ON SEISMIC RETROFIT STRATEGIES OF HIGHWAY BRIDGES -EXPERIENCES LEARNED FROM CHI-CHI EARTHQUAKE

摘要

This paper simulates the performance of Yen-Feng Bridge during the September 21 Taiwan Chi-ChiEarthquake. In this earthquake, very high peak ground accelerations, near fault velocity pulses, as well aspermanent ground displacements were observed in a very wide area. However, the extent of bridgedamage is relatively minor when compared to those observed in the 1994 Northridge earthquake and 1995Kobe earthquake. Most of the bridge damage appeared to be the movement of superstructure andseparation of thermal expansion joints due to sliding or failure at the bearings, with the exception of sevenbridges collapsed due to large fault displacements directly crossed the bridges. It was also observed thatthe number of bridge column damage was surprisingly small. Since most of the bridges in the damagedarea of Chi-Chi earthquake were designed without ductile detailing, it may be in contrast to the currentseismic design concept emphasizing the steel in the plastic hinge zone of the bridge columns. Yen-FengBridge is near the epicenter of the earthquake with only moderate damage. A non-linear finite elementmodel of this bridge is first established to simulate the type of damage and verified by the observedconditions. Parametric studies of seismic performances controlled by the bearing with strong or weakstrengths are then carried out to discuss why similar bridges experienced with minor to moderate damageduring Taiwan Chi-Chi earthquake.