was no damage to bridges 

owned by some local and private agencies. Of particular note 

was the absence of damage to the Bay Area Rapid Transit 

(BART). This absence was particularly fortunate because it allowed commuters an alternative method of transit across the 

Bay and into San Francisco, while the San Francisco-Oakland 

Bay Bridge and other important structures were closed after the 

earthquake. San Francisco's Municipal Railway (which includes 

the cable car system) was also back in operation once electricity 

was restored. Finally, the Golden Gate Bridge, owned and operated by the Golden Gate Bridge Highway and Transportation 

District, went through the earthquake unscathed. 

On the following pages, each state-owned bridge 

that sustained major damage from the Loma Prieta 

earthquake is described in some detail. The term 

"bridge" is used as a generic title for structures used 

to carry a variety of things over a variety of obstacles. 

These structures actually have specific names depending on what is crossing them and what is below 

them. Table 7 provides some of the more common 

names and abbreviations for the different bridge 

structures.

There is a large amount of information available about many of the state-owned bridges that suffered significant damage during the earthquake. Only 

the most essential data is provided in this report. For 

those seeking more information, a brief list of reports that describes the bridge damage in more detail is given at the end of each main section.

REFERENCES

Goldman, Harold B., 1969, Geologic and engineering 

aspects of the San Francisco Bay fill: California 

Division of Mines and Geology Special Report 

97, 130 p.

Figure 7.—Location of city and county bridges damaged during the earthquake.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 11

Table 5.—State bridges with $5,000 to $100,000 of damage

MAP 

LOCATION # 

(see fig 6)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

COUNTY

cc

cc

ALA

ALA

ALA

ALA

ALA

SF

SF

SM

SM

SM

SM

SM

SM

SM

SM

SCR

SCR

SCR

SCL

SCL

SCL

SCL

SCL

SCL

SCL

SCL

SCL

SCL

SCL

SCL

SCL

SCL

SCL

SCL

SCL

SBT

MON

SCL

ROUTE

004

242

080

580

580

980

084

480

001

280

001

001

092

001

280

380

092

152

001

001

101

101

017

017

880

017

101

085

280

280

280

101

101

101

152

101

101

101

001

280

POST 

MILE

R14.61

R03.24

03.79

45.23

45.14

01.98

R29.68

04.51

06.18

R0.01

17.90

R44.88

R13.83

R46.65

R00.30

05.73

T12.78

01.94

10.01

R02.68

R00.70

00.01

05.43

01.14

05.34

06.55

43.85

R18.49

17.78

18.38

R02.87

R04.94

R04.94

R05.08

R09.91

R19.21

03.25

05.21

96.44

11.50

BRIDGE NAME

Route 4/242 Separation

West Connector OC

Powell Street DC

North Connector Viaduct

580/w980 South Connector

East Connector Viaduct

First Street Separation

Marina Viaduct

West Pacific Avenue UC

Alpine Avenue UC

San Gregorio Creek Bridge

Milagra Drive POC

Foster City Lagoon

South Connector OC

San Francisquito Creek

Huntington Avenue OH

Mariners Island OC

Corralitos Creek

Aptos Creek Bridge

Connector Separation

Sargent Bridge and Overhead

Pajaro River Bridge

Sidehill Viaduct

Madrone Drive UC

Coyote Creek Bridge

Main Street OC

Lawrence Expressway OC

West Connector OC

Arastradero Road UC

Page Mill Road UC

Bird Avenue OC

Monterey Road UC

Monterey Road UC

South Gilroy OH

10th Street Separation

Coyote Creek Bridge

Route 101/25 Connector

San Benito River Bridge

Elkhorn Slough

Foothill Expressway

STATE 

BRIDGE #

28-243S

28-249g

33-020

33-302h

33-303h

33-304g

33-398

34-014

34-015

35-0091

35-030

35-188

35-1891

35-204f

35-2341

35-253

35-284

36-001

36-011

36-084f

37-006!

37-007

37-029

37-059

37-065r

37-117

37-152

37-228f

37-251 r

37-252k

37-267

37-3041

37-304r

37-305r

37-325

37-349r

37-475 g

43-0041

44-074

37-2391

EPICENTRAL 

DISTANCE

68

68

60

59

59

59

47

62

62

31

35

54

43

55

31

51

43

11

4

10

20

21

14

10

24

14

26

23

29

29

20

18

18

18

18

15

20

21

17

24

YEAR 

BUILT

78

78

54

70

70

70

65

36

39

69

31

65

67

72

69

71

77

36

48

67

70

41

40

38

52

55

61

67

67

69

69

73

73

73

72

80

89

32

85

67

DAMAGE

Abut. 1 joint damage

Joint seals damaged

Approach slab damage

Hinge diaphragm damage

Crack in C-bent

Crack in C-bent

Cracks in Bent 2 column

Hinge cracks Bents 37-39

Gunite soffit fell Bent 4

Abut. & soffit cracks

Wingwall cracks

Minor crack at Column 2

Column cracks

Spading at Bent 3

Backwall, soffit cracks

Curtain wall damage

Spalls at Pier 2

Cracks in piles

Curtain wall cracks

Abutment 1 shifted

Column & girder cracks

Expansion joint damage

Bearing seats damaged

Abutments rotated

Abut. 4 approach settled

Abut. 3 & bin wall cracks

Cracks and spalls

Cracks and spalls

Column cracks

Column cracks

Abut approach buckled

Barrier rail, approach slab, & jt

seal damage

Appr. Slab & joint damage

Approach slab damage

Slope paving damage

Abutment 4 approach settled &

misc. Cracking

Hinge damage

Pile & girder cracks

Concrete column spalls

Slope paving damaged
12 HIGHWAY SYSTEMS 

Table 6.—City and county bridges damaged during earthquake

Local Bridge

7th street bridge

Fruitridge Avenue Bridge

3rd Street Bridge

3rd Stree.t Bridge

Geary Street P 0 C

San Jose Street P 0 C

East Grand Avenue OH

Produce Avenue Bridge

San Mateo Road Bridge

HickeyBlvd OC

Foster City Blvd Bridge

Shell Blvd Bridge

Hillsdale Blvd Bridge

Beach Park Blvd Bridge

Riverside Bridge

Ocean Village Bridge

Soquel Bridge

San Lorenzo River Bridge

Corrahtos Creek Bridge

Zayante OH

Aptos Creek Bridge

Spreckles Road Bridge

Rodeo Gulch Bridge

Soquel Creek Bridge

Almitos Creek Bridge

Rundell Creek Bridge

Uvas Creek Bridge

Los Gatos Creek

Llagos Creek Bridge

San Antonio Road Overhead

Cliff Drive Bridge

Pajaro Creek Bridge

Elkhorn Road OH

Owner

City of Oakland

Alameda County

City of San Francisco

City of San Francisco

City of San Francisco

City of San Francisco

South San Francisco

South San Francisco

South San Francisco

South San Francisco

Foster City

Foster City

Foster City

Foster City

City of Santa Cruz

City of Santa Cruz

City of Santa Cruz

City of Santa Cruz

Santa Cruz County

Santa Cruz County

Santa Cruz County

Santa Cruz County

Santa Cruz County

Santa Cruz County

City of San Jose

Santa Clara County

Santa Clara County

Santa Clara County

Santa Clara County

City of Mountainview

City of Capitola

City of Watsonville

Monterey County

Map Location # 

(see fig. 7)

1

2

3

4

5

6

7

8

g

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

State 

Bridge #

33C-149UR

33C-147

34C-027

34C-024

34C-043

34C-14

35C-148UR

35C-021

35C-048

35C-032

35C-070UR

35C-070

35C-068

35C-062UR

36C-099

36C-100

36C-105

36C-102

36C-081

36C-092

36C-075

36C-113

36C-042

36C-078

37C-808

37C-174

37C-177

37C-584

37C-167

37C-120

36C-110

44C-55

44C-33

Epicentral 

Distance (mi)

567

544

587

566

603

572

51 3

51 3

51 3

542

41 4

41 5

41 6

41 6

8.7

87

87

87

90

100

40

42

5.8

50

122

12.7

157

11 0

10.0

289

57

11.5

13.4

Damage or repair cost

Approach settlement

$8,778

$5,500

$33,783

Minor column cracks

Movement (very minor)

Spalls at pier & abutment

Wingwall damage

Sidewalk crack @ abut.

Damage at abut 1

Bridge movement

Bridge movement

Spalhng at shear keys

Settlement and spalls

Major damage - closed

Major damage to piers

Cracks to second pier

Abutment damage

Minor cracks

Settlement and hinge spall

Cracks above arch

Approach settlement

Cracks in abutments

Approach settlement

Abut. Shear key damage

Abut backwall cracks

Hinge and abut damage

Pier & abut damage

Pier & abut, damage

Sheared hinge bolts

Approach settlement

Pier and abut, damage

Approach settlement, spalls at

abutments & girders

Table 7.—Functional classification of bridge structures

Bridge Type Description______________________

Usually reserved for structures over water.

A structure carrying a highway over a railroad.

A structure carrying a railroad over a highway.

A structure carrying a local road over a highway.

A structure carrying the highway over a local road.

A separation in grade between two highways.

Structures connecting intersecting roadways.

A low structure over a body of water.

A long structure carrying a highway over many obstacles.

A structure carrying water over many obstacles.

A structure carrying a pipe over a highway.

A structure for carrying people._______________

Bridge (BR)

Overhead (OH)

Underpass (UP)

Overcrossing (OC)

Undercrossing (UC)

Separation (SEP)

Interchange

Causeway

Viaduct

Aqueduct

Pipeline Overcrossing

Pedestrian Overcrossing (POC)
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 13

MAJOR BRIDGE DAMAGE IN THE CITY OF 

OAKLAND

SAN FRANCISCO-OAKLAND BAY BRIDGE: EAST BAY 

CROSSING

DESCRIPTION OF BRIDGE

The San Francisco-Oakland Bay Bridge (figs. 9 and 

10) is actually two separate bridges: a suspension bridge 

on the west side of Yerba Buena Island and a truss bridge 

on the east side of the island (there are also two approach 

structures and a tunnel at Yerba Buena Island). Both 

bridges have an upper and lower five lane deck. Construction was completed on these bridges in 1936. The East 

Bay Crossing is composed of five different segments. From 

Yerba Buena Island there are four 288-foot-long simple 

span trusses (Pier YB1 to El), then a 2,400-foot-long cantilever truss (Pier El to E4), five 504-foot-long simple span 

trusses (Pier E4 to E9), fourteen 288-foot-long simple span 

trusses (Pier E9 to E23), and 16 simple span steel and concrete girder spans for the eastern approach (Pier E23 to 

E39). Concrete Piers YB1 and El are founded on sandstone; steel diagonally braced bents are on spread footings at YB2 to YB4 and on concrete caissons from Piers 

E2 to E5. Steel diagonally braced bents from Piers E6 to 

El6 are on timber piles, and concrete piers from El7 to 

E23 are on timber piles. Pier E9 is a very stiff four-legged 

tower that acts as an anchor for the more flexible piers 

east of the cantilever. Fixed and expansion truss shoes atFigure 8.—Location of railroad bridge damage (courtesy of 

American Railway Engineering Association).

Bridge #33-25 / Route 80 / Post Mile 1.15 

Approximate Latitude & Longitude 

N. Lat. 37° 48.7' W. Long. 122°21.7'

Epicentral Distance 

60 miles

Peak Ground Accel. N/S U/D E/W 

Sandstone on west end 0.06 0.03 0.03 

Bay mud at east end 0.29 0.07 0.27

Length Width Skew Year Built 

22,654' 63.3' 0.00° 1936

Main Span Type

Double deck through steel truss

Average Daily Traffic = 253,400

Figure 9.—The San Francisco-Oakland Bay Bridge 

(East Bay Crossing in background).
14 HIGHWAY SYSTEMS

tach the superstructure to the substructure. Expansion joints 

for temperature movement are located above the double towers atYBS, E4, and El 1. The ground varies from Franciscan 

sandstone at the surface of Yerba Buena Island to over 500 

feet of Bay mud at the eastern approach.

The East Bay Crossing was seismically retrofitted in 

1976. Rod and tie-down restrainers were installed at the east 

approach from Pier E23 to E38. Steel girder restrainers were 

installed at the expansion truss shoes at Piers El7 to E22. 

Figure 11 shows the geology that supports this structure. This 

drawing is based on borings that were done in San Francisco 

Bay in 1995 as part of the effort to retrofit the bridge in 1996.

The bridge motion during the earthquake was highly influenced by the change in geology from rock at the west end 

of the bridge to 500 feet of alluvium at the east side of the 

bridge. This dramatic change in stiffness meant that the east 

side of the bridge moved much more during the earthquake. 

This is reflected in the ground motions recorded near the 

site. The ground on the west side of the bridge had a peak 

acceleration of 0.06 g while the east side had aPGA of 0.29 g. 

Apparently, the high-frequency motion was filtered out by 

the time it reached the bridge and only the long frequency 

motion arrived at the bridge to accelerate the Bay mud over 

the deep alluvium.

BRIDGE DAMAGE

Except for a few minor problems on the West Bay Crossing, all of the earthquake damage occurred on the East Bay 

Crossing. The most significant damage was at Pier E9 where 

the top and bottom decks were pulled off their seats, causing 

them to fall onto a platform and electrical building near the 

top of the pier (fig. 12). The rest of the damage occurred 

from Piers El7 to E23 where anchor bolts failed, earthquake 

restrainers were damaged, stringers moved on their seats, the 

concrete pedestal at El 7 rocked, and expansion joints spalled.

The movement of the decks at Pier E9 was the result of 

all 20 high-strength bolts at each of the east truss shoes breaking (fig. 13). This allowed the superstructure trusses on the 

east side of Pier E9 to move approximately 10 inches to the 

east and 5 inches to the north. The decks at Pier E9 are supported on steel stringers that rest on 6-inch steel angles bolted 

to large floor beams. When the trusses moved to the east, the 

stringers were pulled off the angles on the west end. The 

stringers remained on the bearing seats at the east end, which 

were bent as the west side fell.

The north and south fixed truss shoes at Piers El 8 to 

E22 had all 1 2 one-inch-diameter bolts broken at each pier 

connection to the concrete pedestals. When the fixed shoes 

broke free, the expansion side of the trusses slammed into 

the steel girder restrainers (fig. 14). These restrainers apparently prevented the trusses from falling off the concrete pedestals, at least for the moderate forces generated from this 

earthquake. Elastomeric pads absorbed the impact when the 

truss shoes slammed into the restrainer beams. These damaged restrainers were easily replaced. At Pier E17, instead of 

the fixed truss shoes breaking, as occurred at Piers El 8 to 

E22, the bottom of the concrete pedestals rocked. The concrete at the bottom corners of the pedestals spalled off and 

some vertical reinforcement buckled.

At Pier E23 the rivets connecting the bottom flange of 

the floor beam (fig. 15) to the concrete pier were sheared off, 

allowing the span between Pier E23 and E24 to move. A 9- 

foot drop-in span for the top deck at Pier E23 (figs. 16 and 

1 7) rested on seats attached to this floor beam in a manner 

similar to that described for Pier E9 (fig. 1 8). When the floor 

beam moved, the steel stringer webs were pulled out of the 

guide angles at Pier E23 (similar to Pier E9) and to within 

one-quarter inch of the edge of the bearing seat.

ANALYSIS OF

There were several factors that influenced this bridge's 

performance during the earthquake. The large distance from 

the hypocenter meant that only longer frequency accelerations were arriving at the bridge. Since the west end of the 

bridge sits on bedrock, it was the east end of the bridge (on 

deep Bay mud) that was excited by the earthquake. The bridge 

is designed as a series of very flexible steel piers anchored to 

stiffer anchor piers. Pier E9 is designed to resist all the inertia force from Pier E9 to the expansion joint at Pier Ell. 

This force was much larger than the 0.1 g that the bridge 

had originally been designed to handle during an earthquake. Therefore, the bolts designed to hold the trusses in 

place broke. The bearing seat at Pier E9 was too short to 

handle the subsequent movement of 10 inches longitudinally and 5 inches transversely during the earthquake. If 

these bearing seats had been longer, the trusses could have 

slid around without dropping the bridge decks. Stiff, concrete Pier El 7 was designed to take the inertia force all 

the way from the expansion joint at Pier Ell. Pier E17 

could not handle this force and rocked at the base of the 

pier. The reason the bolts on the fixed bearing did not break 

(as they did from Pier El 8 to Pier E23) was because there 

was a steel jack surrounding the bearings at the top of 

Pier E17 that prevented them from moving. The weakest 

area of Pier E17 was at the base of the pedestals, which 

rocked and spalled during the earthquake.

The spans from Pier El 8 to Pier E23 are simple steel 

trusses with one end fixed and the other end on rollers. At 

every pier the fixed end broke, allowing the truss spans to 

slam into the steel girder restrainers. Similarly, the rivets on 

the floor beam at Pier E23 broke, allowing the span to the 

east of Pier E23 to move, almost pulling a short, 9-foot dropin span off its bearings.

Basically, the inertia force was greater than the design force on the east end of the bridge, causing damage 

at anchorages and points of fixity. Fortunately, this damage generally consisted of broken bearings that resulted 

in spans sliding on their supports. The only serious dam-
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 15

U
16 HIGHWAY SYSTEMS

Figure 12.—Fallen decks at Pier E9 of the East Bay Crossing.

Figure 14.—Steel girder restrainer on East Bay Crossing with damage to 

rods and elastomeric pads after the earthquake.

Figure 13.—Truss shoe at Pier E9 of the East Bay Crossing showing broken bolts and shoe movement after earthquake.

Figure 15.—Pier E23 floor beam with small girder seat that almost dropped 

this span during the earthquake (photograph by Erik Zechlin).

age was .the dropping of the 50-foot span at Pier E9, 

which resulted in an unfortunate loss of life. Since the 

peak ground acceleration from the maximum credible 

earthquake at this bridge is at least 0.5 g, a substantial 

retrofit is required to prevent severe bridge damage 

from a rupture on the San Andreas or Hayward faults, 

which are near this site.

BRIDGE REPAIR

After the earthquake, an emergency contract was 

given to the Smith-Rice Company, who had the biggest derrick barge in the area to repair the bridge. Rigging International was the prime subcontractor. The 

fallen decks at Pier E9 were removed, new girders put 

in place, and precast concrete deck sections (fig. 19)
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 17

Existing 

Concrete 

deck

Existing 

Concrete 

deck

n Existing Stringer 

Cl6x35

UPPER DECK JOINTS AT E23

Figure 16.—Plan drawing of steel girders, floor beams, and girder seats at Pier E23 of the East Bay Crossing.

laid on top. All the truss sections were jacked back into place, 

new high-strength bolts were used, and new joint seals were 

laid.

On Friday, November 17, 1989, one month after the 

bridge was closed, it was reopened. On the first day, only 

pedestrians were allowed on the bridge. Politicians stood on 

the new span and gave speeches. People were allowed to look 

around and assure themselves that the bridge was safe. On 

Monday morning, the bridge was opened to commute traffic.

Since that time, Caltrans has been busy assessing the 

vulnerabilities of this bridge and devising a retrofit strategy 

to prevent major damage from the maximum credible earthquake. The retrofit strategy (fig. 20) that eventually emerged 

was to use reinforced concrete bents embedded around the 

existing steel piers with special bearings to isolate and dampen 

the earthquake motions from the superstructure. The cantilever portion was to have two additional piers and an exterior 

frame to strengthen the structure. However, the cost of this 

retrofit was so high that a replacement structure is now being 

planned instead.

REFERENCES

Altman, Steve, and others, 1995, SFOBB latticed member design 

criteria: Caltrans Publication Unit, 288 p.

Astaneh-asl, Abolhassan, 1992, Seismic retrofit concepts for the 

Bay Bridge: Technical Report to California Department of 

Transportation Department of Civil Engineering, University 

of California at Berkeley, 216 p.

Bridwell, R.R., 1990, The San Francisco Oakland Bay Bridge and 

the Port of Oakland Overcrossing, Loma Prieta Earthquake 

damage/repair report: California Department of Transportation, 33 p.

Buwalda, J.P.. 1938, Geological and seismic conditions affecting 

San Francisco-Oakland Bay Bridge: Division of Geological 

Sciences, California Institute of Technology, 17 p.

Department of California Highway Patrol, 1989, Loma Prieta Earthquake October 17, 1989—1-80 San Francisco-Oakland Bay

Figure 17.—Top deck at Pier E23 of East Bay Crossing showing 9 foot 

drop-in section between floor beams (photograph by Erik Zechlin).
18 HIGHWAY SYSTEMS

Figure 18.—Collapsed lower deck at Pier E9 of the East Bay Crossing showing short girder seats attached to floor beam.

Bridge closure span collapse: 

State of California, 396 p.

Department of Public Works, 1934 

to 1939, Annual progress reports on the San Francisco 

Oakland Bay Bridge [6 volumes]: San Francisco Department of Public Works.

Eidenger, J., and others, 1974, San 

Francisco-Oakland Bay

* Bridge East Crossing earthquake assessment: G and E 

Engineering Systems. 

Goldman, Harold B., 1969, Geologic 

and engineering aspects of the 

San Francisco Bay fill: California Division of Mines and

. Geology Special Report 97,

i 130 p.

Lawson, A.C., 1938, General safety 

of the San Francisco-Oakland

* Bay Bridge from the earthquake point of view: State of 

California, Department of 

Public Works, 4 p. 

Purcell, C.H., Andrew C.E., and Woodruff G.B., 1934 to 1937, Designing and building the San Francisco-Oakland Bay Bridge [a 

series of thirteen articles]: Engineering News Record, 68 p. 

Raab, N.C., and Wood H.C., 1939, Earthquake stresses in the San Francisco-Oakland Bay Bridge: American Society of Civil Engineering National Convention.

Requa, Mark L., and others, 1930, Report of the Hoover-Young San Francisco Bay Bridge Commission to the President of the United States 

and the Governor of the State of California: State of California, 

Department of Public Works, Division of Highways, 234 p. 

Yashinsky, Mark, 1990, Repair of earthquake damage to the Bay 

Bridge, in Proceedings of the Sixth U.S.-Japan Bridge Engineering Workshop: Public Works Research Institute, 10 p.

Figure 19.—Installing new, precast deck panels at Pier E9 on East Bay 

Crossing after the earthquake.

Figure 20.—Proposed retrofit of encasing steel towers in concrete for East Bay 

Crossing (currently (1997) superseded by plans to replace this structure).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 19

CYPRESS STREET VIADUCT

DESCRIPTION OF BRIDGE

The Cypress Street Viaduct (figs. 21 and 22) was a long 

connector that took traffic from the Distribution Structure on 

1-80 south onto 1-880 in the City of Oakland. This structure 

was a two-level, cast-in-place reinforced concrete, box girder 

bridge. Four lanes of traffic on the top and bottom decks were 

supported by two column bents. These bents had 11 different 

configurations as shown in figure 23 and described in table 8. 

Note that some of the top bent caps were prestressed as denoted by the dashed line. Many of the bents had pins (shear 

keys) at the top or bottom of the top columns, as indicated by 

circles in figure 23. All the bents were pinned above the pile 

caps as well. These column pins were four 59-inch-long #10 

bars with fiberboard placed around them at the joint (fig. 28). 

There was a superstructure hinge at every third span on both 

superstructures. Design began on the Cypress Viaduct in 1949, 

and construction was completed in 1957. All these pins and 

hinges were used to simplify the analysis for this long, complicated structure.

Prestressing was just beginning to be used after World 

War II and was considered an innovation on this bridge (fig. 

24). Caltrans' seismic criteria used at that time was to design 

for a lateral force of 0.06 times the dead load for structures on 

pile footings. This structure was seismically retrofit in 1977 

with Type C1 cable restrainer units installed at all the hinges.

BRIDGE DAMAGE

Like the nearby East Bay Crossing, portions of the Cypress Street Viaduct were supported by soft Bay mud; bedrock was more than 500 feet below the ground surface.

Figures 25 and 26 show that the portion of the viaduct that 

suffered damage was supported by this weak soil.

The Cypress Street Viaduct suffered the most catastrophic damage of any structure during the Loma Prieta 

earthquake. A large portion of the upper deck collapsed (fig. 

27). This was from Bent 63 in the south all the way to Bent 

112 in the north. Only Bents 96 and 97 remained standing. 

This collapse was a result of the weak pin connections at the 

base of the columns of the upper frame. Figure 28 clearly 

shows that there was inadequate confinement around the four 

#10 bars to restrain them during the earthquake. Also, the 

strong ground motion was probably influenced by the site 

conditions, as shown in figure 25. The sequence of collapse 

was as shown in figure 29. Although this was the most common collapse mechanism, there were several other types of 

failure as well. At some bents, the top and bottom decks both 

collapsed. Just south of Bent 113, the roadway s'heared off, 

and at some bents where columns were supported by a cantilevered girder, the girder collapsed. Figures 30 shows an aerial 

view of that portion of the structure where the top deck collapsed. Figures 31 to 33 provide details of the damage. Table 

9 lists all the significant damage that occurred. References 

to several papers that provide a complete description of earthquake damage for the Cypress Street Viaduct can be found at 

the end of this section.

RESCUE EFFORTS

The most important task after the earthquake was an intense effort to rescue any survivors on the collapsed freeway. 

Immediately after the quake, residents provided ladders and 

assistance to help people from the collapsed top deck (fig. 

34). After the Oakland Fire Department arrived, everyone 

helped to extinguish burning vehicles and locate and rescue

Bridge #33-178 / Route 880 / Post Mile 32.4

Approximate Latitude & Longitude 

N. Lat. 37° 49.1' W. Long. 12T17.2'

Epicentral Distance 

60 miles

Peak Ground Acceleration N/S U/D E/W 

At Oakland Wharf 0.29 0.07 0.27

Length Width Skew Year Built 

19,330' 52.0' varies 1957

Main Span Type

Two level, cast-in-place reinforced

concrete, box girder bridge.

Average Daily Traffic = 137,700 

Figure 21.—Cypress Street Viaduct.
20 HIGHWAY SYSTEMS

Figure 22.—Plan and section drawings of the Cypress Street Viaduct.

Table 8.—Bent types used on the Cypress Viaduct (see figure 23 to 

identify types

Bent

No.

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

Bent 

Type

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

B4

B5

B5

B5

Bent 

No.

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

Bent 

Type

B5

B5

B6

Bl

Bl

Bl

Bl

Bl

Bl

Bl

B7

B2

B2

B8

B8

B2

B2

B2

B2

B2

B2

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bent 

No.

88

89

90

91

92

93

94

95

96

97

98

99

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

Bent 

Type

Bl

Bl

Bl

Bl

Bl

Bl

Bl

B3

B3

B3

B3

Bl

Bl

Bl

Bl

Bl

Bl

Bl

Bl

B9

B9

BIO

BIO

BIO

Bll

Bll

Bll

survivors. The exterior barrier rail was removed to allow 

workers to crawl under the collapsed deck. Everyone worked 

around the clock in an effort to rescue any survivors. Shoring was installed by contractors using contractor and statefurnished timber. Contractors excavated through the fallen 

top deck to reach the victims and vehicles trapped below. By 

Saturday morning, October 21, the last survivor, Mr. Buck 

Helm, was gently taken off the bridge. The entire operation 

had become a coordinated effort between Caltrans, the California Highway Patrol (CHP), local police, fire, and Sheriff/ 

Coroner personnel. The Sheriff/Coroner's people had responsibility for identification and removal of victims, and the removal of vehicles was handled by the CHP and police. 

Caltrans' job was to provide safe access for search and rescue teams by inspecting the damaged structure and by providing shoring. Initially, the Scene Commander was the 

Oakland Fire Department. However, they quickly had their 

hands full coordinating the efforts of all the other fire departments that came to help. The Oakland Police took over 

command until at a meeting of all the participants there was 

an agreement to have the CHP take over as Scene Commander. Figures 35 and 36 show the Cypress Street Viaduct 

in the days following the earthquake.

To obtain a complete record of people injured or killed 

at the site required constant shoring and excavation of the 

bridge, the careful handling of remains, laborious contacts 

with area hospitals, and a computerized system to organize 

the accumulated information. There was pressure from the 

families of victims, as well as from politicians and the media 

to expedite this effort. An effort was made to keep victim's 

families as well as the media constantly informed. An infer-
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 21

Bent Type B2

Bent Type B3 (skewed) Section at 14th St. Off-Ramp

< ^

1

|

Bent Type B4

li n » i n ii ii j

1 —

Bent Type B6

ii ii » n ii n n if

3

)-

n » n 1 <

Bent Type B5

\ n i i ii n n if i i

Bent Type B7

————————————————————— .

4) <r

Bent Type B8 Bent Type B9

iLDcucnaiiiiDor ——

t41CDI 1 — II II 1 II _

IL^JL^:

R>

—————— —————

Bent Type B1 0

_ii _ » « ii ii

i i a ii ii it ii _ i

Bent Type B1 1

Figure 23.—Cypress Viaduct bent types as described in table 8 

(from Thiel, 1990).

180+00 200+00 

pi[ Rock, sand and rubble fill 

H Very soft to soft silty clay to clay

D Loose to dense clayey sands 

and bedded silts, sands 

and gravels

220+00 

Very stiff clay E Dense to very dense 

silty sand 

npact r^j S||(s sand£ and grave|

ry\ Slightly compact to compact I Clayey silt, silty clay 

t-« clayey silts, sandy silts, sands I— and clay

Figure 25.—Soil profile at Cypress Viaduct (Thiel, 1990).

Artificial fill 

overlying tidal 

marsh deposits 

composed of 

soft bay mud

Figure 24.—Cypress Street Viaduct (1957). Figure 26.—Geological map of Cypress Viaduct area (Thiel, 1990).
22 HIGHWAY SYSTEMS

mation center was set up a block from the command center. 

A Public Information Officer was assigned to provide interviews and press releases for the media.

TESTING AND DEMOLITION

After the last human remains and vehicles were removed 

from the site, the task switched to the expeditious removal of 

the freeway (fig. 37). The biggest problem was finding a place 

to dispose of the debris. The city of Oakland passed an ordinance 

prohibiting disposal of the rubble in the city. It was hoped that the 

debris could be recycled and used as construction material. However, there were difficulties in removing the reinforcement from the 

concrete and obtaining the necessary permits; in the end, almost all 

the material was hauled by trucks and disposed of along the Route 

580 right of way in Castro Valley.

Another issue was making sure that minority contractors were 

obtaining a fair share of the work. This can sometimes be a problem

when working with force account contracts. Caltrans made a special effort to include WBE/DBE contractors in all the work at Cypress. It was also necessary to shore and repair the offramp at 1-980 

to allow vehicles to take 1-980 to 1-80 (see section "Route980 Southbound Connector").

Finally, the portion of this viaduct that was still standing afforded researchers a rare opportunity to do (1) destructive testing to 

help understand the collapse, the behavior of pile groups to failure, 

and new retrofit schemes and (2) testing to compare computed deflection and damage to actual bridge behavior. These tests were carried out by the University of California at Berkeley and Caltrans' 

Division of Structures. Steel jacking platforms were built (fig. 38). 

The bents were modified with different retrofits to provide confinement to vulnerable members. Then vibration tests were done as well 

as transverse loading to failure. However, due to time constraints to 

complete the testing, most of these confinement retrofit schemes 

were of limited value. Of more importance was the pipe seat extender testing. High-strength pipes were inserted in hinges to preSeismic force

Di

Seismic force

Ground acceleration

_ ..A. 

Figure 27.—Pin connection failure at Cypress Viaduct

Shear key 

Fiber-board 20" x 36"

o

PPPE

C D

Figure 29.—Cypress Viaduct collapse sequence for bent type Bl (fromThiel, 1990).

Figure 28.—Pin reinforcement details for Cypress Viaduct.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 23

Figure 30.—Collapse of Cypress Viaduct between Bent 62 and Bent 113.

Figure 31.—Hinge damage at Cypress Viaduct. Figure 32.—Rotation at Bent 76 of Cypress Viaduct (note prestressing 

tendons).
24 HIGHWAY SYSTEMS

Table 9.—Summary of damage to Cypress Viaduct

Bent Bent Bent Condition 

Nos. Type

32-45 Bl Standing, little observed damage.

46-47 Bl Standing, little observed damage, shear cracks in east and west faces of upper deck, 

location of ambient vibration test

48 Bl Standing, little observed damage.

49 Bl Standing, cracking in the critical region.

50 Bl Standing, cracking in the critical region, pounding with exit ramp. 

51-54 Bl Standing, cracking in the critical region.

55 Bl Standing, cracking in the critical region.

56 B4 Standing, extensive cracking in the critical region.

57-61 B5 Standing, extensive cracking in the critical region.

62 B6 Standing, southernmost standing bent, extensive cracking in the critical region.

63-69 Bl Upper level collapsed, upper girder flat on lower girder, typical Bl failure.

70 B7 Upper level collapsed, upper girder flat on lower girder.

71-72 B2 Upper level collapsed, upper girder flat on lower girder.

73 B8 Upper level collapsed, cantilever failed, upper girder flat on lower girder.

74 B8 Upper level partially collapsed, cantilever tailed, transition between upper girder flat

and upper girder tilted. 

75-80 B2 Upper level partially collapsed, upper girder tilted, pin-ended column remained in

place.

81 -94 B1 Upper level collapsed, upper girder flat on lower girder, typical B1 failure. 

95 B3 Upper level collapsed, upper girder flat on lower girder, east column displaced to the

north. 

96-97 B3 Standing, extensive cracking in lower-girder lower-column joint, and evidence of

transverse cracking. 

98 B3 Upper level collapsed, upper girder flat on lower girder, east column displaced to the

north. 

99-103 Bl Upper level collapsed, upper girder flat on lower girder, typical Bl failure.

104 Bl Upper level collapsed, extensive damage to lower girder, upper girder flat on lower 

girder, both upper and lower decks are on the ground at the expansion joint north of 

104, typical Bl failure.

105 Bl Upper and lower levels collapsed, upper girder flat on lower girder, lower girder on 

ground.

106 Bl Upper level collapsed, extensive damage to lower girder, upper girder flat on lower 

girder, typical Bl failure.

107 B9 Upper level collapsed, upper girder flat on lower girder, similar to a Bl failure.

108 B9 Upper level collapsed, upper girder flat on lower girder, shear failure in lower east side

column, similar to a 81 failure. 

109-111 BIO Upper level collapsed, upper girder flat on lower girder, similar to a 81 failure.

112 Bl 1 Collapsed, shear in girder. Abutment showed evidence of transverse motion.

113 Bl 1 Standing, little observed damage, deck sheared completely south of this bent.

114 Bl 1 Standing, little observed damage.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 25

Figure 33.—Bent 70 of the Cypress Viaduct (view to south).

Figure 35.—Rescue efforts at the Cypress Viaduct (by trained personnel) 

continued for 5 days following the earthquake.

Figure 36.—Command Center at Cypress Viaduct.

Figure 34.—Impromptu rescue efforts by people living near the Cypress 

Viaduct (copyright by Roy Williams, Oakland Tribune).
26 HIGHWAY SYSTEMS

vent unseating (fig. 39). This retrofit scheme has since become very 

popular.

By early February 1990 the Cypress Street Viaduct was completely removed and resurfacing and repairs to Cypress Street (now 

Nelson Mandela Parkway) were completed.

NEW BRIDGE CONSTRUCTION

The alignment for the Cypress Street Viaduct replacement as 

well as the design criteria for this project presented many challenges. 

The new route runs beside the Southern Pacific and Bay Area Rapid 

Transit right-of-ways (fig. 40), which has caused many logistical 

and negotiating headaches. Hazardous materials were found along 

the new alignment, which required an expensive cleanup. Also, the 

new alignment runs through several areas of soft Bay mud, which 

required developing site-specific response spectra. The weak soil 

also required designing large, stiff foundations with 42-inch-diameter steel pipe piles. Problems with outrigger bent caps handling the 

large torsional moments for longitudinal earthquakes necessitated 

using pinned bent cap connections. Lack of knowledge on joint shear 

transfer between reinforced concrete columns and bent caps required 

a testing program at the University of California at San Diego and a 

new conservative design for bent cap joints.

This project was divided into seven different sections and each 

section was designed by a different consultant or by Caltrans using 

the same design criteria. At five locations, the new bridge is Caltran's 

typical cast in place, prestressed concrete, box girder design. At the 

horseshoe fly-over at the toll plaza, a steel orthotropic box girder 

was used to eliminate the need for falsework and to handle the tight 

radius curve. On the portion of the project that goes over the existing 

Distribution Structure (on the northeast end of the project), steel 

welded plate girders were used. The project is scheduled for completion by the end of 1998. The cost of this replacement is almost a

billion dollars, due to the City of Oakland's insistence on a new 

alignment and due to removal of toxic waste at the new site.

REFERENCES

Black, I.W., 1956, Cypress Street Viaduct—A double decked answer 

to congestion: Highway Magazine, California Department of 

Public Works, Division of Highways.

Bollo, M.E., and others, 1990, Observations and implications of tests 

on the Cypress Street Viaduct test structure: University of California at Berkeley, Earthquake Engineering Earthquake Center, 274 p.

Degenkolb, O.H., 1956, Prestressed bent caps have provisions for future increase in span: Design News No. 5, California Department of Public Works, Division of Highways.

Degenkolb, O.H., 1957, Load test of concrete cap, Cypress Street Viaduct: Design News No. 21, California Dept. of Public Works, 

Division of Highways.

Department of California Highway Patrol, 1989, Loma Prieta Earthquake October 17, Cypress Street Viaduct, structure collapse: 

State of California, 4 volumes.

Nims, D.K, and others, 1989, Collapse of the Cypress Street Viaduct 

as a result of the Loma Prieta Earthquake: University of California 

at Berkeley, Earthquake Engineering Research Center, 85 p.

Priestley, N.P, and others, 1989, Collapse of the Cypress Viaduct—A 

damage and repair assessment: University of California at San Diego, Department of Applied Mechanics and Engineering Sciences.

Seible, Frieder, and others, 1992,1-880 reconstruction project seismic 

design criteria review: University of California at San Diego, 

Department of Applied Mechanics and Engineering Sciences.

State of California, Department of Public Works, Division of Highways, 1957, As-built plans of the Cypress Street Viaduct.

Thiel, Charles C, 1990, Competing against time—Report to Governor George Deukmejian from the Governor's Board of Inquiry 

on the 1987 Loma Prieta earthquake: State of California, Department of General Services, 264 p.

Figure 37.—Removal of 

the Cypress Viaduct.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 27

Figure 38.—Retrofit strategy being tested with jacking frame on section of the Cypress Viaduct.

<t.Hlnge

4'-6'

2'-0" x 2'-O 

max. access 

opening.

d hoi

l"0 H.S. Threaded 

rod tot. 8

fS «> tot. 4 per bolster

Drill <5 grout 6" Into existing

„,_, I 

0 formec

*8x4'-O" tot. 4

per bay. S«« Section 6-6

9"0 cored hole, see 

"Part Plan" for 

details. TYPICAL HINGE DETAIL

Scale I"=I'-O"

Figure 39.—Pipe seat extender test for the Cypress Viaduct
28 HIGHWAY SYSTEMS

<>^^XXr .-. J" -K ---*, I

^*N*-' ^S^s^-J

sFx^.Jk *^L1**- .' ^^ ^

<?^^-,^~—W '-r^Sstrsr1 ' .*^' T A T^*'

^%^K 1,,^,^ JT -f .1 ^ .*&&**&&% <:^? f^^^^'^^^^5 VfiS^b'-- 1 "^ V' ..'i'J^-^'lW^J'If^S^M.^'* **K ^--v^4^J^-^f ** >^-3 

.< *s.^^^?0

^. ^ ,£*==^S&zmi^
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 29

Bridge #33-483 / Route 980 / Post Mile 0.01

Approximate Latitude & Longitude 

N. Lat. 37° 48.1' W. Long. 122°16.9' 

Epicentral Distance 

58 miles

Peak Ground Acceleration N/S U/D E/W 

At Oakland Wharf 0.29 0.07 0.27

Length Width Skew Year Built 

2,265' 54'& varies varies 1980

Main Span Type

Reinforced Concrete & Prestressed

Concrete Box Girders.

Average Daily Traffic^ 67,500 in 1990 

Figure 41.—Route 980 Southbound Connector.

ROUTE 980 SOUTHBOUND CONNECTOR

DESCRIPTION OF BRIDGE

The Route 980 Southbound Connector is a 19-span, 

1,800-foot-long, cast-in-place, concrete, box girder bridge 

(figs. 41 to 45). It carries traffic from southbound 1-980 onto 

southbound 1-880 in the city of Oakland. Starting at the south 

end, from the hinge at span 24 to the hinge at span 33 the

Route 980 SB 

Connector OC

superstructure is nine 75-foot conventionally reinforced 

spans. Then the superstructure changes to ten 120-foot prestressed concrete spans. The bridge is supported on 

multicolumn bents, outrigger bents, and one "C" bent as it 

steps gingerly around surface streets and expressways. All 

the columns except on the "C" bent are pinned at the base. 

The bent foundations are on spread footings (the log of test 

borings shows dense to compact sands) and the single abutment on the north end is a seat type abutment on steel "H" piles.

BRIDGE DAMAGE

There was quite a bit of superficial damage and a surprising amount of movement to this 

bridge, which was on good soil 

and 60 miles from the fault rupture. It is the only bridge built in 

the 1980's that suffered any significant damage during the earthquake. The serious damage was 

to the west outrigger knee joint 

on Bent 38 (figs. 45 to 49). This 

bent is very close to the hinge at 

span 37, which meant the superstructure could not provide much 

transverse stiffness for this bent. 

When this portion of the bridge

Figure 42—Location of Route 980 Southbound Connector.
HIGHWAY SYSTEMS

Route 980 Southbound 

Connector O. C.

Figure 43.—Aerial 

view of Route 980 

Southbound Connector.

Figure 44.—Plan drawing 

for Route 980 Southbound 

Connector.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 31

moved transversely, the main restraints were the momentresisting cap/column joints at Bent 38. Both joints were 

cracked, the west joint most severely, with the cracks, more 

severe on the hinge side of the bent. Also, the bridge deck 

over the bent sustained some cracks suggesting high 

stresses to the extreme fibers of the bent cap in bending.

The vulnerability of knee joints from opening and 

closing moments had been studied before this bridge was 

built (Park and Paulay, 1975). Caltrans' philosophy has 

been to design very strong joints and bent caps that force 

the damage to occur in the ductile columns. This bridge 

had very ductile columns, but the joints were 

underdesigned. Joint damage to this and other bridges has 

resulted in a major research and testing effort at the University of California, San Diego, to come up with better 

joint details and a coherent philosophy for joint design.

Bent 38's west outrigger knee joint was confined with 

W5 spiral wire which broke along with a #18 vertical reinforcing bar in the joint. Whatever moment capacity this 

joint had was severely reduced by cracking and spalling 

of the concrete after the confinement reinforcement broke. 

The #18 "X" reinforcement in this joint was tested in the 

materials lab after the quake. It was found that the broken 

rebar was of grade 75 steel, while the other bars were grade 

60 steel. Moreover, the broken rebar had a curve radius of 

11 3/8 inches, while the plans showed a bend radius of 18 

inches. It is believed that the difference in grade and the 

sharp bend in the bar caused the failure. The difference in 

grade made the rebar much stronger, causing most of the 

load to be transferred to the stiffer bar. Other bridge damage including spalling of concrete at the wingwall and 

shear keys of the north abutment. There were column 

cracks at Bents 35 to 37 that appear to have occurred prior 

to but were widened by the earthquake. There was damage to the sidewalk, asphalt, and soil around the base of 

these columns, indicating that they experienced a lot of 

movement during the earthquake. The expansion joints at 

the abutment and hinges all showed signs of banging and 

large movements.

BRIDGE REPAIR

As mentioned previously, this connector was essential to move traffic from 1-880 to 1-80 after the collapse of 

the Cypress Street Viaduct. The connector was closed immediately after the earthquake. Subsequently, structural 

personnel examined the bridge and determined a temporary and permanent repair to allow traffic back on the roadway. Emergency repairs began on the bridge on October 

20, 1989. They consisted of timber cribbing under the cap, 

supported by 24-inch-diameter steel pipe shoring capped 

with steel plates and braced with diagonal cables for lateral support. This allowed traffic back on the bridge. Then 

heavy-duty structural steel falsework frames were installed, and the pipe shoring was removed. Traffic was

shifted to the east half of the roadway, and work was 

begun to strengthen the cap/column joints on the west 

side by adding reinforcement and increasing the size 

of the joints. After the concrete was cured, traffic was 

shifted to the west side, and the same procedure was 

done to the east side of the bridge. Then the falsework 

was removed, the surface streets below the connector 

were given minor repairs, and traffic was allowed back 

on the streets below the bridge. All the work was completed as of November 7, 1989. The total cost of this 

repair was just under $100,000. Since the only deficiencies to this modern structure were the weak cap/ 

column joints, this repair was considered sufficient to 

protect the bridge from the maximum credible earthquake.

Figure 45.—Bent 38 of Route 980 Southbound Connector after the earthquake.

Figure 46.—Closer view of knee joint damage to Bent 38 of Route 980 

Southbound Connector
32 HIGHWAY SYSTEMS

REFERENCES

Caltrans, 1985, As-built bridge plans for the 

Route 980 Southbound Connector 

OC.

Norsworthy, Wynn, 1994, Repairs on the 

Route 980 SB Connector: Personal 

Correspondence, 2 p.

Park, R., and Paulay T., 1975 Reinforced 

concrete structures: Wiley, 769 p.

Seible, F, and Priestley, M.J.N., 1991, Performance assessment of cap-column 

joints under seismic loading: International Association for Bridge and 

Structural Engineering, IABSE Colloquium, Stuttgart, 17 p.

Storlarski, P., 1990, Fractured #18 rebar 

from Bent 38 of the Rte 980 SB 

Conn.: Caltrans' memo, 6 p.

a) Distress pattern b) Simplified truss model

Figure 47.—Distress pattern for closing and opening of knee joints (Seible and Priestley, 1991).

,#7@5"

"T"

\l

1,

^° * u

EH

T7JP " 

1

-

-8 x-bars #18

•4y-bars#18

5'-9"

#7 @ 5"

18#5 —

if 5 spirals 

@3.5"

Reinforcement:

Grade 60, assume f = 66 ksi

f'c = 3000 psi, assume f. = 5000 psi

* 5 spiral @ 3.5"

x-bars and y-bars 

d

Figure 48.—Drawing of knee joint reinforcement for Bent 38 of Route 980 Southbound Connector.

PORT OF OAKLAND OVERCROSSING

DESCRIPTION OF BRIDGE

This long viaduct crosses southeasterly over 1-80 (by the Bay Bridge Toll 

Plaza), the Baldwin Railroad Yard, and the 

Oakland Army Base until it meets West 

Grand Avenue at grade. It has 10 alignments that include several on and off ramps 

(figs. 50 to 52; table 10). The superstructure comprises simple and cantilever steel 

stringer spans supported on a variety of 

bents (including an unusual two-column 

bent supporting a single column bent). The 

variety of member types on this structure 

is due to its having been built in the 1930's 

and then substantially extended in the 

1950's. The original 1930's-designed structure is mostly two-column steel bents 

framed into steel floor beams spanning over 

the railroad yard. The 1950's structure is 

mostly reinforced concrete single column 

bents with steel and concrete hammer head 

bent caps. The foundations are typically 

pedestal type concrete footings on untreated timber piles. The log of test borings 

shows soft clays at 1-80 with denser mate-
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 33

"SF" Line

* 16 - bar

f of. 6

ne-.'-r/ca' akouf i-. 

between columns

to Jv. -tot. /:

ELEVATICK

Figure 49.—Reinforcement details for Bent 38 of Route 980 Southbound Connector.

Bridge S33-126L/R / Rte 80 / Post Mile 2.41

Approximate Latitude & Longitude 

N. Lat. 37° 49.6' W. Long. 122° 18.4'

Epicentral Distance 

58 miles

Peak Ground Acceleration N/S U/D E/W

At Oakland Wharf 0.29 0.07 0.27

Length Width Skew _ Year Built 

5,445' 28.0' varies 1937 & 1966

Main Span Tvpe

Steel stringers (rolled sections)

Average Daily Traffic = 9,500 in 1984

Figure 50.—Port of Oakland (West Grand Avenue Viaduct) in 1992
34 HIGHWAY SYSTEMS

^^^^•SSBw^^^^

Figure 51.—Location of Port of 

Oakland Overcrossing.

Figure 52.—Plan drawing of the alignment for the Port of Oakland Overcrossing.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 35

rial to the south. The bridge was retrofitted in the 1970's with 

cable restrainers and catcher blocks.

BRIDGE DAMAGE

The most noticeable evidence that a strong earthquake 

had occurred was the quantity of ejected sand around the 

columns at the north end of the bridge (fig. 53). There was 

substantial minor damage to this bridge during the earthquake. 

Anchor bolts that held the bottom steel girder flange to the 

bent cap were broken at a few locations. Also, some anchor 

bolts that held the steel bent caps to the columns were damaged. Mortar pads under girders had been broken. Keeper 

plates that held the steel bearings in place had been knocked 

loose at many locations. Some girders had moved sideways 

up to 14 inches, buckling the crossbracing. Surprisingly, cable 

restrainers had yielded at several locations (fig. 54). Steel 

girder flanges had buckled at two locations. There was also 

some concrete damage. The deck overhang had spalled from 

banging at expansion joints. There was some shear cracking 

at bent caps. The most serious damage was spalling at the 

base of some of the reinforced concrete single column bents 

(fig. 55). Table 11 summarizes the visual inspection of damage for each alignment. All the evidence suggests that the 

bridge moved primarily in an east-west (transverse) direction during the earthquake. After the earthquake, this bridge 

was used to haul heavy timber for shoring at the nearby Cypress Street Viaduct. However, it was later decided to close 

the structure for a few days while some repairs were made.

BRIDGE REPAIRS

Because of the damage to anchor bolts, welds, etc., the 

first order of business was to bring in a snooper (a truck with 

an articulated arm and large basket) and do a thorough ultrasonic inspection of steel girders and steel connecting elements. After the extent of damage was ascertained, repairs 

were initiated. Concrete cracks were repaired by epoxy injection. Concrete spalls were repaired with dry pack (fig. 56). 

For the spalling at some column bases, additional reinforcement was added to the repair. Because of the decision to replace this structure as part of the 1-880 replacement project 

(fig. 40), repairs were done only to bring this structure back 

to its condition before the earthquake but not to retrofit it to 

survive a stronger event. However, all the existing bolts at 

the steel bent caps were replaced with high strength bolts, all 

the cable restrainers were replaced, and the other extensive 

repairs to this structure probably have improved its seismic 

performance. Because of the extent of minor damage to this 

long structure, the cost of repairs was almost $1 million.

REFERENCES

Bridwell, R.R., 1990, The San Francisco Oakland Bay Bridge 

and the Port of Oakland Overcrossing, Loma Prieta 

Earthquake Damage/Repair Report: Caltrans, 33 p.

Caltrans, Feb. 1937, July 1956. etc., As-built bridge plans 

for the Port of Oakland OC.

Stolarski, P., 1990, Inspection of structures damaged in the 

Loma Prieta Earthquake: Caltrans internal memo, 2 p.

Figure 53.—Sand boil at Bent 3 of the O line at Port of Oakland 

Overcrossing (view to south) (photograph by Li Hong Sheng).

Figure 54.—Restrainer damage at Port of Oakland Overcrossing (Photograph by Philip Stolarski).
36 HIGHWAY SYSTEMS

Table 10.—Alignment for Port of Oakland Overcrossing Table 1 [.—Summary of damage to Port of Oakland Overcrossing

Alignment Location

O line Northbound 1-80 to Port of Oakland.

S line Southbound 1-80 to Port of Oakland.

J line Port of Oakland to southbound 1-80.

A line Port of Oakland to northbound 1-80.

B line Southbound J line to Maritime Street.

C line Maritime Street to northbound J line.

D line Northbound JL line to Maritime Street.

E line Maritime Street to southbound JR line.

JL line West Grand Avenue to northbound J line.

JR line Southbound J line to West Grand Avenue.

Alignment Damage

O line West approach settled about 4 inches. Sand was ejected from around

the foundations of Bent 3 to Bent 10. 

S line Abutment 1 moved about 1 inch in both directions. Pavement around

Bent 4 was cracked and sand was ejected around the column. Bent #6

has some cracks along top west corner. 

J line Approach settled 2 inches. Abutment 1 moved about a half inch

transversely and 2 inches longitudinally. The steel girder bearings at

Abutment 1 moved, spalling some concrete. Bents 2, 3, and 9 had

concrete spalls at their connections with superstructure. Sand was

ejected under Spans 2, 3, and 4. 

A line West approach settled about 5 inches. Pavement crack along north

wingwall indicated soil movement. Abutment showed signs of

movement and had spalls under bearings.

D line Abutment 30 had its two northernmost bearing keeper plates broken. 

JL line Bent JL30 and JL35 had soil cracks around footings, indicating rocking.

Bent JL35 had sand ejected around the footing. Some keeper plates at

hinge were broken. 

JR line Bents JR28 to JR34 have soil cracks around footings and concrete spalls

at column bottoms, indicative of fiexural yielding in east-west direction.

Figure 55.—Spalling at southeast face of Bent 30 on JR line of Port of 

Oakland Overcrossing (photograph by Li Hong Sheng).

Figure 56.—Column damage and repair at Port of Oakland Overcrossing.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 37

Br #33-61 L/R / Rte 580 / Post Mile 46.09 

Approximate Latitude & Longitude

N. Lat. 37° 49.2' W. Long. I22°15.r

Epiccntral Distance

58 miles

Peak Ground Acceleration

At Oakland Wharf

N/S U/D EAV 

0.29 0.07 0.27

Length Width Skew Year Built

3,.996' 45.0' Varies 1935

Main Span Type

Steel girders

Average Daily Traffic = 141.850

Figure 57.—The Distribution Structure in mid-1950's.

DISTRIBUTION STRUCTURE

DESCRIPTION OF BRIDGE

The Distribution Structure (figs. 57 and 58) is the first major interchange on 1-80 after coming off the Bay Bridge. It allows traffic to switch between 1-80, 1-580, and the Cypress 

Viaduct. It is similar to the nearby Port of Oakland OC in its 

history and structure, as well as in the damage it sustained during the earthquake. The structure, built in 1935, is simple span 

steel girders on single-column and two-column bents supported 

on timber piles. The 1953 and 1958 structures are continuous reinforced concrete "T" girders on multicolumn bents 

with steel piles, concrete piles, and some spread footings. 

The log of test borings shows some areas of soft, black clay. 

The alignment for this structure is shown in figures 59 and 

60 and table 12. A typical mid-1970's seismic retrofit was 

done connecting all the expansion joints with cable restrainers.

Figure 58.—Location of Distribution Structure.
38 HIGHWAY SYSTEMS

Figure 59.—Aerial 

view of Distribution 

Structure.

Rgure 60.—Plan 

drawing of Distribution Structure.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17,1989: PERFORMANCE OF THE BUILT ENVIRONMENT 39 

BRIDGE DAMAGE

After the earthquake, this bridge was inspected by the Office of Structural Maintenance (Ng, 1989), the Post Earthquake 

Investigation Team (Zelinski, 1994), and by the Welding and 

Metals Technology Unit (Stolarski, 1990). Reports summarizing these investigations can be obtained from Caltrans. These 

reports (particularly'the Structural Maintenance report) provide 

much more detailed information about bridge damage.

There was a great deal of minor and moderate damage to 

this structure. There was substantial damage to keeper plates, 

anchor bolts, and other steel hardware that kept the bearings in 

place. There was some minor cracking at the bottom of columns. Figures 61 and 62 show the results of transverse rocking 

of bents which caused concrete to spall and anchor bolts to deform at the column-to steel-bent-cap connection. The MB alignment had the most damage. The backwall for Abutment MB1 

was severely cracked. The most significant damage was at Bent 

MB25, where there were many cracks at the bottom of the column, the bearing keeper plates were knocked off, the girder ends 

were bent, the bent cap web had a bow, and the superstructure 

shifted 3 inches to the north. Figure 63 shows the keeper plate 

damage. Table 13 summarizes the structural damage.

BRIDGE REPAIR

Emergency repairs were done on this bridge shortly after 

the earthquake (fig. 64). In 1990, a seismic retrofit was done as 

part of the phase 2 retrofit program. This retrofit was for an 

earthquake with a shorter return period since it was thought at 

the time that a new structure would replace this bridge in a couple 

of years. However, as of 1996 a new retrofit and widening is 

being designed for this structure. Some of this structure is being 

replaced as part of the new 1-880 (Cypress Street Viaduct).

The 1990 retrofit consisted of bearing and restrainer replacements, steel shells that provided confinement for single 

column bents, and an elaborate footing retrofit that required the 

contractor to go under the existing footing and drill holes and 

attach high-strength rods to the existing piles so they could support the footing in tension. Figure 65 shows some of the typical 

retrofit details for this structure.

REFERENCES

Ng, Steve, 1989, Supplementary bridge report for the Distribution 

Structure: Caltrans.

Stolarski, P., 1990, Inspection Report: Caltrans internal memo.

Zelinski, Ray, 1994, Loma Prieta earthquake PEQIT Report: California Department of Transportation.

Figure 61.—Spalls and anchor bolt damage at Bent BC8 of 

the Distribution Structure.

Figure 62.—Closer view of damage at top of Bent BC8 of the Distribution 

Structure.

Alignment [ Location

Table 12.—Distribution Structure 

alignments

CM Route 80 SIB from Berkeley to Toll Plaza.

MC Route 80 NIB from Toll Plaza to Berkeley.

NM Route 880 NIB to Toll Plaza.

NC Route 880 NB to Berkeley.

B M Route 580 NB to Toll Plaza.

MB Route 80 NB from Toll Plaza to Route 580 SB.

MS Route 80 NB from Toll Plaza to Route 880 SB.

SA Route 880 SB.

AN Route 880 NB to Route 80.

CS Route 80 SB from Berkeley to Route 880 SB.

CB Route 80 SB from Berkeley to Route 580 SB.
40 HIGHWAY SYSTEMS 

Table 13.—Summary of damage to the Distribution Structure (Zelinski, 1993)

Alignment Damage

CB Bents CB2 and CB3 have the two interior steel girder keeper plates sheared off. Bent 

CB4 has at least one interior steel girder keeper plate sheared off.

CS At Abut 1, Bent CS2, and Bent CS3, the structure has moved 2 inches in the east-west 

direction. Soil dropped 4 inches around the column at Bent CS2. Signs of foundation 

movement (soil cracks) from Bent CS2 to Bent CS5. Gap at Abutment 1 is about 4 

inches wide and more than 3 feet deep at west side. Pavement crack along west side 

curb of approach.

BM Approach has settled 6 inches. Pavement buckled at end of approach slab. Roadway 

shifted 2 inches to north.

MB Footing rocking can be seen from the soil cracks around the footing. Series of soil 

cracks follow structure alignment. Concrete spalled at bottom of pinned bearing pad 

and above hole of restrainers at Bent MB9. Several bearing plates at Bent MB25 

moved and fell.

CM Roadway crack follows alignment of CM line toward Toll Plaza. Liquefaction can be 

seen along roadside and cracks. North side of roadway shifted 4 inches to north and 

has 6 inches settlement.

Figure 63.—Keeper Plate Damage on the Distribution Structure (photograph by Li Hong Sheng).

Figure 64.—Emergency Repairs to the Distribution Structure.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 41

Exist, steel reinforced 

column

Exist, anchor bolts, 

tot 6*. Replacement 

bolts may have 

been added under a 

previous contract.

Exist, steel 

bent cap

steel casing PLAN

3/4"= I'D"

•Blackout 6 top of column. 

Backfill with lean concrete, 

see "Section C-C". r_..r~n

L.L — .

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ELEVATION

Dowel spacing may be adjusted 

to allow clearance to existing 

cracks if found. Additional 

dowels may be added as 

required by the Engineer.

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within column area

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FOOTING PLAN Figure 65.—Plan and elevation 

drawings of Distribution Structure 

post-earthquake bent retrofit.
42 HIGHWAY SYSTEMS

Figure 66.—Fifth Avenue Overhead (before 1963 widening). 

FIFTH AVENUE OVERHEAD

DESCRIPTION OF STRUCTURE

The Fifth Avenue Overhead (figs. 66 to 68) is a steel girder 

bridge with a concrete deck on mostly concrete (and a few steel) 

multicolumn bents supported on pile foundations in the City of 

Oakland. It was built in 1947, widened in 1963, and seismically 

retrofit in 1985 (fig. 69). The consultant responsible for the retrofit recommended that the bridge be replaced because of soil 

problems, an inadequate substructure, fatigue, etc. However, a 

superstructure retrofit was done instead that provided cable restrainers at the steel girder hinges.

BRIDGE DAMAGE

This bridge was inspected by Structural Maintenance on 

November 16 and 17, 1989, and again on December 12 and 13, 

1989. There was a walk-through examination of the substructure and a random inspection of the bearings and hinges using a

Br #33-027 / Rte 880 / Post Mile 30.38

Approximate Latitude & Longitude 

N. Lat. 37° 47.5' W. Long. 122° 15.6'

Epicentral Distance 

56.4 miles

PGA N/SU/D E/W

Oakland 24-story bldg. 0.18 0.04 0.14

Length Width Skew Year Built 

2,554' 109' Varies 1948

Main Span Type 

Continuous steel T girders

Average Daily Traffic = 176,300

ladder, a pair of binoculars, or at some locations a personnel lift. 

There was a cursory drive-by inspection of the deck surface and 

a binocular inspection of overhangs at the transverse joints and 

at the underside of longitudinal joints. Significant damage was 

limited to the interior supports from Bent 30 to Bent 40, with 

some minor damage elsewhere (figs 70 to 74). Table 14 summarizes the damage. The most unusual damage was to the steel 

wide-flange columns at Bents 36 to 39 (figs. 75, 76). These 

columns showed indications of one or two cycles of inelastic 

deformation and plastic hinging above the pedestals. This damage may have been exacerbated by the pedestals and railroad 

collision walls that made the bases very rigid.

BRIDGE REPAIR AND REPLACEMENT

After the earthquake, Caltrans drew up plans, and repairs 

were made (figs. 77,78). Because of vulnerabilities on this structure, consultants were hired to design a replacement structure. 

However, a variety of problems has pushed this project back to 

the year 2002 or beyond.

Figure 67.—Location of Fifth Avenue Overhead.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 43

lllllllllllll§lfl§fl

Figure 68.—General Plan drawing for 1963 Fifth Avenue Overhead widening.
44 HIGHWAY SYSTEMS

Hinge

Figure 69.—Elevation drawing for the 1985 retrofit of Fifth Avenue Overhead.

Figure 70.—Fifth Avenue Overhead at time of the earthquake (courtesy of Figure 71.—Spall at column base for Bent 35 of Fifth Avenue Overhead 

Earthquake Engineering Research Institute). (courtesy of Earthquake Engineering Research Institute).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 45

Table 14.—Summary of damage to Fifth Avenue Overhead

Location Damage

Abut 1 to Bent 24 No damage.

Bent 25 Cracks to railroad collision wall. Deck spall at hinge in Span 24.

Bent 26 Cracked collision wall. Hairline crack of Column 3 at top of wall.

Bent 27 Hairline crack in Column 1 similar to Bent 26.

Bent 30 1/4" opening in soil around Column 7 and diagonal crack in 

concrete pad at bottom of column.

Bent 31 Spalls on all faces of Column 8 about 6" above ground line.

Bent 32 Column 8 cracked and spalled near ground and at bent cap.

Bent 33 Columns have cracks near the ground and near the cap.

Bent 34 Similar to Bent 33 but more severe.

Bent 35 Similar to Bent 34 but even more severe.

Bent 36 to 39 At this location there are steel three-column bents embedded in 

concrete pedestals and connected to skewed railroad collision 

walls. There was damage at the column to cap connections, and 

plastic hinging of some of the steel columns above the pedestals.

Bent 40 to 42 These columns sit in Merritt Lake Canal. The earthquake spalled 

concrete previously loosened by corrosion damage.

Bent 46 Damage to superstructure hinge in Span 46.

Bent 47 Slight damage to keeper rings at top of rockers at hinge.

Figure 74.—Damaged hinge at Bent 36 of Fifth Avenue 

Overhead (courtesy of Earthquake Engineering Research 

Institute).

Figure 75.—Location of steel columns at Fifth Avenue Overhead (courtesy 

of Abolhassan Astaneh-AslX

Figure 72.—Damage to railroad collision wall of Fifth Avenue Overhead 

(courtesy of Earthquake Engineering Research Institute).

Figure 73.—Broken keeper plate at Bent 35 of Fifth Avenue Overhead (courtesy of Earthquake Engineering Research Institute).

Figure 76.—Steel column damage at Fifth Avenue Overhead (courtesy of 

Abolhassan Astaneh-Asl).
46 HIGHWAY SYSTEMS
tifjV-v'r be^ 

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CENTER COLUMN AT BENT 39 VIEW A-A

AS BUILT PLANSContract NaQAll

Date Completed ft • 2?.- Document Ha.

J.J.GoUippi

' M. Comoc.^0 r"" CALIFORNIA

DEPARTMENT Of TRANSPORTATION

AND INVESTIGATIONS FIFTH AVENUE OVERHEAD

TEMPORARY SUPPORT AT BENT 39

SHEET

1

•rT"TT i i

Figure 78.—Bent repair detail illustrating the use of falsework to support superstructure on Fifth Avenue Overhead.
48 HIGHWAY SYSTEMS

Figure 79.—Location of damaged viaducts in eastern San Francisco.

MAJOR BRIDGE DAMAGE IN THE 

CITY OF SAN FRANCISCO

SAN FRANCISCO VIADUCTS

One of the most significant characteristics of the earthquake was that much of 

the bridge damage occurred 60 miles away 

in the cities of Oakland and San Francisco. 

Figure 40 provides a view of that area of 

Oakland that suffered severe bridge damage. 

The six damaged San Francisco viaducts can 

be located on figure 2. Figure 79 is a photograph of these six San Francisco viaducts. 

Caltrans has a contract with several aerial 

photography firms to survey for highway 

damage after every large earthquake. Many 

of the aerial photographs in this report come 

from those surveys, which provide vertical 

and oblique aerial photos of all the highways 

impacted by the Loma Prieta earthquake.

The following pages provide information on damage to six San Francisco viaducts. All of these viaducts have at least a 

small portion or the whole structure supporting a double deck. Many of these elevated 

expressways were torn down after the earthquake and never replaced. Others are awaiting political decisions before they are rebuilt. 

This process is in sharp contrast to the 1994 

Northridge earthquake, for which the city 

of Los Angeles spared no expense in helping Caltrans replace all the damaged structures in less than a year and reflects the 

different attitudes the two cities have toward 

their elevated expressways.

SOUTHERN FREEWAY VIADUCT

DESCRIPTION OF STRUCTURE

This long viaduct carries 1-280 traffic 

from China Basin to the Alemany Interchange in the City of San Francisco (see figs. 

2, 81). It was built in three contracts. Contract 14T13C17 was the southernmost contract which was begun in 1962. Contract 

14-207034 was for the middle section, begun in 1964. Contract 14-207044 was for 

the north end of the viaduct, begun in 1966.

The configuration of decks and frames 

varies from a two-frame double-deck structure in the south to a very wide single-deck 

structure in the north. Very long outrigger 

bent caps are found where the structure
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 49

changes from a double-deck to a single-deck bridge. Consequently, the bent geometry varies considerably. The double-deck 

bents have prestressed top bent caps and a variety of pinned and 

moment-resisting connections (fig. 81). Like many of the long 

bridges around the bay, one end of this structure is supported on 

sandstone (the south end), which rapidly descends, leaving most 

of the structure on Bay mud. The structure is supported by 14BP102, 

10BP42, and CIDH piles. There are also some spread footings. The 

bridge was retrofitted in the 1970's with restrainer cables (fig. 82).

BRIDGE DAMAGE

All of the earthquake damage occurred to work done under 

Contract 14-207034, which is the middle (double deck) portion of 

the bridge. There was column damage from Bent 46 to Bent 58. 

There was also some superstructure damage including deck spalls 

at spans 17,24,42, and 43 and some transverse cracks in Span 32. 

Almost all the expansion joints were opened about 1.5 to 2 inches.

Bent 46 Left Column.—The column was cracked just below 

the upper deck reinforced concrete bent cap. A nearly vertical crack 

runs across both the north and south faces for about 15 feet.

Bent 47Left Column.—There are three vertical cracks where 

the lower deck bent cap meets the left column. They run from 

the top to the bottom of the cap. There is a spall (2 ft.by 2 in.by 

6 in.) at the top face of the cap where it meets the column.

Bent 48 Left Column.—A large crack occurred all the way 

though the top of the left column (fig. 83). The top of the column is not monolithic with the outrigger bent cap. This pin connection clearly began to fail due to movement of the top deck. 

The framing diagram (fig. 84, 85) shows how the left column 

must carry the upper deck transversely.

Bent 51 Right Column.—Diagonal cracks formed where 

the column frames into the bent caps (fig. 80, 86).

Bent 52 Right Column.—Similar to Bent 51, a shear transfer crack formed at the bottom bent cap.

Bent 58.—The barrier rail and overhang were damaged by 

banging against a column.

REPAIR AND RETROFIT

After the earthquake, temporary supports were placed at 

the damaged bents. Then a temporary retrofit was completed on 

vulnerable columns (fig. 87). However, it was rejected by the 

Peer Review Panel as not providing sufficient ductility, especially at the column to cap connections (the Governor's Board 

of Inquiry recommended that major bridge projects should be 

peer reviewed). The eventual retrofit (fig. 88) includes edge 

beams to pick up flexural moments that otherwise would be 

carried as torsion in the bottom bent cap, oversized joints for 

shear transfer, prestressed top bent caps on pinned connections, 

and new, very ductile columns and footings.

REFERENCES

Orsolini, Greg, 1994, Seismic retrofit of the 1-280 Southern Freeway 

Viaduct: DeLeuw Gather, 11 p.

Liu, David, 1993, Seismic retrofit design for the Southern Freeway 

Viaduct: Imbsen & Assoc. 23 p.

Dameron, R.A., and Kurkchubasche, I.R., 1994, 3D F.E. analysis of 

joint shear in Bent A-78 of the Southern Viaduct: Anatech Research Corp, 4 p.

Br #34-46 / Rte 280 / Post Mile 4.40 

Approximate Latitude & Longitude

N. Lat. 37° 44.9' W. Long. 122°23.5'

Epicentral Distance

56.9 miles

Peak Ground Acceleration N/S U/D E/W

San Francisco Int. Airport 0.24 0.05 0.33

Length Width Skew Year Built

21,588' Varies Varies 1964

Main Span Type

Concrete box girder bridge

Average Daily Traffic = 27,000

Figure 80.—Damage to Bents 51 and 52 of Southern Freeway Viaduct.
50 HIGHWAY SYSTEMS

AS BUILT PLANS

Contrad No

Date Completed 

Document No

P-
Temporary :cK Cov*r

2-0"* K i'-0"t 

Dtck opening

Place concrete, 

full *M'd1fV\ ef tooy

G»"P cored hole

"^ formed hole •

CatoVe Drqm

VIEW A-A SECTION THRU HINGE

K'3 *>ca\e

VIEW B-B

Vio

.-. Restrainer Unv'ts to toe placed norma\

SECTION C-C

Via

Figure 82.—Section drawing of 1972 restrainer retrofit for Southern Freeway Viaduct.

3o5X 

w
52 HIGHWAY SYSTEMS

DAMAGED 

COLUMN

P/S CAP 

—9

Figure 83.—Damage to Bent 48 of Southern Freeway Viaduct.

Figure 85.—Schematic drawing of Bent 48 frame at Southern Freeway 

Viaduct.

£ Column

f Line 363-30.92

Center of gravity of 

prestresslng steel 

to approximate 

o porabolo

Figure 84.—Section drawing of Bent 48 at Southern Freeway Viaduct.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 53

Figure 86.—Damage at Bent 51 of Southern Freeway Viaduct.

Figure 88.—Completed retrofit of the Southern Freeway Viaduct (photograph by Charles Sikorsky).

Figure 87.—Retrofit of the Southern Freeway Viaduct later rejected by 

the Peer Review Panel.
54 HIGHWAY SYSTEMS

CHINA BASIN VIADUCT

DESCRIPTION OF BRIDGE

China Basin Viaduct (fig. 92) is the northernmost portion of the elevated 1-280 in San Francisco. It is the least 

typical of the six damaged San Francisco viaducts because

Figure 90.—China Basin Viaduct.

Br #34-100 /Rte 280 /Post Mile R6.61 

Approximate Latitude & Longitude

N. Lat. 37° 45.8' W. Long. 122°23.5'

Epicentral Distance

57.7 miles

Peak Ground Acceleration N/S U/D EAV

575 Market Street 0.080.060.11

Length Width Skew Year Built

6,364' 137.7' Varies 1971

Main Span Type 

Concrete Box Girder Bridge.

Average Daily Traffic = 35,700

Figure 89.—The China Basin Viaduct before the 

earthquake.

it is single level for much of its length, only becoming 

two level for the tall ramps near the north end. There are 

three alignments used to define this structure. The "A" 

line is the main alignment that dead ends to the left of 

figure 90 (it was originally intended to connect to the Bay 

Bridge). The "S2" line is the shorter, southbound ramp 

below the "A" line in the figure. The "Nl" line is the tall, 

northbound ramp. Figure 91 provides a plan drawing of 

the structure. The bridge's superstructure is a combination of cast-in-place, reinforced concrete box girders, castin-place prestressed box girders, and (predominantly) 

precast prestressed concrete I-girders (that were used to span 

over the many railroad tracks). 

The bents are multicolumn, with 

a few single column and outrigger 

bents for the ramps. The bent 

caps are reinforced concrete 

with some prestressed bent caps 

at the ramps. The foundations 

are a variety of spread footings, 

cast-in-drilled-hole (CIDH) pile 

footings, and driven steel pile 

footings. The soil profile (fig. 

92), which was created after the 

earthquake, shows soft Bay mud 

under the entire structure.

Like many of the other long 

viaduct structures, this bridge 

was constructed under one contract for the northern portion of 

the viaduct and a later contract 

for the southern portion in the 

early 1970's and as a whole was 

without many seismic details. A
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 55

O
56 HIGHWAY SYSTEMS

retrofit contract in the 1980's completed the job of restraining this structure

BRIDGE DAMAGE

The entire structure showed signs of significant movement during the earthquake. The most serious damage was 

to outrigger knee joints similar to the damage at the other 

San Francisco viaducts. Since the ground motion was relatively small, it suggests that outrigger bents require much 

better joint details to survive the maximum credible event. 

There was also signs of large bridge motions along the entire 

viaduct. Table 15 provides the openings of the expansion 

joints measured after the earthquake.

Bent A-J] and A-14.—There was damage to the end diaphragms at Bents A-1 1 and A-14. These were locations where 

the precast I girders were joined over the bents. The hinge 

bolts punched through the diaphragms at these locations.

Bent A-12.—The outrigger bent cap at A-12 suffered 

shear cracks on both sides of the bridge deck (fig. 93).

Bent A-3J.—The tops of the three columns were fixed 

to the bent cap, which suffered some minor cracks at the top 

inside faces of the exterior columns due to transverse movement.

Bent A-32.—This bent is similar to A-31 except that the 

right column here supports an outrigger bent cap. The 

outrigger cap had significant diagonal cracks that extended

from the column up to bridge deck, possibly due to longitudinal movement of the superstructure (fig. 94).

Bent N-35.—This outrigger bent had significant diagonal cracks where the columns frame into the cap and 

where the cap frames into the superstructure. It is reported 

that the cracks from the superstructure to the cap had existed since construction but may have worsened due to the 

earthquake. The cracks around the columns were the result of transverse movement during the earthquake. There 

were 2 inches of longitudinal movement to the hinge just 

north of this bent. Also one could see the outline of the 

column footings in the soil and pavement around these 

columns (fig. 95).

Bent 82-41.—This bent has a shorter outrigger cap 

with two fixed columns and precast I-girders framed to 

the cap. Again, there was cracking that began where the 

bottom of the cap joined the column and extended to the 

bottom of the exterior girder (fig. 96).

Hinge A-44.—This hinge had pre-earthquake problems of excessive opening due to prestress shortening and 

thermal expansion. It appears that the earthquake further 

aggravated that problem. The earthquake restrainers have 

punched through the diaphragm at some of the bays (fig. 

97).

Abutment FN-45.—The approach fill behind this abutment settled about 12 inches. There was also damage to 

the barrier rail above the abutment wingwalls.

Standard iff-80'

Attuvium 

Spectra

Maximum -4 

Spectrs! 1-G 9 

Oretlnate

I

C 

O

'•Si 

3

LU -150

-200

Abut 49

Frfls

Cryanic Sitty Clay (BtymudJ

Send and Siity Sand

Clayey Sfnd and Sandy City

Bedrock (Skal*. Stntftton* and S*tp>4Atin*)

Bent Number

Figure 92.—Soil profile for China Basin Viaduct (courtesy of CH2M Hill).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17,1989: PERFORMANCE OF THE BUILT ENVIRONMENT 57

REPAIR AND RETROFIT

There were several repair/retrofits done to this structure after the earthquake. Immediately after the earthquake, 

crews erected timber shoring under damaged portions of 

the viaduct. Repairs were designed by Caltrans for the 

damaged bents and to repair the hinges and abutment, 

which allowed the structure to reopen. In the meantime, a 

retrofit contract was given to consultants to strengthen the 

bridge to survive the maximum credible earthquake (fig. 

98). Both of these early designs were later rejected by the 

Peer Review panel because the original intent was to prevent collapse, but the criteria from Caltrans and the Governor was that the viaducts should remain serviceable after 

the maximum earthquake. Caltrans developed a soft-soil 

spectra for this site, and the retrofit consultant modified 

their design to include the entire structure and to use the 

new spectra for the location (fig. 92). This new retrofit 

required enlarging existing columns and providing much 

larger footings.

REFERENCES

Stake, Sherman, 1990, China Basin Viaduct earthquake repair: 14 p.

Casey, John, and others, 1993, Seismic bridge retrofit in California— 

A case study: CH2M Hill, 5 p.

Dameron, R.A., Parker D.R., 1993,3D F.E. analysis of seismic retrofitted foundations on the China Basin Viaduct: ANATECH Applications Corp, 10 p.

Zelinski, Ray, 1993, Road to recovery—San Francisco viaducts reconstruction: Caltrans, 19 p.

Figure 93.—Diagonal shear cracks at outrigger cap for Bent A-12 of China 

Basin Viaduct (photograph by Mike Van de Pol).

Table 15.—Expansion joint movement at China Basin Viaduct

Alignment and span number

S2 LINE - SPAN 43

S2 LINE -SPAN 41

S2 LINE - SPAN 38

S2 LINE - SPAN 34

S2 LINE -SPAN 31

S2 LINE - SPAN 30

Nl LINE -SPAN 44

Nl LINE -SPAN 42

Nl LINE -SPAN 41

Nl LINE -SPAN 35

Nl LINE -SPAN 32

Nl LINE -SPAN 28

A LINE - SPAN 35

A LINE - SPAN 32

A LINE - SPAN 26

A LINE - SPAN 23

A LINE - SPAN 20

A LINE -SPAN 17

A LINE -SPAN 14

A LINE - SPAN 1 1

A LINE - SPAN 8

Movement in inches

1"±

1 1/8" ±

3/8" ±

1"±

3/4" ±

1 1/2" ±

1 1/16"

3/4"

1/2"

1/2"

1"

1/2"

1 1/2"

-

1"±

1/4" ±

1"±

2"±

l/2"±

-

1"

Total opening in inches

2 3/4"

3 5/8"

2 7/8"

2 1/2"

2 1/8"

2 3/4"

3"

2 3/4"

3"

3 1/2"

2 1/2"

2 13/16"

45/16"

2 9/16"

2 1/2"

2 7/8"

3 1/4"

3 5/16"

2 1/2"

2 7/8"

2 13/16"
58 HIGHWAY SYSTEMS

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Figure 94.—Damage to Bent A-32 of China Basin Viaduct

Figure 95.—Damage to knee joints at Bent Nl-35 of China Basin Viaduct.

7

Figure 96.—Damage at Bent S2-41 of China Basin Viaduct.

Figure 98.—Similar to the retrofit that was 

done to Southern Freeway Viaduct immediately after the earthquake, this retrofit 

to China Basin Viaduct was also rejected 

because it could not provide a high enough 

level of serviceability after the maximum 

credible earthquake.

Figure 97.—Damage at Hinge A-44 of 

China Basin Viaduct (photograph by 

Mike Van de Pol).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 59

Br #34-55 / Rte 480 / Post Mile 0.54 

Approximate Latitude & Longitude

N. Lat. 37° 47.5' W. Long. 122°23.4'

Epicentral Distance

59.4 miles

Peak Ground Acceleration N/S U/D EAV 

575 Market Street 0.080.060.11

Length Width Skew Year Built

8,804' 52' Varies 1959

Main Span Type

Concrete Slab and Box Girder Bridge.

Figure 99.—Embarcadero Viaduct, view to the northwest from Mission Street.

Figure 100.—Location of Embarcadero Viaduct. 

EMBARCADERO VIADUCT 

DESCRIPTION OF BRIDGE

The Embarcadero Viaduct was that portion of the doubledeck ramps that extended from the Bay Bridge (beyond Bent 56 

of Terminal Separation) as far as Broadway to the north and to 

Sansome Street to the west in the city of San Francisco (figs 

100 to 106). This viaduct carried two reinforced concrete box 

girder superstructures on outrigger bents. The bottom bent cap 

was reinforced concrete with fixed column connections, while 

the top cap was prestressed with pinned column connections. 

The foundations were pile footings with a pinned connection to

the columns. The soil was loose alluvium over Bay mud. 

The bridge was completed in 1959 and retrofitted in 1985 

with cable restrainers that tied the pinned column to cap connection together.

BRIDGE DAMAGE

This bridge had the same inadequate reinforcement details 

as many of the other damaged double-deck viaducts. In fact, it 

was similar to the collapsed portion of the Cypress Viaduct. 

However, the curved alignment and the on and off ramps provided the structure with some transverse stability. Also, the top 

columns were not stubbed into a pedestal as in the Cypress Viaduct. A cursory inspection was made immediately after the earthquake by Caltran's Post Earthquake Inspection Team (PEQIT). 

This survey found that most of the damage was cracking and 

spalling at the interface between the lower columns and lower 

bent cap from Bent 75 to Bent 88. There was also considerable 

damage to the surface road beneath the viaduct. A more thorough inspection was later performed by maintenance engineers. 

Table 16 summarizes their findings. Figures 107 to 113 show 

the typical bent configurations for this structure. Figures 114 to 

120 show typical damage.

DESCRIPTION OF REPAIRS

Immediately after the earthquake, the viaduct was closed 

and timber shoring was brought in to support the superstructure where the columns and bent caps were damaged (from 

Bents 75 to 83). Twenty policemen were needed for the closure at a cost of $ 14,000 a day. Caltrans created a retrofit for 

this structure; however, the City of San Francisco decided it 

had better uses for the land on which the expressway stood 

and Caltrans removed the viaduct.
60 HIGHWAY SYSTEMS

Figure 101.—Structural Plan drawing for Embarcadero Viaduct.

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Figure 102.—Structural Plan drawing for Embarcadero Viaduct.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 61
62 HIGHWAY SYSTEMS

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THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 63
64 HIGHWAY SYSTEMS

Table 16.—Summary of damage to Embarcadero Viaduct

Location Damage

Bent 56 to 64 No damage.

Span 64 Small spall on lower left side of hinge seat.

Bent 65 to 69 No damage.

Span 67 Small spall on lower right side of hinge.

Bent 68 to 69 No earthquake damage.

Bent 70 Left column had a vertical crack where it joined the lower cap.

Bent 71 No damage.

Bent 72 Crack in lower bent cap between two superstructures. Left column cracked at cap.

Bent 73 A fine, vertical crack where left column meets lower cap.

Bent 74 Vertical cracks between all three columns and lower cap (rt col. also had diag. crack)

Bent 75 Cracks and spalls where columns met lower bent cap.

Bent 76 Large diagonal cracks under the lower cap for left and right columns.

Bent 77 Cracks and spalls for all three columns under lower cap.

Bent 78 Right column had serious damage with spalls and cracks on column and lower cap.

Bent 79 Diagonal cracks where left and right columns met lower cap (cap cracked at left col.)

Bent 80 Diagonal cracks where left and right columns met lower cap.

Bent 81 Left column and lower deck shattered at connection to lower cap.

Bent 82 Same as Bent 81. Edge of bottom deck spalled next to columns.

Bent 83 Edge of bottom deck spalled next to columns.

Bent 84 Edge of bottom deck spalled next to columns (obscured by ivy).

Bent 85 Edge of bottom deck spalled next to columns.

Bent 86 No damage.

Bent 87 to 88 Edge of bottom deck spalled next to columns.

Bent 89 to 90 No damage.

Bent 91 Edge of bottom deck spalled next to columns.

Bent 92 No damage.

Bent 93 Edge of bottom deck spalled next to columns.

Bent 94 Edge of bottom deck spalled next to columns.

Bent 95 No damage.

Bent 96 to 97 Edge of bottom deck spalled next to columns.

Bent 98 to No damage.

Abut. 121

Clay St Ramp No damage

Wash. St No damage

Ramp

ELEVATION - BENTS 57 THROUGH 6O

Figure 107. — Elevation drawing of Bents 57 to 60 at Embarcadero Viaduct

Figure 106.—Embarcadero Viaduct under Clay Street Ramp.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 65

ELEVATION BENTS 64 THROUGH 67

Figure 108.—Elevation drawing of Bents 64 to 67 at Embarcadero Viaduct.

Figure 109.—Elevation drawing of Bent 71 at Embarcadero Viaduct.
66 HIGHWAY SYSTEMS

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THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 67
68 HIGHWAY SYSTEMS

Center of ffraw/y of 

prtjfrejiing steel. 

WarAiry farce of 3,36O 

tips. -——-j

ELEVATION

Figure 112.—Elevation drawing of Bent 77 at Embarcadero Viaduct.

Center «/ grtrity of fraf-rtiSing 

jfetl. Wtx-*/ny farce a/ 3,/SO kip* 

for derails naf jrionn, jce Bent T4.

r1, \«f£ Tor 3

LLLVATION

Figure 113.—Elevation drawing of Bent 78 at Embarcadero Viaduct.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 69

Figure 114.—Column damage to west side of Bent 75 at Embarcadero Viaduct.

Figure 115.—Column damage to west side of Bent 76 at Embarcadero Viaduct.

Figure 117.—Column damage on east side of Bent 78 at Embarcadero Viaduct.

ffy

Figure 116.—Damage to sidewalk under Bent 77 of Embarcadero Viaduct. Figure 118.—Column damage on east side of Bent 79 at Embarcadero Viaduct.
70 HIGHWAY SYSTEMS

Figure 119.—Column damage to west side of Bent 79 at Embarcadero Viaduct.

Figure 121.—View after removal of Embarcadero Viaduct.

Figure 120.—Damage to west side of Bent 80 at Embarcadero Viaduct.

TERMINAL SEPARATION

DESCRIPTION OF BRIDGE

The Terminal Separation was a multilevel structure 

built in the 1950's to connect the San Francisco Oakland 

Bay Bridge to the Embarcadero Viaduct and to San Francisco city streets (figs. 121 to 124). It must have been built 

just as the lower deck of the Bay Bridge was changed from 

carrying trains to carrying cars and trucks (as indicated 

by change orders to the lower deck of Terminal Separation during construction). This structure has a complicated 

alignment of circular on and off ramps and connector structures. The location of damage (on alignment "BR") was 

at the only location where the superstructure changed from 

a few steel plate girders to reinforced concrete box girders (fig. 129). The bents are single and multicolumn reinforced concrete with some prestressed bent caps. Most of
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 71

the bridge was supported on 10BP42 (and 14-inch welded) 

steel piles. There were also some Raymond piles (which 

are concrete piles with reinforcement for the top 12 feet) 

on the north end of the structure. Much of the bridge was 

on soft Bay muds (fig. 125).

BRIDGE DAMAGE

Except for Bent 44, this bridge experienced only minor damage from the earthquake. A cursory inspection of 

the bridge by the Post Earthquake Inspection Team on 

October 20 did not detect any damage. An inspection done 

on November 3 by Structures Maintenance found minor 

cracks at Bent 32 and failed rocker bearing bars that 

dropped the steel girders onto the bent cap at Bent 36 (fig. 

126). A more careful examination by Structures Maintenance dated November 9 lists the following damage.

Bent 44 (Column 2).—The lower outrigger bent cap 

was completely fractured with > 1/4-inch cracks extending transversely across the top of the bent cap approximately 6 feet back from the face of the column and 

extending down both sides to the bottom of the bent cap 

at the column face (fig. 127). Concrete was removed using a hammer, which showed fracturing extending into the 

core of the bent cap. The condition of the fractured concrete was rubble. Concrete in this area was lightweight 

Portland Cement Concrete. Estimated cost to repair this 

damage was $250,000.

Bent 48.—The bent cap between Columns 2 and 3 (fig. 

128) was cracked vertically at midspan, with the cracks extending into the soffit. At Column 3 the bent cap was cracked, 

extending from the bottom of the cap at the column inward 

and upward at 45°. The bent cap at Column 4 was cracked at 

the column similarly to that described for Column 3. Repair 

cost at this bent was estimated to be about $50,000.

Bent 49.—No earthquake damage (fig. 129).

Bent 50.—No earthquake damage (fig. 129).

Bent 51.—The bent cap at Column 1 was vertically 

cracked at the column face, with exposed rebar (fig. 130). 

Total estimated cost of repair for this bent was estimated 

as $50,000.

TESTING AND REMOVAL

The repair cost for the entire structure would have been 

$350,000. However, the structure was removed 2 years after 

the earthquake, mainly for political and aesthetic reasons. 

Before the structure was removed the foundations were tested 

in a repeat of the testing done on the Cypress Viaduct. This 

was to confirm the higher values for pile stiffness and ultimate strength that was gathered from the Cypress tests. Engineers wanted to take advantage of these higher values in 

their designs but needed further testing to confirm these 

values. In 1996, plans were being made to retrofit the west 

approach to the Bay Bridge and build new off-ramps to replace the existing Harrison and Terminal Street off-ramps.

Br #34-54 / Rte 80 / Post Mile 5.45 

Approximate Latitude & Longitude

N. Lat. 37° 46.9' W. Long. 122°23.8'

Epicentral Distance

59 miles

Peak Ground Acceleration N/S U/D BAY 

575 Market Street 0.08 0.06 0.11

Length Width Skew Year Built

Varies 28' Varies 1955

Main Span Type

Reinforced concrete box girders, (with 

a few welded plate girders, and 

concrete slabs)

Figure 122.—Terminal Separation.
72 HIGHWAY SYSTEMS

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F Duk»Mr< 11/91

STATE OF

CALIFORNIA

DEPARTMENT OT TRAMSPORTAT1M

DIVISION or STRUCTURES

STRUCTURE DESIGN 2

TERM

1 ' I ' T 

Figure 129.—Elevation drawing of Bent 49 and 50 at Terminal Separation.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 77

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78 HIGHWAY SYSTEMS

CENTRAL FREEWAY VIADUCT

DESCRIPTION OF BRIDGE

The Central Freeway Viaduct was a 2.7-mile-long elevated 

freeway in central San Francisco. Its location is shown on the 

map in figure 2 and on the aerial photographs in figures 131 and 

132. The structure was composed of concrete and steel sections. 

A double-deck reinforced concrete box girder section extended 

from Mission Street north to Turk Street (fig. 134). The portion 

north of the ramps at Oak and Fell Streets where there was earthquake damage was closed and has now been removed (fig. 136). 

There are a few prestressed bent caps and one prestressed superstructure (Span 21 ) spanning over Market Street. A steel girder 

section extends from Mission Street to 1-80 in east San Francisco (fig. 135). There are also three sets of ramps (fig. 133). On 

the east end of the steel structure there are connectors that join 

the bridge to 1-80 north to the Bay Bridge and I-101 south. On 

the west end of the steel structure are on and off ramps to Mission and Van Ness Streets. The double-deck structure has ramps 

at Oak and Fell Streets. The viaduct is supported on pile foundations on a deep, dense sand.

The Central Viaduct was completed in 1959 at a cost of 

$7.7 million. In 1974 it became part of the Phase I retrofit program, with restrainers tying the hinges together and with restrainers that went through the steel bent caps to tie the steel 

girders together. Like most of the other double-deck viaducts, 

the Central Viaduct was given a column retrofit in 1990 that 

was later rejected by the peer review panel. In 1996 a new retrofit was begun for the steel portion of the viaduct. A contract has 

been given to remove the top deck of the concrete portion, and a 

retrofit of the bottom deck is being planned. However, the city 

of San Francisco may eventually raze the concrete structure.

BRIDGE DAMAGE

Figures 137 and 138 show plan views of portions of this 

structure that sustained damage during the earthquake. Figure 

142 (Thiel, 1990) is a schematic diagram of the bents that sustained damage to this structure. The bridge was inspected by 

Structures Maintenance on October 26, 1989, with the following findings:

Bent 8.—The bent cap was spalled below the bearing for 

the right exterior girder on the southbound side (upper deck). 

The bearing appeared to have remained in place, but there was a 

leveling nut exposed under the bearing plate as well as three 

vertical rebars and a horizontal rebar. Approximately 1 to 4 inches 

of the bottom of the bearing plate was exposed. At the time of 

this investigation the girder had not been supported off the bent 

cap with timbers (cost of repair, $5,000).

Bents 36 and 37.—There were some fine vertical cracks in 

the left columns at the lower deck bent cap. These cracks appeared to extend completely through the column since they could 

be seen on both sides. This condition appeared to be stable and 

not structurally significant.

Bents 42, 43, 44, 45,46, and 48.—Column 2 (and Column 

3 for three column bents) had a similar cracking pattern, which 

consisted of mostly heavy and medium cracks proceeding 

through the center (of the sides of the columns facing up and 

down station) and terminating at the opposite sides of each column after following on approximately diagonal path. These 

cracks, starting at the base on the lower deck, proceeded up 

from 10 to 14 feet toward the upper deck. They appeared to be 

of a compression failure nature. In Column 2 of Bent 43 and in 

Column 3 of Bent 48, this cracking was advanced enough to 

form an "X" pattern and to induce significant spalling and incipient spalling at Bent 43 with exposure of main and tie reinBr #34-077 Rte 101 / P.M. R4.25 

Approximate Latitude & Longitude 

N. Lat. 37° 46.2' W. Long. 122°24.9' 

Epicentral Distance

59 miles

Peak Ground Acceleration N/S U/D EAV 

Pacific Heights 0.05 0.03 0.06

Length Width Skew Year Built

13,994' Varies Varies 1955

Main Span Type

Reinforced concrete box girders, 

welded plate girders, and concrete 

slabs

Average Daily Traffic = 133,000

Figure 131.—Central Freeway Viaduct (in foreground).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 79

forcement (figs 139 to 141). In all cases the 

cracks appeared to extend through the entire 

column cross section. At street level, Column 3 

of Bent 48 and Column 2 of Bent 49 had the 

same damage as mentioned above, indicating it 

was distressed and only partially functional. Figure 142 shows all the significant damage that 

occurred at Central Viaduct during the earthquake.

There was also some minor damage including:

Bent 47.—Column 1 had some incipient 

spalling at the right corner near the base of the 

column at the level of the lower deck.

Bent 48.—Column 3 has a minor corner 

spall in left corner where the column joined the 

top bent cap (near the top level).

Bent 54.—Near column 3 there were old 

shear cracks, which may have been worsened 

by the earthquake. A crack proceeded from the 

inside corner of the base of the cap upwards 

to the top of the cap, roughly on a diagonal 

trace. Another fine crack, 6 feet farther out on 

the cap, was roughly parallel to the first crack. 

These cracks were only on the down station 

face of the cap. Column 1 had a 1.5- by 1.5- 

by 2.25-foot-deep spall at the right corner at 

the base of the column at street level. A 2-inch 

length of main reinforcing bar was exposed.

Figure 132.—Central Freeway Viaduct.

Figure 133.—Ramps onto Central Viaduct at Oak and Fell Streets.

Figure 134.—Double-deck portion of Central 

Freeway Viaduct.
80 HIGHWAY SYSTEMS

Figure 135.—Steel girder portion of Central Freeway Viaduct.

Figure 136.—Central Viaduct removal.
rT~ r* j a \ i n I 35

i a i 'MS 'T-

AS LT PLANS Contract No -a 

Completed 

Document

Figure 137.—Structural Plan drawing of damaged area at Central Freeway Viaduct.
82 HIGHWAY SYSTEMS
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 83
84 HIGHWAY SYSTEMS
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 85

W)

E
86 HIGHWAY SYSTEMS

ALEMANY INTERCHANGE REPAIR AND RETROFIT

DESCRIPTION OF BRIDGE

This viaduct (fig. 143) has single and double-deck reinforced concrete box girder superstructures (also a few precast girders) on single and multicolumn bents. It is the 

southernmost of the double-deck viaducts shown in figure 2. 

It connects I-101 with 1-280 on six separate alignments— 

line RW and RE to the north, WU and WL to the south, and 

AL and AU to the east (fig. 144). It is a reinforced concrete 

structure on pile foundations in fairly solid material. It becomes a fairly dense sandy clay below the first 10 feet of 

soil. The bedrock (sandstone with layers of shale) is at 60 

feet below the surface at Abutment WU-1 and rises to 12 feet 

at Bent 10. It then descends to 170 feet at Bent 17 and then rises 

to 65 feet at Bent 23.

BRIDGE DAMAGE

This is the least damaged of the six San Francisco viaducts. Most of the damage appears to be minor spalls from 

banging during the earthquake. However, because it is a 

double-deck viaduct and is just south of the heavily damaged Southern Viaduct, it is included here. Structural Maintenance completed their investigation on October 31, 1989, 

which is summarized in table 17.

WORK RECOMMENDED

Repair column at Bent 27: Cost =$95,000. Place restrainer at Span 27: Cost = $50,000.

This viaduct also had a proposed retrofit that was rejected by the Peer Review Panel. However, a very innovative 

retrofit was done in 1992. This structure, like so many bridges, 

begins on very short bents and gradually ascends on very tall 

columns. To prevent substructure damage on the short, stiff 

bents and to prevent superstructure damage on the tall, strong 

bents, isolators were installed to give the substructure a uniform response along its entire length and to prevent large 

plastic moments from forming on the tall columns (fig. 145).

Table 17.—Summary of damage toAlemany Interchange

Alignment (see fig. 144) Damage

RE line Span 3 Hinge is open 21/2 in. There is a spall on the right barrier

rail. 

RE line Bents 4 to 6 Soil pushed away from columns. Fine diagonal cracks in

bent caps.

RE line Span 6 Hinge is open 2 in. Spalls on right curb pull box and barrier rail.

RE line Span 8 Hinge is open 21/2 in. 

RE line Bent 10 Sand boils at bottom of column. Old drain box pushed 1/2

in. from column.

RE line Span 11 Hinge is open 2 1/2 in. 

RE line Span 15 Hinge is open 2 1/2 in. 

RE line Span 19 Hinge is open 1 3/4 in. 

AL line Span 9 Hinge is open 11/4 in. at bottom, closed at top right, and

open 1 1/2 in. at top left.

AL line Span 14 Hinge is open 2 1/2 in. 

AL line Span 19 Bearings look good. 

AU line No damage. Hinge opening 2 in. Span 4, 2 1/2 in. Span 8,

and 1 1/4 in. Span 11. 

WL line Bent 16 Spall at rail joint.

WL line Span 19 Skewed hinge is open 11/2 in. but has no offset. 

WL line Bent 27 Small spall in left corner. Column has 1 in. wide crack at

side walk. 

WL line Span 27 Hinge opening 2 in. on left and 3 in. on right (assume no

restrainers installed).

WL line Span 30 Hinge is open 3 in. 

RW line Bent 2 to 5 Ground cracks around footing (exposed but no damage

found). 

RW line Span 3 Hinge is open 2 in.

Br #34-070 / Rte 280 / Post Mile R4.07 

Approximate Latitude & Longitude

N. Lat. 37° 44.1' W. Long. 122°24.4'

Epicentral Distance

59 miles

Peak Ground Acceleration N/S U/D E/W 

Diamond Heights 0.12 0.05 0.10

Length Width Skew Year Built

11,541' varies varies 1960

Main Span Type

Continuous concrete box girders

Average Daily Traffic = 151,700

Figure 143.—Alemany Interchange (view to south).
	INDEX OF SHEETS

Stun No. I GtMrol Plon

• • 2 Slruclvrt Pton No. I

• • J Siruflurt PlcnNo.2

• • 4 Slrtcluri Plon No. 3

• * 5 Hlngt Rtilnlntr Dtlolll

• * £ >Mt» Holt Dttolli• • 7 Span DC 17 Nlngi Rtllrnli

DESIGN' A.A.S.H.O. dmd 1969 with rmia'mi and as 

«pp(tm«iit«< bj Elrlty Plormlng an 

normal.

X

tadicales opproiinMIe locorion for Installing hinge nstraintrs

^—£

UVEL0MXN& HS 20-44

REINFORCED CONCRETE < Fs = 24,000 P.S. L, tietpt

= 20,000 PS.I., in trontvtrst tick 

__ sJoln am) stirrups

TTPICtL'TBeN'T^ FC ' 1,300 P.S.L,«Klpl

^W --1,200 P. S.L, In trw««trs« dcd

N -10 

STRUCTURAL STEEL Fc= M.OOO P.S. I.

NO AS. WltT CHANGES

AS BUILT

CORRECTIONS 8r_ 

CONTRACT NO.

Figure 144.—General Plan drawing showing alignment of Alemany Interchange.

ALEMANY INTERCHANGE UNIT LOc«rn».*T THC iNTeRStenoN or *LCHA«Y BLVD. AS BUILT PLANS

Conlract

Date

Document
Figure 145.—Completed retrofit for Alemany Interchange.

Embarcadero 

Viaduct

Bent Types II & III

-Joint shear 

fracture

Central 

Viaduct

Bent Type II

"Column shear 

fracture

Bents 42, 43, 44 & 45

Southern 

Freeway 

Viaduct

Bent Types III & IV

-Joint shear 

fracture

HIGHWAY SYSTEMS

SUMMARY OF DAMAGE TO SAN FRANCISCO VIADUCTS

On the previous pages we have examined how six San 

Francisco viaducts performed during the Loma Prieta earthquake. Figure 146 (Thiel, 1990) gives a good sense of the 

problems that can result from using outrigger bents without 

good seismic details. There was shear and torsional damage 

to columns, bent caps, and girders. There were problems of 

shear transfer in joints. Pin connections performed poorly. 

Much of the research after the Loma Prieta earthquake looked 

at better reinforcement details for member or joint shear.

OTHER BRIDGES WITH MAJOR DAMAGE

ROUTE 92/101 SEPARATION

DESCRIPTION OF BRIDGE

Construction of this interchange was begun in 1971, 

with a portion built as a cast-in-place, prestressed concrete box girder structure on two-column reinforced concrete bents but with the bulk of the interchange made of 

temporary timber stringer spans on timber pile bents. It 

remained this way through the 1970's, probably as a result of lack of funding for highway projects. In 1986 the 

structure was finally completed as a cast-in-place, prestressed concrete box girder interchange with single and 

multicolumn bents (figs. 147 to 149). The newer portion 

was built as a modern seismically resistant bridge using 

all of the new Caltrans innovations such as spiral reinforcement and continuous longitudinal reinforcement in 

the columns. The structure is supported by 70-ton and 100- 

ton concrete piles. The log of test borings completed in 

1986 indicates soft clays for the first 30 feet gradually 

becoming very dense at about 65 feet below sea level (fig. 

150). It appears that this soft clay soil combined with the 

curved alignment caused large movements that overstressed areas of the structure.

China Basin 

Viaduct

Bent Type IV

Outrigger bent 

shear factor

Terminal

Separation

Viaduct

Bent Type I

-Girder shear 

fracture

Figure 146.—Summary of damage to San Francisco Viaducts (Thiel 1990).

BRIDGE DAMAGE

The most significant damage to this structure was failure of elastomeric pads at the hinge for Span 19 of the 

Northwest Connector (fig. 151; table 18). It had been assumed that the greased plates above and below the bearing would allow the hinge to move during the earthquake. 

Apparently the grease and neoprene pads harden over time 

and the pads can fail in shear since they are not designed 

for earthquakes. Replacing bearings at hinges is a difficult and expensive procedure. Large jacking frames had 

to be built on the ground that reached the superstructure 

soffit. A better hinge design is needed that will allow maintenance crews to reach the bearings from inside the cells 

of the box girder superstructures. A report was prepared 

by Structural Maintenance on November 17, 1989, that
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 89

Br #35-252L/R / Rte 92 / Post Mile R11.78

Approximate Latitude & Longitude

N. Lat. 37° 33.2' W. Long. 122°17.7' 

Epicentral Distance 

42.8 miles

Peak Ground Acceleration N/S U/D EAV 

Foster City 0.29 0.11 0.26

Length Width Skew Year Built

4,282' & 4,362' 38' Varies 1971

Main Span Type

Continuous concrete box girders

Average Daily Traffic = 44,350

Figure 147.—Route 92/101 Interchange.

Figure 148.—Location of Route 92/101 Separation.

gives a complete description of bridge damage and repairs. 

The following is a brief summary based on that report.

DAMAGE AND REPAIR TO THE NORTHWEST CONNECTOR

The Northwest Connector consists of three longitudinal frames on single column bents. The superstructure is 

a prestressed concrete box with two vertical, interior girders and two sloping, exterior girders (figs. 152 to 154). 

The depth varies from 5 feet at the abutments to 8 feet in 

the central portion of the bridge. The traveled way is 26.25 

feet on a bridge width of 29.25 feet. The northerly frame 

is about 600 feet long, extending from the hinge in Span 

11 to the hinge at the fifth point of Span 16. Then the

center frame extends about 700 feet to the hinge at the 

five-sixths point in Span 19. From this hinge, the southerly frame runs about 450 feet to Abutment 23.

The hinge at the center frame suffered serious damage due to relative movement between the three frames 

during the earthquake (fig. 155). The elastomeric bearing 

pads did not delaminate, but certain layers were compressed and worn down. Inspection of the joints showed 

that the suspended side of the Span 19 hinge was 1.5 inches 

lower than the support side. On October 25, 1989, work 

began to replace the elastomeric pads at Span 19. The superstructure was jacked up, new elastomeric pads and 

restrainers were placed in the hinge, and the bridge was 

reopened to traffic on November 2, 1989. The Span 16
90 HIGHWAY SYSTEMS
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 91

I
92 HIGHWAY SYSTEMS

hinge is located above a San Mateo city street. On November 9, 1989, the bridge was again closed to traffic to 

replace the bearings at Span 16. The Northwest Connector ramp was re-opened to traffic at 5:20 p.m., November 

12, 1989. The jacking towers were dismantled on November 13. Support timbers and soil were removed and the 

city street was re-opened to westbound traffic on November 

15, 1989.

To a casual observer the Southeast and Northwest Connectors appear to be nearly identical structures. They are only 

350 feet apart at their center frames which are both supported 

by long, single column bents founded on prestressed concrete piles. However, the Southeast Connector has features 

that give it much better stability. The center frame of the 

Southeast Connector is supported on four single-column

Table 18.—Hinge movement for Northwest Connector of Route 92/101 

Interchange [Openings on November 17, 1989 at 55 °E]

Hinge Location On Left Side On Right Side

Figure 151.—Hinge opening at Northwest Connector of Route 

92/101 Interchange due to earthquake.

Northwest Connector Span 1 1 hinge 3 3/4 inches 3 5/8 inches

Northwest Connector Span 16 hinge 6 1/2 inches 6 1/2 inches

Northwest Connector Span 19 hinge 5 1/8 inches 5 1/8 inches

Northwest Connector Abutment 23 2 7/8 inches 2 7/8 inches

Southwest Connector Abutment 1 1 7/8 inches 2 inches

DEVELOPED ELEVATION

Figure 152.—Elevation drawing of the Northwest Connector of Route 92/101 Interchange.

Figure 153.—Plan drawing of the Northwest Connector of Route 92/101 Interchange.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 93

bents, while the Northwest Connector has only three single- clay resting on stiff material. This condition is not present 

column bents. Moreover, at the Southeast Connector, Bent 6 for the Northwest Connector, where there is only a dense 

and Bent 9 each has a 6-foot thickness of sandy gravel mate- blanket of 3 to 5 feet over the 30-foot layer of soft clay. The 

rial at the surface over about 28 feet of soft clay, resting upon stiffer material at the Southeast Connector may have prohigher density, stiff material. Bent 7 and Bent 8 have 1 8 feet vided enough resistance to prevent large hinge movements, 

of stiff highway embankment material over 20 feet of soft

Figure 154.—Northwest Connector on Route 92/101 Interchange. Figure 155.—Spall at Northwest Connector of Route 92/101 Interchange.
94 HIGHWAY SYSTEMS

• i

f

.s
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 95

DAMAGE TO THE SOUTHEAST CONNECTOR

Figure 156 shows the geometry of the eastern portion of 

the Southeast Connector. At the 2-year inspection of this interchange (on February 1, 1990), two spalls were noticed at 

the column of Bent 12SE. The spall in the south side of the 

column is just above the collar around the base of the column. This spall is oblong in shape, measuring about 2 feet 

vertically, and about 1 foot horizontally. It is very shallow, 

only in the surface of the column concrete. The other spall is 

very small, located on the opposite side of the column, also 

at the base of the column, just above the collar.

Because the column of Bent 12SE was spalled near the 

bottom of the column, it was decided to investigate the condition of the footing block concrete and the supporting piling. It was decided also to investigate the condition of the 

footing of Bent 13SE as well, although there were no spalls 

at that column.

The soil around the base of most of the columns of this 

structure in the vicinity of Bent 12SE and 13SE had consolidated because of the October earthquake. There is a small 

crack in the soil around these single column bents, outlining 

the shape of the footing (fig. 157). The consolidation is not 

severe, only an inch or two in some locations. At other locations, only a small crack is visible in the soil, outlining the 

edges of the footing. In most locations, the cover over the 

footing block concrete is only 2 to 3 inches.

As part of the 1990 inspection, Dave Aro, Bridge Supervisor, and Steve Maas, Leadworker, both assigned to the 

Caltrans Foster City Maintenance facility, excavated two sides 

of the footing at two locations: Bent 12SE and Bent 13SE. A 

trench about 3 feet wide was dug along the north edge and 

the east edge of both footings. The soil side of the trench 

along the east edge was sloped to prevent the material from 

caving into the trench while Steve and I were working in the 

excavation. The trench was excavated to a depth of about 6 

feet. (The vertical dimension of the footing block concrete is 

5.00 feet.) The trench along the north side was made deeper

Figure 157.—Foundation movement at Southeast Connector of Route 

92/101 Interchange.

near the northeast corner of the footing to provide a sump for 

ground water to drain while they studied the footing block 

concrete and the condition of the corner pile of the footing. 

In addition to excavating along the two edges of the footing, 

the north and east portions or the top surface of the footing 

were exposed and swept clean. The inspection showed the 

following:

1. There are no spalls at the base of the columns where 

the column joins the top of the footing.

2. There are no cracks in the footing block concrete either in the top surface or in the vertical faces that were exposed by the trench excavations. It was found that there are 

no vertical (punching or vertical shear) cracks, no horizontal 

(delamination) cracks, and no diagonal (horizontal shear) 

cracks.

3. The pile in the northeast corner of each of these two 

footings had no visible distress.

4. There are some fine to medium-wide cracks in the 

concrete collar around the base of the columns. These cracks 

stop at the bottom of the collar. They do not extend into the 

footing.

Since no earthquake damage was found in the footing 

block concrete or in the supporting piling of Bent 12SE and 

Bent 13SE, no further footing excavation and investigation 

is planned. The findings at these two locations indicate that 

the other footings of this structure also remain in good condition.

DAMAGE TO THE NORTHEAST CONNECTOR

In 1991, Professors Saidi and Maragakis from the University of Nevada at Reno made a study of several wide soffit cracks near the hinge of the Northeast Connector (figs. 

158 and 159). These cracks were reported after the earthquake, but an investigation had to wait until access holes were 

cut into the soffit (November 21, 1991). The cracks, along 

with some damage to the barrier rails at the hinge, suggested 

that they were caused by the earthquake (figs. 160 to 162). 

Because the cracks were vertical along the webs, they could 

not have been caused by shear. Because the cracks were near 

the hinge, they could not be caused by flexure. Therefore, it 

was felt that the cracks were caused by tension. The eccentric location of the restrainers could possibly have produced 

a flexural moment which may have caused these cracks. Also, 

the role of prestressing tendons combined with cable restrainers needs more study.

There was also damage to the ramps on this interchange. 

Refer to figure 141 for the orientation of the ramps. Table 19 

summarizes the damage.

CONCLUSION

This interchange may have had some problems during 

construction that were exacerbated during the earthquake. 

These problems could have been from using a poor quality
96 HIGHWAY SYSTEMS
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 97

concrete or from early removal of the falsework that caused 

the many soffit cracks and the poor performance of the bearings that is continuing long after the earthquake. Also the 

maintenance reports on this structure reveal a variety of problems. Since this is a recent structure with modern seismic 

details, the columns performed well and there was no serious damage. However, replacing bearings is expensive and 

requires the temporary closure of parts of the interchange. 

The construction of large, curved interchanges on soft Bay 

muds should be avoided since it causes large movements and 

a lot of banging of hinges and spalling of concrete.

The performance of this structure during the earthquake 

shows that modern seismic details can prevent major damage but cannot prevent a variety of minor damage during large 

earthquakes.

Figure 161.—M. "Saiid" Saidi investigating cracks in interior bay of Northeast Connector of Route 92/101 Interchange.

Figure 159.—Portion of Northeast Connector of Route 92/101 Interchange 

where soffit cracks were investigated.

Figure 162.—Barrier rail damage at hinge of Northeast Connector of the 

Route 92/101 Interchange.

Figure 160.—Soffit cracks on Northeast Connector of Route 92/101 Interchange.

Table 19.—Summary of damage to ramps on Route 92/101 Interchange 

Locations on SE Ramp Damage

Abut. 1

Span 9 

Bent 12

Span 13

Inside face of rail spalled. Joint open

3 in. (wingwall rail to bridge rail

open 6 1/4 in.).

Soffit spalled at hinge in several

places.

Column spalled at reduced section by

ground. Ground cracks match footing

perimeter.

Soffit spalled at hinge and at Bent 13.

Locations on ES Ramp Damage

Span 10 

Span 13

Bent 15

Bent 16

Railing spalled where ramp joins

mainline eastbound.

Left exterior girder spalled at hinge.

Joint open 1 1/2 in.

Top of right column spalled on inner

side.

Top of left column spalled on outer

side.
Br #36-88R/L / Route 1 / Post Mile R1.59 

Approximate Latitude & Longitude

N. Lat. 36° 54.4' W. Long. 12T46.4'

Peak Ground Acceleration N/S U/D EAVWatsonville 0.28 0.66 0.39

Main Span Type

Continuous concrete 'T' girders

Figure 163.—General Plan drawing of 

Struve Slough Bridges.

Epicentral Distance

10.8 miles

Length Width Skew Year Built763'& 800' 28' 30° 1965

Average Daily Traffic = 15,900

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rONST EQUIPMENT LOCOING DIAGRAM
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 99

STRUVE SLOUGH BRIDGES

DESCRIPTION OF BRIDGE

The Struve Slough Bridges were two reinforced concrete "T" girder structures built in 1965 (figs. 163 to 165). 

The superstructures were continuous for several spans, with 

hinges located in spans 6, 11, and 17 on the right bridge and 

6, 1 1, and 16 on the left bridge (21 total spans). The bridges 

were supported on four, 80-foot-long, 14-inch-diameter 

driven concrete pile extensions at each bent that were embedded into special diaphragms that acted like bent caps. The 

reason the piles were so long is illustrated in figure 166, which 

shows that these bridges were sitting in very soft clay. The 

bridges had end-diaphragm-type abutments, which meant that 

temperature movement was controlled at the three hinges. 

The bridges had a seismic retrofit in 1984 which consisted 

of cable restrainers that tied the hinges together.

BRIDGE DAMAGE

The main problem for these bridges was the weak soil 

that supported them. Once the very soft clay started moving,

0123 4 miles

I t I I I

Figure 164.—Location of Struve Slough Bridges.

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100 HIGHWAY SYSTEMS

it dragged the pile extensions along with it, causing severe 

damage to both bridges. The left bridge collapsed from spans 

6 to 17. Many of the piles were crushed. Several piles in 

Bents #14 and #15 were displaced longitudinally, separated 

from the bent cap, and punched though the bridge deck (figs. 

167 to 171).

There was some speculation that the high recorded vertical motion may have had an influence on the bridge damage, particularly since several pile tips were driven through 

the concrete deck slab. However, an analysis of this structure 

(Saadeghvaziri, 1990) showed that the fundamental vertical 

period of 0.20 seconds was far from the power component of 

the ground motion. Also, the vertical mode had a small participation factor.

The restrainers performed surprisingly well during the 

earthquake, holding the hinges together even on the collapsed 

portion of the bridge. There was a great deal of displacement. Abutment 1 of the left bridge moved 6 inches longitudinally, and the approach fill settled 3 inches behind the 

abutment. The bridge superstructure displaced up to 2 feet at 

midspan. Almost all the pile extensions were damaged. There

were large holes hollowed out in the soil around the piles. 

The right bridge did not perform much better. The superstructure dropped several feet at the hinge for Span 11, causing a depression for several spans. Most of the pile extensions 

were severely damaged.

BRIDGE REPLACEMENT

Damage to this bridge stopped all traffic from traveling 

on the Pacific Coast Highway. Because of the severe damage 

and potential for more damage during the next earthquake, it 

was decided to replace the damaged bridges with new structures that could survive the large movement of the soft soil 

during earthquakes. Caltrans Design Section 11 was given 

the task of coming up with a new design in 8 days. At first 

they thought they could use the standard design charts for a 

slab bridge. However, putting in pile extensions that were 

basically unsupported through 70 feet of soft soil required a 

dynamic analysis.

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STRUVE SLOUGH BRIDGE

Figure 166.—Soil profile for Struve Slough Bridges.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 101

rock. The superstructure was designed as two continuous flat 

slabs without joints (figs. 172 to 173. The complete package 

of plans, specifications, and quantities, was ready for contractors bids on November 15, 1989.

This was the first incentive/disincentive contract offered 

by Caltrans. These types of contracts have become very popular as a way to quickly rebuild damaged bridges after disasters. This contract offered an incentive of $30,000 a day to 

finish early and a disincentive for finishing late of $32,000 a 

day, with 90 calendar days to finish the contract. Typically, 

contractors will consider the incentive/disincentive when 

computing their bids, resulting in a bid that is below the estimated cost of construction. For this work the $4.85 million 

contract provided for two 830-foot-long 40-foot-wide slab 

bridges in a swamp. There were environmental constraints 

on the project, as well as problems working on extremely 

soft soil and having to drive 200 new piles (the new pile locations were specified to avoid the existing piles). The existing structures were removed in the first 5 days and it took 

another 27 days to drive the piles. The contractor asked 

Caltrans to allow him to support the falsework on brackets 

attached to the steel shells of the existing piles. Steel stringers spanned between the piles and supported the plywood 

formwork. Ironworkers then came in and placed the reinforcement. Then 4,115 cubic yards of concrete was poured 

and cured. The job was completed in 55 days (35 days before the end of the contract) on January 25, 1990. Work was 

done around the clock and demonstrated why cast-in-place 

bridge construction dominates in California. The construcFigure 167.—Pile damage on Struve Slough Bridges.

Figure 168.—Cable restrainers holding hinge together on Struve Slough 

Bridges (superstructure was unsupported beyond this point).

Figure 169.—South abutment of left Struve Slough Bridge (view to north).
102 HIGHWAY SYSTEMS

tion cost for this structure with the incentive and bonus was 

$83 per square foot. The average cost for slab bridges is about 

$60 per square foot. However, the costs would have been 

slightly higher due to environmental constraints and working in a swamp. The original contract put a $600,000 cap on 

the incentive, but Caltrans amended the contract for a bonus 

payment if work proceeded around the clock. Apparently, 

the State and Federal agencies felt that opening up the Pacific Highway a month early was worth the extra cost. For 

more information about the environmental, economic, and

construction problems on this contract, refer to the references 

listed below.

REFERENCES

Drago, Jim, 1990, Record breaker: Going Places (a now defunct

Caltrans Publication), March/April issue, p. 10-13. 

Cullen, Michael, 1990, The collapse and redesign of Struve Slough 

Bridge: Caltrans internal document, 3 p.

Concrete Reinforcing Steel Institute, 1990, Case history report: Bulletin #41, 4 p.

Saadeghvaziri, M.A., 1990, Response of Struve Slough 

Bridge: New Jersey Institute 

of Technology, p 213-216. 

S., 1990, Special report on 

Struve Slough Bridges: Federal Highway Administration, 6 p.

Thiel, Charles C, 1990, Competing 

against time—report to Governor George Deukmejian 

from the Governor's Board of 

Inquiry on the 1987 Loma 

Prieta earthquake: State of 

California, Department of 

General Services, 264 p.

Siou,

Figure 170 —Piles penetrating deck of left Struve Slough Bridge (view to 

south)

Figure 172.—Completed new Struve 

Slough Bridges.

Figure 171.—Reconstruction of Struve Slough Bridges.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 103
104 HIGHWAY SYSTEMS

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THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 105

GRANT UNDERCROSSING

DESCRIPTION OF BRIDGE

This bridge has a precast, prestressed concrete "T" girder 

superstructure from Span 1 to Span 3 and a reinforced concrete "T" girder superstructure for Span 4 (figs. 174 and 175). 

The span lengths are 54.75, 58.5, 58.25, and 33.5 feet, for a 

total length of 205 feet. The bridge spans from east to west 

on a 850-foot radius curve. The superstructure is supported 

on two rectangular column bents, with the bottom of the columns pinned. The main column reinforcement is 1 -inch-wide 

square bars and one-half-inch hoops at a 12-inch spacing.

Abutment 1 is a pedestal type with a backwall, while 

Abutment 5 is an end diaphragm type. The approaches and 

abutments are in fill. The foundations have pile caps with a 

bottom mat of reinforcement and driven steel piles.

BRIDGE DAMAGE

At Abutment 1 the right wingwall broke off. The fill had 

settled as much as 12 inches on the outside of the wingwalls 

(figs. 176 and 180). The approach also settled about 6 inches. 

There was curb and railing damage all along the structure (figs. 

178 and 179). At Bent 4, Span 3 moved transversely about 1 

inch to the right, spalling the diaphragm and shearing the bearing plate bolts and grout pads. At Abutment 5 the wingwalls 

moved outward, causing the fill to settle (fig. 177).

Figure 175.—Location map of Grant Undercrossing.

The moderate damage sustained at this bridge is typical 

after large earthquakes, particularly for short multispan bridges 

that span between two large embankment fills. These shorter 

structures get hammered by the soil behind the abutments, driving them back and forth longitudinally and transversely.

Figure 176.—Settlement along abutment of Grant 

Undercrossing (photograph by Mike Van de Pol).
106 HIGHWAY SYSTEMS

Figure 177.—Abutment 5 approach to Grant Undercrossing (view to west) Figure 179.—Exterior spall at Bent 4 of Grant Undercrossing (view to south) 

(photograph by Mike Van de Pol). (photograph by Mike Van de Pol).

Figure 180.—Broken keeper plate for Abutment 5 of Grant Undercrossing 

(photograph by Mike Van de Pol).

Figure 178.—Barrier rail on north side of Bent 3 at Grant 

Undercrossing (photograph by Mike Van de Pol).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 107

Br #28-171 / Route 680 / Post Mile 24.46 

Approximate Latitude & Longitude 

N. Lat. 38° 01.5' W. Long. 122° 06.7'

Epicentral Distance

70 miles

Peak Ground Acceleration N/S U/D E/VV 

Martinez VA 0.07 0.03 0.05 

Length Width Skew Year Built

717.7' 29.7' 0 1962 

Main Span Type

Continuous concrete slab ramp 

(connected to welded steel girder) 

Average Daily Traffic = 83,500

Figure 181.—Mococo Off-Ramp in 1996.

MOCOCO OVERHEAD

DESCRIPTION OF BRIDGE

This structure includes two parallel steel girder 

bridges on hammerhead pier walls that carry Route 680 

traffic over railroad tracks and also a concrete slab 

bridge on a tight radius curve that acts as an off-ramp 

to take traffic onto Escabar Street in the city of 

Martinez (figs. 181 to 184). Only the off-ramp had some 

damage during the earthquake. That structure is supported at the bents by six reinforced concrete pile extensions embedded in a very weak soil (20 to 70 feet 

thick) composed of very soft clay and peat above layers of sandstone and siltstone. The off-ramp has a hinge 

in Span 5 and another at Span 11. There was no seismic retrofit.

BRIDGE DAMAGE

The off-ramp had damage to the hinges (fig. 188) and 

to some pile extensions (figs. 185 to 187) during the earthquake. The soft soil did not provide enough support for 

the pile extensions, and they moved enough to have flexural damage at the high moment locations at the bottom 

and the top of the piles. Most of the piles had some damage, but the most cracks were at Bents 4, 5, and 6, particularly for the exterior piles. The pile with the most 

damage was on the left side of Bent 4. The bents vary in 

height, with the shortest bents being closest to the abutment. The taller, more flexible piles had no cracking. However, they showed a permanent deformation in single and 

a few in double curvature.

The movement of the pile extensions also caused hinge 

damage. Hinges for reinforced concrete slab superstructures are made by modifying steel wideflange girders and embedding them into 

the reinforced concrete slab (fig. 189).

Figure 182.—Location of Mococo Off-Ramp.
108 HIGHWAY SYSTEMS

29.667

Of 

Pile Cracking

Zone Of Pile 

Distortion

/• Approx.OG

Figure 183.—Location of connection between Mococo Off-Ramp and Figure 185.—Elevation drawing of damage to pile extensions of Mococo 

Mococo Overhead. Off-Ramp.

\r

Figure 186.—Damage to Mococo 

Off-Ramp concrete pile extensions at 

ground surface.

Escobor Sfrttt 15

Figure 184.—Plan drawing of Mococo Off-Ramp.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 109

Figure 187.—Cracking to top of pile extension of Mococo Off-Ramp.

Figure 188. — Typical hinge damage to Mococo Off-Ramp.

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Figure 189.—Hinge detail for Mococo Off-Ramp.
110 HIGHWAY SYSTEMS

They provide about 5 inches of seat width. They are located at one-sixth of the span length from a bent. Bolts 

go through slotted holes at the top and bottom of the 

hinge to allow for temperature movement while preventing unseating.

Hinge 1 by Bent 6 experienced a uniform longitudinal displacement of about 1 inch. About half of the bolt 

heads at the bottom of the hinge were missing, exposing fresh-looking metal on the bolt shaft. However, the 

bolt heads could not be found from searching the 

ground. No other damage was found to the hinge, and 

the ride over the hinge felt normal. At Hinge 2 by Bent 

12 the gap was closed at the right (inside) edge of deck, 

and widened to about three-fourths inch on the outside 

edge of deck. There was some spalling on the outside 

barrier. Otherwise, the hinge appeared similar to Hinge 

1, with some bolt heads missing but no other damage. 

At Hinge 3, which is at the connection between the steel 

girder and slab superstructures, there was a constant hinge 

opening and spalling on the inside concrete barrier.

REPAIR AND RETROFIT

Because of concerns about the structural integrity 

of this bridge, it was temporarily closed until October 

20, when a Post Earthquake Investigation Team had 

time to inspect it. They concluded that the damage was 

light, that it did not threaten the ability of the structure 

to carry traffic, and the bridge was reopened. However, 

there was some concern as to how this structure would 

respond to a closer event. Emergency repairs included 

epoxy injecting the cracks in the pile extensions and 

the installation of restrainers at the hinges. This was 

accomplished by drilling holes through the deck for the 

bolts to hold the restrainer brackets (fig. 190). The main 

difficulty was in identifying and avoiding the reinforcement in the deck.

In 1991, a contract was written to design a retrofit 

for this structure (fig. 191). Surprisingly, only the mainline structure was retrofit.

t Hinge

Cable End 

Anchorage Bracket

cableftyp.) 

7 per unit

Figure 190.—Elevation drawing of emergency hinge restrainer retrofit of Mococo Off-Ramp.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 111
112 HIGHWAY SYSTEMS

Br #23-064 / Route 37 / Post Mile R7.39 

Approximate Latitude & Longitude 

N. Lat. 38° 07.2' W. Long. 122° 16.7'

Epicentral Distance

78.6 miles

Peak Ground Acceleration N/S U/D EAV

MartinezVA 0.07 0.03 0.05

Length Width Skew Year Built

3,280' 74.3 0 1962 

Main Span Type 

Prestressed precast concrete T girders

Average Daily Traffic = 29,300

Figure 192.—Napa River Bridge before earthquake.

NAPA RIVER BRIDGE

DESCRIPTION OF BRIDGE

This long bridge climbs to over 120 feet as it crosses the 

Napa River near the city of Vallejo (figs. 192 to 195). It has a 

precast prestressed "I" girder superstructure with a concrete 

deck, except for a 188-foot steel girder span over the ship 

channel. Concrete diaphragms were cast at every pier to tie 

the ends of the precast girders together. At certain locations, 

two diaphragms were cast to provide expansion joints for 

temperature movement. These special joints are at the two 

abutments and at Piers 5, 9, 13, 17, and 23.

Most of the piers are flexible reinforced concrete twolegged bents, except for the stiffer four-legged towers at Piers 

2, 7, 11, 16, and 20. There are 25 spans. They are typically 

120 feet long, except for the span over the ship channel and 

the 30-foot spans over the towers. The superstructure rests 

on bearing pads at the fixed locations and steel rocker bearings at the expansion joints. The substructure is supported 

on pile caps with either 54-inch-diameter hollow precast prestressed piles or 24-inch-square precast prestressed piles.

These piles are supported by layers of very soft to very stiff 

Bay mud (fig. 196). The poor material is about 100 feet deep 

at the west end of the structure and narrows to less than 20 

feet at the east end. There was a seismic retrofit in 1984 that 

included cable restrainers at the expansion joints and transverse 

shear keys on top of the bent caps between all the girders.

BRIDGE DAMAGE

This structure has many characteristics that make it sensitive to long-period ground motion. At 80 miles away, the 

motions for this bridge were extremely small but extremely 

long period. This is similar to what occurred during the 1985 

Mexico City earthquake, where damage occurred on very 

soft soils almost 200 miles from the rupture. Soft soil is very 

responsive to very slow motion as is demonstrated by the 

fact that almost all the serious bridge damage that occurred 

during this earthquake was many miles away on weak cohesive soil sites. Also, we have seen that bridges with a history 

of maintenance problems perform particularly poorly during 

earthquakes. Some bridges begin to spall concrete at the joints 

and start to damage bearings and expansion joint devices alFigure 193.—Napa River Bridge before earthquake.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 113

most as soon as they are built. That was the case 

with several of the bridges we have studied, including the Napa River Bridge.

The first investigation of damage was done by 

a Post Earthquake Investigation Team; however, it 

is difficult to effectively examine a tall bridge over 

water without a catwalk or snooper truck. A snooper 

truck became available on October 30, 1989, and 

was used on this bridge for 2 days and then again 

on December 9 (fig. 197).

The basis for much of the damage can be seen 

in figure 198. Almost all the damage was the result 

of the precast "I" girders pulling out of the diaphragms (figs. 199 to 202). They were tied together 

with #6 reinforcement that ran transversely through 

the diaphragms. During the earthquake the girders 

pulled out, delaminating the concrete behind the #6 

reinforcement.

DIAPHRAGM DAMAGE

There were small to large spalls in the concrete 

diaphragms between the girders at the following 

locations. Pier 9 (Span 8 side), Pier 10 (both sides), 

Tower 1 la (Span 10), Pier 12 (both sides), Pier 15 

(both sides), Tower 16 ( both sides), Pier 18 (both 

sides), Pier 19 (both sides), Tower 20 (both sides), 

Pier 21 and 22 (on the span 21 side). The diaphragms for 

Pier 12 at Span 11 and Pier 15 on both sides had major spalls 

and shear key failures.

GIRDER DAMAGE

The girders at Piers 12 and 15 have pulled out of their 

diaphragms. Pullout at Pier 12 (Span 11) side was about 1 

inch toward Pier 11. Pullout at Pier 11 at the Span 12 side 

was less severe. At Pier 15 at the Span 14 side the longitudinal displacement of the girders was at least 3.5 inches. Five 

inches of the girder ends sheared off along the horizontal 

holes for the continuous reinforcement in the diaphragm. 

Hence, the bearing area of the girder was reduced by 5 inches 

for girder loss and by 3.5 inches due to movement of the 

girder toward Pier 14 for a total bearing loss of 8.5 inches at 

the Pier 15 cap. The girder still had about 12 inches of longitudinal seat on the concrete pad.

OTHER DAMAGE

The joint at Pier 15 was designed as fixed for translation 

and free for rotation. After the earthquake it was free to do 

both. The joint width was 4.5 inches at the deck. The hinge 

in Span 13 near Pier 14 has opened an additional 0.325 inch. 

The hinge in Span 13 near Pier 13 has closed an additional 

3.5 inches. The joint seal in the hinge in Span 13 near Pier 14 

has failed. Pier 14 has deflected about 4 inches toward Pier 13,

Figure 194. —Location of Napa River Bridge.

Figure 195.—Two-and-four-legged piers on Napa River Bridge.
114 HIGHWAY SYSTEMS

causing the restrainer cables at Pier 13 to hang loosely. There 

was flutter at the holes for the restrainers at Pier 14 (the restrainers are double wrapped through the holes in the bent caps 

as shown in fig. 203), and the restrainers were probably damaged. However, they held the superstructure on the bents.

There were some 0.0625-inch-wide cracks on the struts that 

separate the columns at Pier 9, Tower 11 (Span 10 side), Tower 

16 (both sides), and Pier 17. At Pier 9 the cap has a shear crack. 

The restrainers and shear keys were damaged at Pier 9 and Pier 

17. At Pier 17 the damage was extensive and required replacement. There was some edge spalling of the concrete bearing 

pads on the Span 11 side of Pier 12 under Girders 3, 4, and 6. 

The Pier 17 expansion joint was opened 7.125 inches between 

the steel angles of the finger joints. Four inches was the normal 

construction plan opening. The joint is in good condition.

BRIDGE REPAIRS

Although this bridge was not damaged enough to require 

closing after the earthquake, the repairs were very expensive. 

The use of a snooper and traffic control to inspect the bridge 

cost about $30,000 for 5 days. The cost of replacing and repairing cable restrainers was over $100,000. Epoxy injection and 

replacing diaphragms was over $200,000. A retrofit for this structure was done by Caltrans. Because of the weak soil, it was 

feared that new foundations would be required; however, some

of the original piles were located near the structure and tested. It 

was found that the existing foundation would be adequate to 

support the structure for the maximum credible event.

LEGEND

Figure 197.—Snooper on top of Napa River Bridge.

Indicates Pl»r Location 

Indlcotts Tow*r Location

Very Soft Clayey Silt to Sllty Clay 

(Young Bay Mud)

Soft Clayey Silt to Sllty Clay 

(Young Bay Mud)

Stiff Clayey Silt to Sllty Clay 

(Old Bay Mud)

Stiff Clayey Silt 

(Old Bay Mud)

Very Stiff to Hard Clayey Silt 

to Sllty Clay (Silt Stone)

24. In Rtctangu or 54 In QlomtUr Cylinder Hollow Pr«tr»»»»d

Hollew Pr*«tr**«»d

-IOO

-120

-140

-I6O

395+OO 4OO+OO 405+OO

Figure 196.—Soil profile for Napa River Bridge.

4IO+OO 415+00 420+00 425+OO 43O+OO
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 115

«. FIXED JOINT 

BENT

LINE OF DOWELS THRU GIRDER 

INTO END DIAPHRAU

-P/C, P/S. I-GIRDER

BENT CAP

NOTES:

1. DIAPHRAGM NOT SHOWN.

2. DAMAGE AT FIXED JOINT 

(WITH NO RESTRAINER 

CABLES).

Figure 198.—Detail drawing of typical damage to Napa River Bridge.

Figure 199.—Diaphragm damage to Napa River Bridge.

Figure 201.—Spoiling on the Span 16 side of Pier 17 at Napa River Bridge.

Figure 202.—Spalled 

diaphragm at Bay 3 

of Span 14 side of 

Pier 15 at Napa River 

Bridge.

Figure 203.— 

Bent cap damage to Pier 17 

of Napa River 

Bridge.

Figure 200.—Spalling at diaphragm of Napa River Bridge.
116 HIGHWAY SYSTEMS

Br #27-010 / Route 101 / Post Mile 4.03 

Approximate Latitude & Longitude

N. Lat. 37° 53.0' W. Long. 122° 31.0'

Epicentrai Distance

68.7 miles

Peak Ground Acceleration N/S U/D E/W 

Point Bonita 0.07 0.03 0.07

Length Width Skew Year Built

2,864' 138' Varies 1957 

Main Span Type

Prestressed precast concrete 'I'girders

Average Daily Traffic = 141,000

Figure 204.—Richardson Bay Bridge and Separation before earthquake.

RICHARDSON BAY BRIDGE AND SEPARATION

DESCRIPTION OF BRIDGE

This bridge is similar to the Napa River 

Bridge in its components and in its performance during the earthquake (figs. 204 to 

207). The superstructure has precast prestressed "I" girders for half of its length, 

with cast-in-place box girders for the rest 

of the structure. The superstructure is 138 

feet wide, 4 feet 7 inches deep, and has 44 

spans, with a total length of 2,864 feet. There 

is also a 597-foot off-ramp structure. The superstructure is supported by ten 36-inch-diameter column bents, by four towers, and by 

two seat-type abutments. All bents are on pile 

footings embedded in Bay mud (fig. 208). The 

bridge was built in 1957 and widened and retrofitted with cable restrainers in 1973.

BRIDGE DAMAGE

Like the Napa River Bridge, a thorough inspection of 

the Richardson Bay Bridge and Separation had to wait for 

the snooper to arrive on the structure. This bridge had moderate damage as a result of the earthquake. The deck finger expansion joints on the right side of the bridge at Bent

Figure 205.—Location of Richardson Bay Bridge and Separation.

26 and Bent 36 failed. The deck concrete sheared at the 

connection with the expansion joints. The segmented rockers at Bent 26 and Bent 36 had various tilts, few were 

normal, and most were near their maximum rotation. There 

were many spalls and cracks in the diaphragms similar to
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 117
118 HIGHWAY SYSTEMS

Figure 207.—Bents at box girder section of Richardson Bay Bridge.

the Napa River Bridge, owing to girder pull out, deflections, bent racking, and from large longitudinal forces from 

the cable restrainers. Many of the restrainers were damaged or stretched taut.

Some of the shear keys were damaged and spalled the 

vertical cap face. At Bent 31 about 50 feet of the key was 

sheared, at Bent 32 about 70 feet was sheared, and at Bent 

35 about 28 feet was damaged.

There was quite a bit of preexisting damage that may 

have been increased by the earthquake. Many of the columns had minor spalls where they join the bottom strut 

above the footing. However, no rebar was exposed. The 

right exterior girder in Span 30 at Bent 31 had a spall that

reduced its bearing area. The hinge in Span 14 had about 

a 5-inch opening on the left side.

REPAIR AND RETROFIT

This bridge had both emergency repairs and a later 

retrofit. Table 20 summarizes the repairs made after the 

earthquake. A retrofit was designed for this bridge in 1993 

(figs. 209 to 211). The strategy was to take all the load at 

the towers by installing stiff pier walls. Although the superstructure could shear off during a large earthquake, it 

would effectively isolate the bridge. Rubber fenders would 

catch the superstructure after about a foot of movement.

Table 20.—Summary of earthquake repairs to Richardson Bay Bridge and Separation

Location Repair Cost

Bent 26 and 36

Bent 26 and 36

Bent 26 and 36

Bent 31, 32, 35, and Hinge 14

Bent 24, 26, 29, 31,32, and 38

Bent 26, 31,32, and 36

Bent 23, 31,32, and 35

Bent 20 to 23, 26, and 35

Bent 26 and 27

Bent 22 to 28, and 43

Replace expansion joint devices. $70,000

Plumb or replace rockers. $80,000

Replace restrainers. $30,000

Install new restrainers $30,000

Repair diaphragms $ 12,000

Replace diaphragms $42,000

Repair cap spalls $37,000

Epoxy inject column cracks $20,000

Epoxy inject strut cracks $ 18,000

Repair column spalls $71,000 

TOTAL COST = $450,000
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 119
120 HIGHWAY SYSTEMS
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 121

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THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 123

Br #35-054 / Route 92 / Post Mile R14.44 

Approximate Latitude & Longitude 

N. Lat. 37° 36.0' W. Long. 122° 12.8'

Epicentral Distance

43.2 miles

Figure 212.—San Mateo-Hayward Bridge.

Peak Ground Acceleration N/S U/D E/VV

Foster City on west (alluvium) .29 .11 .26

Hayward on east (Franciscan) .10 .05 .12

Length Width Skew Year Built

36,069' 59.2' none 1967

Main Span Type

Steel box girder with a concrete girder 

approach

Average Daily Traffic - 72,000

SAN MATEO-HAYWARD BRIDGE 

DESCRIPTION OF BRIDGE

The San Mateo-Hayward Bridge is one of several San Francisco Bay crossings. This structure is about 7 miles long and 

takes traffic westward from Hayward to Foster City, just south 

of San Francisco International Airport (figs. 212 and 213). The 

bridge is just east of the Route 92/101 Separation, which also 

had some damage described in this chapter. Figure 214 shows 

the geology of the area including the San Andreas fault, which 

is 6.9 miles west of the bridge, and the Hayward fault, which is 

5 miles east of the bridge. This bridge has 5 miles of concrete 

trestle on the east end (fig. 215) and almost 2 miles of a double 

steel box girders on the west (figs. 216 and 225).

The concrete portion is a precast "T" girder superstructure, 

54 feet wide, and with 857 simple spans. Each span ends in a 

corbel supported by a dropped bent cap on prestressed concrete 

piles and the next span sits on the corbel of the previous span. 

The piles extend through about 5 feet of water and then through 

20 to 50 of Bay mud into stiffer material.

The steel portion is an 80-foot-wide superstructure of alternating anchor and suspension units. The anchor units sit on 

pin bearings, and the suspension units hang from alternating 

tied and expansion hinges (fig. 217). The shorter 208-foot spans 

are supported by concrete two-legged piers on piles, while the 

longer 292-foot spans and the ship channel span are on twolegged steel towers (figs. 218 and 219). The piles for the steel 

portion are steel "H" piles with tip elevations varying from 40 

feet to 220 feet below sea level. The footings are rectangular for 

the shorter spans and bell shaped for the longer spans. The bridge 

ends on the west side with a 220-foot-long, four span concrete 

"T" beam superstructure on two column bents. It was designed 

and built in the 1960's and was opened to traffic in 1967.

BRIDGE DAMAGE

There was some minor damage to the bridge during the 

earthquake. However, on such an enormous structure even 

minor damage requires a lot of work to examine and repair. 

As was the case for all these tall water crossings, much of 

the inspection had to wait until a snooper was available. Traffic control and rental of the snooper was expensive. Moreover, divers were required to inspect the thousands of 

foundations and pile connections. The damage included:

Bearings at Piers 18 and 21.—Bearings supporting the steel 

box girders had moved 1.5 inches at the north bearing of Pier 18 

and 4.5 inches at the south bearing of Pier 21. Six of the eight 

interior pin caps (1.75-inch screw cap) had broken off. The end 

keeper plates were bent (figs. 220 to 223).

Towers at Piers 16 and 18.—The towers slid on the base 

plates. At Pier 16 the north column slid 2 inches to the south and 

a half inch to the west. At Pier 18 the south column slid 2 inches 

to the north and a half inch to the west. However, this damage 

was not serious because the tower legs are connected to the base 

plates by very long bolts. During an earthquake, these bolts can 

move around without breaking, providing some isolation to the 

towers.

Span 19 Tied Hinges.—The south box girder tie bar located 

inside the south web was broken loose from the 2-inch-diameter 

pins. The south box girder pins at the north web were deformed.

Pier 38.—At the backwall for Pier 38 the trestle earthquake 

restrainer shelf bearings supporting the first trestle span were 

damaged. The painters stairway giving access to the walkway 

behind Pier 38 has fallen into the bay (fig. 224).

Concrete Trestle.—There were some spalls and cracks in 

the socket between the piles and pile caps.

Traveler Rail.—The painter's walkway under Span 15 had 

some cracking, deformation, and connection damage.
124 HIGHWAY SYSTEMS

Figure 213.—Location of San Mateo-Hayward Bridge.

BRIDGE REPAIR AND RETROFIT

Immediately after the earthquake, there was some concern about the condition of this structure. The bridge was 

temporarily closed while Structural Maintenance personnel 

drove across the bridge looking for misalignments. They used 

a motorboat and a flashlight to inspect the concrete trestle. 

Then traffic was allowed to cross the structure. The cost of 

jacking the towers back into place and repairing spalls to the 

concrete trestle totaled over $1 million.

Because this bridge was built before a great deal of consideration was given to seismic loads, it is highly vulnerable 

to a large earthquake from the San Andreas or Hay ward faults. 

Since the earthquake, all of the San Francisco Bay toll bridges 

have been studied to determine the maximum and 400-year 

return period earthquake demands and to identify the vulnerabilities of the structures. In 1995, consultants were hired 

to design seismic retrofits for these structures. Although a

retrofit design has not been completed for the San MateoHayward Bridge the vulnerability analysis recommended 

increasing the seat width for the trestle portion and providing more piles and more ductility to the piers of the steel 

portion.

REFERENCES

Power, M.S., 1993 Seismic ground motion study for San MateoHayward Bridge: Geomatrix Consultants.

White, Richard W., 1990, Supplementary bridge report: Caltrans 

internal document.

Donikian, Roupen R., 1993, Seismic vulnerability assessment of the 

San Mateo-Hayward Bridge: The Cygna Group.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 125

-'-'——/ I————.- —— * —— 7——:

EXPLANATION

1. Bay mud

2. Holocene alluvium

3. Older alluvium and dunes

4. Old bay mud

5. Late Pleistocene Alluvium

6. Pliocene and early Pleistocene

7. Tertiary and Pre-Terliary

8. Franciscan Formation

0_______3 Miles

0 5 Kilometers

Approximate scale

After Atwater. Hedel and Helley, 1977.

-sq

Figure 214.—Soil profile for San Francisco Bay near San Mateo-Hayward 

Bridge (courtesy of Geomatrix Consultants).

Figure 215.—Concrete trestle portion of San Mateo-Hayward Bridge.

2O8' Spans 292' Spans Channel Spans 292' Spans 2O8' Spans

Concrete Deck Steel Deck Concrete DeckII . • • ••.'•.'', f i ) f 1 •

C. 1 . 1 - 1 - • - • - • - ' |

,.•,11111111 • •• 1 ^U__

AU SU Hinge 

2-3 1-2 FE

•

, .1 . . 1 - \ 1 1 1 . 1 -.-.-.-I-.- I..!,,..., t,M

HID i • n i \ u A « i it > i i i i i • i i > • _., „

— Suspended Span fSUl » ——————— F: Tied Hinge

Anr-hnr Unit IAUI

4- 5

6 7

8- 9

10-11

12-13

14-15

16 17

18-19

22-23 

24-25 

26-27 

28-29 

30-31 

32-33 

34-35 

36-37

3 4 

5- 6 

7- 8 

9-10 

11 12 

13-14 

15 16 

17-18 

1920 

21-22 

23-24 

25-26 

27-28 

29-30 

31-32 

33-34 

35-36 

37-38

FE 

FE 

FE 

F-E 

FE 

FE 

FE 

FE 

FE 

EF 

E-F 

E-F 

E-F 

EF 

E-F 

EF 

EF 

E-F

Figure 216.—Elevation drawing of the steel portion of the San MateoHayward Bridge (courtesy of the Cygna Group).
126 HIGHWAY SYSTEMS

Transverse 

Shear Lock

J

4

1

T

-y^

4-^

«

4

M

^ ———— --*-»

_i ——— 

1

-4 ——— -* ———

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Figure 217.—Steel bridge structural system at San Mateo-Hay ward Bridge (courtesy of the Cygna Group).

CHANNEL SPAN

292'SPANS

208' SPANS

Concrete 

t

SL

f Shafts ~j —

Piers 2-5. 

34-37

El. 25.0'

Piers 6-11,

12 and 13 fw/ steel 

30-33 towers) Piers 19 and 20

27-27

Figure 218.—Piers for steel superstructure at San Mateo-Hayward Bridge (courtesy of the Cygna Group).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 127

Figure 219.—Piers supporting the steel superstructure of San Mateo-Hayward Bridge.

Figure 220.—Repair to damage at Pier 21 of San Mateo-Hayward Bridge.
128 HIGHWAY SYSTEMS

5'-5'

rjfc— J. ————— Ji ————————— .4, ———————————— Jn

|

—1—

• ——————

——— i ———

^-SEE INTER 

PIN ASSEME

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OR 

»LY

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5'-61

5'/2 ' DIA. PIN W/ 

RECESSED NUT

ELEVATION SIDE VIEW

5/2 ' DIA. PIN

-LjL.

DIA. x A" 

CAP SCREW

oCK WASHER

DIA.

R" 4%

NTERIOR PIN ASSEMBLY DETAIL

Figure 221.—Details of steel pin support used as bearings at Piers 18 to 21 

of San Mateo-Hayward Bridge (courtesy of Earthquake Engineering Research Institute).

Figure 222.—Signs of movement at bearing (scraped paint) of San MateoHayward Bridge (courtesy of Earthquake Engineering Research Institute).

Figure 223.—Broken cap and washer from bearing of San Mateo-Hayward Bridge (courtesy of Earthquake Engineering Research Institute).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 129

STAIRWAY REiNSTALLATlON DETAIL

esoxv rnorte' ^ r

(A)

IT

L 4X3X1/2 XISECTIQN A-A

Drill and install 

4-3/4" ^Capsule 

anchors(6 5 

embecment)

@6=r-6"

1 » i

ELEVATION

1/2'

Bridge No 35-54 

ADriM, 1990 

Sheet 2 of 2

BOTTOM BRACKET REPAIR DETIAL r=r-o"

L4X3 1/2X2-3* NOTES:

1. All steel angles shall be 

not dip galvanized.

2. Caosule anchors shall be 

skinless steel.

'Stairway L4X3X 1/2

VIEWB-B

Drill and install 

3/4"j# Capsule ancrwrs 

L4X3 1/2 X2-6'

B

'PLAN TOP CONNECTION DETAIL

r=r-cr

Figure 224.—Plan for stairway repair of San Mateo-Hayward Bridge (White, 1990).
130 HIGHWAY SYSTEMS

Figure 225.—Ship channel under San Mateo-Hayward Bridge.

MORA DRIVE OVERCROSSING

DESCRIPTION OF BRIDGE

This lightly traveled bridge goes over Route 280 near 

the city of Los Altos (fig. 227). It is a two-span, continuous, six-cell, prestressed, box girder superstructure with 

a rounded soffit at the overhangs. It is supported on a 

single, reinforced concrete column and two diaphragmtype abutments (fig. 226). The column is very wide transversely, with a large flare where it joins the superstructure. 

The bridge is on a 600-foot radius curve and has a moderate skew with respect to the highway below. It was built 

in a cut section of the highway on what appears to be fairly 

weak material (fig. 228). The abutments are on a single 

row of piles and the column is supported by a spread 

footing.

BRIDGE DAMAGE

The most serious damage to this bridge was several 

wide cracks that appeared to go all the way through the 

column (figs. 229 and 230). These cracks began at the footing on the north side of the column and extended to 10 

feet above the footing on the south side of the column. 

There were also some smaller cracks. Maintenance engineers chipped out about 7 square feet of the cracked portion of the column to a depth of 6 inches. They found some 

of the reinforcement was heavily corroded. The abutments 

also showed signs of movement including some concrete 

spalls where the abutment met the bridge soffit (figs. 231 

and 232).

There are several possible explanations for the column damage. The column had only #4 rebar at 12-inch

Figure 226.—Mora Drive Overcrossing.

Br #37-235 / Route 280 / Post Mile 13.12 

Approximate Latitude & Longitude

N. Lat. 37° 20.6' W. Long. 122° 04.6'

Epicentral Distance

23.9 miles

Peak Ground Acceleration N/S U/D EAV 

Saratoga Aloha Ave. 0.34 0.41 0.53

Length Width Skew Year Built

207' 38.0 Varies 1967

Main Span Type

Concrete box girder bridge

Average Daily Traffic = 700
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 131

spacing for transverse reinforcement. It also had a large 

flare that attracted more shear. The reinforcement was corroded in the area of damage. All these things probably 

contributed to the damage.

BRIDGE TESTING AND REPAIR

On February 22, 1990, a Portable Linear Accelerator 

(MINAC) was used to see if radiology could detect smaller 

networks of cracks in reinforced concrete at this bridge. 

The film was examined using a Quantex image processor,

but only a few minute cracks were found propagating from 

the large crack. It also showed that the cracks on each 

face were not connected.

After the earthquake, a layer of asphalt was spread 

behind the abutment to smooth the approach (fig. 233). In 

1992 the bridge was repaired and retrofitted with a steel 

casing for the column that matched the flare (fig. 234). A 

top layer of reinforcement and concrete was added to the 

existing column footing to allow it to handle the plastic 

moment capacity of the column. Also, the cracked soffit 

concrete was patched near the abutments.

Figure 227.—Location of Mora Drive Overcrossing.
132 HIGHWAY SYSTEMS
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 133

Figure 229.—Damage on northwest side of column at Mora 

Drive Overcrossing.

Figure 231.—Vertical offset of west abutment at Mora Drive Overcrossing 

(courtesy of Earthquake Engineering Research Institute).

Figure 232.—Horizontal offset of west abutment at Mora Drive 

Overcrossing (courtesy of Earthquake Engineering Research Institute).

Figure 230.—Damage on southwest side of column at Mora 

Drive Overcrossing. Figure 233.—Repair to approach of Mora Drive Overcrossing (courtesy of Earthquake Engineering Research Institute).
134 HIGHWAY SYSTEMS
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 135

BRIDGE MOTION

The fault rupture and ground motion during the earthquake has been well documented, and information can be 

found in many reports, some of which are referenced in 

the back of this section (Simpson 1994; Borcherdt, 1994). 

A simple description of the earthquake location, magnitude, and movement is provided in this section for the 

purpose of understanding bridge behavior. Estimates of 

the ground motion at each bridge site along with latitude, 

longitude, and distance to the epicenter were provided in 

the previous section which describes bridge damage. This 

section provides strong motion records for the six bridges 

that were instrumented at the time of the earthquake.

As has been previously stated, the earthquake occurred 

on October 17, 1989, at 5:04 p.m. Pacific Standard Time. 

It is thought that the main shock was the result of a 1.6- 

meter right-lateral strike slip and a 1.2-meter reverse slip 

along a left-stepping bend of the San Andreas fault in the 

Santa Cruz Mountains. At this location, the fault has a 

bearing of N. 50° W. and a dip of 70° SW. Fault rupture 

lasted about 6 to 8 seconds, with strong shaking lasting

I Hayward - BART Elevated Section I

10 to 15 seconds at most sites. The estimated earthquake 

location and magnitude according to the California Division of Mines and Geology is:

Epicenter: 37.037° N., 121.883° W. Depth 18 km 

Magnitude: 7.0 ML (BRK)7.1 MS (NEIS)

A unique feature of this earthquake is the extent of 

bridge damage 100 km or more from the epicenter. It is 

felt that enhanced ground shaking due to areas of "soft 

soil" that amplified the motion caused most of this damage. There has also been speculation of other factors, such 

as the reflection of the seismic waves off the Moho discontinuity (the surface area between the crust and mantle) 

and from directivity effects. However, since a discussion 

of this subject is beyond the scope of this paper, interested readers should refer to the references listed at the 

back of this report.

Records of bridge motion during earthquakes are an 

engineer's best tool for checking assumptions about bridge 

behavior and for improving computer models. Unfortunately, only 10 bridges were instrumented in California at 

the time of the earthquake. After the earthquake the 

Governor's Board of Inquiry recommended instrumenting more bridges (Thiel, 1990), and Caltrans has worked 

out a partnership with the California Division of Mines 

and Geology that has resulted in 28 instrumented bridges 

as of August 1994.

There are strong-motion records for six bridges whose 

instruments were activated by the earthquake. These include 

four bridges with records processed by the California Division of Mines and Geology (CDMG) (fig. 235; table 21) 

(Shakal, 1989) and two partial instrumentations by the U.S. 

Geological Survey (Maley, 1989; Mork, 1994). The four 

bridges instrumented by CDMG are as follows:

1. Sierra Point Overhead is the first bridge in California to be retrofitted with lead/rubber isolation bearings.

2. The Dumbarton Bridge is a long, steel structure 

crossing San Francisco Bay.

3. The Hayward Bay Area Rapid Transit Bridge has 

three simple-span reinforced concrete box girder spans.

4. The San Juan Bautista Route 156/101 Overhead was 

only 20 miles from the epicenter. It is a six span steel 

bridge.

The two USGS-instrumented bridges are as follows:

1. The 101/280/680 Separation in San Jose had three 

instruments in a bay of the first span.

2. The toll building south of the Golden Gate Bridge 

had an instrument in the basement.

Figure 235.—Map of CDMG instrumented bridges that recorded earthquake motion (courtesy of California's Strong Motion Instrumentation Program).
136 HIGHWAY SYSTEMS 

Table 21.—Instrumented bridges and recorded earthquake motion

Name Of Bridge Type of Structure Damage Year No. of Distance Maximum Horizontal

Built Sensors (in miles) Acceleration*

Free-field Base Bridge

Sierra Point OH

Dumbarton Bridge

Hayward-Bart

Viaduct

Rte 156/101 Sep.

101/280/680 Sep.

Golden Gate Br.

10 span steel girder

43 span steel and

concrete box

3 span concrete box

3 span steel girder

3 span concrete box

suspension bridge

none

very

minor

none

none

none

none

1957

1982

1967

1958

1974

1936

13 +

26 +

13 +

12

3

1

FF

FF

FF

53

35

46

20

21

60

•llg .11 g

•13g -13g

.16g .15 g

.14g

-

.24g -

.39g

.44g

(-61 g)

-5/g

(•59g)

.50g

(.94g)

18g

-

*Value in parentheses indicates a spike in the record.

SIERRA POINT OVERHEAD

DESCRIPTION OF BRIDGE

The Sierra Point Overhead carries Highway 101 over 

two sets of Southern Pacific Railroad tracks in South San 

Francisco (figs. 236 and 237). It was built in 1957. The horizontal alignment is a 7,500-foot-radius curve with an orientation of approximately N. 23° E. (figs. 238 and 239). The 

bridge has an unusual geometry. The north abutment has a 

59° skew, and the south abutment has a 72° skew, while the 

column bents are normal to the centerline of the bridge. This 

means that the column bents near the abutments do not extend the full width of the bridge. The bridge has 10 simply 

supported spans varying from 26 to 100 feet in length. The

superstructure is a composite concrete deck supported by 18 

to 54-inch-deep steel girders. The girders are supported at 

the bents by 68-inch-deep transverse beams. One end of the 

girders is supported by rocker bearings, while the other end 

is bolted to the transverse beam. There is an expansion joint 

at each bent and at the two abutments. The transverse beams 

were originally supported by spherical pin-type steel bearings that sit on top of 3-foot-diameter, 25-foot-tall concrete 

columns on spread footings. The bridge is just south of a 

large hill that was cut slightly to make room for the bridge. It 

is also within 1,000 feet of the Bay.

Soil borings were done in 1950 and again in 1981 for 

the connector structure 100 feet south of Sierra Point Overhead (figs. 240 and 241). The 1950 borings were taken on 

the hill north of the bridge, while the 1981 borings were taken

Bridge # 35-130 / Route 101 / Post Mile 23.7 

Approximate Latitude & Longitude

N. Lat. 37.674° W. Long. 122.388°

Epicentral Distance

53 miles

Peak Ground Acceleration N/S U/D EAV 

200'west of bridge 0.11 0.05 0.06

Length Width Skew Yr Bit YrRet

616' 117' @60° 1957 1985

Main Span Type

Concrete deck slab on steel girders.

Substructure Type

Four (3 foot diameter) reinforced 

concrete column bents (or less due to 

skew) on spread footings.

Figure 236.—Sierra Point Overhead.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 137

on the plain south of the hill. The 1950 

log has one boring at the depth of the 

column footings. It indicates a stiff clay 

and fractured sandstone at that depth 

that was suitable to support the structure on spread footings. The 1981 

borings show loose gravel and clay at 

the same elevation, indicating a different geology on the plain.

Sierra Point Overhead has undergone two modifications since it was 

built. In 1967, girders and a deck were 

added to the center of the bridge to increase the number of traffic lanes (fig. 

242). In 1986 the first seismic retrofit 

in California to include seismic isolation was done on this bridge. The retrofit addressed the two seismic 

vulnerabilities of this structure, inadequate column capacity and the steel 

girders falling off the rocker bearings. 

The replacement of the steel bearings 

on the columns with lead/rubber isolation bearings and the addition of longitudinal rod restrainers addressed 

these weaknesses.

The fact that the bridge superstructure is a series of simple spans that are 

still free to rattle and that the end spans 

can bang against the abutments makes 

this bridge slightly less effective for 

isolation. Still, this retrofit should be 

more than adequate to protect the structure from major 

damage during a large earthquake. It is thought that during a large enough event, the back and side walls of the 

abutment would break, isolating the bridge from the 

ground motion. In the meantime, the abutment protects 

the vulnerable columns from the earthquake. Figure 243 

shows the fixed girder ends, the spherical pin-type-steel 

bearing supporting a transverse beam, and the addition of 

longitudinal rod restrainers extending through the transverse beam on the bridge.

Figure 244 shows a lead/rubber isolation bearing installed on top of a column. All 27 columns for this bridge 

had the spherical bearings replaced with lead/rubber bearings. Also, as part of the retrofit, the bridge was instrumented with 13 sensors on the structure and three 

additional sensors nearby on the ground to obtain the 

free-field motion. Figure 245 shows the instruments 

mounted on the two westernmost columns of Bent 7 and 

on that portion of the transverse beam between them.

' £T7^ ' V/O "V

Figure 237.—Location of Sierra Point Overhead.

BRIDGE MOTION

During the earthquake the peak ground acceleration 

was 0.11 g parallel to the bridge and 0.06 g perpendicular 

to the bridge (fig. 246). The acceleration records on the 

bridge show some "chatter" resulting from the movement 

of the two simply supported spans attached to the transverse beam (fig. 247). Also, we see little reduction of acceleration above and below the isolators, reflecting the fact 

that the bridge was not isolated from the abutment motions.
138 HIGHWAY SYSTEMS

f&f

SECTION A -A

Caftan ££K GOO

____Tbra/ lengfrr o'3ru#e 's>. !>-/C3'- 

-j'\ , 7ff'-6~* , 63-Cfr, 76'-O~* 97-6'f _.#'-6'.\ 9'-f>'4'

/tt ,'13 MS 129

ELEVATION

foivarff/039 

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3#a// ito/ £f svdueee/ as a r*5v// of

Figure 238.—General Plan drawing for seismic retrofit of Sierra Point Overhead.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 139

Figure 239.—Aerial view of Sierra Point Overhead (Thiel, 1990).

-ISO

B-t3 

-63—

B-5/

"g Exist. Sierra Point Overhead 

(Rte.lOI)

Proposed Merino Blvd/Sierra Point 

^ /Off-Ramp Overhead

J^_J_.rf^2jg^ B-2 B-I

.•laB-n—gr

P-4

B-K>

"B" Line

B-6

Figure 240.—Location of soil borings at Sierra Point Overhead.
140 HIGHWAY SYSTEMS

90 

RO

70

60

50

40-

30

?0

10

0

Elev. 88

!

I

i

Pavement (6*)

...... Figure 241. — Boring log for Sierra Brown, sandy clay & sllty _. . _ , , 

clay w«h some sandstone Point Overhead, 

fragmenta

Brown, sandy clay & sllty 

clay with some sandstone 

fragments

Fractured sandstone 

with some clay lenses

Brown fractured sandstone 

with pockets of decomposed 

shale

Fractured sandstone 

Sandstone with pebbles of fine

and medium gravel

Blue and brown fractured standstone 

Blue and brown fractured sandstone with decomposed shale 

Hard blue sandstone 

Hard, blue fractured sandstone 

Hard, blue, fractured sandstone with small pockets of blue clay

jt SB-9'* ~f" L'"m 58'-8"t j_

^

1

r 

I- 4 1-

]

a

n

S> 4

' ^''_L!

t|3 ^

\ T —— T^"~" ' T 

I I i I v <L

Figure 242.—Section drawing for widening 

of Sierra Point Overhead.

Figure 243.—Existing bearings 

(before removal) during retrofit of 

Sierra Point Overhead.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17,1989: PERFORMANCE OF THE BUILT ENVIRONMENT 141

Figure 244.—Newly installed lead/rubber bearing during retrofit of Sierra 

Point Overhead.

Nre,

T o S a n Francisco 

(Hwy. 101)

Structure Reference 

Orientation: N= 25

W«st Column

W/E Section of Column Line B7

Figure 245.—Location of instruments on Sierra Point Overhead (courtesy of California's Strong Motion Instrumentation Program).
142 HIGHWAY SYSTEMS

So San Francisco - Sierra Pt 

(CSUIP Slot ion 56539) Structure Reference Orientation N=25°

14

_ -v ^^ ,1.

15

16

012345 10

Free Field - S Max. Accel. = 0.11 g

11 - Up 0.05 g

- E 0.06 g

15 20 Sec.

Figure 246. — Ground acceleration records at Sierra Point Overhead during earthquake (courtesy of California's Strong Motion Instrumentation Program).

SO. SAN FRANCISCO - SIERRA PT. OVERPASS 1989 LOMA PRIETA EARTHQUAKE

TOP OF E. COLUMN. ABOVE ISOLATOR - W MAX ACCEL = 0 IB Q

g i TOP IUP OF U- W. M. COLUMN, LULUMN, BELOW BtLUB ISOLATOR lil - E

-~-S~-~~-~V^v*^-^.——HA^/%A^^/I^————wf—^

BASE OF W COLUMN - W

TOP OF E. COLUMN. ABOVE ISOLATOR - S

-vAvvVr^l|^^

. COLUMN, BELOW ISOLATOR - S

12 TOP OF W. COLUMN, ABOVE ISOLATOR - S

BASE OF W. COLUMN - N

TOP OF E. COLUMN. ABOVE ISOLATOR - Dn

TOP OF W. COLUMN, ABOVE ISOLATOR - Dn

BASE OF W. COLUMN - Up

0.21 g

O.OSg

0.29 g

0.31 g

0.27g

0.09g

O.OBg

0.09 g

0.03 g

10 15 20 

TIME - SECOND

25 30

Figure 247.—Acceleration records for Sierra Point Overhead during earthquake (courtesy of California's Strong 

Motion Instrumentation Program).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 143

Bridge #35-038 /Route 84 /Post Mile R29.25 

Approximate Latitude & Longitude

N. Lat. 37.674° W. Lons. 122.388°

Epicentral Distance

35 miles

Peak Ground Acceleration N/S LTD EAV

3/4 mi north of bridge 0.11 0.05 0.06

Length Width Skew Yr Bit YrRet

8,600' 72' none 1981 none

Main Span Type

Continuous welded steel box girder

Main Substructure Type

Concrete with inclined hollow legs.

RichmondSan Rafael Bridge

Golden Gate Bridge 

Bay Bridge 

BART Tunnel

Piclfle O***n

Figure 249.—Location of all Bay crossings.

Figure 248.—Dumbarton Bridge.

DUMBARTON BRIDGE 

DESCRIPTION OF BRIDGE

The Dumbarton Bridge (fig. 248) is the southernmost 

of the San Francisco Bay crossings (fig. 249). It was designed in the late 1970's, making it the newest of the crossings. Figure 250 shows the Dumbarton Bridge is composed 

of two 2,850.5-foot approach structures and a 3,150-foot 

main span. The approach spans are five prestressed concrete trapezoidal boxes supporting a lightweight concrete 

deck (fig. 251), and the main span is two steel box girders 

(fig. 252). The piers are two hollow, inclined concrete columns supporting a concrete bent cap. Since the site is covered in soft Bay mud, the structure is supported on 90-ton 

concrete piles to a depth of about 60 feet below sea level. 

Soil borings were done in 1995 that showed Franciscan 

bedrock at a depth of about 650 feet (fig. 253). Such a 

deep layer of soil tends to amplify long-period motion.

There are a variety of connections between the superstructure and the bent cap and between adjacent superstructure spans (fig. 254). This figure identifies 10 

expansion joints located on the bridge. Two of these joints 

are deck hinge connections (fig. 255). There are also two 

types of connections between the superstructure and the 

bent cap. The pinned connection between the superstructure and bent cap is a slotted groove (fig. 256). The fixed 

connection between the superstructure and the bent cap 

are vertical bars that go through the superstructure diaphragm and into the bent cap (fig. 257). There was some 

disagreement on the ability of this fixed connection to
144 HIGHWAY SYSTEMS
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 145

Cilttinc stwtun

\ ; \ \ \ lii ,; 1

' —— *

• w»v *•-•»-

1 ^-^ SiriclMral cvncnu

v i

1

I

^--^- - U.I c»... M.cr.»

|

1 

|

U1J

Figure 251 . — Typical Section for approach spans of Dumbarton Bridge.

Cile'lni itiltttun

••-!'_,_ » .1 I!" ^ M'-i- . _!•-»-, ,._ « II- -- M^-t^. l'T »--i:-j: 1

MEW BftlDCE SECTION EXISTXO 8HIDCC SCgnON

Figure 252.—Typical Section for main span of Dumbarton Bridge.
146 HIGHWAY SYSTEMS

(ft)

100.

200

300

400-

500.

600.

700-

751

(m)

-20

-40

-60

-80

-100

-120

-140

-160

-180

'200

-220

-229

Old 

Bay 

Mud

Alameda 

formations

transfer moment at the joints. There have been three global 

analyses done so far on the Dumbarton Bridge. The first was 

a series of analyses done in the 1970's which were done to 

consider different bridge designs and the final design of the 

bridge (Baron and Hamati, 1975). The second analysis was 

to investigate the behavior of the bridge during the earthquake by making a linear, three-dimensional model of the 

bridge using SAP90 and inputting the free-field motion to 

see if the acceleration records from the earthquake could be 

duplicated (Fenves, 1992). An ambitious, nonlinear threedimensional analysis using NIKE3D was to look at the 

bridge's behavior for the maximum credible earthquake 

(Heuze, 1995). However, this project was never completed.

BRIDGE MOTION

The Dumbarton Bridge was instrumented in 1985. The 

instruments were 26 synchronized Kinemetrics CRA-1 forcebalance accelerometers with two recorders using a common 

trigger (fig. 258). An SMA-1 triaxial flexure accelerometer 

was installed near each of the approaches to record the freefield motion (fig. 259). All the instruments were installed by 

Kinemetrics in 1986. During the earthquake, all instruments 

except the east free-field accelerometer and the vertical senFigure 253.—Soil profile for west side of Dumbarton Bridge.

Expansion

joint and deck^4" gap 18" gap 6 gap

hinge gaps

18" gap 4" gap

Figure 254.—Dumbarton 

Bridge with soil profile 

and superstructure connections (courtesy of 

Lawrence Livermore National Laboratory).

& Pinned deck/pier cap connection 

• Fixed deck/pier cap connection 

rj Expansion joint connection 

Deck hinge

Figure 255.—Deck hinge connection at 

Dumbarton Bridge (courtesy of Lawrence 

Livermore National Laboratory).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 147

Deck

Rebar pattern"^

(not continuous into beam)

Figure 256.—Superstructure to pier pin connection (courtesy of Lawrence 

Livermore National Laboratory).

Deck

Figure 257.—Superstructure to pier fixed connection (courtesy of Lawrence 

Livermore National Laboratory).

sor at the foot of Pier 13 recorded the earthquake motion. 

After the earthquake the film was collected by Kinemetrics 

and given to CDMG for processing (Shakal, 1989). The two 

free-field recorders had separate triggers. Consequently, the 

west free-field record started 1.8 seconds after the recorders 

on the bridge. The west free-field accelerometer is located 

approximately three-fourths mile west of Pier 1 on the north 

side of the road (fig. 260). All other accelerometers are shown 

in figure 261. Note that the instruments are located on the 

foundations and bent caps of the west approach structure 

(Piers 13, 14, and 15) and the main channel crossing (Piers 

17 and 21). The free-field channels have a true orientation, 

while the channels on the bridge are oriented to the bridge 

(fig. 261: table 22).

During the earthquake, the Dumbarton Bridge suffered 

very minor damage. Some concrete spalled from around the 

bolts that hold down the big steel plate expansion joints that 

span the 18-inch gaps at Piers 16 and 31. This was the only 

damage found on the bridge. The bridge was briefly closed 

after the earthquake until an inspection could be done. After 

the inspection, it was reopened and the spalls were repaired. 

The bridge inspection report is shown in figure 262.

Information about the free-field motion during the earthquake is available from California's Strong Motion Instrumentation Program (1991), which provides data on 44 

ground-response stations. More detailed free-field and bridge 

motion are also available (California's Strong Motion Instrumentation Program, 1991b). This latter report provides time 

histories and response spectra for seven lifelines including 

the four bridges. There appears to be about 20 seconds of 

strong ground motion (fig. 263) for the Bay mud near the 

Dumbarton Bridge. The response spectra for this site shows 

a large increase in amplitude at 2 seconds. This long-period 

motion for soft clays is particularly dangerous for bridges 

which have long natural periods. The peak ground acceleration at this site was about 0.128 g in both lateral directions. 

This is much lower than would be expected for the maxiFigure 258.—Kinemetrics CRA-1 and recorder (courtesy of Kinemetrics Inc.). Figure 259.—Kinemetrics SMA-1 recorder (courtesy of Kinemetrics Inc.).
148 HIGHWAY SYSTEMS

Figure 260.—Aerial view of free-field accelerometers for the Dumbarton Bridge.

mum credible event at this site. A 

hazard assessment of the 

Dumbarton Bridge (Powers, 1993) 

indicates a peak ground acceleration of 0.5 g. The bridge shows a 

much longer duration of strong 

motion (about 60 seconds at the 

top of the piers) than at the ground. 

This suggests a relatively small 

damping ratio for the Dumbarton 

Bridge. The bridge also shows the 

highest accelerations longitudinally and very low accelerations 

vertically. Piers 17 and 21 show 

high-amplitude spikes, suggesting 

banging of expansion joints. Since 

the expansion joint at Pier 16 is 

18 inches wide, this pounding is 

more likely to have occurred at the 

6-inch hangers between Piers 21 

and 22. The main structure appears 

to have a period of about 2.0 seconds longitudinally and 1.5 seconds transversely. The bridge 

motion is summarized in figures 

264 to 266 and in table 23.

The capacity of the piers 

was well above the forces experienced during the earthquake 

(Fenves, 1992). Fenves suggests 

that the free-field instruments be

placed closer to the bridge and iZ^lltlJSlE,' 

that downhole instruments be 

placed at the site to give a better

picture of the ground motion. Since the earthquake, borings 

were made down to 500 feet and instrumented to obtain 

motions all the way to bedrock for future events. An agreement has been reached with California's Strong Motion 

Instrumentation Program to maintain and process the 

records obtained from these instruments.

SENSOR LOCATIONS

E ^ expansion

Approach 

(concrete Birder) 

Instrurr

-' 5 . '° ^

* (steel flirder) 

ented Section

git f 1 U| ' ' ' ' ' ' '

16

3150'

(concrete girder) 

' I t t t

fan 31 35 4O p,,, 44

•4" Z? "

Elevation

\7 \7 \7

10,

LL

1,9,12

UUULJUU

N/S Section @ 

Piers 13,14,15

N/S Section @ 

Pier 17

Figure 261.—Location of accelerometers at 

Dumbarton Bridge (courtesy of California Strong 

Motion Instrumentation Program).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 149

35-38

Bridg* No. ————————————————

SUPPLEMENTARY BRIDGE REPORT Location ___________ 04-SM-84-R Locati ___________

Di „ . Co.. Rl« . PM . Oly

10./17./89 EARTHQUAKE INSPECTION

Oat* of Investlgatio OctODcr 19. 1933 

DUMBARTON BRIDGE

The bridge was checked on October 18, uy driving across the structure 

and checking for misalignment, cracks and spalls at roadway level.

The bridge was insoected on October 19, by walking the steel span box 

girder (Spans 16-30). The only damage found was at the under side 

of the earthquake expansion joints at Pier IS anc! Pier 31. These 

joints were designed to open and close up to 18 inches plus or minus 

under large earthquake loading with sorae damage. The damage is that 

the hold down Colt boltin? the olate spanning the large gap have ocen 

pulled at top of the Colt sleeves resulting in the spallin« aaout half 

of the slab thickness at each colt.

The substructure, the concrete aoproach spans and the approach trestle 

(slab) spans were inspected from the adjacent fishing piers and from 

a State maintenance boat. No damage was apparent.

RECOMMENDATION

Repair the concrete deck spalls under the deck plate at expansion 

joints at Piers 16 and 31. 40033X89292X R-(H4221) 510,000

Richard W. White, P.E,, 

C16762

Qy /)/ J A tf^S RWW/REK/art 

Robert E. Kcim WMs* /LL^. cc: Oist. 04 (3)

coders

Figure 262. — Post-earthquake inspection report for the Dumbarton Bridge.

Table 22.—Peak ground motion for Dumbarton Bridge

Channel

1

2 

3

Location

West Free Field 

West Free Field 

West Free Field

Orientation

357° 

Up 

267°

Acceleration

(g)

.126 

.058 

.128

Velocity 

(in/s)

7.52 

2.33 

7.56

Displacement 

(in)

1.95 

0.78 

2.92
150 HIGHWAY SYSTEMS

SANTA CRUZ MTNS (LOMA PRIETA) EARTHQUAKE OCTOBER 17, 1989 17:04 POT 

SAN FRANCISCO BAY - DUMBARTON BRIDGE: CSMIP S/N 596

PHASE 2 FILTERED DATA: ACCELERATION, VELOCITY AND DISPLACEMENT 

USABLE DATA BANDWIDTH: 0 17 TO 23 6 HZ (0.04 TO 5 88 SEC) RECORD ID: 58596-S6220-90208 03

700

0

-700 

70

-70 

20

CHN 1: 357 DEC WEST END FREE FIELD

4- 

^

0

-20

700

0

-700 

70

0

-70

20 r

0

-20

r\ \J -" ^

T

CHN 2 UP 

i

WEST END FREE FIELD

q g

700

-700 

70

-70 

20

0

-20

CHN 3 267 DEC WEST END FREE FIELD

wV^ f^^~\—£\—S~\ S~\

MAX = -123 8

19. 1

-4.95

MAX = 56. 9

-5.93

-1.97

MAX - -125.8

-19.2

-7.42

10 20 30 

TIME (SEC)

40 50 60

Figure 263.—Dumbarton Bridge free-field motions (courtesy of California Strong Motion Instrumentation Program).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 151

SANTA CRUZ MTNS (LOMA PRIETA) EARTHQUAKE OCTOBER 17, 1989 17:04 PDT 

SAN FRANCISCO BAY - DUMBARTON BRIDGE: CSMIP S/N 596

PHASE 3 DATA- RESPONSE SPECTRA RECORD ID: 58596-S6220-90208.03 

USABLE DATA BANDWIDTH: 0.17 TO 23 6 HZ (0.04 TO 5.88 SEC)

t? 4

—I——I——I——I——I——I——I——I——I——I——T

CHN 1. 357 DEC

WEST END FREE FIELD

DAMPING VALUES. 0,2,5,10,20%

y 2

wj

CD 1

CHN 2: UP

WEST END FREE FIELD

DAMPING VALUES: 0, 2, 5, 10, 20%

' ' ' | ' i ' ' | 

CHN 3: 267 DEC

WEST END FREE FIELD

DAMPING VALUES: 0, 2, 5, 10, 20*

PERIOD (SEC)

Figure 264.—Free-field response spectra for Dumbarton Bridge (courtesy of California Strong Motion Instrumentation Program).
152 HIGHWAY SYSTEMS

SAN FRANCISCO BAY - DUMBARTON BRIDGE 19B9 LOMA PRIETA EARTHQUAKE

PIER 17. SOUTH SIDE OF CAP - Up Mftx ACCEL = „ _ ,3 g 19

21 PIER 17. NORTH SIDE OF CAP - Up 

———>'~***fH*Wifr*<blJ^^^ ——-v^^-~~v———.—.——^-^—-————————

PIER 17. BASE OF SOUTH BENT COLUMN - Up

20 PIER 17. BASE OF NORTH BENT COLUMN - Up

0.11 g

0.06 g

0.06 g

22 0.33 g

Figure 265.—Acceleration 

records for portion of 

0 17 n Dumbarton Bridge (courtesy 

of California Strong Motion 

Instrumentation Program).

I i i i i I i i i i I i i i i I i i i i I i i i i I i i i i I i i i i I i i i i I i i i i I i i i 

0 5 10 15 20 25 30 35 40 45 50

TIME - SECOND

Table 23.—Peak structural motion for Dumbarton Bridge (courtesy of California's Strong Motion Instrumentation Program)

Channel

1

2

3

4

5

6

7

8

9

10

11

12

13

Location

Pier 13, Footing

Pier 13, Footing

Pier 13, Footing

Pier 13, Cap

Pier 13, Cap

Pier 14, Cap

Pier 15, Footing

Pier 15, Cap

Pier 14, Footing

Pier 14, Footing

Pier 14, Footing

Pier 15, Footing

Pier 15, Footing

Orientation

West

Up

North

West

South

South

North

South

West

Up

North

West

Up

Acceleration 

(9)

0.167

0.077

0.077

0.327

0.097

0.095

0.103

0.103

0.172

0.070

0.100

0.205

Velocity 

(in.s)

12.6

2.48

7.01

26.1

8.23

9.41

7.87

9.84

13.9

2.11

7.56

16.7

no record

Displacement 

(in)

4.13

0.72

2.20

6.34

2.47

2.52

2.48

2.50

4.45

0.69

2.43

4.61
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 153

SAN FRANCISCO BAY - DUMBARTON BRIDGE 19B9 LOMA PRIETA EARTHQUAKE

PIER 21. SOUTH SIDE OF CAP - S MAX ACCEL = „ 10 g

PIER 15. CENTER OF FOOTING - N 0.10 g

PIER 14. SOUTH SIDE OF CAP - S 0.09 g

PIER 14. CENTER OF FOOTING - N 0.10 g

PIER 13. SOUTH SIDE OF CAP - S 0.10 g

PIER 13. CENTER OF FOOTING - N 0.06 g

PIER 21. BASE OF SOUTH BENT COLUMN - Up O.OBg

PIER 14. CENTER OF FOOTING - Up

PIER 13. CENTER OF FOOTING - Up

i i i I i i i i I i i i i I i i i i I i i i i I i i i i I i i i i ! i i i

Figure 266.—Acceleration

records for remainder of

O 07 q Dumbarton Bridge (courtesy

____ of California Strong Motion

Instrumentation Program).

0.06 g

Table 23.—Peak structural motion for Dumbarton Bridge (courtesy of California's Strong Motion Instrumentation Program)—Continued

Channel

14

15

16

17

18

19

20

21

22

23

24

25

26

Location

Pier 1 7, S. Column Base

Pier 17, S. Column Base

Pier 17, S. Column Base

Pier 17, Cap

Pier 17, Cap

Pier 17, Cap

Pier 17, No. Column Base

Pier 17, No. Cap

Pier 21, Cap

Pier 21, Cap

Pier 21, So. Column Base

Pier 21, So. Col. Base

Pier 21, So. Column Base

Orientation

West

Up

North

West

South

Up

Up

Up

West

South

West

Up

North

Acceleration

(g)

0.307

0.064

0.126

0.442

0.155

0.115

0.061

0.118

0.327

0.176

0.266

0.057

0.107

Velocity 

(in.s)

15.9

2.65

8.54

14.0

8.43

3.89

2.46

3.73

14.9

13.2

13.3

2.49

8.98

Displacement 

(in)

3.77

0.84

2.34

5.94

2.49

0.93

0.79

0.85

5.47

3.58

3.61

0.91

2.47
154 HIGHWAY SYSTEMS

HAYWARD BAY AREA RAPID TRANSIT 

ELEVATED STRUCTURE

DESCRIPTION OF BRIDGE

The instrumented portion of the Hayward Bay Area 

Rapid Transit Viaduct is a three-span portion of a long, elevated structure composed of single column bents, simply 

supported prestressed box girders, and continuous-steel rails 

(figs. 267 to 270). The columns are of hexagonal section with 

5 feet between opposite faces, with two rings of #18 bars 

and an outer wrap of #5 spiral rebar at a 3-inch pitch (fig. 

271). The columns sit on square footings with 16 to 18 1- 

foot-diameter reinforced concrete piles. The piles are 40 to 

50 feet long, and all the outer piles are battered. Figure 272 

shows the piles and the soil profile based on three soil borings 

taken at the site. Ground water was found at about 60 feet 

below the surface. The girders are attached on the north end 

by 5-inch-diameter concrete-filled pipes and sit on elastomeric bearings at the south end (fig. 273).

BRIDGE MOTION

This bridge suffered no damage from the earthquake. It 

was designed in 1980's using new seismic criteria. The bridge 

was instrumented with 16 sensors by California's Strong 

Motion Instrumentation Program (fig. 270). Three additional 

sensors were installed in a nearby parking lot to capture the 

free-field motion. The bridge motions are shown in figures 

274 to 276. An analysis was done to study the bridge's performance for the earthquake and for the maximum event 

(Penzien, 1991).

Hayward BART 

ALAMEDA

Figure 268.—Location of Hayward BART Viaduct.

Bay Area Rapid Transit Structure 

Approximate Latitude & Longitude

N. Lat. 37.671° W. Long. 122.087° 

Epicentral Distance 

46 miles

Peak Ground Acceleration

Parking Lot at bridge

N/S U/D EAV 

0.15 0.05 0.15

Length Width Skew Yr Bit YrRet

3 span 26' none 1967 none

Main Span Type

Prestressed concrete box girders

Main Substructure Type

Single column reinforced 

bents on piles

concrete

Figure 267.—Instrumented portion of Hayward BART Viaduct (courtesy 

of California Strong Motion Instrumentation Program).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 155

Figure 269.—Aerial view of the Hayward Bart Viaduct and instrumented section.

SENSOR LOCATIONS

77' 77'

Structure Reference 

Orientation: N= 310

-*-_t

'' f.pFree Field

E/W Section 

Bent 132

E/W Section 

Bent 135

Figure 270.—Plan, elevation, typical section, and instrumentation for Hayward BART Viaduct (courtesy of California 

Strong Motion Instrumentation Program).
HIGHWAY SYSTEMS

SFCTfOH A

Onr rmt of man> mnfore*mrnt *ko*m 

Str Dr+oilt f*r

Figure 271.—Column details for Hay ward BART 

Viaduct (courtesy of Joseph 

Penzien).

Surface 

Fill

Sandy 

Clay

Sllty 

Sand

Figure 272.—Soil profile at 

Hayward BART Viaduct 

(courtesy of Joseph Penzien).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 157

1"

HII r~l—Elastome 'ic 

Material

5-in. steel pipe 

LONGITUDINAL SHEAR KEY DETAIL TRANSVERSE SHEAR KEY DETAIL

Elastomeric 

g Pad

n a /

|1 ___Elasto:

I f Bearin

• i • i

^^LZ] ! D

-H——^——ea a N / a . LU

"Longitudinal 

Shear Key

Concrete-filled 5-in. PIER BEAM T0p VIEW 

diameter steel pipe

PIER BEAM SIDE VIEW

Figure 273.—Bearings on Hayward BART Viaduct (courtesy of Joseph 

Penzien).

17 - Free Field - N Max. Accel. - 8.16 9

•----•^**-<k«^^

19 - Free F,eld- Nax. Accel. = 8.16

18 - Fne Field -Up H«. Accel. = B.B8 j 

———lt~*W**»tot)b^^ ————

5.8 1B.B 15.E 

Tine (Sec)

29.1 25.B

Figure 274.—Free-field ground motions for Hayward BART Viaduct (courtesy of California Strong Motion Instrumentation Program).
158 HIGHWAY SYSTEMS

17Fre*Fi*ld - N 

" 13 Free Fi*ld - H 

— 18 Free Field -Up

Frequency (cps)

Figure 275. — Free-field response spectra for Hay ward BART Viaduct (courtesy of California Strong Motion Instrumentation Program).

HAYWARD - BART ELEVATED SECTION

.. BENT 13a. DECK, SOUTH OF JOINT - H

1989 LOMA PRIETA EARTHQUAKE 

MAX. ACCEL. = 0.41 g

g BENT 134, DECK, SOUTH OF JOINT - N . 0.21 Q 

———~~~VW'^'UV/WWVVM/N^^ —————^————^————~

7 BENT 133, DECK. SOUTH OF JOINT - N 0.25 g

BENT 13a. DECK, SOUTH OF JOINT - N 0.23 g

———~^^/>V\/^V~\/>ft<~TM/\/\^^ ———~

BENT 132, DECK, NORTH OF JOINT - N 0.24g

BENT 132. TOP, EAST END - N 0.21 g

———~-v/w"Wv^w-A^w^M/\AA/WV^^ ———~

BENT 132, TOP, CENTER - N 0.22 g

Figure 276.—Acceleration records for 

Hayward BART Viaduct (courtesy of California Strong Motion 

i i I i i i i I i i i i I i i i i—I—i—i—i—i—1 Instrumentation ProTIME - SECOND

gram).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 159

Bridge #44-107 / Rte 156 / Post Mile 95.44 

Approximate Latitude & Longitude

N. Lat. 36.862° W. Long. 121.578°

Epicentral Distance Geology

21 miles Alluvium

Peak Ground Acceleration N/S U/D E/W

Hollister South & Pine 0.18 0.20 

0.38

Length Width Skew Yr Bit YrRet

326' 35.5' 35° 1959 None

Main Span Type

Six span, steel girder bridge

Figure 277.—Route 156/101 Separation (courtesy of California Strong 

Motion Instrumentation Program).

Main Substructure Type

Two column reinforced concrete bents on 

spread footings

SAN JUAN BAUTISTA-ROUTE 156/101 SEPARATION BRIDGE MOTION

DESCRIPTION OF BRIDGE This bridge was instrumented and recorded movement during the earthquake. Figure 278 shows instruments on Bents 3,

The Route 156/101 Separation is an older, steel composite 4, and 5. Figure 279 provides acceleration time histories at these 

bridge on two-column bents. It carries two lanes of traffic over locations. Station 8 (at the top of the right steel girder) recorded

Highway 101 near the town of San Juan Bautista (fig. 277).

SENSOR LOCATIONS

an acceleration of 0.50 g in the longitudinal direction. Unfortunately, there was not a free-field instrument nearby to study the 

input motion. However, two foundation-level 

instruments were used to study the bridge's behavior in a report written for California's Strong 

Motion Instrumentation Program (Kasai 1995). 

Moreover, during the 1979 Coyote Lake earthquake, a free-field recorder was located at a gas 

station across from the bridge. A doctoral thesis 

was written on this bridge's behavior during the 

Coyote Lake earthquake using strong motion 

records (Wilson, 1986). This bridge was the closest instrumented structure to the epicenter of the 

earthquake, but there was no damage.

B6 A7

FOUNDATION PLAN

'• A *' I/

23° 55'

/ / ».•' . B sV /•? 

Concrete 5'«/——) / \f SVe*(typU.l)^ 4 y// ^-°

fl_^ /-Steel Girder ^-Bearings j R

3> ""7I IT I "T J—A A AL A «J*^i

20'

1

1^

"---i r--- J

L.

./To San Juan 

/ — Bautlsta W - E Section of Bent 5

^"Concrete Bent/ /

DECK PLAN

4,5 mounted on top of bent 5 

6,7,8,9 mounted on

deck of span 4

Figure 278. — Plans and instrument location for 

Route 156/101 Separation (courtesy of California Strong Motion Instrumentation Program).
160 HIGHWAY SYSTEMS

SAN JUAN BAUTISTA - 101/156 OVERPASS 1989 LOMA PRIETA EARTHQUAKE

BENT 3, BASE OF £. COLUMN - E 0.13g

—~<~~***si\/iM ^l^^(^^ll^Jfl|^^^M^M —v—w—~~—^^—,

BENT 5. BASt OF E. COLUMN - N D 09 g

BENT 3. BASE OF E- COL'JHN -'N o.io g

BENT 5. BRIDGE DECK - Up

• ..-~^l'''.'«yivl^y||lMAJVyVV<>S^^ ———rt^V^j^^w———TAIV——.——

0 21 g

BENT 5. BASE OF E. COLUMN - Up 0.06g

BENT 3. BASE OF E. COLUMN - Up D.DBg

35 ?0

TIKE - SECOND_______

30

Figure 279.—Strong motion records for Route 156/101 Separation (courtesy of California Strong Motion 

Instrumentation Program).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 161

Bridge #37-285F / Rte 280 / Post Mile 0.00 

Approximate Latitude & Longitude

N. Lat. 37.340° W. Long. 121.851°

Epicentral Distance Geology

21 miles Alluvium

Peak Ground Acceleration N/S U/D EAV

CSMIP Sta. 57356 0.07 0.08 0.09

Length Width Skew Year Built Yr Retrofit

276' 28' None 1974 None

Main Span Type

Three span prestressed cast-in-place 

box

Main Substructure Type

Two column reinforced concrete bents 

on pile footings

Figure 280.—Aerial view of 

Route 280-680/101 Separation.

271-6"

ROUTE 280-680/101 SEPARATION

DESCRIPTION OF BRIDGE

This is a fairly typical Caltrans' bridge 

(fig. 280). It is supported by end-diaphragm 

abutments that rest on footing seats with 

vertical pins. The columns have a large flare 

near the top and are cast monolithically 

with the deck but are pinned at the pile 

foundations (fig. 281). The bridge rests on 

deep alluvium, and the piles are driven into 

good material, as shown in the soil profile 

(fig. 283).

BRIDGE MOTION

Three instruments in the superstructure 

near Bent 2 recorded the bridge's motion 

during the earthquake (fig. 282). The freefield instruments for this structure, like the 

Route 156/101 Separation Structure just described, were not 

working during Loma Prieta. This limits the usefulness of 

these records. No analysis was done of this bridge after Loma 

Prieta. The ground records (from a nearby building) and the 

bridge records (fig. 284) are both surprisingly low.

ELEVATION

1

68'

u

TYPICAL SECTION

fl

PLAN

Figure 281.—Plan, elevation, and typical section 

of Route 289-680/101 Separation.
162 HIGHWAY SYSTEMS

OJ •o

°a _

tO £~

n •«

c ?

S o

o

(E) DD

\

\

\ \

•a

_o "o

O

00
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 163

U.S. STROHG-HOTIOH NETWORK 

Station No. 1571 37.340N. 121.851V 

Sen Jose 101/280/680 Fuy Interchange 

SKA-1 No. 288 USGS/COOT (Bridge) 

EARTHQUAKE OF

18 October 19B9 - 0004 G.a.t.

DIRECTION 

322*

Up 

232*

CONSTANTS

Sens. 

Freq.

Damp.

Sens. 

Freq. 

tamp.

Sens. 

Freq.

Damp.

1.63 cm/g 

26.3 Hz 

0.6 crit

1.84 cm/g 

26.3 Hz 

0.6 crit

1.B1 ot/g 

25.6 Hz 

0.6 crit

Flta speed * 1 cm/sec

HAX. ACCELERATION 

O.lSg

O.OSg 

0.13g

Figure 284.—Acceleration records for Route 280-680/101 Separation (courtesy of U.S. Geological Survey).

Location of USOS electronic 

seismic detection unit. It

GOLDEN GATE BRIDGE

This bridge (figs. 285 and 286) is owned 

and operated by the Golden Gate Bridge, 

Highway, and Transportation District. During 

the earthquake an instrument in the basement 

of the Administration Building of the Toll 

Plaza recorded the ground motion (fig. 287). 

There was a maximum horizontal acceleration 

of 0.24 g and no damage to any portion of the 

bridge. However, concern about a much larger 

earthquake has caused the District to begin a 

massive retrofit program for the bridge.

Route 101 between Marin and San 

Francisco Counties.___________ 

Approximate Latitude & Longitude

N. Lat. 37.806° W. Long. 122.472°

Epicentral Distance Geology

62 miles Alluvium

Peak Ground Acceleration N/S U/D EAV

Administration Building 0.12 0.06 0.24

Length Width Skew Year Built Year Retrofit

8450' 90' None 1937

Main Span Type

Suspension bridge

Main Substructure Type

Two 700' steel towers

None

Figure 285.—Aerial view of Golden Gate Bridge.
164 HIGHWAY SYSTEMS

REFERENCES

Baron, Frank, and Hamati R.E., 1975, Determination of the seismic 

design criteria for the Dumbarton Bridge replacement structure: Volume 1, Description, theory, and analytic modeling of 

bridge and parameters: University of California at Berkeley, 

Earthquake Engineering Research Center, Report EERC 75-1.

Borcherdt, Roger D.,1994, The LomaPrieta, California, earthquake 

of October 17,1989—Strong ground motion: U.S. Geological Survey Professional Paper 1551-A.

California Strong Motion Instrumentation Program, 199la, Processed strong motion data from the Loma Prieta earthquake 

of October 17, 1989—Ground response records: Strong 

Motion Instrumentation Program, California Department of 

Conservation, Report No. 91-06.

————199Ib, Processed strong motion data from the Loma Prieta 

earthquake of October 17, 1989, Lifeline records, Strong 

Motion Instrumentation Program, California Department of 

Conservation , Report No. 91-08.

Figure 286.—Golden Gate Bridge (courtesy of the Golden Gate Bridge, 

Highway, and Transportation District).

U.S. STRONG-MOTION NETWORK DIRECTION 

Station No. 1678 37.806N. 122.472V 360* 

San Francisco - Golden Gate Bridge 

SNA-1 No. 298 (USGS) Abutment Bldg. Up 

EARTHQUAKE OF

18 October 1989 - 0004 G.m.t. 270*

CONSTANTS

Sens. 

Freq. 

Damp.

Sens. 

Freq. 

Da«p.

Sens. 

Freq.

Daap.

1.95 »/g 

25.4 Hz 

0.6 crit

1.80 cm/g 

26.7 Hz 

0.6 crit

1.95 n/g 

25.5 Hz 

0.6 crit

Film speed - 1 at/sec

Fenves, Gregory L., and others, 1992, Response of the Dumbarton 

Bridge in the Loma Prieta earthquake: University of California 

at Berkeley Earthquake Engineering Research Center, Report 

EERC 92/02,170 p.

Heuze, Francois, and others, 1995, Seismic studies of the Dumbarton 

Bridge: Quarterly Report to Caltrans Division of Structures, 

Lawrence Livermore National Lab.

Huang, M.J., and others., 1994, Bridge records by California's Strong 

Motion Instrumentation Program: California Department of 

Conservation, personal communication

Kasai K., et al., 1994, Effect of relative displacements between adjacent bridge segments, Data Utilization Report : Strong Motion 

Instrumentation Program, California Department of Conservation, p. 9-1 to 9-12.

Maley, R., et al., 1989, U.S. Geological Survey strong-motion records 

from the Northern California (Loma Prieta) earthquake of October 17, 1989: U.S. Geological Survey Open-File Report 89- 

568,1989

Mayes, Ronald L, 1990, Sierra Point Overhead, anticipated and recorded seismic performance: Dynamic Isolation Systems, 

Lafayette, CA, personal communication. 

Mork, P.N., 1994, U.S. Geological Survey Bridge Records: Personal

communication.

Penzien, J., and others, 1991, Seismic performance investigation of 

the Hayward-BART elevated section instrumented under 

CSMIP, in Seminar on seismological and engineering implications of recent strong-motion data: California Department of 

Conservation.

Pomeroy, E. G., 1986, Sierra Point Overhead—Seismic isolation retrofit, in Proceedings of a workshop on base isolation and passive energy dissipation: Applied Technology Council, ATC-7. 

Power, Maurice S., 1993, Seismic ground motion study for the 

Dumbarton Bridge: Prepared for Caltrans Division of Structures by Geomatrix Consultants.

Shakal, A, and others, 1989, CSMIP strong motion records from the 

Santa Cruz Mountains (Loma Prieta), California earthquake of 

17 October 1989: California Department of Conservation. 

Simpson, Robert W, 1994, The Loma Prieta, California, earthquake of 

October 17,1989—Tectonic processes and models: U.S. Geological Survey Professional Paper 1550-F.

Thiel, Charles, May 1990, Competing against time: State of California, Office of Planning and Research, 264 p.

Tseng, W, and others, 1992, Seismic performance investigation of the 

Hayward-Bart elevated section: Strong 

Motion Instrumentation Program, Data 

Utilization Report (CSMIP 92-02), California Department of Conservation, 1992 

Wilson, John C, and Jennings, Paul C., 1985, 

Spatial variation of ground motion determined from accelerograms recorded 

on a highway bridge: Bulletin of the Seismological Society of America, v. 75, no. 

6, p. 1515-1533."

Wilson, John C, 1986, Analysis of the observed 

seismic response of a highway bridge: 

Earthquake Engineering and Structural 

Dynamics, v. 14, p. 339-354.

HAX. ACCELERATION 

O.I2g

0.06g

0.24g

v^rtrvv%^^nrvnnrvvTr\Juvvnnru

Figure 287.—Earthquake records of Golden Gate 

Bridge (courtesy of U.S. Geological Survey).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 165

HIGHWAY DAMAGE

There was a great deal of damage to highways from 

landslides, liquefaction, and ground deformation that occurred as a result of the earthquake. Although there was 

no surface rupture, there were surface deformations that 

caused substantial damage to roadways. This section describes the performance of streets, roads, and highway 

structures other than bridges during the earthquake.

The area of road damage was quite extensive. Rock 

and land slides occurred in the Santa Cruz Mountains close 

to the fault and for 70 miles northward. Liquefaction-induced road damage was similarly spread out from 

Monterey County south of the fault to the City of San Francisco and Highway 80 about 60 miles north of the fault. 

The one constant was that wherever road damage occurred, 

poor soils were usually present. Although there were many 

damaged roads, the cost of bridge damage far exceeded 

road damage, owing to the heavy cost of repairing or replacing the double-deck bridges.

Roadways, along with culverts and retaining walls, 

sustained more damage from soil movement and ground 

deformation, than from shaking. In general, landslides 

were more damaging in areas of cuts, while settlement 

was more damaging in areas of fill. Caltrans currently does 

not design roads, culverts, and retaining walls for a seismic load, nor does doing so seem appropriate from what 

was seen after the earthquake.

There has been some speculation that earth-retaining 

structures, such as abutments and retaining walls, should 

be designed for a much larger earthquake force. However, 

Caltrans has not seen any damage from Loma Prieta or 

any other strong earthquake that would justify designing 

earth-retaining structures for an additional seismic load. 

There was no damage to any Caltrans retaining wall as a

result of Loma Prieta. There were some signs of movement to locally owned retaining structures.

California has always had a problem with landslides 

on roads along its coast and mountain passes. Slide removal is routinely done to keep some roads open. Heavy 

rains frequently cause slides by increasing the overburden and reducing soil friction. This situation is exacerbated, not created, by earthquakes like Loma Prieta.

Highway damage from settlement, lateral spreading, 

and soil liquefaction are just beginning to be addressed 

(mostly in Japan) by soil modification before the facility 

is built. Roads built on well-engineered material suffered 

little damage during the earthquake.

It would appear that research and study into highway 

damage was not as intensive as research into bridge damage after the earthquake. However, geotechnical studies, 

particularly on the seismic behavior of weak clays and 

loose alluvium, have intensified as a result of the earthquake. Table 24 and figure 288 summarize state highway 

damage from the earthquake. The source for much of the 

information on highway damage comes from Heyes 

(1990). This is an excellent source of information on the 

earthquake.

There was also substantial damage to city and county 

streets and roads. Table 25 lists all local roads that were 

repaired with Federal emergency funds. Other information on local road damage comes from reports by city and 

county engineers, as well as researchers and geotechnical 

engineers that studied the damage. Not only city and 

county roads, but roads owned by state parks and beaches, 

roads owned by military bases, and private roads were 

impacted by the earthquake. Some of that damage is listed 

in table 26. These three tables, although not a complete 

listing, contain most of the major road damage that occurred.

Table 24.—Damage to State highways and related facilities from the earthquake.

Location Damage

Route 17 in Santa Cruz and Santa 

Clara Counties

Route 9 in Santa Cruz County

Route 152 at Heckler Pass in

Santa Cruz County

Route 236 in Santa Cruz County

Route 35 in Santa Clara County

Route 101 near Gilroy in Santa

Clara County

Route 280 in Santa Clara County

Route 1 and Mountain Lake in San 

Francisco

Route 1 in Marin County

Many landslides and rockslides. Roadway damage from soil 

settlement. Ground surface rupture caused a vertical uplift of the 

road near the top of Santa Cruz Mountains. 

Moderate slide closed this road for several days. 

Rockslides, highway cracks, and settlement.

Few small slides closed this road after earthquake.

Road was closed for 2 days while 6 small slides were removed.

Median barrier railing was badly cracked by Sargeant Overpass.

Soil heaved damaging roadway in fill area near Magdalena

Avenue.

Liquefaction of fine-grained foundation soils severely damaged

300 feet of roadway. Roadway had to be repaired several times

before settlement was controlled.

Lone Tree landslide was accelerated by earthquake. ______
166 HIGHWAY SYSTEMS

Table 25.—Federal emergency relief funding of local roads

Road's Damaged Location Cost

Figure 288.—Location of State highway damage.

Table 26.—Damage to roads and tunnels not covered elsewhere

Cervantes Street

Bay Street

Marina Blvd.

4th Street

Laguna Street

6th Street

5th Street

Mission Street

Folsom & Embarcadero

Folsom Street

South Van Ness

Valencia Street

14th Street

7th Street

Townsend Street

Hyde Street

Grove Street

17th Street

Sacramento Street

Washington Street

Pine Street

Stuart Street

Harrison Street

Howard Street

Market Street

Beach Park Blvd.

Santa Theresa Blvd.

Soquel-San Jose

Summit Road

Capitola Drive

Brommer Street

East Cl iff Dr

Grahamhill Rd.

Portola Road

Valencia Road

Freedom Blvd.

Pierce Road

Various Locations

7th Street

Cliff Drive

Granite Creek Rd.

1-80 West Frontage

Industrial Blvd. &

Laurel Street

California & Broadway

Bayshore & Rollin Rd.

Bear Valley Rd.

Two Locations

West Frontage Rd.

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

San Francisco

Foster City

Santa Clara Co.

Santa Cruz Co.

Santa Cruz Co.

Santa Cruz Co.

Santa Cruz Co.

Santa Cruz Co.

Santa Cruz Co.

Santa Cruz Co.

Santa Cruz Co.

Watsonville

Saratoga

Los Gatos

Oakland

Capitola

Scotts Valley

Emeryville

San Carlos

Burlingame

Burlingame

Marin Co.

Redwood City

Berkeley

194,374

67,792

452,242

67,233

12,960

435,792

275,077

161,897

19,383

321,532

20,228

377

134,116

546,768

29,852

3,115

89,871

27.276

66.320

17,224

25,401

19,400

54,667

80,351

39,300

10,920

6,885

2.358,371

612,935

74.998

12.497

63,473

39.093

18,920

71,144

7,500

44.027

77,688

25,089

59,579

364,726

7,160

21,125

26,600

26,600

4,555

15,064

213.100

Road Damage

Jetty Road - Moss Landing State Beach in Monterey

County

Treasure Island roadways 

San Juan Watsonville Rd. south of Aromas Rd. in

Monterey County 

Cienega Rd. 0.3 miles south of Union Rd. in Santa Benito

County 

San Thomas Expwy. between Campbell and Hamilton in

Santa Clara County 

Industrial Blvd., Laurel St., Elm St., Cedar St., and

Alameda Dr., City of San Carlos, San Mateo County 

Broadway Street Tunnel between Mason and Hyde in San

Francisco

Liquefaction and lateral spreading of soil caused the roadway to cave in and damage to a corrugated metal culvert.

Road damage due to liquefaction at the Naval Base.

North side of roadway bank has slid 100 feet. Repair cost 

$4,000.

Pavement buckled. Repair cost, $0.

55 soundwall panels tilted. Repair cost, $47.016. 

Some new culvert cracks noted. Repair costs, $23,660. 

Minor movement diaplaced some tiles. Cost, $0.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 167

DAMAGE TO ROADS

Roads were damaged in a number of ways during this 

earthquake. Land and rock slides were prevalent throughout 

the mountains and along the coast. Liquefaction-induced 

settlement and lateral movement of roadways was common 

around San Francisco Bay where loose fills had been placed 

over the Bay mud. Close to the fault rupture, roads were damaged due to surface deformation of the ground. The location 

of road damage can be found on figure 288.

DAMAGE ON STATE HIGHWAY 17

The most significant road damage was on State Highway 17, which was closed for about 12 miles (fig. 289 to

291). This is at a location within a few miles of the epicenter 

of the earthquake. Some of the damage was rock and land 

slides that blocked the highway at several locations. In addition, densification of soil at embankments and behind retaining walls caused road settlements and cracked pavements. 

The concrete median barrier was damaged at several locations. A surface rupture with a vertical uplift of 1.5 feet damaged the roadway near the summit of the Santa Cruz 

Mountains. Repairs to the roadway left the highway closed 

to everyone except local residents and carpools for 32 days. 

The roadway was reopened on November 19. The repairs 

included excavation and flattening of slopes, grout injection, 

soil nailing, and rock fences.

Limits of Route 17 

Road Damage.

Epicentr y /

Figure 289.—Location of damage to Highway 17.
168 HIGHWAY SYSTEMS

Figure 290.—Route 17 landslide.

Figure 291.—Route 17 landslide.

LONE TREE LANDSLIDE ON ROUTE 1.

This is an ancient landslide along the coastal bluffs of 

Marin County. It was remobilized but controlled by Caltrans 

following very heavy rains of January 1982. However, the 

Loma Prieta earthquake created a much faster rate of soil 

movement (figs. 292 to 295), eventually requiring a new road 

alignment behind the landslide. A detailed report describing 

this landslide is provided by Van Velsor and Walkenshaw 

(1992).

Landslides due to the earthquake also closed State Highways 9, 152, 236, and 35. More information is available on 

these landslides in the lifeline section of a report by Heyes 

(1990).

I

-123°

Laamad from the Lc

George Plafker and John P. Galloway, Editors. 

U.S. Geological Survey Circular 1045.

Note: Segment that

LOCATION MAP \ LomPa dprieta Earthquake^ 

VICINITY OF LONE TREE LANDSLIDE /

MARIN COUNTY, CALIFORNIA

Figure 292.—Location of landslide in Marin County (courtesy of Joan Van 

Velser).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 169

Figure 293.—Landslide along Route 1 in Marin County (courtesy of Joan Van Velser).

Figure 294.—Landslide damage along the coast (courtesy of Joan Van Velser).
170 HIGHWAY SYSTEMS

Figure 295.—Sand 

boils and heaving at 

Interstate 80.

EASTERN APPROACH TO THE SAN FRANCISCO OAKLAND 

BAY BRIDGE.

Interstate 80 runs south along the San Francisco Bay in 

Emeryville and then turns west and widens to become a toll 

plaza before crossing the Bay. Approximately 2 miles of this 

roadway from Powell Street to the Bay Bridge was damaged 

due to heaving, settlement, cracking, and lateral spreading following the earthquake (figs. 295 to 298). This damage did not 

affect traffic because a dropped span on the Bay Bridge closed 

this section of roadway. The road was regraded every day for a 

week before the movement subsided.

Figure 296.—Lateral spreading at Interstate 80.

Figure 297.—Aerial photo showing location of Interstate 

80 liquefaction damage.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 17 1

Figure 298.—Repairs to Interstate 80.

SAN FRANCISCO CITY STREETS

Streets in San Francisco that were built on Bay mud or 

loose fills were damaged during the earthquake. This damage was often in the very same locations that had sustained 

damage during the 1906 San Francisco earthquake. Figure 

299 was taken at the corner of Divisadero and Jefferson 

Streets in the Marina District. Differential settlement of the 

ground with accompanying buckling of asphalt pavement was 

common throughout the Marina (fig. 300).

Figure 299.—Road damage in San 

Francisco's Marina District (courtesy 

of Earthquake Engineering Research 

Institute)
172 HIGHWAY SYSTEMS

SAN FRANCISCO BAY

J

EXPLANATION

_ IBS1 SHOHELUE (AFTER US. COAST SURVEY)

— LATERAL SPHEADNG CRACKS

• BULDNG SETTLEMENT

PAVEMENT/CURB*CEWALK BUCKLING 

• SANDBOL-VOLUME <lm3

NOTES

LATERAL SPREADMG CRACKS. SETTLEMENT

AND BUCKLING. MAPPING BY JA EGAN.

IGEOMATTOX CONSULTANTS).

SAND BOILS MAPPMG BY J.A. EGAN. FLB.

SEED(UC BERKELEY). M BENNETT

(US. GEOLOGICAL SURVEY). AND J P BARDET

O SANDBOL-VOLUhC >lm3

Figure 300 —Damage map of San Francisco's Marina District (Egan, 1990).

JETTY ROAD AT MOSS LANDING 

STATE BEACH.

South of the city of Santa Cruz, 

the approach road to Moss Landing 

State Beach was damaged due to liquefaction of the soil (figs. 301 and 

302). About 300 feet of roadway subsided as much as 3 feet and spread 20 

feet laterally.

Figure 301.—Damage to the access road at Moss Landing State Park (courtesy of Earthquake Engineering Research Institute) (view to north).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 173

Figure 302.—Damage to the access road at Moss Landing State Park (courtesy of Earthquake Engineering Research Institute) (view to south).

Figure 303.—Aerial view of southern part of Treasure Island (at top).

Figure 304.—Lateral spreading damage to roadway at Treasure 

Island (courtesy of U.S. Geological Survey; photograph by 

Michael Bennett).

TREASURE ISLAND

Treasure Island is a Naval Station in the middle 

of San Francisco Bay. Land access to the island is 

limited to a causeway from Yerba Buena Island (fig. 

303). During the earthquake this causeway (an embankment built over sand and Bay mud) experienced 

lateral spreading with cracks several inches wide. 

There was also widespread liquefaction damage to 

most of the roads on the island (fig. 304).

Several excellent reports analyzed the damage 

to the island after the earthquake. One is included in 

this Professional Paper series (Power, in press). Another report, to the United States Navy, also described the damage (Power, 1990).
174 HIGHWAY SYSTEMS

Figure 305.—Areas of compression damage along northeastern edge of 

Santa Cruz Mountains (rectangular area at lower right is area of fig. 308) 

(courtesy of Earthquake Engineering Research Institute).

SAND HILL ROAD AT 1-280 NEAR PALO ALTO

The fault rupture did not reach the ground surface; 

however, there were other types of surface deformation 

that occurred due to the earthquake. "Zones of compressional deformation run along the northeastern foot of the 

Santa Cruz Mountains between Blossom Hill and Palo 

Alto," according to Ponti (1990). "These are second-order tectonic features; they are probably not seismogenic 

but were triggered by tectonic rupture at depth," concludes 

the report.

These "second-order tectonic features" caused asphalt 

pavement to buckle and concrete curbs and sidewalk to 

break on city streets from Los Gates north to Los Altos 

(fig. 305). At Sand Hill Road there was a movement of the 

ground that pushed a section of the road together until it 

failed in compression (figs. 306 and 307). Similar damage 

occurred to State Route 17 and Interstate 280.

Figure 306.—Buckled roadway (by traffic island) at Sand Hill Road.

Figure 307.—Close-up of damage at Sand Hill Road.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 175

(17

VECTOR SCALE

Figure 309.—Damage to Morrill Road from 1989 (Loma Prieta) earthquake.

MORRILL ROAD AT THE SAN ANDREAS FAULT

There were many surface fractures in the Summit Road/ 

Skyline Ridge area near the San Andreas Mountains in Santa 

Clara County (fig. 308). This resulted in substantial road 

damage in the area (Ponti, 1990). Damage can occur to roads 

on good basement material when the pavement is within several miles of an active fault. Morrill Road suffered a transverse crack that closed the road after the earthquake (fig. 

309). Surprisingly, a similar crack at the same location closed 

the road after the 1906 earthquake (fig. 310).

Figure 308.—Location of damage along Summit Road (fractures shown by heavy lines; arrows show direction of movement) (courtesy 

of Earthquake Engineering Research Institute).

Figure 310.—Similar damage to Morrill Road from 1906 earthquake.
176

DAMAGE TO TUNNELS

Tunnels without vulnerable structural elements like 

columns typically experience little earthquake damage. 

The rock and soil around the tunnel act to support it during ground shaking. This suggests that cut-and-cover tunnels must be more carefully designed for earthquakes than 

tunnels which are bored through the earth.

A potential problem for tunnels is due to changes of 

soil stiffness along their length. This could cause differential displacement, resulting in structural damage. Another problem occurs if a tunnel crosses a fault, which is 

also a problem for above-ground structures. Additionally, 

liquefaction is a problem for shallow tunnels, as it has been 

for culverts (see next section). Caltrans currently has no 

seismic design code for tunnels.

Several highway tunnels were in the area that suffered 

bridge damage from the earthquake. Caltrans underground 

structures unit investigated tunnel and culvert damage 

(Zelinski, 1993). There was no damage to any Bay Area 

Rapid Transit tunnel, including the long trans-Bay tube, a 

watertight steel shell extending under the San Francisco 

Bay, and the Berkeley Hills tunnel crossing the Hay ward 

fault. No damage was reported for tunnels belonging to 

other light and heavy rail companies, cities, and counties. 

A railroad tunnel, the Wrights-Laurel tunnel (fig. 308), 

has been long abandoned but apparently has an offset from 

the 1906 earthquake; whether the 1989 movement of the 

San Andreas fault affected this tunnel is not known, as it 

is boarded up.

THE WEBSTER STREET AND POSEY STREET TUBE CROSSINGS

The only significant tunnel damage was to these 4,500- 

foot-long tubes which carry two lanes of traffic in each direction under the Oakland Estuary between the cities of 

Alameda and Oakland (figs. 311 and 312). The Posey Street 

Tube was built in the 1920's, and the Webster Street Tube

was built in the 1960's. They are reinforced concrete tubes 

with a bituminous coating for water proofing , and they descend to about 70 feet below sea level. After Loma Prieta, 

some of the connections between the tube segments began 

leaking. It was thought that liquefaction of the soil around 

the tubes caused deformation at the joints. Earthquake repair 

drawings were made, and the tubes were epoxy injected to 

stop the leaking. In 1997 a more elaborate retrofit was planned 

that included (1) creating very stong, water-proof hinges at 

the joints, (2) compacting the soil, adding stone columns, 

and building a curtain wall to prevent liquefaction and pore 

pressure from pushing up the tubes, and (3) jet grouting columns to support the ends of the tube segments.

Figure 311.—Alameda entrance to Posey Street Tube (courtesy of Ben C. 

Gerwick Inc.)

-*- . ^ 

tHdifipos£0**nf~i 'VUxsixliaxaaau E DE.&//S .ske

/#:B<r/fW-.1~"'v>isc»J'on_e,o u s/D'e

Figure 312.—Plan drawing of Posey and Webster Street Tubes showing location under Oakland Estuary.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 177 

FORT CRONKITE TUNNEL (Br. #27-39) TUNNEL AT GEARY AND FIRST AVENUE IN SAN FRANCISCO

This in an unreinforced concrete arch built in 1954 

that allows a single lane of traffic to go under Highway 

101 in Marin County. It is 17 feet tall at its crown, 20 feet 

tall at its base, and 1,109 feet long (fig. 313). Although 

there were some indications of movement, and the tunnel 

was briefly closed by the Golden Gate Park Service, there 

was no earthquake damage to this tunnel.

PRESIDIO PARK TUNNEL (Br. #33-16)

This is a reinforced concrete arch tunnel built in 1955. 

It carries traffic on State Route 1 north to the Golden Gate 

Bridge. It is 1,300 feet long, 45 feet wide, 30 feet tall, and 

has a 17-foot minimum vertical clearance (fig. 314). It 

had no earthquake damage.

CALDECOTT TUNNEL (BR. #28-15)

These twin reinforced concrete arch tunnels take Route 

24 traffic under the Oakland Hills between the Alameda 

and Contra Costa Counties (fig. 315). They were built in 

1964 and carry two lanes of traffic each. They were inspected and found to be in excellent condition after the 

earthquake. This tunnel was instrumented and although 

the records are of low magnitude, they provided the first 

information on tunnel movement during an earthquake (fig. 

316).

This is a four-lane two-directional reinforced concrete 

box tunnel. It had no earthquake damage.

STOCKTON STREET TUNNEL BETWEEN SACRAMENTO AND 

BUSH STREETS IN SAN FRANCISCO

This tunnel had no earthquake damage. There were 

some cracks in barrier rails at both ends of tunnel.

BROADWAY STREET TUNNEL BETWEEN MASON AND HYDE 

STREETS IN SAN FRANCISCO

This tunnel had very minor earthquake damage. 

Ground shaking removed about 15 tiles from the tunnel.

Figure 313.—Fort Cronkite Tunnel.
178 HIGHWAY SYSTEMS
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 179

u

<4-H

o 

so

O
180 HIGHWAY SYSTEMS

Oakland - Caldecott Tunnel (Hwy 24, North Tunnel, 3100 feet long) 

(CSUIP Station 58359) Record 58359-C0162-&9297. 01

>mm,mmmm»i

V Wes

8

9

10 1/2

11

12

13 1/3

14

15

16

T7 

18

19

*L,T - 

Notp;

t Portal - L*(251°) T:Trlgg«r tlm* 00:04:37.0

- Up

" - T*C161°)

- Length Polht - L (223°)

- Up

- T (133°)

-Length Point: North Wall - L (223")

" South Wall - Up

Roof - T (133°)

Nov-.h Wall - T (133 6 ) _

_^__

" South Wall - T (133°) 

" North Wall - Up

" Roof - Up

Longitudinal, Transverse to Tunnel Axis. 

Sensors 1-6 were removed due to environmental pro'jlp.ms.

Max. Accel. = 0.06 g

0.03 g

0.06 g

0.02 g

0.02 g

0.03 g

0.04 g

0.03 g

0.03 P

0.04 g

0.04 ,3 

0.03 g

0.03 g

n 1 7 .1 4 5 10 15 20 Sec. 

Figure 316.—Strong motion records for Caldecott Tunnel (courtesy of California Strong Motion Instrumentation Program).

DAMAGE TO CULVERTS

Culverts are commonly used to allow water to drain 

under (rather than across the surface of) roadways. There 

are several types of culverts, and each had its own type of 

earthquake damage. Corrugated metal pipe (CMP) culverts 

are most commonly crushed or pushed out of the ground 

during earthquakes as a result of liquefaction of the base 

material. Occasionally these culverts will be damaged 

when fill material slides downhill, as a result of being set 

on sloping ground or because of land-slides. Reinforced 

concrete box culverts are occasionally damaged due to 

poor connection details between the walls and the roof or
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 181

38. 122'30 122«00- 

00'

37'

30'

37' 

00'

v\v •'"'.'.; \ aoeruoov^J^v

• ^Vicfe \. VO *«vc© S» > ' \ ••»7T:i \\ N*...,._^.r\.VfcX. • —

A V-1TO^

V

Approximately 20 

CMP Culverts Along v , 

Summit Road

Spanish Ranch Road 

CMP Culvert

jetty Road

CMP Culvert ' ——

km

- Elkhorn Slough: 

CMP Culvert k

CONTOUR INTERVAL 

' 150 I"

»--u»- .

;« ( • . "j

"" '& ' •••* "^ i '••.....>•• c ' vX

Figure 317.—Location of culvert damage (Youd, 1997).
182 HIGHWAY SYSTEMS

floor of the culvert. If the roadway is at an angle to the culvert, one side may have less soil against the walls, which can 

cause problems during shaking.

A few culverts sustained damage during the earthquake 

(fig. 317). Much of the information on culvert damage comes 

from Youd (1997). With a few exceptions, the location of 

culvert damage matches the location of road damage. Usually, where ground deformation, liquefaction, or landslides 

damaged roads, they also damaged culverts, the exceptions 

being where structural damage occurred to concrete box culverts or where, surprisingly, the CMP survived roadway damage.

JETTY ROAD AT MOSS LANDING STATE BEACH

The liquefaction that damaged the access road to Moss 

Landing State Beach also damaged a 30-inch CMP used to 

allow tidal flow and drainage of Elkhorn Slough. Actually, 

the culvert had been partially plugged, creating a beautiful 

fresh water lagoon inland of the access road.

During the earthquake the soil around the culvert settled, 

allowing the roadway to fracture the culvert and forcing the 

two ends up and out of the water (figs. 318 and 319). The 

damaged culvert was replaced with six new culverts that converted a fresh water marsh to a barren tidal marsh (Youd, 1997).

Figure 318.—Culvert damage at Jetty 

Road (courtesy of Leslie Youd).

Figure 319.—Aerial view of culvert 

damage at Jetty Road (the culvert has 

been bent until it sticks out of the water) (courtesy of Leslie Youd).
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 183 

ELKHORN ROAD CULVERTS SUMMIT AND MORRILL ROAD CULVERTS

Similar to the damage at Moss Landing State Beach, 3 miles 

inland where Elkhorn Road crosses Elkhorn Slough are seven 

36-inch-diameter CMP culverts. Again, liquefaction settled the 

supporting soil, crushing the culverts and pushing the ends as 

much as 2 feet out of the water (fig. 320). There has been little 

repair at this location. However, the culverts still seem to be 

functioning, with the ends submerged during high tide.

SPANISH RANCH ROAD CULVERT

This was the only example of culvert damage as a result of a 

landslide during the earthquake. This was a 36-inch-diameter CMP 

consisting of three 20-foot-long segments tied together with a 1- to 

2-foot overwrap at each joint. During the earthquake, the outer third 

of the roadway slid down about 3 feet, slightly damaging the roadway (fig. 321). The overlaps at the joints were long enough to prevent the culvert from being pulled apart, although the culvert was 

slightly displaced and reoriented by the ground movement.

The third broad category of culvert damage is ground deformation as a direct result of or as a secondary effect of fault rupture. 

There were about 20 CMP culverts in the area of surface cracking, 

as shown in figure 318. No culvert damage was observed. This may 

have been good culvert performance for this kind of ground behavior or may have been simply a matter of luck. Youd (1997) observed 

that none of the culverts were intersected by the crack locations on 

the map. There was also a box culvert under Morrill Road in the 

same area. There was some damage to the culvert which, on closer 

inspection, is believed to have occurred before the earthquake.

TEMESCAL CREEK CULVERT

There was damage to a box culvert as a result of the earthquake. Temescal Creek flows under 1-80 in Emeryville. The 

culvert is a double 10 by 10 foot reinforced concrete box, about 

220 feet long, built under the freeway (fig. 322). There are also 

two 96-inch-diameter reinforced concrete pipe culverts immediately to the north. After the 

earthquake, the northernmost 

cell was inspected by rowboat. 

The adjacent cell was filled with 

mud and could not be accessed 

by boat (as were the pipe culverts). Cracks ran along the soffit and exterior wall of the north 

cell, and an expansion joint 

about 55 feet from the east end 

opened about 1 foot. This culvert is located where a great 

deal of liquefaction-related 

damage occurred to 1-80. Apparently, this is another case 

where liquefaction damaged the 

roadway and the culvert. Figure 323 shows the general plan 

for the repair of earthquake 

damage to this culvert.

Figure 320.—Damaged culverts at Elkhorn Road.

pavement

CMP pipe sections

joints

Figure 321.—Spanish Ranch Road culvert.

Figure 322.—Temescal Creek culverts.
184 HIGHWAY SYSTEMS
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 185

DAMAGE TO EARTH RETAINING STRUCTURES

Where space for a roadway is limited, a variety of retaining 

walls have been devised to hold back the soil and provide enough 

room for a road. Caltrans considers its current retaining-wall 

design procedure so conservative that no special provisions for 

earthquake loads has been added. This policy has stood up well 

despite several large earthquakes; little damage has ever occurred 

to any Caltrans-designed retaining wall. These walls tend to receive some support from the adjacent soil during earthquakes.

There are many different types of retaining walls, including a variety of reinforced earth walls, soil-nail walls, tieback 

walls, gravity walls, etc., in the area that experienced bridge 

damage, and all performed well during the earthquake. The only 

walls known to have suffered damage were some crib walls in 

the Santa Cruz Mountains. The information on these walls was 

provided by Lew and Chieruzzi (1990).

CRIB WALL AT HIGHLAND ROAD IN SANTA CRUZ COUNTY

Crib walls are cells made out of precast concrete, metal, or 

timber elements that are filled with earth. Several crib walls in 

the Santa Cruz Mountains showed distortions due to settlement 

of the backfill (behind the wall) and movement of the wall face. 

The wall shown in figure 324 showed major distress halfway up 

the face and had backfill settlement of more than a foot. This 

wall may have been built at a previous landfill site.

SOIL-NAIL WALL AT THE UNIVERSITY OF CALIFORNIA AT 

SANTA CRUZ

Soil-nail walls are used to temporarily hold back the soil 

during construction and sometimes as a permanent retaining 

wall. There were many soil-nail walls in the area of earthquake damage, including one (fig. 325) near the rupture zone. 

They all performed very well during the earthquake.

Figure 324.—Crib wall (courtesy of Earthquake Engineering Research Institute).

Figure 325.—Soil-nail wall 

(courtesy of Earthquake Engineering Research Institute).
186 HIGHWAY SYSTEMS

DAMAGE TO LOCAL HIGHWAY SYSTEMS

City streets and county roads were also damaged by the 

earthquake. Some of the damage was identified through correspondence and is listed in table 27. Other damage was ascertained through requests for Federal disaster relief as shown 

in table 25. Still more local damage was discovered by earthquake engineers conducting investigations. Finally, some cities and counties have written reports and even books 

describing the earthquake's impact to their streets and roads. 

For instance, the City of San Francisco has written a comprehensive summary of damage to road systems (City and 

County of San Francisco, 1993), and Santa Clara County has 

written a volume on bridge damage and their retrofit program (Randall, 1994). The cost of highway damage for the 

city of San Francisco is summarized in table 28.

REFERENCES

City and County of San Francisco, 1993, The Loma Prieta earthquake— 

Repair of damage to San Francisco's Road Systems.

Egan, J.A., 1990, Map of liquefaction in the Marina District— 

Geotechnical Aspects:EERI's Loma Prieta Earthquake Reconnaissance Report.

Table 27.—Damage to city transportation systems

Heyes, David, 1990, Summary of highway damage from the lifeline chapter: EERI's Loma Prieta Earthquake Reconnaissance 

Report.

Lew, Marshall, and Robert Chieruzzi, 1990 Geotechnical aspects: 

EERI's Loma Prieta Earthquake Reconnaissance Report.

Ponti, D.J., and others, 1990, Surface rupture aspects from the geoscience chapter: EERI's Loma Prieta Earthquake Reconnaissance Report.

Power, Maurice S., 1990, Road damage at the approach to the East 

Bay Bridge: Geomatrix Consultants Inc.

————1993, Loma Prieta earthquake damage to Treasure Island 

roadways: Personal correspondence.

————in press, Loma Prieta earthquake damage to Treasure Island roadways—Liquefaction-induced damage: U.S. Geological Survey Professional Paper 1552

Randall, J.R., 1994, Santa Clara County, Loma Prieta earthquake 

bridge damage and Transportation Agency seismic retrofit 

program: Santa Clara County Bridge Design Unit.

Van Velser, Joan, and John Walkenshaw, 1992, Earthquake induced 

acceleration of landslide movement following the October 

17, 1989 Loma Prieta earthquake on the San Andreas Fault 

in Santa Cruz, California: Conference Proceedings for the 

Annual Meeting of the Transportation Research Board.

Youd, T.L., in press, Highway culvert performance during earthquakes: 

National Center for Earthquake Engineering Research.

Zelinski, Ray, 1993, Loma Prieta earthquake PEQIT report: California Department of Transportation.

City or County Impact Commentary Official

Livermore No None

Sonoma No None

Monterey No None

Sausaiito No None

Half Moon Bay No None

Sebastapol No None

Seaside No Cracks on secondary roads

Novato No None

Hayward No None

Clayton No None

Daly City Yes Repair of cracks and uplift took 1 yr

Palo Alto Yes Bike and Pedestrian Bridges

Fremont No Began bridge retrofit program

Alameda Yes Liquefaction Damage

Berkeley Yes Still working on repairs in 1993

San Francisco Yes 13.4 million dollars in damage

John Hines, Public Works 

Richard Rowland, Public Works 

Tom Reeves, City Engineer 

O. Gary Plunkett, City Engineer 

William Smith, City Engineer 

Larry Koverman, Public Works 

Richard Guillen, City Engineer 

Bob Weil, Senior Civil Engineer 

Bud Simmons, Sr Civil Engineer 

Cathie Kelly, Secretary 

Mohinder Sharma, City Engineer 

Michael Jackson, Public Works 

T.M. Blalock, Public Works 

T.D. Edwards, City Engineer 

Jeffrey Egeberg, Engineering 

Department of Public Works

Table 28.—Highway costs for the City of San Francisco

Description

Streets

Traffic Control

Bridges

Road Structures

Number of 

Facilities

68

17

5

21

Project Cost

$12,951,981

$152,430

$20,000

$281,045
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 187

CHANGES TO ENGINEERING PRACTICE

Caltrans began designing for earthquake loads soon 

after the 1933 Long Beach earthquake. However, it was 

the 1971 San Fernando earthquake that resulted in most 

of the changes to the seismic specifications for bridges. 

After that earthquake, Caltrans began designing bridges 

for seismic loads using the maximum credible earthquake 

from Greensfelder (1974). Taking the maximum acceleration from the bridge location on a map along with the appropriate depth of alluvium at the site, the bridge engineer 

could choose the appropriate response spectra to perform 

a multimodal dynamic analysis of the structure. The response spectra were normalized from five significant California earthquakes on rock, amplified based on the depth 

of alluvium at the bridge site, and reduced for 5 percent 

damping. For a large bridge project, a site-specific response spectra was developed.

The bridge model included a bridge-abutment stiffness limited to a yielding force of 7.9 kips/ft2. Column 

foundations were originally modeled as pinned or fixed. 

Column moments taken from this elastic multimodal 

analysis were then reduced by a risk and ductility factor 

to approximate the true, nonlinear behavior of the bridge. 

This reduction in moments was based on Newmark (1971), 

who stated that for long-period structures (periods greater 

than about 0.7 seconds), the maximum displacement of 

elastic and inelastic structures (with the same period) is 

about equal. Therefore, although it was the moment that

MIL

Idea ized Linear Behavior

Idealized Nonlinear Behavior

Equal Displacement Theory

Au Mu

1) The Ductility Factor 1^='^' = yfy

2) Linear and Nonlinear Structures having 

equal natural periods (>.7 sec.) have 

equal maximum displacements.

was being considered in the analysis, it was really the 

maximum displacement that was being controlled by the 

ductility factor (fig. 326). The values for ductility were 

based on tests done in New Zealand that showed that wellconfined columns can undergo large displacements and 

curvature without failing (Park, 1971). An additional factor which considered the risk associated with different 

bridge elements was added to the ductility factor, resulting in the risk and ductility factor "Z" shown in figure 

327 (Caltrans, 1983).

Using this reduced moment and the appropriate axial 

load, the column section and the amount of column steel 

were selected from an interaction diagram or the program 

YIELD from McBride (1992). This limited the forces in 

the bridge to the largest plastic moment that these columns could develop. Adjacent members, such as footings 

and bent caps were designed to be at least as strong as the 

plastic column moments. This forced yielding to occur in 

the columns, where damage could be controlled by wellconfined spiral reinforcement. The abutments were then 

designed to add significant damping to the system. Sufficient seat widths and restrainers were provided at bridge 

joints to keep the superstructure from falling. Thus, during a very large earthquake, column reinforcement would 

yield, bridge joints might bang and spall, and the soil behind the abutment might degrade, but the bridge would be 

able to handle the earthquake due to the ductility of the 

bridge columns.

Assumptions of column ductility underwent intense 

scrutiny after the earthquake, (Priestley and Seible, 1991). 

They found that well-confined columns were able to 

achieve the ductility assumed in Caltran's design. Testing 

was also done to determine the ductility of old, unconfined columns, steel-shelled columns, and fiber-wrapped

Wall confined ductile 

•ingle column bent* (3.0)

Piers, ^butmont wwl§v And winowMt {2 • 2.0)

Well reinforced concrete thaw key* (2 - 0.8)

0 0.2 0.4 0.6 0.8 1.0 2.0

Period of Structure (Sec) T 

Adjustment for Ductility and Risk Assessment

Figure 326.—Equal displacement theory for seismic bridge design. Figure 327.—Ductility and risk factor "Z" used in the seismic design of bridges.
188 HIGHWAY SYSTEMS

columns. This was essential for the seismic retrofit effort 

that Caltrans undertook after the earthquake.

Looking at the bridge damage from the earthquake 

reveals a couple of significant contributing factors. Bridge 

columns designed after the 1971 San Fernando earthquake 

performed well. However, older columns with poor confinement and lap splices in areas of plastic hinging showed 

their vulnerability. Caltrans, therefore, accelerated the 

Phase 2 retrofit program, which provided column confinement with a steel shell for older single-column bents. These 

retrofits often required a column footing retrofit and sometimes an abutment retrofit as well. This was because the 

shelled column now could form a plastic moment which 

had to be resisted by the footing or because modifying the 

abutment was sometimes a cheaper way of protecting the 

columns, particularly for short bridges. Caltrans also began a program to retrofit bridges with multicolumn bents. 

This usually required checking the moment capacity of 

the bent cap. Along with the seismic retrofit program came 

a much more intense research program to test the assumptions of the seismic retrofit strategies. In many cases a 

seismic retrofit had to wait for test results to show the 

effectiveness of a design strategy.

After the earthquake, Caltrans began spending money 

on research equal to 1 percent of its construction budget, 

or about $5 million a year. The most important research 

done immediately after the earthquake was to test the ductility of older column designs and the ductility of the seismic retrofits of columns (Chai, 1991). Other significant 

research was the testing of shear walls (Haroun, 1993), 

studies of the shear capacity of column-superstructure and 

column-footing joints (Stojadinovic, 1995; Seible, 1994; 

Ingham, 1994), footing retrofit tests (Xiao, 1994), and 

studies on column shear and P-Delta effects (Priestley, 

1993; MacRae, 1993; Ascheim, 1992; Mahin, 1991). 

Through this intense research effort, reliable values for 

the shear, moment, and displacement capacities of various bridge members were established, which were of great 

benefit to Caltrans' retrofit program.

The cost of designing a new bridge to perform well 

for a large earthquake is relatively small compared to the 

cost of retrofitting an existing bridge to perform as well. 

This is because it is difficult to change the dynamic behavior of a structure after it is built. The bridge research 

paid for itself many times over by identifying a larger seismic resistance in many bridges. Investigations into the 

damping values of bridges (Werner, 1993), research on 

the stiffness of soil-structure elements by Romstad (1996), 

Po Lam (1986, 1991), and others, and work to provide 

Caltrans with a nonlinear bridge-analysis program by 

Powell and Campbell (1994) and Prakash (1994), all contributed to an increased understanding of bridges and new 

analysis techniques that aided Caltrans' retrofit efforts.

Funds for seismic retrofits came from several sources. 

The State of California raised its sales tax one-quarter cent

for a limited period to provide revenue for the seismic retrofit program. Federal funds that would have been used 

for the state transportation program were diverted to pay 

for retrofits. A total of $750 million was spent retrofitting 

1,039 state-owned bridges. After the 1991 Northridge 

earthquake, phase 2 of this program was begun to retrofit 

an additional 1,155 state bridges at a cost of about $1.05 

billion. A third retrofit program was begun to retrofit stateowned toll bridges. A $2 billion bond measure (Proposition 192) was passed by the people of California in 

November 1995 to pay for the phase 2 retrofit program. 

However, the cost of the toll bridge program will most 

likely exceed the remaining funds. A decision has yet 

(1997) to be made on how the additional funds will be 

obtained. The Golden Gate Bridge retrofit was paid for by 

raising tolls from $1 to $3. A program was also begun to 

retrofit locally owned bridges using Federal bridge replacement and rehabilitation funds. Additional retrofit programs 

may be required in the future for specific routes and locations. For instance, California and the Federal government 

are interested in a higher performance level for essential 

routes that must remain open after a disaster. This will 

require a future retrofit program. Bridges that are deemed 

vulnerable to large velocity pulses from nearby faults may 

one day be retrofitted. Likewise, most California bridges 

have not been analyzed for very long duration earthquakes. 

However, these retrofit programs may have to wait for large 

and very damaging earthquakes. In 1992, the 7.6 magnitude Landers earthquake occurred, but because it caused 

little damage, it was quickly forgotten. The driving force 

for money to improve the seismic vulnerability of highway systems has been disasters of a magnitude to evoke 

concern to the media, the government, and the public (not 

necessarily in that order).

Since there is a relatively small amount of money to 

make the 12,000 state bridges (and the 12,000 locally 

owned bridges) capable of surviving a maximum credible 

earthquake, a great deal of effort was expended in refining analysis tools and eliminating bridges from the program. The first step in this process was the development 

of a risk algorithm to list all bridges according to their 

vulnerability to the maximum credible earthquake. This 

algorithm looked at factors such as the year built, length, 

daily traffic, etc. The algorithm was run using a database 

that was created through a general plan review of all state 

bridges. Those bridges with good seismic details were 

eliminated from the database for this first general plan 

review. The result was a list of all state bridges from the 

most vulnerable, with a value of one, to the least vulnerable, with a value of zero. A total of 440 bridges, which 

included all vulnerable single-column bent bridges as well 

as all toll crossings, was removed from this list for immediate analysis and retrofit. Some single-column bridges 

with difficult details or some with single and multicolumn 

bents were left in the list for later review and retrofit. The
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 189

rest of the bridges in the list went through a rank analysis, 

which was a refinement over the previous algorithm and 

considered such things as distance from a major fault. This 

algorithm (Sardo, 1993) was based on recommendations 

by the Caltrans Seismic Advisory Board. Then a second 

review of the most vulnerable bridges was begun by engineers to eliminate those from the retrofit program with 

good seismic details. The most vulnerable bridges from 

the database were put together into projects usually based 

on their location. This made it easier for a contractor to 

retrofit several bridges at once. Caltrans' Local Assistance 

Branch was in charge of turning the retrofit list into 

projects with separate expenditure authorizations. Because 

Caltrans' management felt their designers could not perform their regular work as well as all the retrofit work, 

the decision was made to hire consultants to do most of 

the retrofit design. A similar program to retrofit the 12,000 

local agency bridges also was started. Local bridges in 

Los Angeles and Santa Clara Counties were managed by 

those counties, while the rest were managed by Caltrans. 

Federal bridge replacement funds became available to retrofit some of these bridges.

After a consultant or design section was given a retrofit project, they usually spent some time running calculations and coming up with a retrofit strategy. Then a 

strategy meeting was organized. This was usually attended 

by Caltrans engineers who had experience and expertise 

in seismic retrofits. The retrofit project engineer would 

describe the analysis procedure they followed and the retrofit strategy they proposed. Then Caltrans staff would try 

to find flaws in the strategy, things the engineer might have 

missed, possible mistakes, and tried to get the engineers 

to sharpen their pencils. This was because Caltrans was 

trying to eliminate all unnecessary expense. This resulted 

in many innovations in retrofit design. The dominant new 

retrofit strategy was to limit the displacement demand to 

less than the displacement capacity at the columns and by 

taking as much force as possible at the abutments. This 

strategy depended upon two excellent programs. The program COLX (which later became XSECTION) calculated 

the displacement capacity of single columns and the program FRAMEX (which later became wFRAME) calculated the displacement capacity of frames (Seyed-Mahan, 

1995). The original method of comparing column moment 

demands from a multimodal analysis with column moment 

capacities (and checking the shear) would suggest a great 

deal of retrofitting was needed. By going to a displacement analysis, engineers could make retrofits that handled 

the maximum credible event with very little damage.

How much damage a structure was allowed to sustain 

during an earthquake became the subject of intense review after Loma Prieta. Eventually standards were developed for one bridge capacity at a functional demand level 

and a second capacity at a safety demand level for two 

types of bridges, important and regular structures. This

criteria was developed with Caltrans' Seismic Advisory 

Board. However, for the vast majority of retrofits the criteria remained "no collapse." Therefore, much of a strategy meeting's effort was to eliminate retrofits whose 

purpose was to prevent damage rather than collapse.

Many different retrofit strategies and analysis procedures came out of Loma Prieta. The premier handbook 

for retrofit design after the event was by Priestley and 

Seible (1991). Caltrans revised its seismic retrofit specifications (Caltrans, 1995). These sources became standard 

practice by designers and consultants. The most important values for designers were column-displacement capacities and column-shear capacities since these values 

determined how much money was required for a retrofit.

Caltrans funded the Applied Technology Council 

(ATC) to look at Caltrans' seismic procedures and recommend improvements similar to what they did for the Federal Highway Administration (FHWA) after the 1971 San 

Fernando earthquake [ATC-6, 1981]. This work eventually became ATC-32 (Nutt, 1996). Among the innovations 

in this document are new response spectra, new ductility 

factors, and improved procedures for member shear and 

joint shear design.

Not only did Caltrans engineering practice change as 

a result of the Loma Prieta earthquake, but concerns following this earthquake led to new policies for most bridges 

in the United States. Information on the national impact 

of the earthquake was provided by Buckle (1995). Immediately after the earthquake, the Federal Highway Administration (FHWA) required that all federally funded bridges 

be designed using ATC-6 seismic provisions, which were 

more rigorous than the current specifications used by most 

states. The American Association of State Highway and 

Transportation Officials (AASHTO) contracted with the 

National Cooperative Highway Research Program 

(NCHRP) to develop a new bridge specification using load 

and resistance factor design and modifications based on 

knowledge gained from the Loma Prieta earthquake. In 

1990, the ATC-6 specifications became Division 1-A of 

the Standard Specifications. Moreover, AASHTO asked 

NCHRP to review these provisions in light of the Loma 

Prieta earthquake. The National Center for Earthquake 

Engineering Research (NCEER) began this work as project 

NCHRP 20-7/45 and published its final report in 1991 

(American Association of State Highway and Transportation Officials, 1991).

In 1991 the United States Congress authorized the 

Intermodal Surface Transportation Efficiency Act 

(ISTEA). Among its provisions were a 6 year research 

program into the vulnerability of existing highway systems. Some of the information provided in this report, like 

the performance of culverts and roadways, was obtained 

through this research project. Another part of this project 

was the revision of FHWA directives (Buckle, 1995). All
190 HIGHWAY SYSTEMS

this work was begun out of concerns with older highway 

performance shown during the Loma Prieta earthquake.

In 1992 the FHWA awarded a research contract to 

NCEER to study performance criteria, spatial variations, and 

seismic details for moderate seismic zones.

In 1993, many states began to examine the seismic vulnerability of their large bridges out of concern with the damage sustained by the San Francisco-Oakland Bay Bridge 

during the Loma Prieta earthquake.

The Loma Prieta earthquake also influenced the bridge 

design codes in Canada and Japan. Researchers from all over 

the world came to study highway damage and what the implications were for their own countries. The earthquake 

showed all too clearly what could happen when a highway 

department has a large inventory of older, seismically deficient bridges. It also showed how the earthquake could damage bridges many miles from the fault rupture. Most 

importantly, it provided an increased level of funding to evaluate and respond to these problems.

REFERENCES

American Association of State Highway and Transportation Officials, 1991, Guide specification for seismic isolation design.

Aschheim, Mark, and Moehle, Jack, 1992, Shear strength and 

deformability of RC bridge columns subjected to inelastic 

cyclic displacements: UCB/EERC-92-04.

ATC-6, 1981, Seismic design guidelines for highway bridges.

Buckle, I.G., 1995, Seismic retrofitting manual for highway bridges: 

Publication No. FHWA-RD-94-052.

Caltrans, 1983, Bridge design specifications; Chapter 3, Loads.

Caltrans, 1995, Memos to designers 20-4.

Chai, Y.H., and others, 1991, Flexural retrofit of circular reinforced 

concrete bridge columns by steel jacketing—Experimental 

studies: UCSD/SSRP-91-06.

Greensfelder, R.W., 1974, Maximum credible rock acceleration 

from earthquakes in California: California Department of 

Conservation, Division of Mines and Geology.

Ingham, James, and others, 1994, Seismic performance of bridge 

knee joints; Volume II, Circular column/cap beam experimental results: UCSD/ SSRP - 94/17.

Haroun, Medhat A., 1993, Cyclic behavior of bridge pier walls for 

retrofit: University of California at Irvine, RTA No. 59N974

Ingham, James,and others, 1994, Seismic performance of bridge 

knee joints, Volume I: UCSD/ SSRP-94/12.

MacRae, Gregory A.,and others,1993, P-D design in seismic regions: UCSD/ SSRP-93/05.

Mahin, S., Boroschek R., 1991, Influence of geometric nonlinearities on the seismic response and design of bridge structures: Report to California Department of Transportation, 

UCB.

McBride, Steve, 1992, Bridge computer manual; Volume 2, YIELD: 

Caltrans

Newmark, N.M., and Rosenblueth, E., 1971, Fundamentals of earthquake engineering: Prentice-Hall, Englewood Cliffs, N.J.

Nutt, Richard, 1996, Improved seismic design criteria for California bridges—Provisional recommendations: ATC-32, Applied Technology Council, Redwood City, CA.

Park, R, and others, 1971, Reinforced concrete members with cyclic loading: Journal of the Structural Division, ASCE, v. 

98, ST7.

Po Lam, Ignatius, and Martin, Geoffrey R., 1986, Seismic design 

of highway bridge foundations; Volume I to Volume III: 

FHWA/RD-86/101-103.

Po Lam, Ignatius, and others, 1991, Modeling bridge foundations 

for seismic design and retrofitting, in Proceedings of the 3rd 

TRB Bridge Conference.

Prakash, V, and others, 1994, DRAIN-3DX, Base program description and user guide, Version 1.10: UCB/SEMM-94/07.

Powell, Graham, and Scott Campbell, 1994, DRAIN-3DX element 

description and user guide for element typeOl, type04, 

typeOS, typeOS, type09, type 15, type 17, version 1.10: UCB/ 

SEMM-94/08.

Priestley, M.J. Nigel, and Sieble, Frieder, 1991, Seismic assessment and retrofit of bridges: UCSD/ SSRP-91/03.

Priestley, M.J. Nigel, and others, 1993, Seismic shear strength of 

reinforced concrete columns: UCSD/ SSRP-93/06.

Romstad, Karl, and others, 1996, Longitudinal strength and stiffness behavior of bridge abutments: UCD-STR-96-1.

Sardo, Ann D, 1993, Developments in seismic prioritization of 

bridges in California: Caltrans.

Seible, F, and others, 1994, Full scale bridge column/ superstructure connection tests under simulated longitudinal seismic 

loads: UCSD/ SSRP-94/14.

Seyed-Mahan, M., 1995, User's manual for wFPREP and 

wFRAME, 2-D push analysis of bridge bents and frames, 

Version 1.13, (C) 1994, 1995: Mark Seyed-Mahan.

Seyed-Mahan, M., 1995, User's Manual for xSECTION, cross section analysis program, Version 2.11, (C) 1994, 1995: Mark 

Seyed-Mahan.

Stojandinovic, B, and Thewalt, C.R., 1995, Upgrading bridge 

outrigger knee joint systems: UCB/EERC-95-03.

Werner, S.D., 1993, Study of Caltrans seismic evaluation procedures for short bridge overcrossing structures: Dames and 

Moore.

Xiao, Yan, 1994, Seismic assessment and retrofit of bridge footings: UCSD/SSRP-94/11.
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17, 1989: PERFORMANCE OF THE BUILT ENVIRONMENT 191

CONCLUSION

This report summarizes some of the ways that the Loma 

Prieta earthquake impacted highway systems. Some areas are 

discussed more thoroughly than others. For instance, the 

impact on state and Federal highways is addressed more than 

city streets and county roads. More information is provided 

on bridges than on other highway structures. The concerns 

of engineers are more represented than f x>se of planners or 

administrators. However, information on these other topics 

is available. Specific references are listed for each bridge 

and at the end of each main section. Readers looking for a 

more complete listing of references related to the Loma Prieta 

earthquake can refer to the Earthquake Engineering Research 

Center (EERC) National Information Service for Earthquake 

Engineering (NISEE) Library. They have recently completed 

two large projects to provide references for the Loma Prieta 

earthquake. The first project was funded by the National Science Foundation (NSF) Loma Prieta Clearinghouse Project 

of Ongoing Research Reports with an annotated bibliography of 2,224 references. The second project is aUSGS-funded 

archive for a permanent record of raw research data sets. Both 

of the projects will be available on CD-ROM and on the world 

wide web. Their internet address is "http:// 

www.eerc.berkeley.edu". Caltrans also has a homepage that 

provides information about California's highway system. 

However, this homepage is not as comprehensive. One day, 

all the information in the world will be easily accessible from 

a personal computer. Until then, bridge plans can be obtained 

by writing to Caltrans Office of Structural Maintenance and 

Investigations, P.O. Box 942874, Sacramento, CA 94274.

Large earthquakes can cause human casualties, costly 

damage, and closures on highway systems. We have seen 

how the Loma Prieta earthquake resulted in death and injury 

on older structures such as the Cypress Viaduct (an elevated 

freeway) and the San Francisco-Oakland Bay Bridge (a long 

truss bridge). Recent earthquakes demonstrate that Caltrans 

has learned the life safety lessons of the Loma Prieta earthquake well. They have prioritized their entire bridge inventory, performed a structural analysis on the most vulnerable 

structures, and developed retrofits that are meant to prevent 

serious injury during future earthquakes. They are supporting a research program to make certain that all seismic procedures are state-of-the-art, and they have developed 

performance criteria to assure that life safety is maintained 

for the maximum credible earthquake. However, more work 

needs to be done on the lifelines and economics issues. Road 

closures caused by the Loma Prieta earthquake resulted in 

significant impacts to the area's economies. The collapse of 

a section of the East Bay Bridge required commuters to take 

ferries or drive far south to the San Mateo Bridge or north to 

the Richmond Bridge to cross the Bay. The collapse of the 

Struve Slough Bridges on the Pacific Highway isolated the 

communities in that area and required a long detour. Likewise, landslides in the mountains and along the coast closed

several highways and created economic impacts to those regions. Caltrans addresses economic issues with a second 

performance level that sets serviceability requirements for a 

more frequent event. However, the cost of developing a probability-based earthquake for the bridge site and the expense 

of designing bridges for a much higher performance level 

has resulted in its use only on important bridges. Unfortunately, politics or the cost of a retrofit often determines a 

bridge's importance rather than a detailed risk assessment.

Therefore, Caltrans may be dealing more effectively with 

technical rather than the social and economic issues following this earthquake. These technical issues include the following:

1. The behavior of connections and particularly how 

shear is transferred at reinforced concrete joints has become 

a major issue in research and in many new retrofits. Immediately after the earthquake the solution for column to superstructure joints was to provide so much reinforcement in the 

joint that they became very expensive and difficult to build. 

A testing program has resulted in an empirical method for 

joint design that should give good performance during large 

earthquakes. Outrigger knee joints are still an area of concern. For new and retrofit designs, Caltrans has been using 

pinned connections wherever possible or providing edge 

beams to reduce the torsion in outrigger bent caps.

2. A more sophisticated determination of site-specific 

ground motions using the shear-wave velocity of the soil, 

the peak ground acceleration at the site, and the magnitude 

of the event is now used in bridge design.

3. Geotechnical considerations have assumed much 

greater importance following Loma Prieta. More realistic soil 

stiffnesses at foundations and abutments and site-specific 

ground motions at locations with problem soils are now standard. Concerns with liquefaction have prompted soil 

remediation at several bridge sites.

4. More sophisticated analysis procedures including the 

use of nonlinear analysis for important bridge projects are 

now routinely done at Caltrans.

5. More sophisticated retrofit strategies that consider the 

stiffness, strength, and ductility of bridge elements and systems to keep capacities above demands are routinely done.

Highways are an important part of American life. They 

are used to get to work, to transport goods, to carry emergency vehicles, and to bring equipment to damaged lifelines. 

And like other lifelines, highway performance can be severely 

diminished as a result of large earthquakes. The Loma Prieta 

earthquake was a moderate event and yet it had a large impact on highways throughout the Bay Area. Those responsible for highways in areas of high seismicity may do well to 

consider the lessons of the Loma Prieta earthquake. The main 

lesson is that by reducing the vulnerability of highway facilities from damage, human lives, other lifelines, and the 

economies of communities can be protected.

U.S. GOVERNMENT PRINTING OFFICE: 1998 - 673-048 / 20103 REGION NO. 8

SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS

Periodicals

Earthquakes & Volcanoes (issued bimonthly). 

Preliminary Determination of Epicenters (issued monthly).

Technical Books and Reports

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of wide and lasting interest and importance to professional scientists and 

engineers. Included are reports on the results of resource studies and of 

topographic, hydrologic, and geologic investigations. They also include 

collections of related papers addressing different aspects of a single scientific topic.

Bulletins contain significant data and interpretations that are of 

lasting scientific interest but are generally more limited in scope or geographic coverage than Professional Papers. They include the results of resource studies and of geologic and topographic investigations; as well as 

collections of short papers related to a specific topic.

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to professional geologists, hydrologists, and engineers. The series covers 

investigations in all phases of hydrology, including hydrology, availability of water, quality of water, and use of water.

Circulars present administrative information or important scientific information of wide popular interest in a format designed for distribution at no cost to the public. Information is usually of short-term interest.

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Maps

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geology. Maps generally include brief texts; some maps include structure 

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Geophysical Investigations Maps are on topographic or planimetric bases at various scales, they show results of surveys using geophysical 

techniques, such as gravity, magnetic, seismic, or radioactivity, which reflect subsurface structures that are of economic or geologic significance. 

Many maps include correlations with the geology.

Miscellaneous Investigations Series Maps are on planimetric or 

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Coal Investigations Maps are geologic maps on topographic or 

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stratigraphy, and structural relations in certain coal-resource areas.

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of geohydrologic data of both regular and irregular areas; the principal 

scale is 1:24,000, and regional studies are at 1:250,000 scale or smaller.

Catalogs

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listings of U.S. Geological Survey publications are available under the 

conditions indicated below from USGS Map Distribution, Box 25286, 

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over the counter in paperback booklet form only.

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Selected copies of a monthly catalog "New Publications of the 

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free subscription to the monthly catalog "New Publications of the U.S. 

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Note.-Prices of Government publications listed in older catalogs, 

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charged may differ from the prices in catalogs, announcements, and publications.