GIS-based Building Damage Assessment due to A Scenario Earthquake in Metro Manila, Philippines Saburoh MIDORIKAWA1/
[email protected] Kazuo FUJIMOTO1/
[email protected] Hiroaki YAMANAKA1/
[email protected] Hiroyuki MIURA1/
[email protected] Benito M. PACHECO2/
[email protected] Bartolome C. BAUTISTA3/
[email protected] 1) Tokyo Institute of Technology, Japan 2) Vibrametrics, Inc., Philippines 3) Philippine Institute of Volcanology and Seismology, Philippines Abstract This paper presents the procedure for GIS-based building damage assessment which is applicable to mega cities in the Asia-Pacific region. The procedure consists of ground motion estimation using the hybrid simulation technique, building response estimation using the capacity spectrum method, and damage distribution estimation using the GIS building inventory data. The procedure is applied to Metro Manila, Philippines. The results should be useful for the stakeholders such as administrators and structural engineers, in order to plan disaster mitigation strategies. Key Words:
damage assessment, building, vulnerability, seismic risk, Metro Manila
1. Background and Objectives Concentration of population to urban areas is a common problem in developing countries including the Asia-Pacific region. The number of mega-cities, which are vulnerable to disasters, is increasing. The disaster mitigation activities in mega-cities should be strengthen immediately. In order for efficient earthquake disaster mitigation planning, the earthquake loss estimation is indispensable. It is, however, common that the data necessary for the loss estimation is not fully available in developing countries. As a result, it is difficult to practice the reliable loss estimation such as the GIS-based damage assessment. In this paper, we propose a simplified procedure for the GIS-based damage assessment which is applicable to the Asia-Pacific region. The procedure consists of ground motion estimation using the hybrid simulation technique, building response estimation using the capacity spectrum method, and damage distribution estimation using the GIS building inventory data. The procedure is applied to Metro Manila, the capital of Philippines, where the influx of population and the urban sprawl have been strongly observed. The results will be provided to the stakeholders as a part of the Metro Manila case study. 2.
Methodology In order to provide basic information for disaster planning, the building damage due to a scenario earthquake is assessed. The flow of the damage assessment is shown in Fig. 1. The ground motion at engineering bedrock is computed by the hybrid simulation method. Then, the ground motion at surface is computed by the equivalent-linear soil response analysis using the soil profile model at each site. 1
The building response is evaluated by the capacity spectrum method. The buildings are classified into several categories. The capacity curve for each category is developed by integrating the expert opinions. The nonlinear response of the building is estimated from the capacity curve and the ground motion spectrum. The damage state for each building category is defined by the building response and fragility curve. Based on the existing GIS data together with the field survey and the high resolution remote sensing data, the building inventory data is constructed. Combining the building inventory data and the damage state of each building category, the distribution of the building damage is computed. 3. Building Damage Assessment in Metro Manila (1) Social and Natural Environments of Metro Manila Metro Manila consists of seventeen cities and municipalities including Quezon City, Manila, Makati and Marikina. In the downtown such as Manila, densely built-up areas with low- and mid-rise buildings have been developed. In the new business zones such as Makati and Ortigas, many high-rise buildings have been constructed. Population and property are concentrated in Metro Manila. High population density in the metropolis produces environmental problems in urban development, transportation and disaster mitigation. Figure 2 shows a geomorphological classification map of Metro Manila (Matsuda et al., 1998). The area is divided into three major parts; Central Plateau, Coastal Lowland, and Marikina Valley. Central Plateau is on stiff soils with a elevation of 15 to 30 meters. Coastal Lowland extending Manila Bay is on soft sand and clay deposits. The thickness of the deposits is several to 40 meters. Marikina Valley is surrounded by Central Plateau and Mountains and consists of a delta and a muddy flood plain. The maximum thickness of the surface soft deposits is 50 meters. There are two active faults in the area. One is the west Marikina fault between Marikina Valley and Central Plateu, and another is the east Marikina fault between Marikina Valley and Mountains. These faults have high potential to produce a damaging earthquake with magnitude of 6 to 7 (Nelson et al., 2000). Disaster mitigation planning to the earthquake seems an urgent issue for Metro Manila. (2) Ground Motion Estimation The west Marikina fault is selected as the source of the scenario earthquake, because the west fault is closer to the central part of Metro Manila. Several sets of the fault parameters are used for the calculation because of uncertainty in the source modeling. Using the fault parameters, together with the deep underground model, the ground motion at engineering bedrock whose shear-wave velocity is about 400 m/s, is computed by the hybrid simulation method (Yamada et al., 2003). In constructing the underground model, the data from the seismic refraction test and microtremor array measurements are compiled (Yamanaka et al., 2001). Figure 3 shows the distribution of peak ground velocities at engineering bedrock computed from the uniform slip model of the earthquake. Then, the ground motion on surface is computed by the equivalent linear soil response analysis. In order to obtain the surface soil model for the soil response analysis, about 400 boring data are collected and compiled. The surface soil model with the 500-m mesh system is constructed from the boring data, the geomorphological map and microtremor measurements. Figure 4 shows the acceleration time histories and velocity response spectra computed at Manila and Quezon. (3) Building Response Estimation The capacity spectrum method is used to compute the building response (FEMA, 1999). The demand curve is defined by the response spectrum of the estimated ground motion. The capacity curve is developed as a following process (Vibrametrics, Inc., 2003); a) select and document several structural types of building that comprise the big majority of buildings in Metro Manila, considering the applicable height range in the low-rise, mid-rise and high-rise ranges; b) develop seismic capacity curves for each building type, considering the expert judgment of 2
experienced structural engineers. The following eight building types, comprising the big majority of buildings in the subject area, are considered: 1) CHB: concrete hollow block buildings, 1-story or 2-story (1-story). 2) C1L: concrete moment frame buildings, 1-story to 3-story (2-story). 3) C1M: concrete moment frame buildings, 4-story to 7-story (5-story). 4) C1H: concrete moment frame buildings, 8-story to 15-story (10-story). 5) C2H: concrete shear wall buildings, 8-story to 15-story (10-story). 6) C2V: concrete shear wall buildings, 16-story to 25-story (20-story). 7) C2E: concrete shear wall buildings, 26-story to 35-story (30 story) 8) C2S: concrete shear wall buildings, 36-story and higher (40-story). For each building type, three sub-types on the design vintage are also considered to take into account of change of the seismic code. (4) Building Inventory In Metro Manila, the GIS base map from the 1/10,000 scale topographic map edited in 1989 has been constructed. In the base map, the footprints of the buildings and the congested housing areas are included. The number of the buildings whose footprints are shown is about 280,000. In Metro Manila, however, the total number of the buildings and houses is about 910,000 as of 1989 (Sarausad, 1993). The difference of the numbers suggests that about 630,000 houses are located in the congested areas. The 630,000 two-story buildings which are uniformly distributed in the congested areas, are added in the GIS data. For the buildings whose footprints are shown, the attributes are not assigned in the GIS data. Most part of Metro Manila is the residential area where low-rise houses are located. Mid-rise or high-rise buildings are mostly situated in the major commercial zones such as Makati, Ortigas, Manila and Quezon Avenue. The building height survey was conducted in these zones. To update the data at recently developed commercial zones, the high-resolution satellite image data (IKONOS) is used to identify newly-built buildings. 4.
Tentative Results Figure 5 shows the building response displacements for several building types computed at Manila, Ermita, Quezon, Makati, Ortigas, Marikina and Taguig. The results are plotted on the fragility curve. The results suggest that 1) the concrete hollow block buildings might suffer complete damage at Coastal Lowland and Marikina Valley, 2) the mid-rise buildings might suffer extensive damage at Coastal Lowland, 3) the high-rise buildings might suffer moderate damage at many of the sites, and 4) the damage of super high-rise buildings might be slight. References FEMA (1999). HAZUS 99 SR2 Technical Manual. Matsuda, I. et al. (1998). Regional division of Metro Manila on the basis of geological and geomorpho-logical conditions, Bull. of Institute of Science and Technology, Kanto Gakuin Univ., 25, 101-112. Nelson, A. R. et al. (2000). Multiple large earthquakes in the past 1500 years on a fault in Metropolitan Manila, the Philippines, Bulletin of the Seismological Society of America, 90 (1), 73-85. Sarausad, F. (1993). Infrastructure condition in Metro Manila, Disaster Prevention and Mitigation in Metropolitan Manila Area, 93-107. Vibrametrics, Inc. (2003). Survey of Experts’ Judgment on Earthquake Capacity of Selected Building Types in Metro Manila. Yamada, N. et al. (2003). Strong ground motion simulation in Metro Manila, Philippines, Journal of Structural Engineering, 49B, 1-6. Yamanaka, H. et al. (2001). Estimation of S-wave velocity profiles in Metro Manila from long-period microtremor array measurements, Proc. of the International Workshop on the Integration of Data for Seismic Disaster Mitigation in Metro Manila, 13-29 3
SCENARIO EARTHQUAKE
Seismic Refraction Test Microtremor Array Observation ↓ DEEP UNDERGROUND MODEL
HYBRID SIMULATION METHOD GROUND MOTION AT ENGINEERING BEDROCK
Geomorphological Map Boring Data, PS-logging ↓ SURFACE SOIL MODEL
SOIL RESPONSE ANALYSIS GROUND MOTION AT SURFACE
Ground Motion
Seismic Code, Expert Opinions, Delphi Method ↓ CAPACITY CURVES CAPACITY SPECTRUM METHOD RESPONSE OF BUILDINGS
Expert Opinions ↓ FRAGILITY CURVES
DAMAGE RATIO OF BUILDINGS
Building Response
GIS Data, Field Survey, Remote Sensing Data ↓ BUILDING INVENTORY DISTRIBUTION AND AMOUNT OF BUILDING DAMAGE
Fig. 1
Building Inventory and Damage
Flow of Building Damage Assessment
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Building Response Displacements at Manila, Ermita, Quezon, Makati, Ortigas, Marikina and Taguig 6
