臺灣位處於地震頻繁之地區，國內對於結構物耐震能力需求極為重要，尤其土木建築物使用年限通常較久，所以對其進行耐震評估也是結構生命週其中相當重要的養護工作，然而臺灣國內橋梁高達數萬座，其中不乏許多歷經地震損害後修復完工後繼續使用或因地形因素，導致橋梁結構呈不規則，本研究選取一座現存橋梁，作為研究實例，將地震損傷量化後進行易損性分析，針對其結果探討不規則橋梁因不同觀測點的差異性。研究結果顯示，對於不規則橋梁之耐震分析，在考慮結構能量消散情況下觀測點相異有著極大的差異性，無法以整體最大位移代表橋梁之耐震能力，需謹慎選擇觀測點並考量構件之能量消散。

Taiwan is located on a high seismic hazard area. Seismic demand often plays a very important role in structural analysis. In particular, the life cycle for an infrastructure is considerably long. Therefore, bridge safety evaluation against seismic excitations becomes the goal of the current study. There are many bridges in Taiwan which contains plenty of irregular bridges which is mainly caused by restoration or retrofitting. In view of uncertainties is inevitable in seismic evaluation, this study proposes to use fragility analysis to consider the aforementioned randomness, in which a damage index, consisting of energy dissipation and displacement, is adopted to measure the structural performance. To demonstrate the proposal method, a numerical study which is an actual bridge, is used. Based on the simulation results, some important conclusions are found: For an irregular bridge, variability in seismic damages at different locations are found to be significant. The maximum displacement alone is not able to provide enough information for seismic damage. Careful selection of the observation location and consideration of the energy dissipation are suggested for bridge seismic assessment.

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