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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
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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).
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[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
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: - 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].
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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.
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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.
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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].
H. Miura et al. / Soil Dynamics and Earthquake Engineering 28 (2008) 764777 767
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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
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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].
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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),
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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.
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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.
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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).
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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
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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.
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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
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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.
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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
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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.
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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).
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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
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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
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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.
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