Performance-based Seismic Fragility Analysis Of RC Bridges

Most bridge seismic fragility analysis is based on the damage states of the bridges, performance-based seismic fragility analysis directly gives the failure probability of the structures corresponding to different functional levels, therefore performance-based fragility analysis has more practical value. So far, there are no performance-based structural vulnerability analyses in the field of bridges, the main difficulty lies in the definition of the quantitative performance metrics appropriate to the structure performance levels. In this paper, based on summarizing the relevant research both at home and abroad, on the properties of reinforced concrete bridge based on vulnerability analysis method were studied. The main research contents include:(1)Four performance levels of RC (reinforced concrete) bridges are defined based on the limit states of the structure. Taking the drift rate of the pier as quantitative performance metric, a seismic vulnerability analysis method based on the performance of RC bridges is proposed.(2)Taking a four-span continuous RC bridge as an example, using OpenSees to build finite element models of the structures and considering the randomness of ground motion, performed nonlinear dynamic time history analysis based on IDA(incremental dynamic analysis). Finally, based on the method proposed, performance-based structural vulnerability analyses are performed on the middle piers of the non-isolated bridge and the isolated bridge, and get fragility curves. Fragility curves of the middle piers of the non-isolated bridge and the isolated bridge are compared, and then analyze the impact of isolation bearing on the pier vulnerability.(3)Made a simple introduction of Pushover method and its principle, emphasize the Pushover method of lateral force distribution mode and the method that transform multi degree of freedom system to a single degree of freedom system.Then, Introduces the capacity spectrum method based on the Pushover, including detailed introduces several R-μ-T relationship which is very important in the process of formation of inelastic demand spectrum and t some of the ways to determine the target displacement. Finally, based on the above theory, a bridge pier vulnerability analysis method based on Pushover is proposed.(4)Using the performance levels proposed in this paper, vulnerability analysis based on Pushover was carried out on the bridge, compared the analysis results with the results of dynamic time history method, testing the effectiveness of the bridge vulnerability analysis method based on Pushover.