Seismic Performance Research Of Bridge Near Active Faults Considering SSI Effect

Along with the increasing of earthquake records near active fault, promulgating the characteristics of strong ground motion near active fault comprehensively becomes possible. Seismic motion near active fault is obviously different from that far away from the fault. Its hanging wall effect, rupture directive effect and Fling step effect are the important characteristics of ground motion near active fault. The girder-bridge is used as the structural style generally in highway bridge of our country and its seismic performance is the topic which is worth paying attention to.Referencing this article's research of《Safety evaluation Report》where bridge site in near active fault zone, three US earthquake records and three Chinese Wenchuan records conformed to the characteristic of near active fault were selected, three artificial records which according to《Safety Evaluation Report》were selected as well.Use the method of fine nonlinear time history analysis, considering the flexible effect of ground and carry on the research of highway bridge's seismic performance.The Soil-Structure-Interaction is always the difficult point of seismic study of bridge construction. The capacity spectrum method considering the SSI in FEMA440 provides an effective way to solve this problem, so the simplified calculation method of kinetic effect and foundation damping effect and the improved equivalent linearity method can be considered. In this paper, firstly a highway girder bridge model considering the foundation flexibility effect was built, and through pushover analysis the curve of base shear and displacement at the top of pier was obtained, and turn it to capacity spectrum curve. Applying the method that considering kinetic effect and foundation damping effect in FEMA440, the reduced structure seismic demand spectrum was developed, and through capacity spectrum curve and demand spectrum curve the structure seismic behavior under corresponding action of earthquake can be solved, and also compared with the nonlinear time-history analysis result. The main work of this paper is as follows:1. Collection and selection of earthquake recordThe materials of earthquake record near active fault were collected in worldwide widely, particularly the strong Wenchuan earthquake records near active fault in our country in 2008; according to the characteristic of near active fault, three American records, three Wenchuan records,and three artificial earthquake records as the demanded input of nonlinear seismic analysis were selected.2. Establishment of bridge modelConsidering the ground's flexible effect of soil-structure interaction under earthquake,using the earth springs to simulate the pile-soil interaction,and considering the power performance of supports, the finite element model of bridge was established,by finite element software SAP20003. seismic performance research to the model established(1) Nonlinear time history analysis considering flexible foundation effectsUsing Wenchuan earthquake records,the US earthquake records and the atificial earthquake records as the earthquake input, dividing into two standards which are ELI and the EL2 (respectively corresponding PGA of 0.262g and 0.351g), the time history analysis to the entire bridge was carried on. the response characteristic and security of the displacement at the top of pier,the plastic hinge at the bottom of the pier, relative deformation between pier and beam,and deformation of expansion joint was searched, the obtained results unifying《08 Guidelines》under two standards were checked. The checking calculation result indicats that the other targets can satisfy the request except some supports under two standards.(2)Pushover analysis considering three effects of SSIPushover analysis was put to the model established and the curve of base shear and displacement at the top of pier was obtained and transformed as the capacity spectrum curve;Then separately the method that considering kinetic effect and foundation damping effect in FEMA440 was used for the reduction of the structure seismic demand spectrum, and through capacity spectrum curve and demand spectrum curve,the structure seismic behavior under corresponding action of earthquake can be solved, and also compared with the nonlinear time-history analysis result. The contrast result show that FEMA440 is more advantageous to the earthquake resistance analysis.