Performance-based Seismic Fragility Analysis Of Concrete Cable-stayed Bridge

The frequent seismic hazards cause the damage of the bridge structure even collapse, which arouses the attention of society in recent years. As we all know, the bridge structure is the hub and throat of transportation lifeline, especially for the important bridges with irregular shapes. Design for these bridges have beyond the scope of the traditional seismic design codes. Improving the seismic capacity of cable-stayed bridge and reducing its response caused by the earthquake is the main research contents in the bridge seismic engineering community. Besides, it is also the ultimate goal for the seismic design. Therefore, analyzing the vulnerability of the long-span cable-stayed bridge has the social and economic significance.Based on the a long-span cable-stayed bridge called Ma Sangxi bridge, the IDA and seismic fragility analysis for it in vertical and horizontal direction were carried using the finite element software named SAP2000. The main research contents of this paper are as follows:(1) The research and development of seismic fragility analysis for bridge structures were introduced thoroughly. And the establishment method of fragility curves was summarized.(2) This paper adopted two general methods which are the time-history analysis and increment dynamic analysis(IDA). The time-history analysis is more suitable for periodic structures with lower error. This method could calculate the responses(internal forces and deformations) of component and structure every moment under earthquake, which could provide references for the evaluation and maintenance of damaged structures. The incremental dynamic analysis needs larger amount of calculations and higher demand for computer. It sets a series of multiplier by the ground motion records as the load, then the IDA curves are obtained.(3) Based on the structure of the performance objectives, the calibration method for bridge component damage was discussed. And the key sectional curvature of main pylon for cable-stayed bridge was calibrated.(4) The bridge was analyzed through the time history analysis method. The main tower and key sections of the auxiliary piers curvature status changes caused by increasing ground motion intensity were studied. Then the process affected by different seismic wave, with the increase of earthquake intensity and the main tower enveloping curvature from entering minor damage to damage of the whole process were observed. Finally, the key section of main tower and auxiliary piers earthquake vulnerability curve were drew.The research indicates under the vertical seismic waves, the end section of main pylon and pier for cable-stayed bridge tower are vulnerable. Under the transverse seismic waves, piers, towers became more vulnerable at the end of the section. The bottom sections of Pier and side pylon, the top section of main pylon are still vulnerable. The bottom of mid tower connecting with the main beam tends to be completely destroyed.