Research On Seismic Fragility Of Span Hybrid Girder Cable-stayed Bridge Under Near-fault Earthquake Motion

Bridges are one of the most crucial parts of the transportation network and studying its seismic performance during seismic events has profound theoretical and practical significance. Studies have shown that the velocity pulse effect of near-fault ground motions has a strong destructive effect on bri dge structures. Currently, the seismic design of span cable-stayed bridge and near-fault earthquake are discussed in detail by domestic and foreign scholars, however, there are few studies on the seismic resistance of span cable-stayed bridge under near-fault earthquake, particularly with regard to hybrid girder cable-stayed bridge which is different from the general engineering structure in terms of dynamic behavior. Therefore, it is necessary to carry out further research on the seismic behavior of span h ybrid girder cable-stayed bridge under near-fault earthquake in order to facilitate China’s continuous improvement of bridge seismic design objectively. In this paper, a span hybrid cable-stayed bridge is selected to study the seismic behavior under near-fault earthquake. T he main contents are as follows:(1)T he form of earthquake damage to the bridge structure, span cable-stayed bridge seismic design and near-fault earthquake are introduced an d reviewed, based on comprehensive reading and understanding of related literature home and abroad, it indicates that there is a need to study the fragility of span hybrid girder cable-stayed bridge under near-fault earthquake. Methods and research status of bridge seismic fragility analysis are described.(2)Taking a domestic span hybrid girder cable-stayed bridge as an example, the nonlinear dynamic analysis model of whole bridge is established based on Open SEES source code platform, the mechanical simulation of the bridge main components including girder, support, pillars etc., the correctness of the model are checked.(3)Based on the Open SEES nonlinear dynamic analysis model,15 near-fault ground motion records and three standardized fitting seismic waves are selected, the seismic response of the structure under each longitudinal seismic wave input is calculated through nonlinear time history response analysis and the response rules are obtained. Also the structures reasonable isolation measures under the near fault earthquake are studied.(4)T he paper describes the process of building bridge seismic fragility curve. Selecting 100 near-fault ground motion records, the earthquake-bridge samples are analyzed through nonlinear time-history method for the bridge dynamic analysis model; the peak displacement PGD is chosen as ground motion intensity parameter and the seismic fragility analysis of bearing and tower is implemented; the change of fragility curves under near-fault earthquake is studied and the influence of different isolation measures on fragility curves is discus sed.