Miura Earthquake damage estimation in Metro Manila

8/14/2019 Miura Earthquake damage estimation in Metro Manila

1/14

Soil Dynamics and Earthquake Engineering 28 (2008) 764777

Earthquake damage estimation in Metro Manila, Philippines based on

seismic performance of buildings evaluated by local experts judgments

Hiroyuki Miuraa,, Saburoh Midorikawab, Kazuo Fujimotoc,Benito M. Pachecod, Hiroaki Yamanakae

aCenter for Urban Earthquake Engineering, Tokyo Institute of Technology, G3-3, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, JapanbDepartment of Built Environment, Tokyo Institute of Technology, Yokohama, Japan

cDepartment of Risk and Crisis Management System, Chiba Institute of Science, Choshi, JapandVibrametrics Inc., Quezon, Philippines

eDepartment of Environmental Science and Technology, Tokyo Institute of Technology, Yokohama, Japan

Received 31 May 2006; received in revised form 7 September 2007; accepted 11 October 2007

Abstract

Building damage due to a scenario earthquake in Metro Manila, Philippines is estimated based on seismic performance of the buildings

evaluated by local experts judgments. For the damage estimation, building capacity curves and fragility curve are developed from

questionnaire to the local experts of structural engineering. The Delphi method is used to integrate the experts opinions. The derived

capacity curves are validated by comparing with the result of pushover analysis for typical buildings. Building responses due to simulated

ground motions are estimated by the capacity spectrum method. Damage ratios are calculated from the fragility curves and the building

responses. Distributions of the damaged buildings are computed by multiplying the damage ratios and the building inventory. The

distribution and the amount of the damaged buildings in this study show significant difference from the estimation with the capacity

curves of HAZUS, suggesting the importance of evaluation of the region-specific building performance.

r 2007 Elsevier Ltd. All rights reserved.

Keywords: Building damage estimation; Seismic performance; Capacity spectrum method; Local experts; Delphi method; Metro Manila

1. Introduction

Population growth and urban expansion in mega-cities

increase vulnerability to disasters in developing countries.

In order to establish efficient earthquake disaster mitiga-

tion planning, earthquake loss estimation is indispensable.

In particular, building damage estimation is important forloss estimation since the damaged buildings result in great

economic loss and casualties.

In order to carry out building damage estimation, it is

necessary to evaluate following three points: (1) estimating

the ground motions due to a scenario earthquake by

modeling the source and the underground structure in the

area of interest, (2) evaluating the damage ratio based on

the seismic performance of the local buildings, and (3)

computing the damage distribution and the number of

damaged buildings by multiplying the damage ratio by the

building inventory. Therefore, it is important to gather the

data for underground structure, vulnerability of buildings

and building inventory. This study is mainly focused on the

evaluation of the building performance for the damageestimation in a developing country.

One of the standardized tools for earthquake loss

estimation is HAZUS [1] developed in the US. In HAZUS,

the seismic performance of typical buildings in the US is

given. The seismic performance of buildings, however,

should be region-specific because of the different design

level and construction quality in each region. Therefore, it

is not appropriate to apply the building performance in

HAZUS to other regions. For developing countries, simple

tools for loss estimation have been proposed in RADIUS

ARTICLE IN PRESS

www.elsevier.com/locate/soildyn

0267-7261/$ - see front matterr 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.soildyn.2007.10.011

Corresponding author. Tel.: +8145 9245602; fax: +81 45 9245574.

E-mail address: [email protected] (H. Miura).
http://www.elsevier.com/locate/soildynhttp://dx.doi.org/10.1016/j.soildyn.2007.10.011mailto:[email protected]:[email protected]://dx.doi.org/10.1016/j.soildyn.2007.10.011http://www.elsevier.com/locate/soildyn


2/14

[2] and GESI [3]. The reliability of the estimation by

RADIUS or GESI, however, would not be high because

the tools were developed for highly simplified loss

estimation.

The Philippines is one of developing countries located in

a zone of high seismicity. Metro Manila, the capital of the

Philippines, is a mega-city that is highly populated in theurban areas. Building damage estimation due to scenario

earthquakes in Metro Manila has been conducted based on

HAZUS [4], GESI [5], and vulnerability functions con-

structed from observed damage data of the 1990 Luzon

earthquake [6]. The vulnerability functions, however, were

developed only for low-rise buildings in the Philippines. It

is necessary to examine the seismic performance of mid-rise

and high-rise buildings for more reliable damage estima-

tion in urban areas.

The capacity spectrum method (e.g., [7,8]) is a simplified

procedure estimate non-linear building response from the

capacity of a building and the demand of ground motion

on the building. In the method, the seismic performance of

buildings can be incorporated rationally. For obtaining the

capacity of the buildings, it is a valid way to integrate

experts judgments when the available experimental and

actual damage data to evaluate the building performance is

limited.

In this study, questionnaire for local experts of structural

engineering in Metro Manila is applied to develop seismic

capacity curves of the buildings for more reliable building

damage estimation. The derived capacity curves are

validated by comparing with result of pushover analysis

for typical buildings. Building damage due to a scenario

earthquake is computed by multiplying damage ratioestimated from the capacity curve and simulated ground

motion by building inventory. The estimated damage

distribution is compared with that by the capacity curves

of HAZUS to examine the effects of the region-specific

building performance on the damage estimation.

2. Earthquake environment in Metro Manila, Philippines

Metro Manila consists of seventeen cities and munici-

palities including Manila, Makati, Quezon and Marikina.

Fig. 1 shows the location of Metro Manila and the urban

sprawl [9]. In around 1950 the urbanized area was less than

100 km2 with a population of 1.6 million, but now is

expanded to more than 600 km2 with a population of 10

million. In the old areas in Metro Manila such as Manila

city, densely built-up area with low-rise and mid-rise

buildings has been developed. In the newly developed

commercial zones such as Makati and Marikina, many

high-rise buildings have been constructed. According with

the sprawl of the urbanized area, new commercial zones

have been expanded.

Fig. 2 shows the geomorphological classification map of

Metro Manila [10]. The area is divided broadly into three

parts: Central plateau, Coastal lowland and Marikina

valley. The central plateau is on stiff soils with an elevation

of 1530 m. The coastal lowland extending along the

Manila bay is on soft sand and clay deposits with a

thickness of several to 40m. The Marikina valley is

bounded by the central plateau and the Sierra Madre

range, and consists of a delta and a muddy flood plain. The

thickness of the surface soft deposits reaches 50 m at a

maximum.

Since the Luzon Island including Metro Manila is

located between the Eurasian Plate to the west and the

Philippine Sea Plate to the east, the seismic and volcanic

activities are high. After the Spanish Empire colonized the

Philippines in the 15th century, description or accounts of

earthquakes have been maintained in various letters and

chronicles. The historical earthquake data in Metro

Manila, as well as the instrumentally derived earthquake

data gathered in the 20th century, have been compiled in

ARTICLE IN PRESS

: - 1948

: - 1966

: - 1975

: - 1996

Developing Period

Fig. 1. Location of Metro Manila with urban sprawl after Doi and Kim

[9].

: Coastal Lowland: Marikina Valley: Central Plateau: Mountain

Geomorphological Unit

SierraMadre

Range

Laguna de Bay

ManilaBay

0

Makati

Manila

10 km

Fig. 2. Geomorphological classification map and active faults in Metro

Manila after Matsuda et al. [10].

H. Miura et al. / Soil Dynamics and Earthquake Engineering 28 (2008) 764777 765


3/14

the previous study [11]. According to the earthquake data,

seismic intensity more than VII in Modified Rossi-Forel

intensity scale have been recorded for 28 times during

recent 400 years. As an example of the recent earthquakes,

in the Luzon earthquake of July 16, 1990 (M7.8), Intensity

VII was recorded and minor building damage was caused

in Metro Manila. The average return period for adestructive earthquake (Intensity VIII) was roughly esti-

mated at about 80 years [11].

In the Metro Manila area, there are two major active

faults. One is the West valley fault located between the

central plateau and the Marikina valley, and another is

the East valley fault situated between the Marikina valley

and the Sierra Madre range. Trench-excavation survey at

the northern end of the West valley fault suggests the

recurrence of hundreds rather than thousands of years [12].

Besides, these faults have high potential to produce a

damaging earthquake with magnitude of 67 [12]. Disaster

mitigation planning to the earthquakes triggered by these

faults seems as urgent issue for Metro Manila.

3. Flow of building damage estimation

3.1. Overview

Fig. 3 shows the flowchart of the building damage

estimation adopted in this study. After setting parameters

for a fault model of a scenario earthquake in Metro

Manila, ground motions at surface are computed using

hybrid simulation technique [13,14] and soil response

analysis [15] based on underground structure model.Building response due to the ground motion is evaluated

by the capacity spectrum method. First, the buildings

existing in Metro Manila are classified into several

categories. Capacity curve for each category is developed

by integrating the experts opinions. The non-linear

response of the building is estimated from the capacity

curve and demand curve converted from the ground

motion spectrum. Damage state for each building category

is determined by the building response and fragility curves.

Finally, combining the damage state of each buildingcategory and building inventory data, the distribution of

the building damage is computed.

3.2. Ground motion estimation

The West valley fault is selected as the source of a

scenario earthquake because the fault is closer to the

central part of Metro Manila. The ground motions due to

the West valley fault are simulated using the fault model

and the underground structure model. Fig. 4(a) and (b)

shows the fault model and major fault parameters used in

the simulation. After determining the fault length from the

geomorphology in and around the fault, the other fault

parameters such as the fault width, the seismic moment, the

area of asperities and the average slip are estimated based

on the recipe for predicting strong ground motions [16].

The fault length and the moment magnitude of the

earthquake are set as 40 km and Mw 6.7, respectively.

Two asperities are located in the fault and the rupture

starts from northern bottom of the fault.

The underground structure model with a 500 m mesh

system is constructed from the about 400 boring data, the

geomorphological classification map [10] and the geophy-

sical explorations [17]. The ground motions on the

engineering bedrock with the shear-wave velocity of about400 m/s are computed by the hybrid simulation technique

[13,14]. The simulation technique consists of the stochastic

green function for ground motion with short period (less

than 1 s) and the 3-D finite difference method for ground

motion with long period (more than 1 s).

The ground motions at the surface are computed by the

soil response analysis with the SHAKE program [15]. The

surface soils in Metro Manila are broadly classified into

three types: clay, sand and gravel. The dynamic soil

properties proposed in the previous study [18] are applied

in the computation. Fig. 5 illustrates the relationships

between the shear modulus ratio, damping factor and shear

strain for each soil type used in the analysis.

Fig. 4(c) shows the computed peak ground velocity

(vectorial summation of two horizontal motions) on the

surface. Fig. 6 indicates 5%-damped velocity response

spectrum and demand curves at Ermita and Quezon

computed from the simulated ground motions. The

demand curve is defined by the relationship between the

spectral response displacement and the response accelera-

tion. The maximum velocity response at Ermita reaches

almost 5 m/s, while the response at Quezon is less than 1 m/

s. This is because that the ground motion at Ermita is

strongly amplified due to the thick soft soil deposits in the

coastal lowland area.

ARTICLE IN PRESS

Distribution and Amountof Building Damage

Estimation of Damage Ratio

Capacity Spectrum Method

Computation of SurfaceGround Motion

Hybrid Simulation andSoil Response Analysis

Scenario Earthquake

Capacity Curves

Fragility Curves

Building Inventory

Fig. 3. Flow of building damage estimation.

H. Miura et al. / Soil Dynamics and Earthquake Engineering 28 (2008) 764777766


4/14

3.3. Building inventory

In Metro Manila, there had been the building inventory

data digitized from 1/10,000 scale topographic maps edited

in 1989 [19]. The authors have updated the inventory data

using the satellite remote sensing data [20]. In the inventory

data, the attribute for number of stories, which mainly

controls the vibration period during ground shaking, is

included for each building. The inventory for the mid-rise

and high-rise buildings was updated using the high-

resolution satellite IKONOS images. The dotted squares

in Fig. 7 indicate the coverage of the images that coverabout 75% of Metro Manila including the major commer-

cial areas such as Manila, Makati, Quezon and Marikina.

The locations of the newly constructed buildings were

extracted from the difference between the IKONOS images

and the existing inventory data. The number of stories

was estimated for each building using the shadow lengths

of the buildings obliquely observed from the satellite. The

inventory for the low-rise buildings was updated from the

land cover classification map derived from the multi-

temporal Landsat images [21]. The detail of the analysis

for the updating is described in the authors previous

study [20].

Fig. 7 shows the updated building distribution with a

500 m mesh system. The total number of buildings in the

updated inventory was estimated at about 1.29 million.

According to the recent national census in 2000 [6], the

total number of buildings in Metro Manila is approxi-

mately 1.32 million. The updated number of the buildings

shows good agreement with the census data. Due to the

updating, the number of buildings is increased by about

40% over the 15-year period. As shown in Fig. 7, the

buildings are densely concentrated in the western coastal

area such as Manila. A lot of the buildings are distributed

also in the northern, southern and eastern areas with the

expansion of the urbanized areas as shown in Fig. 1.

ARTICLE IN PRESS

North N200E

South N190E

90

4116.6

Asperity Area As1 76

(kmkm) As2 1010

6.7

Total 1.681026

As1 3.011025

As2 9.491025

As1 1.6

As2 2.3

Bg1 0.3

Bg2 0.4

Faultarea (kmkm)

AverageSlip (m)

DipAngle (deg.)

Strike (deg.)

MomentMagnitude (Mw)

M0(dynecm)

4km

13.6km

North

3.1km

Surface

0.5km

As2As1

South

Bg1Bg2

Startingpointofrupture

16.6

km

41km

Fig. 4. (a) Fault model of scenario earthquake. As1, 2 and Bg1, 2 show areas of asperities and backgrounds, respectively. (b) Fault parameters. (c)

Distribution of peak ground velocity due to the scenario earthquake.

0.5

0

106 105 104 103 102

1

Shearmodulusratio,

G/G

0

0.2

0.4

0

Dampingfactor,h

ShearStrain,

G/G0

h

Clay

Sand

Gravel

Clay

Sand

Gravel

Fig. 5. Relationships between shear modulus ratio, damping factor andshear strain proposed by Imazu and Fukutake [18].



5/14

In order for rational building damage estimation, not

only the number of stories but also the structural type and

the design vintage for each building are indispensable. Only

the footprints and the number stories, however, are

assigned in the inventory data. The estimation of structural

type and design vintage for each building is discussed in

Section 5.1.

4. Evaluation of seismic performance of buildings

4.1. Classification of buildings

In the capacity spectrum method, building response

during ground shaking is estimated from an intersection

of building capacity curve and demand curve. The capacity

curve needs to be obtained for each building type. First,

buildings in Metro Manila are classified considering the

structural type, the number of stories and the design

vintage as shown in Table 1.

The structural types are classified into three major

categories: CHB (Concrete hollow block building), C1

(Reinforced-concrete moment frame building) and C2

(Reinforced-concrete shear wall building). CHB buildings

ARTICLE IN PRESS

Period (s)

Vel.Response

Spectrum(

m/s) Ermita

0.1 1 100.01

0.1

1

10

Period (s)

Vel.Response

Spectrum(

m/s) Quezon

0.1 1 100.01

0.1

1

10

SD(m)

SA

(m/s/s)

Quezon

00.2 0.4 0.6 0.8

10

20

30

SD(m)

SA

(m/s/s)

Ermita

00.2 0.4 0.6 0.8

10

20

30

NS

EW

NS

EW

NS

EW

NS

EW

Fig. 6. Five percent damped velocity response spectra and demand curves at Ermita and Quezon.

: Coverage of IKONOS images

1,000

500

300

100

1

No. of buildings

0 10 km

999

499

299

99

Fig. 7. Building distribution of inventory data updated by Miura and

Midorikawa [20].



6/14

are typically single-family or small, multiple-family dwell-

ings that are usually not engineered. Seismic resistance of

these buildings depends on mostly on CHB walls, which

are usually provided with lintel beams and vertical stiffen-

ers at an average spacing of a few meters. C1 buildings

have a frame of reinforced-concrete columns and beams.

Lateral loads of these buildings are resisted by beam-

column frame action. C2 buildings are mostly tall buildings

having concrete shear walls that are usually bearing walls

as vertical components of the lateral-force-resisting system.

Other structural types, such as wooden buildings,

bamboo buildings and steel buildings, are existed in Metro

Manila. According to the questionnaire to the building

officials and the local government engineers in Metro

Manila [22], the percentages of other structural types in thecity/municipality were estimated at approximately 20%.

Since the number of other structural types is limited, all the

buildings are classified into the three major building types

(CHB, C1 and C2) in this study.

The range of stories is classified into six categories: low-

rise buildings (13 story), mid-rise building (47 story) and

high-rise buildings (815, 1625, 2635, 36+ story).

The national structural code of the Philippines (NSCP)

was firstly established in 1972 [23]. The code has been

revised in 1981, 1986, 1992 and 2001 [2427]. Generally,

design base shear coefficients increased in NSCP1981 from

NSCP1972, then decreased in NSCP1986. As a result of the

lessons learned from the 1990 Luzon earthquake, signifi-

cant changes in special requirements for earthquake

resistant design of RC buildings were formally incorpo-

rated in NSCP1992. The design base shear coefficients

increased in NSCP2001 for all the building types, especially

for buildings located near the fault. The increase of design

base shear in NSCP 2001 was mainly motivated by

observations in the 1994 Northridge earthquake and

the 1995 Kobe earthquake. Considering the period for

the revision of the building code, the design vintages of the

buildings are classified into three categories: Sub-type 1

(built after 1992), Sub-type 2 (built between 1972 and 1991)

and Sub-type 3 (built before 1971).

4.2. Building capacity curves derived from experts

judgments

To construct the capacity curve of each building

category, the two-round questionnaire is applied to the

experts of structural engineering comprised of the profes-

sors and the local engineers in Metro Manila [28]. Theresponses of the experts are integrated by the Delphi

method (e.g., [29]). The Delphi method is based on a

structured process for collecting and distilling knowledge

from a group of experts by means of a series of

questionnaires interspersed with opinion feedback. The

method has been also utilized to obtain estimates of the

damage due to earthquakes in ATC-13 [30].

In the first round of the questionnaire, 22 experts

participated. In the second round, 21 experts joined the

survey. Five engineers who participated in the first round

were not able to join the second round because of their

urgent obligations, and four engineers are added in the

second round survey. A total of 26 experts participate the

questionnaire. The questionnaire documents with instruc-

tion and explanatory notes for seismic capacity of buildings

are distributed to the experts by mail in both round

surveys. The responses of the experts are gathered also by

mail. To make parameters queried in the surveys more

relevant, a follow-up workshop among the experts is

organized after the second round questionnaire.

The capacity curve consists of spectral displacement and

acceleration at yield- and ultimate-capacity points. The

questionnaires are mainly composed of the questions for

six parameters: anticipated natural vibration period of each

building type, seismic mass of building, design strength,strength at yield and ultimate point, and ductility. Self-

rated experience/knowledge level (Ei) and certainty level

(Ci) of each respondent (i) are also asked in the

questionnaires. As with the ATC-13 study, the responses

are processed by computing a weighting factor, ECi factor,

defined as the following equation:

ECi E4i CiPn

i1

E4i Ci

. (1)

Here, n in the equation indicates the number of the

respondents. Higher EC indicates higher self-evaluation

of the response. Fig. 8 illustrates an example of the results

in the first round and the second round surveys. The

horizontal axes represent EC and the vertical axes

represent l the ratio of the ultimate strength to the yield

strength for C1L Sub-type 1 building. Solid point indicates

the response of each respondent. Solid line and dotted lines

show the average of the responses and its standard

deviation, respectively.

As shown in the first round survey in Fig. 8(a), difference

of experience and certainty level between the respondents is

not significant since all the EC factors show smaller than

0.15. In the second round survey shown in Fig. 8(b),

ARTICLE IN PRESS

Table 1

Classification of buildings in Metro Manila

Structural types Stories Design vintage

CHB Concrete hollow block 13 Sub-type 1, 2, 3

C1L Concrete moment frame 13 Sub-type 1, 2, 3

C1M 47 Sub-type 1, 2, 3C1H 815 Sub-type 1, 2, 3

C2H Concrete shear wall 815 Sub-type 1, 2, 3

C2V 1625 Sub-type 1, 2

C2E 2635 Sub-type 1, 2

C2S 36 Sub-type 1

Sub-type 1: Constructed after 1992.

Sub-type 2: Constructed between 1972 and 1991.

Sub-type 3: Constructed before 1971.



7/14

however, ECfactors of some respondents show higher than

0.15. It indicates that the number of respondents who

evaluate their certainty level in the second round higher

than in the first round is increased. Besides, the standard

deviation in the second round is declined to about 0.3 while

that in the first round is about 0.5. It means that the

responses for the parameter are converged with approxi-

mately 1.5 by the opinion feedback. Similar convergence is

also observed in other parameters. The spectral values at

the yield and ultimate points for each building category are

determined from the median values of the responses in the

second round survey. Fig. 8 illustrates the derived capacity

curves of the building types highlighted in bold face type in

Table 1. Table 2 shows the spectral displacements and

accelerations at yield and ultimate points for all the

capacity curves derived in this study.

Fragility curve is a probability function of being in, or

exceeding, a damage state for a given spectral displacement.

ARTICLE IN PRESS

4

3

2

1

00 0

4

3

2

1

0

0.1 0.2 0.3

EC

0.1 0.2 0.3

EC

C1L (Sub-Type1)

:Ave.

:Ave.

C1L (Sub-Type1)

:Ave.

:Ave.

Fig. 8. Comparison of EC factors between first and second round. (a) First round. (b) Second round.

Table 2

Data for capacity curves and fragility curves derived by the Delphi method

Type Sub-type Capacity curve Fragility curve

DY (m) AY (m/s/s) DU (m) AU (m/s/s) Displacement at damage state (m) bc

Slight Moderate Extensive Complete

CHB 1 0.002 3.82 0.010 5.00 0.005 0.007 0.018 0.045 0.7

2 0.002 4.02 0.007 5.98 0.005 0.007 0.018 0.045 0.7

3 0.002 4.12 0.007 5.98 0.005 0.007 0.018 0.045 0.7

C1L 1 0.008 2.94 0.058 4.10 0.021 0.037 0.10 0.26 0.5

2 0.005 2.84 0.018 4.31 0.019 0.032 0.088 0.23 0.5

3 0.005 3.04 0.014 4.21 0.019 0.030 0.075 0.19 0.5

C1M 1 0.020 1.96 0.150 2.74 0.035 0.061 0.17 0.42 0.5

2 0.021 2.74 0.083 3.92 0.035 0.061 0.17 0.42 0.6

3 0.019 2.74 0.067 4.21 0.035 0.057 0.14 0.35 0.6

C1H 1 0.064 1.57 0.54 2.01 0.054 0.11 0.32 0.86 0.4

2 0.10 2.84 0.44 4.21 0.054 0.11 0.32 0.86 0.6

3 0.10 3.14 0.36 4.70 0.054 0.093 0.25 0.64 0.7

C2H 1 0.060 1.37 0.40 1.86 0.038 0.094 0.28 0.75 0.4

2 0.093 2.45 0.34 3.72 0.038 0.094 0.28 0.75 0.6

3 0.08 2.25 0.24 3.43 0.038 0.079 0.22 0.56 0.5

C2V 1 0.13 0.98 0.75 1.57 0.075 0.19 0.56 1.5 0.4

2 0.23 2.45 0.83 3.72 0.075 0.19 0.56 1.5 0.6

C2E 1 0.21 0.98 1.40 1.47 0.11 0.28 0.54 2.2 0.4

2 0.38 2.45 1.30 3.33 0.11 0.28 0.84 2.25 0.6

C2S 1 0.39 1.18 2.80 1.57 0.17 0.43 1.29 3.4 0.6

DY: displacement at yield point (m), DU: displacement at ultimate point (m), AY: acceleration at yield point (m/s/s), AU: acceleration at ultimate

point (m/s/s).



8/14

The fragility curve is developed from the result of the

second round survey based on following equation:

PdsjSd F1

bcln

SdSd;ds

, (2)

where P[ds|Sd] is the probability of a particular damagestate, ds (slight, moderate, extensive and complete), at the

given spectral displacement, Sd. Sd;ds and bc are the median

value and its standard deviation of spectral displacement at

which the building reaches the damage state. F is the

standard normal cumulative distribution function.

Here, Sd;ds is expressed as multiplication of drift ratio

and building height. Since the drift ratio at a damage

state of buildings in Metro Manila is poorly examined,

the drift ratio of the nearest building type in HAZUS is

used in this study considering the structural type, building

height and design level [31]. bc is expressed as square root

of sum of squares of the standard deviations derived

from all the answers in the second round survey. Fig. 9

illustrates the constructed fragility curves of the low-rise

building (CHB and C1L), the mid-rise building (C1M) and

the high-rise building (C1H). Table 2 also shows the

displacements at the damage states and bc for all the

building categories.

4.3. Comparison with pushover analysis

In order to validate the capacities derived from the

Delphi method, they are compared with result of the

pushover analysis [32] for typical buildings in Metro

Manila. Analytical values for the capacity of a structure

can be obtained from the pushover analysis. The pushoveranalysis is applied to two-story RC building (C1L Sub-

type 1) and 10-story RC building (C1H Sub-type 3). Fig. 10

illustrates the frame geometry of the two-story and

10-story building. The two-story and the 10-story buildings

represent a typical school and residential building, respec-

tively.

In the pushover analysis, the sizes and the reinforce-

ments of the members of the frame are determined based

on the drawings of the buildings. The material models such

as shear-strain relationships for concrete and reinforcement

steel are defined basically based on the design practice in

the Philippines [33,34]. The distributions of lateral loading

assumed in the analysis are based on fundamental mode

shape of the frames.

Fig. 11 shows the building capacity curves derived from

the pushover analysis with the capacity curves derived from

the Delphi method. For the C1L building, the capacity

displacement by the Delphi method is smaller than that by

ARTICLE IN PRESS

10

5

0 0.01 0.02 0.03 0.04

SA

(m/s/s

)

SD (m)

10

5

0

SA

(m/s/s

)

0.1 0.2 0.3 0.50.4

SD (m)

10

5

0

SA

(m/s/s

)

1 2 3

SD (m)

CHB (Sub-Type3)

C1L (Sub-Type3)

C1M (Sub-Type3)

C1H (Sub-Type2)

C2V (Sub-Type1)

C2E (Sub-Type1)

C2S (Sub-Type1)

Fig. 9. Building capacity curves derived from the Delphi method. Low-rise, Mid- and high-rise and high-rise.

SD(m) SD(m) SD(m) SD(m)

DamageRatio

1

0.8

0.6

0.4

0.2

0 0.1 0.2 0.3 0 0.1 0.2 0.3 0 0.1 0.2 0.3 0 0.1 0.2 0.3

Damage state : : Slight : Moderate : Extensive : Complete

Fig. 10. Fragility curves derived from the Delphi method. CHB: Sub-Type3, C1L: Sub-Type3, C1M: Sub-Type3 and C1H: Sub-Type2.



9/14

the pushover analysis, and the capacity accelerations

(strengths) are comparable or smaller. Here, the capacity

of C1L building by the Delphi method would represent

standard residential/commercial buildings because the

number of residential/commercial low-rise buildings is

predominant in the urban area. As described before,

the capacity by the pushover analysis represents a typicalschool building. The difference between the seismic

capacities is caused because public buildings such as school

generally would have higher potential to resist for seismic

loading than residential/commercial buildings.

For the C1H building, on the contrary, the capacity

accelerations by the Delphi method are little higher than

those by the pushover analysis. Only the lateral load

bearing elements such as columns and beams are modeled

in the pushover analysis. The actual high-rise building,

however, is likely stronger than the result of this analysis

because non-structural elements such as partition walls

provide additional strength in actual high-rise building. It

indicates that the capacity curves of actual building would

correspond better with the curves by the Delphi method.

Although the number of the examined cases is limited, the

capacity curves derived by the Delphi method areconsistent with those by the pushover analysis.

The capacity curves derived by the Delphi method are

compared also with result of static lateral loading experi-

ment for existing buildings in Metro Manila [35]. Accord-

ing to the forcedisplacement curve obtained from the

experiment for an existing two-story CHB building,

the displacements at the yield and ultimate points were

approximately 0.004 and 0.006 m, respectively. As shown

in Fig. 12 and Table 2, the displacements at the yield and

ultimate points of the CHB building are estimated at about

0.002 and 0.0070.01 m, respectively. The capacity of the

CHB building derived from the Delphi method shows good

agreement with that of the actual building.

5. Building damage estimation

5.1. Selection of structural type and design vintage

The building damage due to the scenario earthquake is

estimated by using the derived capacity curves, the fragility

curves, the simulated ground motion and the building

inventory data. The number of damaged buildings of the

low-rise (CHB and C1L), the mid-rise (C1M), and the high-

rise (C1H) buildings are computed by multiplying the

distribution of the damage ratio in each damage state bythe building inventory data.

The structural types of both CHB and C1L are

contained in the low-rise buildings in Metro Manila.

Besides, the strengths of the buildings vary in each design

vintage. As described before, the building population of the

categories needs to be approximately estimated although

ARTICLE IN PRESS

7.0m2.5m

4.45m

3.2 m

22.8m

7.6m3.8m3.8m

4.0m

3.0m

31.0m

Fig. 11. Frame geometry of 2-story and 10-story buildings for pushover

analysis. (a) 2-story building. (b) 10-story building.

8

6

4

2

0 0.05 0.1 0.15

SA

(m/s/s)

8

6

4

2

0 0.2 0.3 0.40.1 0.5

SA

(m/s/s)

SD (m)SD (m)

Push-OverAnalysis (Sub-Type1)

DelphiMethod (Sub-Type1)

Push-OverAnalysis (Sub-Type3)

DelphiMethod (Sub-Type3)

Fig. 12. Comparison of capacity curves derived from the push-over analysis and the Delphi method. (a) C1L Building. (b) C1H Building.



10/14

the structural type and the design vintage of each building

are not included in the inventory data.

The building population in Metro Manila has been

investigated by the questionnaires for the building officials

and the local government engineers [22]. In the survey, the

number of buildings for each building type in each city/

municipality was approximately estimated by the buildingofficials and engineers. Based on the survey, the relation-

ship between the percentages of CHB and C1L buildings in

each city/municipality is broadly classified into three

categories as shown in Table 3. In the region A such as

Caloocan, Valenzuela and so on, the number of CHB is

dominant compared with that of C1L. On the contrary, the

number of C1L is dominant in the region B such as

Marikina, Makati. In the region C, almost all the low-rise

buildings consist of C1L. Based on the result of the survey,

the ratios between the number of CHB and that of C1L in

each region are approximately estimated at 2:1, 1:2 or 0:3

as shown in the table.

As shown in Fig. 1, the urbanized areas had covered

approximately 60% of Metro Manila by 1975 including

major residential and commercial zones. It indicates that

Sub-type 3 design vintage is predominant for the low-riseand mid-rise buildings. Therefore, Sub-type 3 is applied for

CHB, C1L and C1M buildings in the damage estimation.

Since most of the high-rise buildings would be rather newer

than the low-rise and mid-rise buildings, the Sub-type 2 is

adopted for C1H buildings in the estimation.

5.2. Results of building damage estimation

In order to examine effects of the region-specific building

performance, the damage estimation of this study is

compared against that with capacity curves of nearest

building types in HAZUS. To compare with the damage of

CHB buildings, URML buildings in HAZUS is used

because the structural type almost corresponds with CHB.

Low-code is adopted for URML, C1L and C1M buildings

in HAZUS because Sub-type 3 buildings in Metro Manila

would not be fully engineered. Moderate-code is applied to

C1H buildings in HAZUS since Sub-type 2 C1H buildings

would have a certain level of resistance for seismic loading.

Fig. 13 shows the comparison of the capacity curves

derived from the Delphi method and the curves of HAZUS

used in the damage estimation. The yield and ultimate

ARTICLE IN PRESS

Table 3

Approximately estimated ratio of number of CHB buildings and that of

C1L buildings in each city/municipality

Region City/municipality Ratio

CHB C1L

A Caloocan, Valenzuela, Quezon,

Navotas, San Juan, Mandaluyong,

Manila, Pasig, Pasay, Pateros,

Paranaque, Muntinlupa

2 1

B Mar iki na, Maka ti, Tagu ig, La s Pi nas 1 2

C Malabon 0 3

SA

(m/s/s)

SA

(m/s/s)

SD(m) SD(m)

SD(m) SD(m)

0 0.04 0.08

5

10

0 0.04 0.08

0 0.05 0.1

5

10

0 0.3 0.6

CHB (Sub-Type3)

URML (Low-code)

C1M (Sub-Type3)

C1M (Low-code)

C1H (Sub-Type2)

C1H (Moderate-code)

C1L (Sub-Type3)

C1L (Low-code)

Fig. 13. Comparison of capacity curves by the Delphi method and HAZUS used in the damage estimation. Low-rise, low-rise, mid-rise and high-rise.



11/14

ARTICLE IN PRESS

Fig. 14. Building distribution and distribution of damaged buildings. (a) Building distribution. (b) Extensive or complete damage (with capacity curves of

this study). (c) Extensive or complete damage (with capacity curves of HAZUS). (d) Building distribution. (e) Extensive or complete damage (with capacity

curves of this study). (f) Extensive or complete damage (with capacity curves of HAZUS). (g) Building distribution. (h) Moderate damage (with capacitycurves of this study). (i) Moderate damage (with capacity curves of HAZUS).



12/14

strengths (accelerations) by the Delphi method are higher

than those of HAZUS in all the types. On the other hand,

the displacement of the ultimate point by the Delphi

method show smaller than those of HAZUS except for the

C1H building, indicating the ductility of the buildings inMetro Manila is lower than that in the US.

Fig. 14 shows the distribution of the damaged buildings

due to the scenario earthquake based on the capacity

curves developed in this study and those of HAZUS.

Fig. 14(a), (d) and (g) shows the distributions of the low-

rise, mid-rise and high-rise buildings in the inventory data,

respectively. Fig. 14(b) and (c) shows the distribution of

the completely or extensively damaged low-rise buildings.

Fig. 14(e) and (f) shows the distribution of the completely

or extensively damaged mid-rise buildings. Fig. 14(h)

and (i) shows the distribution of the moderately damaged

high-rise buildings. Table 4 shows the number of the

damaged buildings and the damage ratio at each damage

state.

The damage distribution of the low-rise buildings in this

study is significantly different from that with the capacity

curves of HAZUS. In this study, the damage is concen-

trated only in the soft soil areas such as the coastal lowland

and the Marikina valley. In the estimation with the

capacity curves of HAZUS, on the contrary, the severe

damage is distributed to the whole area of Metro Manila.

According to the number of damaged buildings shown in

Table 4, the number of damaged buildings in this study

is larger than that in the other estimation. As shown in

Fig. 13, the low strength of the capacity in HAZUS causes

the severe damage not only in the soft soil area but also in

the stiff soil area such as the central plateau. This trend is

also observed in the damage distribution of the mid-rise

buildings as illustrated in Fig. 14(e) and (f).

Most of the high-rise buildings would suffer moderatedamage but not severe damage. One of the reasons is the

spectral characteristic of the ground motion. The magni-

tude of the scenario earthquake Mw 6.7 is not large enough

to generate a strong ground motion with long period more

than several seconds, which contributes to the response of

higher buildings. As shown in Fig. 14(h) and (i), the

significant difference between the distributions of the

moderately damaged high-rise buildings is not observed

in the estimations. As shown in Table 4, the number of the

completely or extensively damaged buildings in the

estimation with the capacity curves of HAZUS is larger

than that in this study since the capacity strength in

HAZUS is rather small.

6. Conclusions

The seismic performance of the buildings in Metro

Manila, Philippines is evaluated by integrating the local

experts judgments for the building damage estimation.

First, the buildings are classified into 20 categories

according to the structural type, the number of stories

and the design vintage. The questionnaire is applied to the

local experts in Metro Manila to integrate the opinions of

the experts by the Delphi method. The building capacity

curve and the fragility curve for each building category are

ARTICLE IN PRESS

Table 4

Comparison of number of damaged buildings

Building type Damage state (a) Estimation with capacity curves of this

study

(b) Estimation with capacity curves of

HAZUS

No. of damaged

buildings

Ratio (%) No. of damaged

buildings

Ratio (%)

Low-rise (13 story) Complete 114,900 9.0 295,800 23.1

Extensive 66,700 5.2 245,700 19.2

Moderate 123,300 9.6 235,000 18.3

Slight 86,900 6.8 161,500 12.6

Total 391,800 30.6 938,000 73.2

Total no. of buildings 1,281,400 1,281,400

Mid-rise (47 story) Complete 240 8.4 634 22.1

Extensive 407 14.2 918 32.0

Moderate 413 14.4 927 32.3

Slight 311 10.8 219 7.6

Total 1371 47.8 2698 94.0

Total no. of buildings 2869 2869

High-rise (815 story) Complete 5 0.6 14 1.7

Extensive 91 11.2 153 18.8

Moderate 452 55.7 363 44.7

Slight 160 19.7 147 18.1

Total 708 87.2 677 83.4

Total no. of buildings 812 812



13/14

developed from the result of the questionnaires. The

derived capacity curves are consistent with the result of

the pushover analysis. It indicates that the integration

of the experts opinions provide the reliable seismic

performance for the local building.

The ground motions due to a scenario earthquake are

computed using the simulation technique based on theunderground structure model. The capacity spectrum

method is applied to estimate the building response due

to the simulated ground motion. The damage ratios are

calculated from the fragility curves and the building

responses. The distributions of the damaged buildings are

estimated by multiplying the damage ratios and the

building inventory data.

In the estimation of this study for the low-rise and mid-

rise buildings, the severely damaged buildings are mainly

concentrated in the soft soil areas such as the coastal

lowlands and the Marikina valley. In the estimation with

the capacity curves of HAZUS, on the contrary, the severe

damage is obtained not only in the soft soil areas but

also in the stiff soil areas such as the central plateau.

The differences of the damage distributions are caused by

the capacity curves used in the estimations. These results

indicate the importance of the evaluation of the region-

specific building performance for the reliable building

damage estimation.

Acknowledgments

This study was done as a part of Development Earth-

quake and Tsunami Disaster Mitigation Technologies and

Their Integration for the Asia-Pacific Region (EqTAP)Project sponsored by MEXT (Ministry of Education,

Culture, Sports, Science and Technology) of Japan.

References

[1] Federal Emergency Management Agency (FEMA). HAZUS99 SR2

technical manual. Washington, DC, 1999.

[2] United Nations Initiative Towards Earthquake Safe Cities. Risk

assessment tools for diagnosis of urban areas against seismic disasters

(RADIUS). International Decade for Natural Disaster Reduction,

2000.

[3] GeoHazards International and United Nations Center for Regional

Development (UNCRD) Disaster Management Planning Hyogo

Office. Global earthquake safety initiative (GESI). Pilot project.Final report, 2001.

[4] Midorikawa S, Fujimoto K, Arai J. Preliminary assessment of

building damage due to a scenario earthquake in Metro Manila,

Philippines. Paper no. LE-1f. In: Proceedings of the 7th US national

conference on earthquake engineering; 2002.

[5] Hasegawa K, Hayashi H, Topping K, Maki N, Tatsuki S, Banba M,

et al. Development of participatory seismic risk assessment procedure

that reflects community needs: a case report from Marikina City,

Metro Manila, Philippines. Paper no. 2256. In: Proceedings of the

13th world conference on earthquake engineering; 2004.

[6] Japan International Cooperation Agency (JICA), Metropolitan

Manila Development Authority (MMDA), Philippines Institute of

Volcanology and Seismology (PHIVOLCS). Earthquake impact

reduction study for Metropolitan Manila, Republic of the Philip-

pines. Final report, 2004.

[7] Applied Technical Council (ATC). Seismic evaluation and retrofit of

concrete buildings. Redwood City: ATC-40; 1996.

[8] Chopra AK, Goel RK. Capacity-demand-diagram methods based on

inelastic design spectrum. Earthquake Spectra 1999;15(4):63756.

[9] Doi K, Kim K. Role of strategic modeling approach in the

formulation of the framework of sustainable metropolitan policies.

In: Proceedings of 1st workshop on environment conservation of

Metro Manila; 1998. p. 1325.[10] Matsuda I, Enomoto T, Banganan EL, Narag IC. Regional division

of Metro Manila on the basis of geological and geomorphological

conditions. Bull Inst Sci Technol, Kanto Gakuin Univ 1998;25:

10112.

[11] Daligdig JA, Besana GM. Seismological hazards in Metro Manila.

In: Proceedings of the natural disaster prevention and mitigation in

metropolitan Manila area. UNCHS (Habitat) Project INT/90/70;

1993. p. 941.

[12] Nelson A, Personius SF, Rimando RE, Punongbayan RS, Tungol N,

Mirabueno H, et al. Multiple large earthquakes in the past 1500 years

on a fault in Metropolitan Manila, The Philippines. Bull Seism Soc

Am 2000;90:7385.

[13] Kamae K, Irikura K, Pitarka A. A technique for simulating strong

ground motion using hybrid Greens function. Bull Seism Soc Am

1998;88:35767.[14] Irikura K, Kamae K. Strong ground motions during the 1948 Fukui

earthquakeestimation of broad-band ground motion using a

hybrid simulation technique. J Seisimol Soc Jpn 1999;52:12950

(in Japanese with English abstract).

[15] Schnabel PB, Lysmer J, Seed HB. SHAKE: a computer program for

earthquake response analysis of horizontally layered sites. Report no.

EERC 72-12. Earthquake Engineering Research Center, University

of California, Berkeley; 1972.

[16] Irikura K, Miyake H. Prediction of strong ground motions for

scenario earthquakes. J Geol 2001;110(6):84975 (in Japanese with

English abstract).

[17] Yamanaka H, Takezono M, Ogata Y, Eto K, Banganan EL, Narag

IC, et al. Estimation of S-wave velocity profiles in Metro Manila from

long-period microtremor array measurement. In: Proceedings of the

international workshop on the integration of data for seismic disastermitigation in Metro Manila; 2000. p. 1329.

[18] Imazu M, Fukutake K. Dynamic shear modulus and damping of

gravel material. In: Proceedings of 21th Japan national conference on

soil mechanics and foundations engineering; 1986. p. 50912

(in Japanese).

[19] Japan International Cooperation Agency (JICA). 1/10,000 scale

urban contoured map. Report on establishment of graphic informa-

tion base project of the national capital region, Republic of the

Philippines, 1989.

[20] Miura H, Midorikawa S. Updating GIS building inventory data

using high-resolution satellite images for earthquake damage assess-

ment. Earthquake Spectra 2006;22(4):15168.

[21] Yamazaki F, Mitomi H, Yusuf Y, Matsuoka M. Urban classification

of Metro Manila for seismic risk assessment using satellite images. In:

Proceedings of 5th multi-lateral workshop on development ofearthquake and Tsunami disaster mitigation technologies and their

integration for the Asia-Pacific Region; 2003. p. 18 (CD-ROM).

[22] Vibrametrics Inc. Survey among building officials and local govern-

ment engineers on population distribution in Metro Manila. EqTAP

Metro Manila case study, Final report, 2003.

[23] Association of Structural Engineers of the Philippines. National

structural code of the Philippines (NSCP). First edition, 1972.


structural code of the Philippines (NSCP). Second edition, 1981.


structural code of the Philippines (NSCP). Third edition, 1986.


structural code of the Philippines (NSCP). Fourth edition, 1992.


structural code of the Philippines (NSCP). Fifth edition, 2001.

ARTICLE IN PRESS



14/14

[28] Vibrametrics Inc. Survey of experts judgment on earthquake

capacity of selected building types in Metro Manila. EqTAP Metro

Manila case study, Final report, 2003.

[29] Linstone HA, Turoff M. The Delphi method: techniques and

application. Addison Wesley Longman Publishing Co.; 2002.

[30] Applied Technical Council (ATC). Earthquake damage evaluation

data for California. Report ATC-13. Redwood City, 1985.

[31] Vibrametrics Inc. Development of fragility curves for selectedbuilding types. EqTAP Metro Manila case study, Final report, 2003.

[32] Seismo Struct. Computer program for static and dynamic nonlinear

analysis of framed structure. /http://www.seismosoft.comS, 2002.

[33] Vibrametrics Inc. Pushover analysis of an internal frame of a

standard 2-story school building. Final report of EqTAP Metro

Manila case study, 2003.

[34] Vibrametrics Inc. Pushover analysis of an internal frame of a 10-story

sub-type3 (oldest) C1H building. Final report of EqTAP Metro

Manila case study, 2003.

[35] Suzuki S, Tanaka S, Horie K, Maki N, Mizukoshi K, Ohmori T,

et al. A study on dynamic parameter properties and earthquakeresponse characteristics of non-engineered housings in Marikina city,

Philippines. J Soc Safety Sci 2005;7:18 (in Japanese with English

abstract).

ARTICLE IN PRESS

http://www.seismosoft.com/http://www.seismosoft.com/

Documents

Miura Earthquake damage estimation in Metro Manila