CORRELATION OF BUILDING DAMAGE WITH INDICES OF SEISMIC GROUND MOTION INTENSITY DURING THE 1999 CHI-CHI, TAIWAN EARTHQUAKE

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1 International Workshop on Annual Commemoration of Chi-Chi Earthquake Taipei, Taiwan, R.O.C., September 18-20, CORRELATION OF BUILDING DAMAGE WITH INDICES OF SEISMIC GROUND MOTION INTENSITY DURING THE 1999 CHI-CHI, TAIWAN EARTHQUAKE Jun ichi Miyakoshi Izumi Research Institute, Shimizu Corporation, Tokyo, Japan Yasuhiro Hayashi Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan Abstract In order to clarify a relation between building damage and seismic ground motion characteristics during the 1999 Chi-Chi, Taiwan earthquake, the percentages of damaged buildings around many observation stations were investigated by the authors, and the results were reported in this paper. In addition, indices of seismic ground motion intensity were calculated by using strong motion records. By calculating the building responses based on earthquake response analyses, the frequency characteristics of seismic ground motions that related to building responses were examined. Furthermore, by comparing correlation coefficients of vulnerability functions, which related percentages of damaged buildings with indices of seismic ground motion intensity, the indices corresponding to building damage were studied. Finally, by comparing the vulnerability functions of building damage during the 1999 Chi-Chi earthquake to those of building damage during the 1995 Hyogo-ken Nanbu earthquake, the differences of the seismic performances of reinforced concrete buildings in Taiwan and in Kobe, Japan were indicated. Introduction The Chi-Chi earthquake that occurred in the central part of Taiwan on 21 September 1999 caused unprecedented building damage. Over 300 records of the mainshock were collected by the strong motion network of Taiwan (Lee et al., 1999). These records were extremely valuable to examine a relation between building damage and seismic ground motion characteristics and to clear up the cause of the building damage. The purpose of this paper is to clarify a relation between the building damage and the index of seismic ground motion intensity during the Chi-Chi earthquake. We try to answer the

2 following three questions. First, what size of seismic ground motion intensity is necessary to cause serious building damage? Second, compared to the 1995 Hyogo-ken Nanbu earthquake, how was the seismic performances of buildings in Taiwan? Third, what index of seismic ground motion intensity best explains the building damage? We investigated the percentages of damaged buildings around many observation stations and the damage of school buildings at the stations. First, the results of these investigations are reported in this paper. Next, four indices of seismic ground motion intensity are calculated by using the strong motion records of the Chi-Chi earthquake. The indices are peak ground acceleration (PGA), peak ground velocity (PGV), spectral intensity (SI) by Housner (1965), and instrumental seismic intensity (I JMA ) by the Japan Meteorological Agency (JMA, 1996). Furthermore, we also examine the relation between frequency characteristics of the seismic ground motions and building responses calculated by earthquake response analyses under simple models and these records. Finally, calculating correlation coefficients of vulnerability functions, which relate percentages of damaged buildings with indices of seismic ground motion intensity, we discuss the index that simply expresses building damage during this earthquake. In addition, by comparing the vulnerability functions based on building damage during the Chi-Chi earthquake to the vulnerability functions during the 1995 Hyogo-ken Nanbu earthquake, we discuss the seismic performance of reinforced concrete (RC) buildings in Taiwan and Japan (Kobe). Investigation of building damage We investigated the percentages of damaged buildings around observation stations and the damage levels of school buildings at the stations, since most of the stations in Taiwan were set up at primary schools or junior high schools. Figure 1 shows the locations of the 33 observation sites where the authors investigated building damage. The surface fault and the epicenter of the mainshock are also shown in Figure 1. We principally investigated reinforced concrete (RC) buildings with 5 or fewer stories. Two types of investigations were carried out. One investigations was to judge RC buildings on six damage levels: collapse, severe damage, moderate damage, minor damage, slight damage, and no damage, according to the Architectural Institute of Japan (AIJ, 1980) shown in Figure 2. Another investigation was to survey a percentage of collapsed or severely damaged buildings. At sites TCU079 and TCU084, we were not able to investigate the percentages of damaged buildings as there was an insufficient number of total buildings. The survey sheet used to judge the building damage levels is shown in Figure 3. The detailed items used in the building damage investigation were number of stories, use, structure, and damage level of the building. The damage ranks of buildings around each site were classified into four levels according to the percentages of collapsed or severely damaged buildings (P C+S ). Damage ranks A, B, C, and D correspond to the P C+S range of more than 0.2, 0.1 to 0.2, 0.05 to 0.1, and less than 0.05, respectively. The results are shown in Figure 1 and Table 1. At sites TCU052,, TCU067, TCU068, TCU075, and, the building damage was possibly the result of factors other than earthquake ground shaking. One factor could be surface fault ruptures. The damage index DI S of school buildings was calculated by using the following equation: DI S N wi = i= 1 N (1)

3 24 20' 24 10' 24 00' 23 50' Taichun Taipei :Damage rank B :Damage rank C :Damage rank A Surface fault 72 Epicenter km :Damage rank D : Not investigated site Black:Recorded White:Not recorded Number: Station No ' ' ' ' Figure 1. Location of investigated observation stations. where w i is the constant given according to the damage level of each school building and N is the total number of investigated school buildings. The constants of collapse, severe damage, moderate damage, minor damage, slight damage, and no damage are 1.0, 0.6, 0.3, 0.1, 0.01, 0.0, respectively, and refer to the damage rate according to the Japan Building Disaster Prevention Association (1991). Table 1 shows the total number of investigated school buildings and DI S in each site. A total of 132 school buildings were investigated. Figure 4 shows distributions of damage ratios for school buildings classified into two grades according to the damage rank. It is noted that the damage rank of buildings is correlated to the damage ratio of school buildings, since the damage of school buildings was severe with the highest grade. There were no moderately damaged buildings, and most of the buildings with more than minor damage were severely damaged or collapsed. Therefore, we conclude that most of the damaged school buildings were very brittle. Indices of seismic ground motion intensity The seismic ground motion intensities in each investigated site were calculated by using the acceleration records observed by the Central Weather Bureau (CWB) in Taiwan. The base lines of all records were revised (Ohsaki, 1994). The revised motions were converted into the velocity motions by using the numerical integration. The velocity motions were low cut with a cosinetype function from 0.05 to Hz. The four basic indices of seismic ground motion intensity were peak ground acceleration (PGA), peak ground velocity (PGV), spectral intensity (SI) by Housner (1965), and instrumental seismic intensity (I JMA ) by the Japan Meteorological Agency (JMA, 1996). The PGA and PGV

4 Damage Level Description Sketches Collapse (V) Failure or overturning of the entire structure or complete failure of a single story. Severe Damage (IV) A large portion of building frame is damaged, permanent deformation of the structure may cause imminent collaps Moderate Damage (III) Significant structural damage is visible. Permanent deformation between stories exists but with low possibility of collapse. Minor Damage (II) Minor structural damage, although nonstructural members may have damages. Slight Damage (I) No structural damage is visible. Nonstructural members may have slight damage. Figure 2. Categories of damage to RC buildings in our investigation (AIJ, 1980). No. Number of Stories Use Structre Damage Level Apartment Severe 1 3 RC House Damage Photo No. 1 (b) Survey sheet (a) Photo of damaged building Figure 3. Sample of building damage investigation. Damage rank A-C Damage rank D No damage or slight damage Minor damage Moderate damage Severe damage or collapse Figure 4. Damage ratio distribution of school buildings classified by the damage rank of RC buildings around them.

5 Table 1. Results of the investigations; Indices of seismic ground motion intensity, damage ranks of reinforced concrete (RC) buildings, number of investigated school buildings, and damage index of school buildings at observation stations. Station No. PGA (cm/s 2 ) *1 PGV (cm/s) *1 SI (h=0.2) [0.1,2.5] (cm/s) *1 I JMA *2 SI (h=0.2) [0.2,0.9] (cm/s) *1 PGA PGV (1/s) Damage Rank of Buildings *3 Number of School Buildings Damage Index DI S *4 TCU D 3 0 TCU (D) TCU D 4 0 TCU D TCU D TCU D 5 0 TCU D (A) TCU D TCU (D) TCU (C-D) TCU C TCU D TCU A TCU A-B TCU (D) 3 0 TCU D TCU A (B) TCU TCU B TCU TCU D TCU D TCU D 5 0 TCU D TCU D TCU B TCU D TCU B-D TCU D 4 0 TCU D 3 0 TCU A *1 PGA: peak ground acceleration, PGV: peak ground velocity and SI (h) [T 1 ]: spectral intensity are the maximum values of two horizontal components, in which h is the damping ratio and [T 1 ] is the period range to integrate. *2 I JMA : JMA instrumental seismic intensity (JMA, 1996). *3 Damage rank A: P C+S > 20%, damage rank B: 10% < P C+S < 20%, damage rank C: 5% < P C+S < 10%, damage rank D: P C+S < 5%, in which P C+S is the percentage of collapsed or severely damaged buildings around each observation station. : P C+S is equal to zero. *4 DI S =Σ (w i / N): damage index of school buildings, in which w i is the constant given according to the damage level (refer to Figure. 3) of each school building. The constant of collapse, severe damage, moderate damage, minor damage, slight damage, and no damage are , 0.3, 0.1, 0.01, 0.0, respectively. : DI S is equal to zero.

6 are the maximum values of two horizontal components to the revised acceleration motions and the converted velocity motions, respectively. The SI is given by: 1 T2 SI( h,[ T1, T2]) = SV ( h, T) dt T1 T T (2) 2 1 where S V (h, T) is the pseudo-velocity response spectrum for damping ratio equal to h, and T is the natural period. The SI (h, [T 1 ]) is the maximum value of two horizontal components. The I JMA is calculated by using three component motions (JMA, 1996). The values of the four indices calculated in the investigated sites are shown in Table 1. Figure 1 shows the distinction between the sites which recorded strong motions and those which recorded no strong motions. It is noted that the building damage around sites TCU077 and TCU143 was very serious, but these sites did not record strong motions. Relation between building responses and indices of seismic ground motion intensity The building responses of a single-degree-of-freedom (SDOF) system were calculated based on earthquake response analyses under the strong motion records in order to examine the relations between the building responses and the indices of seismic ground motion intensity. Figure 5 shows the analysis models. The skeleton curve and the hysteresis rule were trilinear model and origin-oriented type, respectively, because most of the RC columns failed in the shear. The yield deformation angle was 1/200. The natural periods of buildings were in the range of 0.07 to 0.10 times the number of stories as the results of observations of microtremors on RC buildings with no damage or slight damage (Midorikawa and Fujimoto, 1999). The natural periods T 0 of the models are given by: T0 = 007. N (3) where N is the number of stories of the buildings. The base shear coefficients C y were calculated by using T 0 as shown in Figure 5. T 0 and C y are, for example, 0.21 sec and 1.0 to 3-story buildings, 0.35 sec and 0.6 to 5-story buildings, respectively. Figure 6 shows the relations between the P C+S and the maximum values of deformation angle (R max ). It is noted that the P C+S is correlated to the R max. However, we are not able to discuss the relationships quantitatively, because the H e =0.7350N W K D RDH e Q y 0.3Q y Q K 0.3K D y 0.01K 0 D T0 = 007. N 2 4π W K0 = T0 2 g 03. K0 Cy = W D y Dy = HeRy R = 1 / 200 y Figure 5. Analysis model and its hysteresis model. N: number of stories, H e : equivalent height, W: weight of building, K 0 : initial stiffness, D: deformation, R: deformation angle, Q: shear force, C: base shear coefficient, g: acceleration of gravity, subscription y: yield point.

7 Damage ratio P C+S N=3N=5 N: number N=3 of stories N=5 1 TCU072 TCU / / / Deformation angle R max PGA < 400 (N=3)PGA < 400 (N=5) 400 < PGA (N=3)400 < PGA (N=5) PGA<400 PGA: Peak (N=3) ground acceleration PGA<400 (cm/s (N=5) 2 ) 400<PGA N: Number (N=3) of stories 400<PGA (N=5) 0.08 Deformation angle R max T = c = T T c /T c 0 Figure 6. Relation between the maximum of deformation angle R max and the percentage of collapsed or severely damaged buildings P C+S. Deformation angle R max (N=3) (N=5) (N=3) (N=5) T T c <1.5 T c <1.5 T c <1.5 T c <1.5 c < 1.5 (N=3)1.5 < T c < 4 (N=3)4 < T c (N=3) 1.5<T c <4 1.5<T c <4 1.5<T c <4 1.5<T c <4 T 4<T c / T c < 1.5 (N=5)1.5 < T 0 4<T c /T c < 4 (N=5)4 < T 0 4<T c /T c / T 0 4<T 0 (N=5) c /T N: Number of stories TCU Peak ground PGA acceleration (cm/s 2 ) (cm/s 2 ) Figure 7. Relation between T 0 / T c and the maximum of deformation angle R max : in which T 0 is the natural period of the model in Eq. (3) and T c is the frequency characteristic of strong motion records in Eq. (4). Deformation angle R max Figure 8. Relation between the maximum of deformation angle R max and (a) the peak ground acceleration (PGA) or (b) the peak ground velocity (PGV). T 0 is the natural period of the model in Eq. (3) and T c is the frequency characteristic of strong motion records in Eq. (4) TCU068 TCU052 Peak ground PGV velocity (cm/s) (cm/s) yield base shear coefficients (C y ) and the yield deformation angle (R y ) of the models do not necessarily express actual buildings. In order to examine the relations between building responses and frequency characteristics of observation records, the frequency characteristic T c (AIJ, 1993) is given by: T = 16. π c PGV / PGA (4) Figure 7 shows the relations between the R max and the ratios of the frequency characteristics to the natural periods of models T c. The R max are large in the T c range of 1.5 to 4. However, Even if the PGA are more than 400 cm/s 2, the R max are small out of the range. The T c range of

8 Damage ratio P C+S PGA/PGV < 4 PGA/PGV < 4 4 < PGA/PGV < 16 PGA 4 / < PGV PGA/PGV < 44 < 16 < PGA / PGV < 1616 < PGA/PGV < / PGV Regression 16 < PGA/PGV curve Vulnerability function of the Regression Hyogo-ken curvenanbu earthquake Regression curve Hayashi et al. (2000) TCU072 TCU TCU TCU074 TCU068 TCU TCU052 Damage ratio P C+S Damage ratio P C+S PGA/PGV 400 < ,000 4 < PGA/PGV < 16 Peak 16 ground < PGA PGA/PGV acceleration (cm/s 2 ) (cm/s 2 ) Regression curve 0.6 TCU TCU TCU JMA instrumental seismic intensity I JMA Damage ratio P C+S PGA/PGV 100 < < PGA/PGV < 16 Peak 16 ground < PGA/PGV PGV velocity (cm/s) (cm/s) Regression curve 0.6 TCU TCU SI (h=0.2, T=[0.2,0.9]) (cm/s) Figure 9. Relations between the percentages of collapsed or severely damaged buildings P C+S and the indices of seismic ground motion intensity: (a) peak ground acceleration (PGA), (b) peak ground velocity (PGV), (c) JMA instrumental seismic intensity (I JMA ), and (d) spectral intensity (SI (h=0.2, T=[0.2,0.9])), in which h is the damping ratio and T=[T 1 ] is the period range to integrate. Thick lines are the vulnerability functions calculated by using damage data of the sites that P C+S is not zero in the PGA / PGV range of 4 to 16. Thick broken line is the vulnerability function calculated by using damage data from RC building with 5 or fewer stories constructed before 1971 during the 1995 Hyogo-ken Nanbu earthquake by Hayashi et al. (2000). 1.5 to 4 corresponds to the PGA / PGV range of 4 to 16 for 3- or 5-story RC buildings. Figure 8 shows the relations between R max and PGA or PGV. The R max within the T c range of 1.5 to 4 (TCU052, TCU068, TCU129, etc.) are very small. However, the R max in the T c range of 1.5 to 4 are correlated to indices of seismic ground motion intensity. This corresponds to the results of the building damage investigations. We can say that the relations between the periods of buildings and the frequency characteristics cannot be ignored when discussing the relations between the building responses and the indices of seismic ground motion intensity. Relation between percentages of damaged buildings and indices of seismic ground motion intensity In order to discuss the indices of seismic ground motion intensity that simply expresses building damage, the correlation coefficients to each index are compared. The coefficients are calculated

9 Damage index DI S PGA/PGV < 4 PGA/PGV < 4 PGA 4 < PGA/PGV / PGV < < PGA / PGV < < PGA/PGV < < / 16 PGV 16 < PGA/PGV 16 < PGA/PGV Regression curve curve Regression curve 1.0 TCU074 TCU TCU TCU072 TCU TCU ,000 Peak ground PGA acceleration (cm/s 2 ) (cm/s 2 ) Damage index DI S 0.2 TCU SI (h=0.2, T=[0.2,0.9]) (cm/s) Figure 10. Relations between damage index DI S of school buildings and indices of seismic ground motion intensity: (a) peak ground acceleration (PGA) and (b) spectral intensity (SI (h=0.2, T=[0.2,0.9])), in which h is the damping ratio and T=[T 1 ] is the period range to integrate. Thick lines are the vulnerability functions calculated by using damage data of the sites that DI S is not zero in the PGA / PGV range of 4 to 16. by using the vulnerability functions which relate the building damage with the indices. The vulnerability function is written by: ( ) P = Φ ( x µ )/ σ (5) where P is the percentage of collapsed or severely damaged buildings P C+S or the damage level DI S of school buildings, Φ is the standard normal distribution function, x is the index of seismic ground motion intensity, µ and σ are average and standard deviation of x, respectively. The parameters of the functions, µ and σ, are calculated based on the method of least squares. The functions are calculated by using two types of data sets, data set I and data set II. Data set I selects the damage data of the sites where P C+S or DI S is not zero. Data set II selects the damage data of the sites where P C+S or DI S is not zero in the PGA / PGV range of 4 to 16. The investigated sites in the PGA / PGV range of less than 4 or more than 16 are TCU052, TCU068, TCU075, TCU101, TCU102, TCU103, TCU110, and TCU129 as shown in Table 1. Table 2 shows the correlation coefficients to four indices of seismic ground motion intensity, namely, PGA, PGV, SI (h=0.2, T=[0.1,2.5]), and I JMA, calculated by using two types of data sets (data set I and data set II). The correlation coefficients calculated by using data set I are higher than those calculated by using data set II except for the PGA for the damage index of school buildings. Therefore, we point out that the relations between the periods of buildings and the frequency characteristics are important when discussing the relations between the percentages of damaged buildings and the indices of seismic ground motion intensity. Figures 9 and 10 show the relations between the indices of seismic ground motion intensity and P C+S and the relations between the indices and DI S, respectively. The vulnerability functions calculated by using data set II of the sites where P C+S or DI S is not zero in the PGA / PGV range of 4 to 16 are also shown in Figures 9 and 10. It is noted that only a few buildings were severely damaged in the investigated areas where PGA, PGV, and I JMA were less than 400 cm/s 2, 50 cm/s, and 5.5, respectively.

10 Table 3. Correlation coefficients of vulnerability functions. Data set I selects the data of the sites that P C+S or DI S is not zero. Data set II selects the data of the sites that P C+S or DI S is not zero in the PGA / PGV range of 4 to 16. Indices of Seismic Ground Motion Intensity Peak ground acceleration (cm/s 2 ) PGA (cm/s 2 ) 1,000 Percentage of RC Buildings Damage Index of Collapsed or Severely Damaged School Buildings P C+S DI S Data Set I Data Set II Data Set I Data Set II ln PGA ln PGV ln SI (h=0.2, T=[0.1,2.5]) I JMA ln S A (h=0.05, T=1.0) ln SI (h=0.2, T=[0.2,0.9]) PGA: peak ground acceleration (cm/s 2 ), PGV: peak ground velocity (cm/s), SI (h, [T 1 ]): spectral intensity (cm/s), I JMA : JMA instrumental seismic intensity, S A (h, T): elastic acceleration response (cm/s 2 ), in which h is the damping ratio, T is the natural period (s), and [T 1 ] is the period range to integrate. TCU129 TCU TCU052 TCU TCU Peak ground PGV velocity (cm/s) (cm/s) Damage rank A Damage rank B Damage rank C Damage rank D Hyogo-ken Nanbu (Non-liquefied) Hyogo-ken Nanbu (Liquefied) Figure 11. Relation between peak ground velocity (PGV) and peak ground acceleration (PGA) during the 1999 Chi-Chi earthquake and the 1995 Hyogo-ken Nanbu earthquake. Sakai et al. (2000) described that the elastic acceleration response S A (h=0.05, T=1.0) for the damping ratio h=0.05 and the natural period T=1.0 sec in the indices of seismic ground motion intensity was more highly correlated to building damage during the Chi-Chi earthquake. The natural period T=1.0 sec predominated in strong motion records during the Hyogo-ken Nanbu earthquake. It was considered that buildings were unprecedentedly damaged due to the correspondence between the predominate period and the equivalent period of wooden houses or mid-to-high-rise RC buildings. However, we expected that the building damage would agree with the earthquake response in less than T=1.0 sec better than S A (h=0.05, T=1.0). Therefore, we propose the SI integrated in the period range of 0.2 to 0.9 sec in Eq. (2): SI (h=0.2, T=[0.2,0.9]) as a new index of seismic ground motion intensity. The period range of 0.2 to 0.9 sec corresponds to the period range of the natural periods written by Eq. (3) and the equivalent periods to the ductility factor µ=2 for 3- or 5-story RC buildings. The SI (h=0.2, T=[0.2,0.9]) calculated in each site are also shown in Table 1. The correlation coefficients to indices, namely, S A (h=0.05, T=1.0) and SI (h=0.2, T=[0.2,0.9]), are also shown in Table 2. The correlation coefficients to S A (h=0.05, T=1.0) are higher than those to the four indices, but are lower than those to SI (h=0.2,

11 T=[0.2,0.9]). We point out that the periods of buildings as well as the frequency characteristics of strong motions ought to be reflected by the index of seismic ground motion intensity to simply express building damage. The vulnerability functions and the relation between PGA and PGV during the 1999 Chi- Chi earthquake were compared to those during the 1995 Hyogo-ken Nanbu earthquake. Figure 11 shows the relations between PGA and PGV of strong motion records to discuss the PGA / PGV range. The relations at each station during the Chi-Chi earthquake were classified into four ranks of building damage, those during the Hyogo-ken Nanbu earthquake were classified into two types: liquefied sites and non-liquefied sites. The PGA / PGV range of 4 to 16 is much wider than the range of the Hyogo-ken Nanbu earthquake, and includes a range of liquefied sites at which only a few buildings with earthquake ground shaking were severely damaged. We will expect to examine the PGA / PGV in detail including strong motion records of the Hyogo-ken Nanbu earthquake. Figure 9 (b) shows the vulnerability function for the Hyogo-ken Nanbu earthquake calculated by using damage data from RC buildings with 5 or fewer stories constructed before 1971 (Hayashi et al., 2000). It is noted that the seismic performance of RC buildings in Taiwan was lower than that in Kobe, Japan. Conclusions In this paper, we discussed the relations between the building damage and the indices of seismic ground motion intensity during the 1999 Chi-Chi, Taiwan earthquake. We examined relations between the indices of seismic ground motion intensity calculated by using strong motion records, the percentages of damaged reinforced concrete buildings investigated around many observation stations, and the building responses calculated by earthquake response analyses. The indices were peak ground acceleration (PGA), peak ground velocity (PGV), spectral intensity (SI), and JMA instrumental seismic intensity (I JMA ). The conclusions are summarized as follows. (1) The investigation of damaged school buildings revealed that there were no moderately damaged buildings, and most of buildings with more than minor damage were severely damaged. Therefore, we concluded that most of the damaged school buildings were very brittle. (2) Only a few buildings were severely damaged in the investigated areas where PGA, PGV, and I JMA were less than 400 cm/s 2, 50 cm/s, and 5.5, respectively, as examinations of the relations between the indices of seismic ground motion intensity and the percentages of damaged buildings or the damage index of school buildings showed. (3) Building responses calculated by earthquake response analyses were very small within the PGA / PGV range of 4 to 16, but were correlated to indices of seismic ground motion intensity in the PGA / PGV range of 4 to 16. The correlation coefficients of the vulnerability functions, which related the building damage with the indices of seismic ground motion intensity, were calculated. The results showed that most of the correlation coefficients to the indices calculated in the PGA / PGV range of 4 to 16 were higher than those calculated in the whole range. Therefore, we concluded that the frequency characteristics of strong motions were important when discussing the relations between the building damage and the indices of seismic ground motion intensity. (4) A comparison was made of the correlation coefficients to indices of seismic ground motion intensity in the PGA / PGV range of 4 to 16. The results showed that most of the correlation coefficients to SI (h=0.2, T=[0.2,0.9]) for the periods of buildings were higher than those to the other indices. Therefore, We indicated that the periods of buildings as well as the frequency

12 characteristics of strong motions ought to be reflected by the index of seismic ground motion intensity to simply express building damage. (5) By comparing the vulnerability functions based on building damage during the Chi-Chi earthquake with those based on building damage during the Hyogo-ken Nanbu earthquake, we indicated that the seismic performance of reinforced concrete buildings in Taiwan was lower than that in Kobe, Japan. Acknowledgments This investigation of building damage was conducted with Masafumi Mori and Hiroshi Kambara at Shimizu Corporation, and we would like to thank them for their valuable comments on this paper. Dr. Saburo Midorikawa gave us useful suggestions on the sellection of investigation sites. We used GMT (Generic Mapping Tools) by Wessel and Smith (1998) to plot Figure 1. References Architectural Institute of Japan (AIJ) (1980), Reconnaissance Report of the 1978 Miyagiken-oki Earthquake, (in Japanese). Architectural Institute of Japan (AIJ) (1993), Recommendations for Loads on Buildings, 406 (in Japanese). Hayashi, Y., J. Miyakoshi, A. Tasai, and Y. Ohno. (2000), Seismic Performance of RC Buildings During Hyogo-ken Nanbu Earthquake, Journal of Structural and Construction Engineering (Transactions of Architectural Institute of Japan), 528, (in Japanese). Housner, G. W. (1965), Intensity of Earthquake Ground Shaking near the Causative Fault, Proceedings of the third World Conference on Earthquake Engineering, I, III-94-III-115. Japan Building Disaster Prevention Association (1991), Judgement Criteria of Damage Level and Recommendations of Technical Restoration for Buildings Damaged due to Earthquakes (Reinforced Concrete Buildings Version), 1-37 (in Japanese). Japan Meteorological Agency (JMA) (1996), On JMA Seismic Intensity -- Basic Knowledge and Its Application --, Gyosei Inc. (in Japanese). Lee, W. H. K., T. C. Shin, K. W. Kuo, and K. C. Chen (1999), CWB Free-field Strong-motion Data from the 921 Chi-Chi Earthquake: Volume 1. Digital Acceleration Files on CD- ROM, Pre-publication Version (December 6, 1999), Seismology Center, Central Weather Bureau, Taipei, Taiwan. Midorikawa, S. and K. Fujimoto (1999), Reconnaissance Report of the 1999 Chi-Chi Earthquake -- On Strong Motion Records and Soil Conditions at Observation Stations --, Research Report on Earthquake Engineering, Earthquake Engineering Research Group, Tokyo Institute of Technology, 72, (in Japanese). Ohsaki, Y. (1994), New Introduction to Spectral Analyses of Seismic Motion, Kajima Institute Publishing Co., LTD. (in Japanese). Sakai, Y., S. Yoshioka, K. Koketsu, and T. Kabeyasawa (2000), Earthquake Response Analyses of Reinforced Concrete Buildings Damaged by the 1999 Chi-Chi Earthquake, Taiwan, Concrete Research and Technology, Japan Concrete Institute, 22, (in Japanese). Wessel, P. and W. H. F. Smith (1998), New, Improved Version of Generic Mapping Tools Released, EOS, AGU.