Detailed investigation of demaged briges due to Chi-Chi earthquake.

本研究以集集地震中受损桥梁为研究对象，进行以下几项数值分析：1）集集大桥遭受严重的破坏，这在此类桥梁的抗震设计中是不可接受的。如墩底、主塔、主梁均产生塑性铰，锚固段有斜拉索被拔出等。结合现场实测结果和台湾桥梁管理部门提供的详细图纸，采用框架模型对该桥的破坏机理进行了分析。分析结果表明，拉索锚固力不足是导致拉索拔出的主要原因。2）对1999年台湾集集地震中受损的长庚大桥进行了地震损伤分析。这座桥遭受了特殊的破坏，即使主梁没有显示出任何断层位移，也有两个主梁掉到了地上。坠落的原因被认为是大梁在地震荷载下碰撞时的水平位移。根据现场实测结果和大桥管理人员提供的详图进行非线性动力分析，确认了地震荷载作用下主梁被推向胸墙并从后方碰撞，导致桥墩坠落。

Several following numerical analyses were performed which were modeled dameged bridges due to Chi-Chi earthquake.1)Ji-Ji-Da Bridge suffered problematic damage which is unaccetable in terms of seismic design of this type of bridge. For example, Plastic hinges were produced not only at the pier bottom but also in the main pylon and main girder, and one diagonal cable pulled out from the anchorage section. The damage mechanism of this bridge was analyzed using a frame model, with the incorporation of field measurement results and detailed drawings obtained from bridge administrators in Taiwan. It was found that the cause of cable pullout was the unsufficient anchoring strength.2)Seismic damage analysis was conducted on the Chang-Geng Bridge damaged in the 1999 Chi-Chi Earthquake in Taiwan. This bridge sustained peculiar damage that two girders fell to the ground even though the girder did not show any fault displacement. The cause of the fall was assumed to be the horizontal displacement of the girders when they collided under seismic loading. Through nonlinear dynamic analysis using field measurement results and detailed drawing obtained from the administrator of the bridge, it was confirmed that the girders were pushed toward the parapet and collied from the back under seismic loading, resulting in the fall from the piers.