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

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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.