Seismic Vulnerability Analysis For Bridge Structures

Bridges are the most important structures in a highway system. Owing to the neglect of bridge earthquake-resistance and therefore low design criteria, the seismic capacity of many constructed bridges in our country are weak. So the study on seismic vulnerability of bridge is necessary. While performing a seismic risk analysis, fragility curves are found to be useful tools for predicting the extent of probable damage. The fragility curve shows the possibility that the response of a structure goes beyond it's capability of resistance to damage, when the structure acted by earthquake with different intensity. To analyze bridge seismic vulnerability, this thesis has done some research as follows:(1) In this thesis, the state of the art of studies on the seismic vulnerability of bridges is reviewed. The main methods for seismic vulnerability analysis of bridges are introduced comprehensively and contrast. The construction of empirical and analytical fragility curves is presented and problems which need to be investigated further are pointed out.(2) Using peak ground acceleration (PGA) as the ground motion intensity index, it is determined to use the displacement-ductility ratio as an indicator of pier damage, combining with the research on damage state and damage index at home and abroad. And then the criterion of bridge ductility is fixed on.(3) Using traditional reliability method and numerical simulation method, the theoretical fragility curves of reinforced concrete bridge piers is established. Then the study on the curve rules and their differences is done.(4) The height of pier is changed only to analysis the effect of pier height on the fragility curve, without altering the quality of the upper structure, the cross-section form of pier, the bearing type, the pier reinforcement and the soil foundation.(5) The influence of site type on the fragility curve is carefully considered, with other conditions unchanged.