EarthquakeTsai, Engineering Hsiao, Bruneau: and Engineering Overview Seismology of building damages in 921 Chi-Chi earthquake 9393 Volume 2, Number 1, March 2000, pp. 93–108

Overview of Building Damages in 921 Chi-Chi Earthquake

1) 2) 3) K.C. Tsai Chiang Pi Hsiao Michel Bruneau

1) Professor, Department of Civil Engineering, National University, Taipei, Taiwan 10617, R.O.C. 2) Director, Architecture and Building Research Institute, Ministry of Interior, Taipei, Taiwan, R.O.C. 3) Professor, Department of Civil Engineering and Deputy Director, Multidisciplinary Center for Earthquake Engineering Research, SUNY at Buffalo, USA.

ABSTRACT

The 921 Chi-Chi earthquake caused approximately 9,000 buildings col- lapses or damages of various degrees. A large percentage of buildings that collapsed are un-reinforced clay block masonry cottages and non- engineered and one-to-three stories reinforced concrete frame structures constructed with brick in-fill partitions and exterior walls. Many collapsed buildings had a pedestrian corridor and open front at the ground floor. More than two dozen modern reinforced concrete moment resisting high- rise apartment buildings overturned or collapsed. The observed damages on reinforced concrete structures suggested a large effect of masonry and lightly reinforced concrete nonstructural components. The observed damages also suggest that only ductile details be used in all new construc- tions and in the repair of damaged structures, and buildings having “soft- story” characteristics should not be allowed in new constructions.

INTRODUCTION with more than 6,000 others partially collapsed and countless others damaged On 1:47a.m. of September 21, 1999, a to various degrees. While it will take magnitude ML = 7.3 earthquake struck considerable effort and time to inventory the central region of Taiwan. Following that damage to a level of refinement that the 921 Chi-Chi earthquake, two after will allow formulation of a reliable critique shocks of ML = 6.8 occurred about 30 of current building codes and practices, hours and 127 hours after the main preliminary observations indicate that shock. Preliminary data indicates that buildings that collapsed typically exhibit- approximately 3,000 buildings totally ed non-ductile reinforcing details collapsed as a result of the earthquakes, compounded by detrimental building 94 Earthquake Engineering and Engineering Seismology, Vol. 2, No. 1 configurations. A large percentage of accounts for the majority of the complete buildings that collapsed due to the main building collapses near the epicenter due shock or strong aftershocks are old un- to severe ground shakings. Many school reinforced clay block masonry cottages buildings suffered extensive and severe and non-engineered and one-to-three damages. The “short-column” type of stories reinforced concrete frame struc- damage in these reinforced concrete tures constructed with brick in-fill structures is rather common in the partitions and exterior walls. Many direction parallel to the exterior corridor collapsed buildings had a pedestrian outside the classrooms where windows corridor and open front at the ground above half-height in-fill shortened the floor, and only one wall at the back of the effective length of almost all the columns building along the street direction (Photo 2). (Photo 1). This type of building damage

Photo 1 Collapse of the typical building Photo 2 Shear failure of RC columns having pedestrian corridor due to the short column effect

However, in the affected area, more (UBC) used in the United States, albeit than two dozen modern 10-to-20 stories generally one edition behind the latest apartment buildings overturned or published. Seismic force requirements collapsed. These were reinforced con- of building designs in Taiwan for the past crete moment resisting frames, most of 25 years are given in Table 1. The them constructed with cast-in-place seismic zonation maps in 1974, 1982 and 15cm thick exterior wall and 12cm thick 1997 editions of Taiwan Building Stan- partition walls (Photo 3). The observed dards (BTS, 1974, 1982 and 1997) are damages on reinforced concrete struc- given in Fig. 1 through Fig. 3, respectively. tures suggested a large effect of masonry In the Nanto county, where most of the and lightly reinforced concrete non- damage occurred, the specified peak- structural components. These building ground-acceleration to consider for were typically designed following re- design was 0.23g (for the 475 years quirements for moment resisting frames return-period earthquake), which trans- identical to the Uniform Building Code lates into a design coefficient of Tsai, Hsiao, Bruneau: Overview of building damages in 921 Chi-Chi earthquake 95 approximately 0.11g for short period Many of them appear to have tall floor and structures. Incidentally, that coefficient open plaza features in the ground level. was 0.05g from 1974 to 1982, and 0.08g Commonly encountered were failed from 1982 to 1996, before the higher columns with widely spaced stirrups aforementioned value was adopted in (unconfined plastic hinge zone), splices 1997. Note that Nanto was located in with inadequate development length or Taiwan’s Seismic Zone 2, and that design located in the hinge region, light or force 22% and 43% higher were mandated inexistent joint transverse reinforcement, in Seismic Zones 1A and 1B, respectively stirrups with 90°, etc. Strong-beam (Fig. 3). Alternatively, the code permits weak-columns systems apparently the use of a slightly larger seismic force to common, might have resulted in numer- size members with some relaxation on the ous story collapses following excessive ductile detailing of the reinforcement, column damage. This was particularly following what is prescribed in the UBC. frequent in the first story of buildings, as Surprisingly, many of the buildings that the larger openings and higher story collapsed were engineered and construct- height there translate into a lower struc- ed in the last decade. However, none tural stiffness and strength, leading to exhibited evidence of ductile detailing. “soft-story” mechanisms (photo 4).

Photo 3 Collapse of a apartment build- Photo 4 Collapse of a high-rise apart- ing in Fengyuan ment building in Dali

Table 1 Seismic Force Requirements in Taiwan

Year Seismic Base Shear Remarks Z = 1.25, 1.0, 0.75 1974 Vw = Z K C W K = 0.67, 0.8, 1.0, 1.33

Cmax = 0.10, W = D + 0.25 L Z = 1.0, 0.8, 0.6 K = 0.67, 0.8, 1.0, 1.33 1982 Vw = Z K C I W I = 1.0, 1.25, 1.5

Cmax = 0.15, W = D Z = 0.33, 0.28, 0.23, 0.18 Z I C W I = 1.0, 1.25, 1.5 1997 V = Cmax = 2.5, W = D 1.4 a y Fu ay = 1.2 (WSD), ay = 1.5 (USD)

Fu » 2.9, 2.5, 2.1 96 Earthquake Engineering and Engineering Seismology, Vol. 2, No. 1

Fig. 1 Seismic zonation map in 1974 Taiwan Building Codes

Fig. 2 Seismic zonation map in 1982 Taiwan Building Codes Tsai, Hsiao, Bruneau: Overview of building damages in 921 Chi-Chi earthquake 97

1997

Fig. 3 Seismic zonation map in 1997 Taiwan Building Codes

BUILDING DAMAGE STATISTIC Island-wide

BY GEOGRAPHIC REGION The 921 earthquake has resulted in a tremendous amount of damages in the Overview of Building Damage central part of Taiwan. Figure 4 indi- Statistic cates that approximately 90% of the 8,773 damages are concentrated in Shortly after the occurrence of the and its adjacent Taichung 921 earthquake, the National Center for County. Over 300 damaged buildings Research on Earthquake Engineering are also observed in the , as (NCREE), the Architecture and Building well as in the Taipei County. The detail Research Institute (ABRI) and the private organizations had quickly formed the damages of Nantou County, Taichung reconnaissance team to investigate the County, and Taipei County are described island-wide building damages. There below. were 8,773 structural damages recorded Nantou County using the Building Damage Survey Form [1]. Each damage report was filed for Nantou County was severely impacted either an individual structure or a con- by this earthquake due to its epicenter secutively connected building block; location and the surface faulting. More therefore, the number of the actual than 4,500 structures, which equivalent damages had exceeded the reporting to 53% of the island-wide damages, were figure noted above. surveyed in Nantou. Figure 5 illustrates 98 Earthquake Engineering and Engineering Seismology, Vol. 2, No. 1

that Nantou City, Tsautuen Village, and Taichung County Jungliau Village are the top three most Being a highly populated county adja- damaged areas in this county; and their cent to Nantou, Taichung County also damaged building figures are 937, 846 experienced significant damages of 3,200 and 823 respectively. The survey indi- building failures. It is observed from Fig. cates that Nantou City, Tsautuen Village, 6 that these damages in the Taichung Jushan Village, and Mingjian Village County were concentrated at Dungshr received substantial damages, because Village, Shrgang Village, Fengyuan City, of the direct impact of the Chelungpu and Shinshe Village. The regional damage ratios of these four areas are 28%, Fault. 24%, 19% and 14% respectively.

0% 53% 0% Wufeng Dadu (13) Dali (108) (151) 4% 0% 0% Taiping 4% Fengyuan 5% (159) 0% 0% (548) 6% 2% 2% 19% 1% 2% Shrgang (653) Tantz (8) 24% 4% 0% 2% 32% Shinshe Taichung City(110) Taichung County(2815) (397) Taipei City(157) Taipei County(337) 14% Nantou County(4637) Miaoli County(348) Taoyuanj County(13) (156) Hsinchu City(24) (15) Shengang Wur (12) Dungshr Chiai City(2) Chiai County(7) (11) 0% (766) (152) 0% 28%

Fig. 4 Distribution of damaged buildings Fig. 6 Distribution of damaged buildings in Taiwan (number and percent- in Taichung County (number and age) percentage)

Taipei County Taipei County, a special seismic zone Tsautuen Village Puli Village 18% in the north region, is applicable to a 10% Guoshing Village different earthquake design requirement 4% because of the Taipei basin location. Yuchr Village Under a normal circumstance, the Nantou City 2% earthquake damage should be less 24% Lugu Village significant since the Taipei County is so 4% distant away form the epicenter. How- Jiji Village 4% ever, as the assessment indicates that the Jushan Village level of damage in Taipei County was 9% Jungliau Village greater than most of the counties in the Mingjian Village 18% 5% Shueili Village northern region. Figure 7 indicate that 2% the earthquake damages were concen- trated at the Shinjuan City and the Fig. 5 Distribution of damaged buildings Junghe City, and their damaged building in Nantou County numbers are 122 and 66 respectively. Tsai, Hsiao, Bruneau: Overview of building damages in 921 Chi-Chi earthquake 99

Yingge The epicenter location, Chi-Chi Village is 0% Bali Sanchung located near southeast portion of the Sanshia Lujou 4% 6% Shulin 1% 1% Chelungpu fault. The rupture length of 1% Tucheng the Chelungpu fault in this earthquake is 3% over 100km long in the north-south Shinjuang direction, and its impacts are enormous. 35% Junghe 20% According to the post-earthquake geologi- cal investigation, the earthquake caused Wugu many permanent landslides and surface 3% faulting in Miaoli County, Taichung Yunghe Shindian 4% 7% County, Taichung City and Nantou Shijr Danshuei Taishan Banchiau 2% County. Twelve areas are directly 2% 5% 6% impacted: Juolan Village, Dungshr Village, Shrgang Village, Fengyuan City, Tantz Fig. 7 Distribution of damaged buildings in Taipei County Village, Beituen Village, Taiping City, Wufeng Village, Tsautuen Village, Nantou Chelungpu Fault Area Building City, Mingjian Village, and Jushan Village. Damage Statistic Figure 8 illustrates that 5,088 damages The tectonic movement of the Che- were reported, which is equivalent to 58% lungpu faults causes the 921 earthquake. of the island-wide damages.

1200

1000

800

600

400 Number of buildings

200

0 Tantz Juolan Nantou Jushan Taiping Wufeng Beituen Shrgang Mingjian Dungshr Tsautuen Fengyuan Fig. 8 Number of damaged buildings in cities near Chelungpu Fault

Overview of Observed Building Damage Level, (2) Structural Height, (3) Damages Structural Type, (4) Structural Construc- To further the study of the earthquake tion Period, (5) Structural Usage, (6) damages, the observed data has been Structural Plan Configuration, and (7) Structural Vertical Configuration. The analyzed in seven aspects: (1) Structural 100 Earthquake Engineering and Engineering Seismology, Vol. 2, No. 1

assessment presented here is based on Building, (4) Structural Steel Building, (5) the visual inspection of the exterior Light Metal Building, (6) Timber Building, damage only. Prior to the completion of (7) Steel Reinforced Concrete Building. It the report [1], some minor adjustments is important to note that unless the maybe applicable to the investigated data; building is taller than 25 stories, the most however, these small adjustments can be popular material for building construc- considered to have negligible affect on the tion in Taiwan is reinforced concrete. overall result of the analysis. The top three damaged structural types are the reinforced concrete structures, Structural Damage Level the un-reinforced brick structures and To facilitate the damage study, five the un-reinforced clay block buildings. Damage Classification Indexes are used The reinforced concrete failures in this to assess the damage level. The five earthquake is significant amount; how- indexes are: (1) Collapse, (2)Tilt, (3)Severe ever, compared to the total amount of Damage, (4) Moderate Damage, and (5) reinforced concrete buildings in Taiwan, it Minor Damage. A collapsed or tilted should be just a small percentage. On building is considered to be a total the other hand, the poor seismic resis- structural failure. Nantou County and tance of the un-reinforced brick buildings Taichung County are the top two most and the un-reinforced clay block cottages severely damaged area in Taiwan, and are observed during this earthquake. most of their damages are classified as Since these two construction materials collapse or severe damage. In Taipei were commonly used in the early age, County and Miaoli County, most of the most of these damages were occurred in building failures are classified as minor the rural areas in Nantou County and damages. Taichung County. Lack of a well seismic Structural Height design and ductility is the major cause of the great failure of the un-reinforced brick Five categories are used to classify the and clay buildings. building height in this damage survey; they are: 1 to 3-story height, 4 to 6-story height, 7 to 11-story height, 12 to 15- story height, and over15-story height. BUILDING DAMAGE ANALYSIS The survey indicates that 85% of the BY CONSTRUCTION TYPES reported damages are less than 4-story height. Among these low-rise building Analyzing the seismic performance of damages, the un-reinforced brick or the the RC buildings, the un-reinforced brick un-reinforced clay block buildings repre- buildings, the un-reinforced clay block sent a large portion. In the urbanized buildings, and the structural steel build- area, such as Taipei City and Taipei ings, their damage profiles are discussed County, the majorities of the damaged in this section. buildings are 4 to 6-stories height [1]. Damage of the Reinforced Concrete Structural Material (RC) Building Damaged structures have been clas- Damage Level Analysis sified into seven categories: (1) Reinforced

Concrete Building, (2)Un-reinforced Brick Due to the improvement of the con-

Building, (3) Un-reinforced Clay Block struction technique in Taiwan, reinforced Tsai, Hsiao, Bruneau: Overview of building damages in 921 Chi-Chi earthquake 101 concrete structures become commonly structures are surveyed as sever damaged constructed and represent a large portion or more seriously damaged. of buildings. As the 921-earthquake damage survey indicates that the total Building Height Analysis number of the damaged reinforced The 921 earthquake created a tre- concrete buildings has reached 4,325. mendous amount of damages in both Figure 9 indicates that 15% of the RC Nantou and Taichung County. Since damaged buildings are the collapsed type, 10% of the damaged buildings are the many low-rise single family houses are tilted type, and 23% of the failures are the constructed and widely spread over these severely damaged type. The result two areas; therefore, large numbers of indicates that over 48% of the RC damaged low-rise buildings failures are recorded in this assessment. Figure 10 shows that about 75% of the damaged RC buildings moderate minor damage are the 1 to 3-story buildings, and 52% of damage 29% these damaged low-rise buildings are 23% classified as the severely damaged. It was observed that 17% of the damaged structures are the 4 to 6-story height, and the lesser damages were observed for the collapse higher buildings. Although only five 15% percent of the total damages is the high- severe rise failures, but each accident has an damage tilt immediate impact on the safety of dozens 10% 23% of residents and families. The unsatis- fied seismic performance of these 200 Fig. 9 Damaged percentage of RC modern high-rise building are unexpected structure and needs to be carefully investigated.

900

800 collapse 700 tilt

600 severe damage moderate damage 500 minor damage 400

300 Number of buildings 200

100

0 1~3F 4~6F 7~11F 12~14F 15F~

Fig. 10 Number of damaged RC structures with different number of stories 102 Earthquake Engineering and Engineering Seismology, Vol. 2, No. 1

Construction Period Analysis general, it was observed that the newly In order to find out the correlation constructed buildings suffered a fewer between the structural damage level and damages. Approximately 30% of the RC the construction period, five construction damages were constructed between 1975 periods are used in this survey: before to 1982, and approximately 20% of 1974, 1975 to 1982, 1983 to 1989, 1990 damages were constructed between 1983 to 1997, and after 1997. This break to 1989, and from 1990 to 1997. One down can reflect the level of seismic exception is observed that the number of design requirements prescribed by damaged buildings constructed during different versions of the design code. 1990 to 1997 is higher than the number Figure 11 illustrates the damage level and of damaged buildings constructed during the construction period of the damaged 1983 to 1989. In order to find out RC buildings. Since limited RC struc- reasons, further investigations on the tures were constructed prior to 1974; total number of buildings constructed in therefore, roughly 7% of the total RC these two periods of time are required. failures are constructed at that time. In

1200 minor damage

moderate damage 1000 severe damage

800 tilt collapse

600

400 Number of buildings

200

0 ~1974 1983~1989 1997~ Fig. 11 Number of damaged RC structures with respect to construction periods

Usage Analysis However, approximately half of these In Taiwan, most of the buildings are damaged residential structures are constructed for the residential purpose, described as severely damaged or worse, and a certain percentage of the buildings which has caused a significant impact on are the retail stores and the residential/ the human life. It was also observed that commercial mixed buildings. In com- 20% of the RC damages are the residen- parison, the historical buildings, the tial/commercial mixed buildings. The hospitals, and the offices are the minority. school buildings also suffered significant Figure 12 indicates that about 65% of the damages, over 60% of the failed buildings RC damages are the residential buildings, were classified as severely damaged or this high percentage of damages is related worse. Since the factory, the offices, the to their large constructed amount. hospitals, and the historical buildings are Tsai, Hsiao, Bruneau: Overview of building damages in 921 Chi-Chi earthquake 103 less common, therefore, the number of Figure 13 indicates that approximately damages reported is also lesser. 84% of the RC damaged structures are the pedestrian corridor buildings, and Vertical Configuration Analysis roughly 45% of the pedestrian corridor Due to the long raining season in Taiwan, buildings are classified as severely the Taiwanese developers commonly damaged or worse. The damage ratios of construct the buildings with the pedestri- the other vertical configurations are an corridor, and this popular style relatively lesser. Approximately 7% of becomes a local practice and is prescribed the damages are the buildings with a tall in the building codes. Thus, the pedes- floor on ground level, 6% of the damages trian corridor buildings represent a large are the buildings with an overhang on the portion of the failed structures, and 2nd floor, and 1.5% of the damages are experienced different level of damages. building with setback on the 2nd floor.

3000

2500 minor damage

moderate damage 2000 severe damage 1500 tilt

collapse 1000 Number of buildings 500

0 retail office mixed others school factory hospital historical residential government Fig. 12 Number of damaged RC structures with respect to building usage

700

600 collapse

500 tilt

severe damage 400 moderate damage

300 minor damage

Number of buildings 200

100

0 pedestrian high ground 2nd floor 2nd floor others corridor floor overhand setback Fig. 13 Number of damaged RC structures with respect to vertical configuration 104 Earthquake Engineering and Engineering Seismology, Vol. 2, No. 1

Damage of the Un-reinforced Brick Damage level of brick structures Building （ Data:4325 records) Damage Level Analysis In the early agricultural age, the un- moderate reinforced brick buildings were commonly damage 18% constructed due to its low cost and severe damage simple manufactory. Because the un- minor damage 25% reinforced brick block has a low seismic 12% resistance, 2,014 un-reinforced brick building damages were recorded during tilt this earthquake. The un-reinforced 7% brick damaged buildings represent the collapse second large group of the damaged 38% structures. Figure 14 indicates that Fig. 14 Damaged percentage of brick 1,428 damaged buildings, approximately structure 70% of the total damage, were classified as severely damaged or worse. The percentages of the damages for the also used in some rural area. Figure 15 collapsed buildings, the tilted buildings, shows that the majorities of the damaged and the severely damaged buildings are structures are either rectangular shape or 38%, 7%, and 25% respectively. The U shape floor plans. There are 1,615 poor seismic response and the brittle damaged buildings with rectangular floor failure of the brick buildings had clearly plan, which are equivalent to 84% of the illustrated during this earthquake. total failures. And the buildings with the U shape plan configurations are another Plan Configuration Analysis 10% of the failed structures. The re- The typical plan configuration for a maining 6% of the damaged building are un-reinforced brick buildings is rectan- either cross shape, H shape, or other plan gular shape, and the U shape floor plan is configurations.

700

600 collapse

500 tilt

severe damage 400 moderate damage

300 minor damage

Number of buildings 200

100

0 rectangular L U cross H others Fig. 15 Number of damaged brick structures with respect to plan configuration Tsai, Hsiao, Bruneau: Overview of building damages in 921 Chi-Chi earthquake 105

Vertical Configuration Analysis ings with pedestrian corridors. Other It was observed form Fig. 16 that the types of vertical configurations are the majorities of the damages are the build- minorities.

180

160 collapse 140 tilt 120 severe damage 100 moderate damage 80 minor damage 60 Number of buildings 40

20

0 pedestrian high 2nd floor 2nd floor others corridor ground overhand setback floor Fig. 16 Number of damaged brick structures with respect to plan configuration

Damage of the Un-reinforced Clay Damage of the Un-reinforced Clay Block Building Block Building Damage Level Analysis Damage Level Analysis In the early agricultural age, prior to In the early agricultural age, prior to the introduction of the seismic design, the the introduction of the seismic design, the un-reinforced clay block is simple for the un-reinforced clay block is simple for the manufacture and the common usage manufacture and the common usage for for one story cottage construction. one story cottage construction. Lacking Lacking the seismic design concept, these the seismic design concept, these build- buildings were constructed as a shelter ings were constructed as a shelter for the for the weather protection only. Under weather protection only. Under the the strong earthquake shaking, the severe strong earthquake shaking, the severe damages were observed. In this report, damages were observed. In this report, total 1,099 un-reinforced clay block total 1,099 un-reinforced clay block cottages were damaged, which represent cottages were damaged, which represent the third large group of the structural the third large group of the structural failures. Figure 17 indicates that over failures. Figure 17 indicates that over 75% of the failed cottages are collapsed, 75% of the failed cottages are collapsed, 5% of the damaged buildings are tilted, 5% of the damaged buildings are tilted, and 12% of the failed structures are and 12% of the failed structures are severely damaged. The poor seismic severely damaged. The poor seismic resistance of this brittle material is shown, resistance of this brittle material is shown, such that over 93% of these damaged such that over 93% of these damaged cottages are recorded as severely dam- cottages are recorded as severely dam- aged or worse. aged or worse. 106 Earthquake Engineering and Engineering Seismology, Vol. 2, No. 1

Damage level of clay block structures peak ground accelerations obtained from （ Data:1099 records) the main shock range between 0.2 and 0.3g. Several tall steel buildings have been constructed in the past decade. minor damage 2% collapse During the 921 Chi-Chi earthquake, there 76% moderate were two steel buildings, one 14-story damage (MRF) department store and one 45-story 5% severe (MRF/EBF dual system) office/hotel damage tower under construction. Before the 12% tilt earthquake, most of the steel works in 5% Fig. 17 Damaged percedntage of clay these two building have been completed block structure and the concrete slabs were poured. However, fire proofing, window walls and partitions were not installed yet and all Damage of the Structural Steel the steel beam-to-column joints were still Buildings visible following the earthquake. Noted In Taiwan, most of the steel buildings that the 14-strory building adopted the are constructed in the last ten years. typical details described above and the Steel frame structural systems are quite 45-story structure employed reduced common for buildings taller than 25 beam sections with the radius cut details. stories. In order to cost-effectively Detailed inspections conducted for these satisfy the seismic and wind forces two buildings following the earthquake requirements, moment resisting frames indicate no apparent connection damages. (MRFs) coupled with concentrically or Except the collapse of a few old light metal eccentrically braced frame (EBF) dual structures, damage to steel buildings had system are rather popular. In these steel not been reported at the time of this buildings, most of the beams are built-up writing. However, experience in other wide flange sections using the A36 or post-earthquake investigations shows A572 grade 50 steel while the columns that such damage take much longer time are built-up box sections using the A572 to discover as steel members and joints grade 50 steel. In most of the cases, are generally covered by fire proofing or moment connections were made for each architectural finishing. Further investi- beam-to-column joint. Most of the gations are required in order to confirm beam-to-column connections adopt the extent of the steel building damages bolted web and welded flanges details in in the severely shaken regions. which run off tabs and backings are left in place after the flange welds. In some of CONCLUSIONS AND these connections, the beam web was RECOMMENDATIONS welded to the shear tab. The most common welding procedures adopted in Findings from this earthquake concur the field practice are SMAW using E7016 with those from prior events, emphasizing electrode. In some cases, FCAW proce- the need for stringent enforcement of dures have been employed in the field implementation of ductile detailing using E70T-7 NR311 electrodes. requirements. All failure modes ob- In Taichung City, about 50km north- served are well known and have been west of the epicenter where the recorded extensively described in the past. In Tsai, Hsiao, Bruneau: Overview of building damages in 921 Chi-Chi earthquake 107 many instances, the contribution of non- critically reviewed to re-assess the structural partitions to seismic response national seismic risk and desired had apparently a positive impact. earthquake protection levels. This Although generally neglected by the simultaneously entails a critical reas- designer while considering lateral-load sessment of the design-spectra in resistance, the use of reinforced concrete light of the new data. as in-fills transformed the structural 3. The extensive vulnerability of the system from moment frames to shear existing building inventory, as re- walls. Preliminary results of some case vealed by this earthquake, must be studies indicate that the greatly enhanced addressed before other equally de- supplied strength have more than over- structive earthquakes strike again in come the increased demand resulting the country. A particular attention from the lower structural fundamental should be paid to buildings having period of vibration. This could explain soft stories and open front. This re- why so many buildings survived where quires the establishment of priorities, strong shaking peak ground acceleration timetable, policies and criteria for exceeded 0.3g. Unfortunately, in many seismic retrofit. It is not fiscally pos- cases, only a few such walls or partitions sible to retrofit all structures in cities existed at the ground level, which proved having extensive building inventories, fatal when ductile reinforcing details were but key post-emergency building not implemented. In the perspective of (such as hospitals and other critical the damage reported above, the following facilities) require special measures to recommendations are made for consid- ensure that they will be made avail- eration during the initial recovery period: able. 4. In light of the damages observed in 1. Given the extensive damage suffered by reinforced concrete building the school buildings, it is recom- clearly exhibit lack of ductile detailing, mended that the lateral force it is essential that steps be taken to resisting system in the direction par- ensure that only ductile details be allel to the exterior corridor for new used in all new constructions and in school buildings be carefully config- the repair of damaged structures. ured in order to avoid the occurrence Furthermore, until further research of “short column” brittle failure mode. findings become available, buildings The observed damages also suggest having “soft-story” characteristics the urgent need of retrofitting the ex- should not be allowed in new con- isting vulnerable school buildings. structions. In light of the fact that some of this knowledge is currently ACKNOWLEDGEMENTS present in the enacted codes, it seems that efforts must be directed, through The financial support provided by the education, professional development, National Science Council and the Archi- and legislation as appropriate, to en- tecture and Building Research Institute sure a better understanding and (ABRI) for the post-earthquake reconnais- enforcement of capacity design prin- sance work is very much appreciated. ciples and full implementation of During the earthquake damage survey ductile detailing. and the subsequent data reduction, the 2. Seismic zonation maps has been assistance provided by many university 108 Earthquake Engineering and Engineering Seismology, Vol. 2, No. 1 professors and graduate students na- sance report for the 921 Chi-Chi tion-wide is gratefully acknowledged. earthquake,” Architecture and Building The ABRI quickly prepared the digital Research Institute, Ministry of Interior, survey form and NCREE provided the GIS R.O.C. (in Chinese) system for the analysis of damage statis- 2. Building Technology Standards (1974, tic. Their efforts are very much 1982, 1997). Ministry of Interior, R.O.C. appreciated. 3. Lee, G.C. and Loh, C.H. (1999). “Preliminary Report From MCEER- REFERENCES NCREE Workshop on the 921 Taiwan Earthquake,” Multidisciplinary Center 1. ABRI (1999). “Preliminary reconnai s- for Earthquake Engineering Research.