Seismic Performance of Highway Bridges 5555 Volume 2, Number 1, March 2000, Pp
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Earthquake EngineeringChang, Chang,and Engineering Tsai, Sung: Seismology Seismic performance of highway bridges 5555 Volume 2, Number 1, March 2000, pp. 55–77 Seismic Performance of Highway Bridges 1) 2) 3) 4) Kuo-Chun Chang Dyi-Wei Chang Meng-Hao Tsai Yu-Chi Sung 1) Professor, Department of Civil Engineering, National Taiwan University, Taipei, Taiwan 10617, R.O.C. 2) Manager, Structure Department I, China Engineering Consultants Inc., No. 185, Sec. 2, Hsin-Hai Road, Taipei, Taiwan 106, R.O.C. 3) Postdoctoral Research Fellow, Department of Civil Engineering, National Taiwan University, Taipei, Taiwan 10617, R.O.C. 4) Project Vice-Manager, Structure Department I, China Engineering Consultants Inc., No. 185, Sec. 2, Hsin-Hai Road, Taipei, Taiwan 106, R.O.C. ABSTRACT The 921 Taiwan Chi-Chi earthquake incurred tremendous disaster to the central region of the island, particularly to Taichung and Nantou counties. Most of the bridges on the provincial and county routes in Taichung, Nantou, Changhua, and Yunlin counties escaped from serious damage, while approximately 20% of them suffered minor-to-major damage. The construction completion dates of those bridges range from 1960 through 1999. Damage to these bridges include fault rupturing, collapsed spans, landslides, soil settlement, slope failures, flexural and/or shear failures, and liquefaction. This paper begins with a brief description on the evolution of seismic design code for bridges in Taiwan, followed by a general depiction of the performance of highway bridges located in the four counties during the earthquake. Several major damaged bridges with typical damage modes are illustrated and explored. Lessons learned from the field observations and suggestions made on research needs are also discussed. INTRODUCTION buildings or houses collapsed and 7,500 were damaged. About 20% of the bridge A devastating earthquake with the inventory on the provincial and county magnitude of ML = 7.3 struck the central routes in the disaster area suffered region of Taiwan in the early morning on minor-to-major damage. September 21, 1999. It was known as There are approximately 1,000 the 921 or Chi-Chi earthquake. As highway bridges spread on the provincial exhibited by the statistics [1], over 2,350 and county routes in Taichung, Nantou, people were killed, 10,000 were injured, Changhua, and Yunlin counties, which and 35 were missing in the earthquake. were the regions with major catastrophe, Moreover, approximately 10,000 especially Taichung and Nantou counties. 56 Earthquake Engineering and Engineering Seismology, Vol. 2, No. 1 Most of the bridges escaped from serious out-of-date and did not conform to the damage, while approximately 20% of progress made in bridge engineering, the them suffered minor-to-major damage Ministry of Transportation of Taiwan due to fault rupturing, collapsed spans, issued the “Design Code for Highway landslides, soil settlement, slope failures, Bridges” in 1987 [3]. Seismic resistant flexural and/or shear failures, and conception, geological characteristics of liquefaction. The construction local sites, and dynamic amplification completion dates of those bridges range factors were included in that design code from 1960 through 1999. announced in 1987. Complying with This paper begins with a brief more understanding of structural description on the evolution of seismic dynamic behavior and development on design code for bridges in Taiwan, bridge engineering techniques, a need to followed by a general depiction of the revise the seismic resistant design performance of highway bridges located approach described in the “Design Code in the four counties during the for Highway Bridges” was realized. earthquake. Several major damaged Based on the research on earthquake bridges with typical damage modes are engineer- ing in Taiwan with reference to illustrated and explored. Lessons the seismic design methodologies for learned from the field observations and bridges in Japan and United State, the suggestions made on research needs are current “Seismic Resistant Design Code also discussed. for Highway Bridges” was elaborated and announced by the Ministry of Transportation in 1995 [4]. EVOLUTION OF SEISMIC DESIGN CODES HIGHWAY BRIDGE In Taiwan, consideration of seismic PERFORMANCE demand on bridge structures may be traced back to the “Pocket-Size General Observation Engineering Handbook” issued by Taipei The primary disaster area in the 921 Branch of the Chinese Engineer Chi-Chi earthquake is composed of four Association in 1954. It was suggested counties, Taichung, Nantou, Changhua that there were two different seismic and Yunlin. According to the zones in Taiwan, corresponding to two preliminary bridge-disaster horizontal seismic design coefficients of reconnaissance reports [5,6], there are 1.0 and 1.5, respectively. In 1960, the approximately 1,000 highway bridges “Engineering Design Code for Highway spread on the main provincial and Bridges” was announced by the Ministry county routes in the disaster area. The of Transportation [2]. However, there construction completion dates of those was no specific guideline established for bridges range from 1960 through 1999, seismic design in that design code. and hence are involved in the Therefore, the suggestion provided by the evolutionary history of seismic design “Pocket- Size Engineering Handbook” was codes. As shown in Table 1, most of the adopted in that era. damaged highway bridges are located in Since the simple seismic coefficient Taichung and Nantou because of being design approach adopted in 1960s was close to the epicenter. There were 52 Chang, Chang, Tsai, Sung: Seismic performance of highway bridges 57 and 13 bridges that experienced survey. Most of those damaged highway minor-to-moderate and major damage, bridges have simply-supported, respectively, in Taichung, as well as 82 reinforced or prestressed concrete and 13 bridges, respectively, in Nantou. slab-and- girder superstructures, In fact, these two counties are the although continuous steel plate-girders disaster zones with the most casualties and long-span cable-stayed girders are during the Chi-Chi earthquake. In also included. addition, there were 17 highway bridges Table 2 lists all the major damaged in Changhua and 18 in Yunlin that highway bridges in the inventory, the suffered moderate damage, while no associated routes, and their primary severely damaged bridge was found. It damage modes. Approximate locations should be noted that the damage degree of these bridges and their proximity to the was evaluated by somewhat subjective Chelungpu fault are shown in Fig. 1, observation in the preliminary damage Table 1 An aggregation of highway bridges by located counties and damaged extent Number Total inspected Minor-to-moderate Major County bridges damaged damaged Taichung 196 52 (26.5%)* 13 (6.6%) Changhua 199 17 (8.5%) 0 Nantou 410 82 (20.0%) 13 (3.2%) Yunlin 176 18 (10.2%) 0 ‘ * ’: the percentage is based on the total inspected bridges in each county. Table 2 Major damaged highway bridge Name Route Year Span (m) Length (m) Damaged mode Shi-wei Provincial 3 1994 25 75 collapse Chang-geng local 1987 25 300 collapse Dong-feng Provincial 3 1962/1988 26 572 girder/column Pi-feng local 1991 25 300 collapse E-jian County 129 1972 11 264 collapse Wu-shi Provincial 3 1981/1983 34.7 624 collapse/column Mao-loh-shi Provincial 3 1999 40 ~ 70 500 column Ming-tsu Provincial 3 1990 25 700 collapse Ji-lu local 1999 150 300 pylon/bearing Tong-tou County 149 1980 40 160 collapse Guang-long local 1986 28 56 deck/abutment Guan-de local 1977 20 60 collapse Bei-keng County 129 1959 5.7 5.7 deck/abutment Long-an County 129 1986 35 280 column Cheng-feng County 136 1986 25.6 184 column/abutment Yan-feng Provincial 14 1984 35 455 column Pu-ji Provincial 16 1979 35 105 pier cap Hsing-shi-nan County 127 1994 50 500 column/bearing Yan-ping Provincial 3 1986 13 78 abutment Hsin-yi Provincial 21 1981 29 180 column Long-men Tou 53 1982 40 480 collapse Li-yu Tou 53 1988 39 546 bearing Ping-lin Tou 6 1969 25 500 collapse/column 58 Earthquake Engineering and Engineering Seismology, Vol. 2, No. 1 Mo-keng No.1 Provincial 16 1996 14.6 14.6 abutment Mo-keng No.2 Provincial 16 1996 40 40 abutment Da-feng Chung 105 1992 deck Fig. 1 Location of the major damaged bridges and the Chelungpu fault [5] Chang, Chang, Tsai, Sung: Seismic performance of highway bridges 55 where some peak ground accelerations (PGA) measured from ground motion sensing stations by the Central Weather fault rupture and land dislocation. The Bureau, the main national freeway distorted rail and a vertical drop of about (Chung-shan Freeway), and some provin- 3.0 meters are shown in Fig. 2(c) and Fig. cial highways are shown as well. As 2(d). This branch of the railway still observed from Table 2 and Fig. 1, most of remains closed today. the major damaged highway bridges are located on or very close to the Chelungpu fault, or are in the vicinity of the epicenter at Chichi. It was noticed that for those bridge sites where the Chelungpu fault passes through, the highway bridges experienced collapsed spans in most cases, such as the Chang-geng bridge, Pi-feng bridge, E-jian bridge, Wu-shi bridge, Ming-tsu bridge, and Tong-tou bridge. Most of these collapsed bridges were installed with unseating prevention devices. Moreover, it is seen that the PGAs measured in the east of or close to Fig. 2(a) Damage to the column of the the Chelungpu fault are in the range of Ta-chia-shi bridge 400 gal to 980 gal, and are generally larger than those in the west of it. Thus, most of the damaged highway bridges are close to or in the east of the Chelungpu fault.