On Sept. 21, 1999, at 1:47 a.m. (local time), central Taiwan experienced a destructive earthquake. As a result of this earthquake, more than 2,400 lives were lost, and more than 10,000 people were injured, according to the Taiwanese official report. Approximately 10,000 buildings and homes collapsed, and about 7,000 were severely damaged.
Highway bridges, including those constructed under modern seismic design codes, were severe damaged. According to the Taiwanese Highway Bureau's preliminary report, at least nine bridges were severely damaged, including three bridges that were under construction. Five bridges collapsed due to fault rupture, and seven bridges were moderately damaged.
This earthquake, called the Chi-chi Earthquake, measured 7.6 on the moment magnitude (Mw) scale. Moment magnitude is based on the concept of seismic movement, and although it is more difficult to compute than other magnitude scales, it is more uniformly applicable to all sizes of earthquakes. In particular, for very large earthquakes, moment magnitude gives the most reliable estimate of earthquake size. However, all magnitude scales should yield approximately the same value for any given earthquake.
The U.S. Federal Highway Administration (FHWA) and the Ministry of Transportation and Communication (MOTC) of Taiwan formed an investigative team to evaluate Taiwanese highway bridge performance under the Chi-chi earthquake. The team members came from FHWA, the Taiwanese Highway Bureau (THB), and the National Expressway Engineering Bureau (NEEB) of MOTC. The team visited 10 bridge sites, including two NEEB bridge sites and eight THB bridge sites.
This paper presents the preliminary findings and lessons learned from the team's investigation, which was conducted Nov. 15-17, 1999.
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