Original Research Papers

Bulletin of IISEE, 49, 39-61, 2015

LESSONS LEARNT FROM DAMAGE TO BUILDINGSBY BOHOL EARTHQUAKE AND TYPHOONYOLANDA 2013 IN THE PHILIPPINES
Tatsuo Narafu1, Toyokazu Shimizu2, Yasushi Sanada3, Yukio Tamura4, Noriyuki Mita5,
Susumu Takahashi6, Hayato Nakamura1, Atsuko Itsuki1
ABSTRACTThe authors conducted surveys on damaged reinforced concrete (RC) buildings by Bohol Earthquake
and Typhoon Yolanda (Haiyan internationally)in the Philippines, and found heavy damage in
non-structural members, huge difference in degree of damage among buildings in similar situation,and each of heavily damaged buildings has its own specific causes. The causes could be categorized
into 1) improper design, 2) poor/insufficient quality of materials, 3) poor workmanship/improper
construction works, and 4) lack of maintenance works. This report introduces overview of damage andcauses, considers the background and presents some recommendation on basic policy to improve thesituation as 1) creation of common understanding of designs, 2) improvement on designs anddescription/documentation, 3) comprehensive capacity development of relevant stakeholders .

1. BACKGROUND, OBJECTIVES AND OUTLINE
1.1
Background and objectives
The Philippines experienced two natural disasters in succession in 2013, namely the Bohol Earthquakeon October 15 and the Typhoon Yolanda (Haiyan internationally) November 6-9. Both caused serious
damage to the Philippines in various aspects in wide area. Among them buildings are one of the mostheavily damage infrastructures. JICA dispatched experts to grasp the damage, causes, social
background of causes and draw lessons which could contribute to mitigate disaster in future. This
paper summarizes results of the field surveys, analyses causes and the background, and presents
recommendation based on the surveys. Targeted buildings of this report are reinforced concrete (RC)buildings and most of them are public building because those were buildings the authors could rapidly
obtain permissions to conduct detail survey. Please refer to other reports regarding to other types suchas historical buildings of masonry structure and detached houses of concrete block masonry structure.
1.2
Outline of research
1.2.1
The first field survey
The first survey was conducted as follows,
Cebu and Bohol
1 Japan International Cooperation Agency
2 Expert Advisor, Public Buildings Association (PBA), Advisor, Penta- Ocean Construction Co
ltd
3 Osaka University
4 Tokyo Polytechnic University
5 Polytechnic University
6 Nagoya Institute of Technology- 39 -

Date: November 29 to December 2, 2013
Members: Dr. T. Narafu, D. Y. Sanada, Dr. S. Takahashi, Mr. H. Nakamura and staff of Department of
Public Works and Highways (DPWH), staff and consultants of the World Bank
Leyte and Samar
Date: December 4-6, 2013
Members: Dr. T. Narafu, Ms. A. Itsuki and staff and consultants of JICA
1.2.2
The second field survey
It is observed in the first field survey that damage occurred not only in structural members likecolumns and beams but also in various members like shelter walls, partition walls, ceilings and roofing.
The members of buildings other than structural members are called “non-structural members” andusually designed by architects. Causes of damage also vary in wide range from design, toworkmanship and materials. Damage in Bohol was caused by shaking motion and that of Leyte, bystrong wings and inundation. These facts require survey team members with wider expertise inaddition to structural engineering. Therefore the second survey team was organized to consist ofexperts from construction engineering, construction management, workmanship, materials, and windengineering as follows,
Bohol
Date: January 7-8, 2014
Members: Dr. T. Narafu, Mr. T. Shimizu, Dr. N. Mita, Mr. H. Nakamura, staff and consultants of JICA,
and staff of Department of Public Works and Highways (DPWH)
Leyte and Samar
Date: January 9-11, 2014
Members: Dr. T. Narafu, Mr. T. Shimizu, Dr. N. Mita, Dr. Y. Tamura, Dr. Y. Sanada, Ms. A. Itsuki,
staff and consultants of JICA, and staff of Department of Public Works and Highways (DPWH)
1.2.3
Analysis, discussion and elaboration of recommendation
During the field surveys the survey team analyzed causes of damage from various point of views withthe wide range of expertise of the team members. The survey team also conducted survey on
construction practice in the Philippines such as preparation of drawings and specification for
procurement of construction service, usual procedures of construction management on site by staff of
DPWH. Based on the results of the survey, the team discussed social background of causes andconcluded that most of the background of two different natural disasters is common even though thenatural hazards (the earthquake and the typhoon) and actions to buildings by the hazards (shaking
motion, pressure by strong winds, and inundation) are different. Based on this finding, the teamelaborated recommendation in the context of actual construction practice in the Philippines.
1.3
Overview of previous reports/papers and features of this report
1.3.1
Overview of previous reports/papers
Every time large scale natural disasters occur, engineer and researcher community usually conduct
field surveys in affected areas to grasp damage, analyze causes and draw lessons to mitigate damage
by future disasters. Many reports/papers of field reports on damage by earthquakes were presented atinternational conferences like World Conference of Earthquake Engineering (WCEE, one of thelargest world conference on earthquake engineering held every four years. The last one held in 2012 in
Lisbon, Portugal, had about 4,000 participants and about 3,400 papers were presented.). Among papers
presented at 15th World Conference of Earthquake Engineering 2012 (15WCEE), several different
approaches were found as a) management or planning point of view dealing with numbers of affected
people, analysis of damage including response/behavior of people to hazards, analysis by socialgroups like gender, age, disabled, influential factors like preventive measures, preparedness, etc., b)socio economic point of view dealing with impacts to local economy, households and so on, and c)engineering point of view. Ones from engineering point of view (approach c) could be categorized into
three groups as below. Several typical papers are listed for each of the groups. (source: Proceedings of- 40 -

15WCC in USB with index search by names of authors, titles of paper or keywords)
Group 1 on Earthquakes: to grasp total damage
H. Kit MIYAMOTO and Amir SJ Gilani, Urban Earthquake Damage Assessment and Reconstruction:2010 Haiti Earthquake
Satoshi TANAKA and Kishie SHIGEKAWA, Analysis of the Building Damage Evaluation for the2011 Great East Japan Earthquake
Group 2 on Earthquakes: to focus on specific aspects, types of buildings, members and so on
Masaki Maeda et al. Damage Survey on Reinforced Concrete School Buildings in Miyagi after the2011 East Japan
I. Senaldi, G. Magenes and J. M. Ingham, The seismic performance of unreinforced stone masonrybuildings during the 2010-2011 Canterbury earthquake sequence
Masatoshi Yamazoe, Joji Sakuta, Kazuya Mitsuji, and Masaki Maeda, Field Investigation and
Dynamic Analysis of Damaged Structure on Pile Foundation during the 2011 off the Pacific Coast of
Tohoku Earthquake
Group 3 on Earthquakes: to analyze behavior of structure, causes of failure etc. on specific buildings
J. Sherstobitoff, P. Cajiao and P. Adebar, Analysis and Repair of an Earthquake-Damaged High-rise
Building in Santiago, Chile
YAN Peilei and SUN Baitao, The Analysis of Non-Linear Seismic Response between a Collapsed anda serious damage Infilled Frame Structure in Yingxiu Town–the Heavy Disaster Areas of Wenchuan
Earthquake
The categorization above can be applied for reports/papers on field surveys on areas affected bytyphoons, cyclones and similar disasters. Typical ones are listed below. Reports/papers of group 6) on
this disasters are not so many because of characteristic of damage to buildings with similar materials
in similar construction methods are usually also similar and analysis on specific buildings is not sosignificant compared with cases of earthquakes.
Group 1 on Typhoons:to grasp total damage
G. Davenport, The impact of structural damage in Jamaica due to hurricane Gilbert and the prospects
for disaster reduction, Journal of Wind Engineering and Industrial Aerodynamics, Vol. 36, Part 1,
pp.53-62. , 1990
A.M. Goliger, J.V. Retief, Severe wind phenomena in Southern Africa and the related damage, Journalof Wind Engineering and Industrial Aerodynamics, Vol.95, Issues 9–11, pp.1065-1078. , 2007
M. C. McCullough, A. Kareem, A. S. Donahue, J. J. Westerink, Structural Damage Under Multiple
Hazards in Coastal Environments, Journal of Disaster Research, Vol.8, No.6, pp.1042-1051. , 2013
Group 2 on Typhoons: to focus on specific aspects, types of buildings, members and so on
A.M. Cruz, E. Krausmann, Damage to offshore oil and gas facilities following hurricanes Katrina andRita: An overview, Journal of Loss Prevention in the Process Industries, Vol. 21, Issue 6, pp.620-626. ,2008
H. Liu, H. S. Saffir, P. R. Sparks, Wind Damage to Wood‐Frame Houses: Problems, Solutions, andResearch Needs, Journal of Aerospace Engineering, Vol.2, No.2, pp.57-70. , 1989
P. R. Sparks, H. S. Saffir, Mitigation of wind damage to non-engineered and marginally engineeredbuildings, Journal of Wind Engineering and Industrial Aerodynamics, Volume 36, Part 2, pp.957-966. ,1990
Group 3 on Typhoons: to analyze behavior of structure, causes of failure etc. on specific buildings
D. Henderson, C. Williams, E. Gavanski, G. A. Kopp, Failure mechanisms of roof sheathing underfluctuating wind loads, Journal of Wind Engineering and Industrial Aerodynamics, Volume 114,
pp.27-37. , 2013
O. Mahrenholtz, H. Bardowicks, Aeroelastic problems at masts and chimneys, Journal of Wind
Engineering and Industrial Aerodynamics, Vol.4, Issues 3–4, pp.261-272. , 1979
1.3.2
Features of this report
This report is written on damage by recent two disasters in the Philippines from view point ofengineering focusing on reinforced concrete buildings and should be categorized in approach c and- 41 -

Group 2 on Earthquakes and Group 2 on Typhoons according to the categories in the previous section.
This report has specific features of being comprehensive and practical as below thanks to very wide
fields of expertise of the eight co-authors with practical experiences.
- covering damage by two different types of natural disasters (earthquake and typhoon) with three
types of actions (shaking motion, pressure by strong winds and inundation by water), which reveal
different types of vulnerability of actual buildings in the Philippines- covering damage to both structural members which are designed by engineers, and non-structuralmembers (partition walls, ceiling boards, roofing and so on) by architects, whereas most of previous
reports/papers are prepared by engineers on structural members- analyzing causes of damage in whole procedures of construction from design, procurement,
construction works on site including workmanship and materials, to management and supervision

2. Overview and analysis of damage
2.1
Overview of damage
2.1.1
Overview of damage by two disasters
Overview of damage by the two natural disasters is shown in Table 1. The damage occurred both instructural members and non-structural members. Total design of buildings is managed by architects
and that of structural members is usually by engineers, which appears in drawings for practical use inreview stated Section 3.2. (Drawings are consisted of four kinds of architectural, structural,mechanical or electrical) stated in 3.2. It should be noted that architects and engineers graduate fromdifferent department of universities in the Philippines whereas both from the same, “architectural
engineering” in Japan. Qualification scheme for design profession managed by Professional
Regulatory Commission (PRC) also follows the same division.
Table 1 Overview of damage by the two natural disasters

2.1.2
Damage by Bohol Earthquake
A large scale earthquake of Mw 7.2 (depth of focus: 12 km) hit central part of the Philippines (Figure1) on October 15, 2013 (Philippine Institute of Volcanology and Seismology PHIVOLUCS) andcaused serious damage in Bohol and Cebu islands as below (NDRRMC update SitRep No. 33 issued
on October 31, 2013),
Dead: 222 people
Missing: 8 people
Injured: 796 people
Affected: 671,103 families, 3,221,248 people
Damaged houses: 13,249 houses totally, 53,683 houses partially- 42 -

Figure 1. Epicenter of Bohol Earthquake 2013

Table 2 Overview of damage to RC buildings
DamageMuniciparity

buildings

Use

Pictures in Figures
Structure

Non-stractural walls Ceilings

OthersMediumMuniciparity officex

SlightSlightMediumTagbilaran University Hospitalx-

MediumHeavy

School of nursingx-ExtremeHeavy (most fell down) Slight

Municipal officexMediumExtremeHeavy

District Health carecenterx

Medium (damage in beam, cracks in columns) Medium

Heavy

Schoolx

SlightSlightNo ceilign boards

Municipal officexMedium (damage in columns)

ExtremeMediumMarket buildingx

Medium (failure in beams, etc.)

ExtremeExtremeHospital building 1x-

Heavy (most fell

MediumHospiral building 2

x

SlightExtremeExtremeHospiral building 3x

SlightExtremeExtremeHeavy

Municipal office building 1

x

SlightMediumExtremeHeavy

Municipan builiding 2

50% -MediumMedium (2nd fl.)4(upper)

Barangay office

10% Heavy (2nd fl. Tilted)

ExtremeExtreme13, 20(right)

District Health carecenter20% -MediumMediumSagbayan

Catigbian

down)

Extreme2,4(lower), 11,19(right), 22, 23(left)

1216
Extreme17, 18, 19(left), 21,
22(right)

Loon

Antequera- 43 -

The highest intensity of the shaking motion is reported VII in PHIVOLCS Earthquake Intensity Scale(PEIS) (smallest I to largest X, http://www.phivolcs.dost.gov.ph/index.php? option =com_ content&task = view&id=45&Itemid=100) Many totally collapsed buildings are found to have furniture
withstanding inside them. Figure 2 shows an example of Municipal building of Sagbayan, Bohol. Left
photo shows heavy damage to shelter walls, partition walls, ceiling boards and so on in spite thatdamage to structure is limited (Orange circle shows position related to Figure 11 and 22). Right photoshows inside the buildings where most of cabinets, lockers and other furniture were foundwithstanding. Usually in developed countries buildings may collapse by far strong shaking motion
than ones causing furniture fall (Figure 3). This implies buildings in the affected areas are very
vulnerable. Table 2 shows all the RC buildings which are heavily damaged and investigated in detail(steel structures are excluded). In spite of none or slight damage to structural members (like cracks orothers), many buildings were still out of use at the end of November (one and a half months after theearthquake) mainly because of heavy or extreme damage to non-structural members.
Huge difference in degree of damage is observed. Figure 4 shows huge Difference among municipal
buildings of Antequera and Sagbayan, Bohol. Upper left photo shows Municipal office of Antequera(Building 2) suffered little and upper right shows the conditions of the first floor of the upper left thatit suffered little and started operation soon after the earthquake. Lower left photo shows exterior viewof Municipal office of Sagbayan (refer to Figure 2). Lower right photo shows heavy damage tonon-structural members of partition walls and ceiling boards, etc. On the other hand damage tostructure is limited. It will be demolished due to the damage.
Another significant finding is that each of heavily damaged buildings has its own specific causes
which seemed to invite the heavy damage. The causes can be categorized into 1) improper design, 2)
poor/insufficient quality of materials, 3) poor workmanship/improper construction works, and 4) lackof maintenance works

Figure 2. Municipal building of Sagbayan, Bohol: (Left) Heavy damage to shelter walls and so on, and(Right) Inside the buildings
PERCEIVEDSHAKINGNot felt

Weak

Light

Moderate

StrongVery strong

SevereViolent

Extreme

Heavy

Very heavy

POTENTIAL DAMAGE

none

none

none

Very lightLight

Moderate

Moderate/
Heavy

PEAK ACC (%g)

< 0.170.17 - 1.4

1.4 - 3.9

3.9 - 9.2

9.2 - 18

18 - 34

34 - 65

65 - 124> 124

PEAK VEL (cm/s)< 0.1

0.1 - 1.1

1.1 - 3.4

3.4 - 8.1

8.1 - 16

16 - 31

31 - 60

60 - 116> 116

INSTRUMENTALINTENCITY

I

II - III

IV

V

VI

VII

VIII

IX

X

MMI VII or higher: some furniture may fall down
MMI X or higher: vulnerable buildings may collapse such as stone masonry

Figure 3 Descriptive Table of Modified Mercalli Intensity (USGS)- 44 -

Figure 4 Huge Difference among municipal buildings of Antequera and Sagbayan, Bohol (Upper left)
Municipal office of Antequera (Building 2), (Upper right) First floor of Upper right (Lower left)
Municipal office of Sagbayan (Lower right) Interior view of Lower left
2.1.3
Damage by Typhoon Yolanda
The Typhoon Yolanda went through in the middle of the Philippines November 6-9, 2013 (Figure 5)
and caused heavy damage in large area along its track. It is reported that the hazards were extreme.
Severe Weather Bulletin (SWB) No. 6 issued by National Disaster Risk Reduction and Management
Council of Philippine Government reported the highest maximum sustained winds of 235 km/h andgustiness 275 km/h (recorded highest sustained wind speeds reported by Philippine Atmospheric,Geophysical & Astronomical Services Administration (PAGASA): 160 km/h and gustiness: 195 km/h
both at Guiuan, East Samar). National Structural Code of the Philippines (NSCP) defines wind loads
in terms of gustiness as 250 km/h for Zone I, 200 km/h for Zone II, 150 km/h for Zone III). Heavily
damaged areas by the typhoon locate in Zone I (Samar Island) and II (Leyte Island).(Figure 6）
Maximum depth of sea water above ground level by storm surge is estimated 5-8 meters estimated by
an expert group of Japan Disaster Relief Team (JDR). The strong winds and the storm surge caused
extraordinary heavy damage as below (SWB No. 104 issued on January 29, 2014).
Dead: 6,201 people
Missing: 1,785 people
Injured: 28,626 people
Affected: 3,424,593 families, 16,078,181 people
Damaged houses: 550,928 houses totally, 589,404houses partially
Damage to buildings is caused by two different actions of pressure by strong winds (Figure 7) andinundation by water (Figure 8). Table 3 shows buildings which are analyzed in Section 2.2. Most ofbuildings suffered from both strong winds and inundation. Huge difference is also observed in degreeof damage among buildings even in similar condition. Typical examples are shown in Figure 9 and 10.
Figure 7 shows comparison of damage of large buildings by the typhoon. Left is Leyte Convention
Center in Palo, which total collapsed. On the other hand, Toyota showroom in Tacloban (Right) got- 45 -

limited damage to roofs and ceilings and started operation about one month after the disaster.

Figure 5 Track of Typhoon Yolanda (Philippine Atmospheric, Geophysical & Astronomical
Services Administration: PAGASA)

Figure 6 Wind Zone Map of National Structural Code of the Philippines (NSCP)- 46 -

Figure 7 Typical damage by strong winds by the typhoon: (Left) Heavy damage in roofing: Customers’center of private company in Palo, Leyte, (Right) Damage to both roofing and roof trusses. Sagkahan
National High school, Tacloban, Leyte

Figure 8. Typical damage by storm surge caused by the typhoon in coastal area of Tacloban city,
Leyte

Table 3 Overview of damage buildings by the typhoon analyzed in this paper
Municipality

buildings

Use Structure (including roof
truss)

Tacloban

Sagkahan National
High School 1(grant
aid by Japan)
Sagkahan National
High School 2
Sagkahan National
High School 3
Sagkahan National
High School 4
Toyota Showroom
Leyte Convention
CenterPalo

Customers' Center
Supermarket Metro

TanauanTanauan National
High School 1
Tanauan National
High School 1

DamageRoofing

Ceilings

OthersPictures in Figures

x

None

slightslightMedium (windows) 10（upper right）

x
x

None

slightslightMedium (windows) 10(lower left）

Collapse

Collapse

Collapse

Collapse

x
x
x
x
x
x
x

slightslightslightMedium (windows) 25(left)

None

slightslightMedium (doors,
shutters)

Collapse

Collapse

Collapse

Collapse

9(left)slightExtremeExtremeExtreme7(left)Collapse

Collapse

Collapse

Collapse

15

Collapse

Collapse

Collapse

Collapse

14(left)

Collapse

Collapse

Collapse

Collapse

14(right)- 47 -

7（right）
10（lower right）

Figure 9. Comparison of damage of large buildings: (Left) Leyte Convention Center in Palo (Right)
Toyota showroom in Tacloban

Figure 10. Comparison of damage of school buildings in Sagkahan National High School in
Tacloban, Leyte: (Upper left) Overview of the school, (Upper right) a building by Grant Aid project byJapan, (Lower left) a building with limited damage (Lower right) a building with heavy damage
Figure 10 is an example of school buildings in Sagkahan National High School in Tacloban, Leyte.
Upper right is a building by Grant Aid project by Japan which suffered little. Lower left is another one
with limited damage to roof flash and ceiling boards. Lower right is one with heavy damage of blown
away of roofing and failure of roof trusses
It is also observed that each of heavily damaged buildings has its own specific causes which seemed toinvite the damage. Most of the causes could be categorized into 1) improper design,2)poor/insufficientquality of materials, 3) poor workmanship/improper construction works, and 4) lack of maintenanceworks just same as those on the earthquake.

- 48 -

2.2
Analysis of damage
2.2.1
Improper designs
Several cases of damage by improper structural design were found during the field surveys. Typicalones are shown in Figure 11-15. Figure 11,12 and 13 are similar type that structural designs are notregular which invited unexpected force and stress. Irregularities are, Figure 11: beams of canopy were
not attached to main structure in consistent manner and were connected to a beam at points without
support of columns, Figure 12: levels of beams differ to each other, which caused unexpected stress incolumns, Figure 13: irregular configuration of columns and imbalanced layout of non-structural walls
might invite torsional force to the total structure.
Figure 14 is an example of damage in gable walls and roof trusses. This might be caused by improper
designs (load estimation or design strength is not appropriate) or construction might not comply withthe designs. Figure 15 is an example of a steel structure. Many failures occurred in connection wherewelding without gusset plates were applied. Such direct welding may damage parent/base materials
and reduce strength of connecting sections. In both cases of Figure 14 and 15, the authors could notclarify the real causes (improper designs or incorrect construction works) as they could not examine
drawings and specifications for the buildings.

Figure 11. An example of improper structural design in Municipal building of Sagbayan, Bohol (by theearthquake) (Exterior view: refer to Figure 2) (Left) damaged connection of beams of canopy andmain structure (Right) Detail of the damage

Figure 12. An example of improper structural design (by the earthquake)（Left) Exterior view ofDistrict Health Care Center of Sagbayan, (Right) connection of a column and beams- 49 -

Figure 13 An example of improper structural design in Barangay office in Antequera (by theearthquake): (Left) exterior view, (Right) damaged columns by irregular configuration

Figure 14 Tanauan National High School in Leyte (by the typhoon): (Left) Collapsed gable walls of
CHB. (Right) Roof truss heavily damaged without sufficient reinforcement in longitudinal direction

Figure 15 Supermarket Metro in Leyte (by the typhoon): (Left) Roof truss was completely destroyed,(Right) Welding without gusset plates.
2.2.2
Poor/insufficient quality of materials
As stated in 2.1.1, damage to non-structural members is dominant by the two disasters. Among themconcrete hollow block (CHB) walls are one of the most common damage. One of the major causes ofthe damage is poor strength of CHB. It is often observed that rebar in wall and mortar filled in hollows
remains but most of CHB disappears due to extremely low strength like in Figure 16 .Regarding
damage to ceilings, use of usual type of nails to fix ceiling boards is one of the causes of heavy
damage. Appropriate nails for fixing ceiling boards or nails with washers should be used.

- 50 -

2.2.3
Poor workmanship/improper construction works
Poor workmanship/improper construction works seems to be another dominant causes both in Boholand Leyte. The authors find various types of defects shown in Figure 17-21. In a case of Figure 17,
several improper construction works are identified. Longitudinal rebar is positioned inaccurately(placed inside than the designed position). All the overlap splices of longitudinal rebar locates at thesame level of a critical position, the bottom of the columns. (A red pipe in right photo is a pipe forelectric wire installation) In a case of Figure 18 failures of concrete occurred at the one of the mostcritical part of structures, panels (crossing parts of columns and beams), where hoops are absent (rightphoto). Honeycomb caused by insufficient compaction of concrete are often found (Left photo of
Figure 19). There found some cases that pieces of board penetrate into columns which might be used
to prevent fresh concrete coming out through gap between form panels (Right photo of Figure 19).
Figure 20 shows improper rebar works. The left photo is a case that spacing of hoops is too large,
which might allow inside concrete coming out (Barangay Office in Antequera) and the right photo has
several improper rebar works: bending of hooks of hoops is 90 degree, all the overlap splices oflongitudinal rebar locate at the bottom of a column.
Figure 21 shows examples of improper anchorage of CHB walls to RC members in Market Buildingof Loon. The left photo is a case that horizontal rebar in a wall is not correctly anchored to a column
and the right is a case that anchorage to a beam seems not work well. Figure 22 shows improper
installation of concrete gutters in Sagbayan Municipal Office that a precast concrete gutter fell down
to ground by shaking motion (exterior view and original position of the the gutter: refer to Figure 2).
Figure 23 shows cases of ceiling boards. The left photo shows extreme damage that most of ceilingboards were damaged in Sagbayan Municipal Building and the right is a case ceiling of second floor
fell down onto a stairway in Market Building in Loon.

Figure 16 An example of poor quality of concrete hollow blocks (CHB) (by the earthquake): (Left)
Damaged non-structural walls in Municipal Office of Catigbian, (Right) Details of a damaged wall.

- 51 -

Figure 17 Examples of improper rebar works in Market Building in Loon (by the earthquake): (Left)
Heavy damage at the bottom of most of columns, (Right) Detail of the damage.

Figure 18 An example of improper rebar works in Market Building in Loon (by the earthquake):(Left) Failures at panels, (Right) Detail of damaged part

Figure 19 Examples of improper concrete placing (by the earthquake): (left)
Loon, (Right) Sagbayan Municipal Office- 52 -

Market Building inFigure 20 Examples of improper rebar works (by the earthquake): (left)
Antequera, (Right) A building under construction, Basey National High School

Barangay Office inFigure 21 Examples of improper anchorage of CHB walls to RC members in Market Building of Loon(by earthquake): (Left) a case of horizontal rebar, (Right)a case of vertical rebar

Figure 22 An example of improper installation of concrete gutters in Sagbayan Municipal Office (bythe earthquake)- 53 -

Figure 23 Examples of improper fixing of ceiling boards (by the earthquake): (Left)
Municipal Building, (Right) Market Building in Loon.

Sagbayan

2.2.4
Lack of maintenance works
Lack of maintenance works invited heavy damage in several situations. Corrosion of steel members by
rusting, damage to woods by termites, fatigue of roofing sheets by cycles of expanding and shrinking
by sunlight are the typical examples. Figure 24 left photo shows a case of a wood column heavily
damaged by termites at St. Joaquin Central Elementary School, Palo, Leyte (by the typhoon), and theright, a heavily corroded steel column at Cogon Norte Elementary School, Loon, Bohol (by theearthquake).

Figure 24 Examples of failures by lack of maintenance: (Left) St. Joaquin Central Elementary School,
Palo, Leyte (by the typhoon), (Right) Cogon Norte Elementary School, Loon, Bohol (by theearthquake)

2.2.5
Damage by inundation
Most of buildings are designed without consideration of inundation and do not use water-proof
materials except roofing. Therefore various inundated materials got damage shown in Figure 25. The
left photo of Figure 25 shows situation that the storm surge brought much mud into builidngs, Basey
National High School, Samar, and the right photo is an example of damage to ceiling boards byinundation（Sagkahan National High School in Tacloban, Leyte. Figure 26 is a case of Municipal
Health Office of Basey, Samar, which employ simple finishing of concrete walls with durable painting
and ceiling without boards. It allows easy recovery and quick restart of operation within several weeks- 54 -

by just washing of finishing.

Figue 25 Examples of damage by inundation (by the typhoon): (Left) Basey National High School,
Samar, (Right) Sagkahan National High School in Tacloban, Leyte

Figue 26 Municipal Health Office of Basey, Samar (Left) exterior view, (Right) interior view of thefirst floor

3. Consideration on background of damage and recommendation
The authors conducted studies on legal and technical framework on building control in the Philippines
as well. The National Building Code of the Philippines (NBCP), and revised implementing rules andregulations are basic legal documents and the National Structural Code of the Philippines (NSCP) is atechnical standard on structures (Figure 27). Several examples of drawings for practical use were also
reviewed and interviews/discussion with Philippine engineers was organized for better understandingon situation and practice concerning building construction. Several recommendations are elaborated
based on these activities.
3.1
Study on legal and technical framework on building control in the Philippines
The Basic legal document in the Philippines is the National Building Code of the Philippines. It wasissued as Presidential Decree No. 1096 in 1977. Many of technical standards are prepared by each oforganizations of specific expertise. As to structure, Association of Structural Engineers of thePhilippines (ASEP) prepares standards. Current standard on structure for buildings is National
Structural Code of the Philippines (NSCP) 6th edition Volume 1: Buildings, towers, and other verticalstructures, approved by Department of Public Works and Highways (DPWH) as a referral code of
NBCP. The preface of 6th edition of NSCP states that it is referenced from Uniform Building Code- 55 -

UBC-1997, International Building Code IBC-2009, America Society of Civil Engineers ASCE/SEI
7-05 and other 7 codes/standards/handbooks in the United States. Philippine engineers state that mostof Philippine engineers use reference information and tools such as structural calculation softwarefrom the United States.

Figure 27 Documents concerning building control in the Philippines: (Left) National Building Code of
the Philippines(NBCP) and revised implementing rules and regulations, (Right) National Structural
Code of the Philippines (NSCP) 6th edition Volume 1
3.2

Review of drawings for practical use

The authors reviewed examples of drawings of several buildings. They found most of them would
have certain level of performance when they are constructed in compliance with description ofdrawings, and in following usual practice in the US in cases where detailed information is notdescribed on drawings. In other words detailed information on designs and specification is not enoughon drawings in practice. In most of countries like the US or Japan, detailed information on design,material/parts/components, construction methods are provided with reference technical documents likestandard detail design drawings and standard specifications. During the survey they could not findstandard detail drawings and did find a document on standard specifications in a dusty book shelfwhich has not been used for a long time.
3.3

Consideration on background of damage

3.3.1
Lack of common understanding among relevant groups
Basis of constructing buildings of good quality is common understanding of design among all the
relevant groups such as designers, supervisors, contractors, foremen, workers and so on. The authors
observe that lack of common understanding is one of the most crucial situations in the Philippines.
Documents for construction of buildings shown in Figure 28 are tools to create common understandingin Japan. The review of drawings in practice reveals 1) information provided by documents bydesigners (drawings, detail drawings, specifications) is not sufficient, 2) reference documents(standard detail drawings, standard specifications) in not prepared/utilized, 3) practice of preparing
shop drawings are not usual, and 4) supplemental documents are not prepared/utilized. Thesesituations result lack of common understanding on what kind of construction works should be
implemented on site. Typical examples of damage caused under the conditions are described below.
<Position of longitudinal rebar>
As to design of section of columns or beams, most of them have no description on position of rebar(Figure 29). The designed position could be figured out only when description of concrete cover
thickness in another sheet of drawings is referred. These may lead workers without enough technicalknowledge to think number of rebar is significant but position in not in that way, which might invite- 56 -

the defects and damage like in Figure 17. (The positioning of longitudinal rebar and bending work ofhoops are consistent, which supports the supposition) Another possible way to avoid this kind ofproblems could be training to make standard coverage of concrete to be common knowledge to all theworkers.
<Fixing of ceiling boards>
As to design of ceiling boards. description on drawings is usually only on type and quality of materials,
not on design of ceiling frames and hungers, and fixing methods like type of nails and spacing.
Therefore workers could not understand proper way of fixing and might fix them in a way they like,which might invite the defects and damage like in Figure 23.

Figure 28 Various documents usually prepared for construction of buildings in Japan

Figure 29 Description of design of section of beams in usual drawings
3.3.2
Design of structures
The Philippine structural code adopts “capacity design” with structural members of smaller section
areas especially in columns, which expects large ductility and allows large deformation of structure.
This type of design with slender portion of structural members requires precise construction works invarious phases like 1) lot of rebar of complicated bending schedule both in longitudinal and ties, 2)
precise positioning of rebar, 3) complete compaction of concrete especially in parts with congested
rebar. More redundant design is recommendable which could avoid serious damage even when

- 57 -

buildings have certain level of inaccurate construction works. For the purpose push-over analysis
could be an effective tool in addition to usual method, which provides with deformation of structure bypush-over loading (large deformation may cause serious crack in concrete and failure of coverconcrete of rebar). It provide with 1) failure mechanism of total structures which informs possible
vulnerable types of failure such as failures at ends of columns, which might lead to total collapse ofstructure, 2) types of failure (shear failure or flexure one) at each point, which suggest effective way of
improving resilience of total structure, and 3) deformation of each of stories, which might indicatespossible soft story collapse. All these information could contribute to realize redundant designs by
avoiding vulnerable types of failures and increasing resilience.
Another important point is application of types of values of wind load for structural designs for roof
trusses and others. In the Philippines, jalousie or other type of opening for ventilation is commonly
used. Appropriate wind force coefficients for walls and roofs should be applied in accordance withcondition of openings. Wind loads for buildings with openings can be larger than those for usual
closed-type buildings.

3.3.3
Design and construction of non-structural members<CHB walls>
CHB non-structural walls (shelter walls and partition walls) are one of the most vulnerable parts
especially by shaking motion. It has several issues to be solved such as 1) quality/strength of CHB, 2)
filling/compaction of mortar in hollows, 3) installation of reinforcing rebar in CHB walls, 4)connection/anchorage of CHB walls to columns and beams.
<Roofing> Roofing is the parts which suffer most from the strong wind by Typhoon Yolanda. Most ofdamage is caused by local negative (uplift) pressures caused by rapid flow of air. There is description
on wind load in the Structural Code of the Philippines but usually calculation based on wind load isapplied only to structural members of roof trusses and other structural members, not to roofing
materials, purlins, rafters, nails and others in the Philippines. Materials and detail design of roof andrelated members have to be designed considering the wind loads and properly described in drawings
or other documents. In this case application of appropriate value of wind load in accordance to typesof opening is important as well as in structural design.
It is clearly proved that eaves or ends of roofing are the most critical parts for damage from strong
winds and additional reinforcement and appropriate finishing worked well, which is shown in thebuilding by Grant Aid project in Figure 10. This could be a good practice for prevention of damage
from strong winds.
<Ceiling>
Ceiling is another most heavily suffered parts. Damage is caused both by strong wind (pressure by air
flow coming into roofs, etc.) and shaking motion (damage of nail fixation by shaking motion, collisionof ceiling boards to adjacent boards or walls) It seems usual in the Philippines that there is statement
only on materials of ceiling boards on drawings, not frames, hangers, nails and spacing. These should
be designed considering possible hazards and described clearly for foremen and construction workers
to show how to construct ceilings on design documents.
3.4

Recommendation on basic policy for strategies to reduce damage

Since the causes of damage and the background are wide and diverse, comprehensive approach isnecessary. Another important aspect is that many groups are involved in construction of buildingssuch as designers (architects and engineers), contractors(engineers, foremen, and workers),
manufactures of materials, administration and research community(Figure 30). Therefore intersectoral and inter-disciplinary approach is necessary. The authors elaborate basic policy stated below
for strategies to reduce damage in context of practice in the Philippines based on the surveys and thestudies.
3.4.1

Creation of common understanding of design among relevant groups- 58 -

Creation of common understanding of designs among all the relevant groups should be the first basic
policy. For the purpose, provision of more detail information in easy and user-friendly manner is abasic way. Usual tools of communication are drawings, specifications, shop drawings, supplemental
documents shown in Figure 28. Every possible dissemination/communication activities like briefings,
lectures, guidance on site should follow it. Inspection on site could be categorized in this activity.
Capacity development for those groups would create a basis because it will enhance capacity tounderstand designs, which are further to be stated in 3.4.3.

Figure 30 Construction sector and relevant groups for construction of buildings
3.4.2
Improvement of designs and description/documentation
Appropriate design both on structural and non-structural members should be the next basic policy.
Designs must be reviewed from various points of view like safety against every possible hazard aswell as functionality, cost effectiveness and others. For structural design, more redundant design isrecommended in 3.3.2. As to non-structural members, more intervention of engineering is required asstated in 3.3.3. In these cases, feasibility on site and acceptability by workers should be taken into
consideration as all the construction works are conducted by workers on site. Buildings of goodquality could not be realized when design and detailing requires complicated or difficult works on site
so as that workers became reluctant to follow the design. Appropriate description/documentation of thedesign is also necessary for better understanding mentioned in the previous section.
3.4.3

Comprehensive capacity development of relevant stakeholders in both supply and demand
sectorCapacity development of all the relevant groups would create a basis of common understanding ofdesigns. Engineers working in design and supervision are key actors. In addition, engineers, foremen- 59 -

and workers working in contractors should be focused considering the situation in the Philippines that
improper construction works are one of most prevailing causes of heavy damage. Training on
construction skills for workers needs special consideration as they usually have limited engineeringknowledge and need specific trainings methods, which should be different from that for engineers.
Concerning non-structural members, architects are key players in designs and manufactures are theother ones in manufacturing.
Besides the supply sector mentioned above, demand sector of customers should be also target group,
who are responsible to decide quality of buildings by order/instruction to supply sector. Administration
is another important group, especially officials in local governments who work in practice.
Both supply and demand sector usually pay little attention to maintenance works. Awareness raising ofengineers and architects on importance of maintenance should be the first step, who are the mostappropriate people to disseminate it to customers.

CONCLUSIONSThe two natural disasters in 2013 revealed vulnerability of buildings in the Philippines. Vulnerability
exists not only in structural members but also in various non-structural members like shelter walls,
partition walls, ceiling, roofing, ornaments and so on. The causes of damage are identified as 1)
improper designs, 2) poor/insufficient quality of materials, 3) poor workmanship/improper
construction works and 4) lack of maintenance works. Based on the survey, study and analysis, theauthors recommend 1) creation of common understanding of design among relevant groups, 2)
improvement of designs and description/documentation, 3) comprehensive capacity development ofconstruction sector and relevant groups. Lessons learnt from disasters with “very expensive fees” haveto be fully utilized to mitigate future damage.

ACKNOWLEDGMENT
The authors owe the staff of JICA Philippine Office and staff of Department of Public Works andHighways (DPWH), the Philippine Government, especially in the field surveys and express gratitude
for all the supports and contribution.

REFERENCE
The National Building Code of the Philippines with revised implementing rules and regulations,philippine law gazette
National Structural Code of the Philippines (NSCP) 6th edition Volume 1, Association of StructuralEngineers of the Philippines
Proceedings of 15th World Conference on Earthquake Engineering (15WCEE, 2012 )Journal of Wind Engineering and Industrial Aerodynamics, Vol. 14 （1979）Vol. 36（1990）, Vol. 95（2007）Vol. 14 (2013）
Journal of Disaster Research, Vol. 8, No. 6 （2013）
Journal of Loss Prevention in the Process Industries, Vol. 21（2008）
Journal of Aerospace Engineering, Vol. 2（1989）
Severe Weather Bulletin (SWB) by National Disaster Risk Reduction and Management Council of
Philippine Government (NDRRMC):
http://www.ndrrmc.gov.ph/index.php?searchword=yolanda&ordering=&searchphrase=all&Itemid=1&option=com_searchPhilippine Atmospheric, Geophysical & Astronomical Services Administration (PAGASA):- 60 -

http://www.pagasa.dost.gov.ph/Philippine Institute of Volcanology and Seismology (PHIVOLCS): http://www.phivolcs.dost.gov.ph/
Reference materials for Quick Report Meeting on Damage Survey on the Earthquake and the Typhoonin the Philippines 2013 and the Heavy Snow in Japan 2014, Architectural Institute of Japan (AIJ):in Japanese language- 61 -