Performance-based Seismic Design Criteria, Vulnerability Analysis And Application For Offshore Isolated Bridge

With the mature of isolation technology and the updates of isolation device,isolation technology has been widely applied in the field of construction. Bridge asthe lifeline of the project, and the earthquake relief was drawn high attention of thecountry. In view of this, isolation technology has been applied in the field of bridgeengineering in our country, for example, some railway bridges and offshore bridges.Isolation technology were used in Large bridges in order to minimize the disaster ofthe earthquake and the reasonably earthquake seismic standards must to be formulatedsimultaneously. At present, there were no seismic standard about offshore isolatedbridges in our country. According to the present situation, a series of studies wereundertook by introducing design philosophy of the state-based seismic in this paper,the three aspects were: the formulate of reasonably earthquake seismic standards、theanalysis on seismic vulnerability of typical bridge and the economic risk analysis ofearthquake. The main research contents in this paper are as follows:(1).The research on the standard of performance-based seismic design foroffshore isolated bridge: The offshore isolated bridges’ fortification levels werecategorized into three grades according to the bridges features; The multi-levelfortification ideas were applied into practice by defining three fortification levels;Five behavior levels were proposed and12lowest behavior objectives were built.Finally, this paper puts forward different seismic design classification for bridge withdifferent levels under all levels of ground shaking, providing a reference for thedesigner.(2). The analysis on vulnerability of a typical bridge based on seismic behavior:Established a six-span continuous girder bridge model based on behavior standardsand created a nonlinear analysis model isolated bridge.The coefficient of variationcan be obtained from the mechanical parameters of isolators by statistical analyze thetest data from manufacturers. Taking into account of the uncertainty of the groundmotion、the bridge structure and the parameters of isolators,90samples of groundmotion-structure were generated by using random Latin hypercube sampling. Takeninto consideration of the hydrodynamic pressure and wave force of offshore bridge,and analyze each sample of nonlinear dynamic time history by softwareSAP2000;The damage index of supports with different failure state was determinedand the resistance index of pier was calculated by moment-curvature analysis and thedisplacement ductility factor and bearing shear strain as discrimination index for the damage level at the same time; The fragility curves of piers and supports can bedrawn through the linear regression method and the results curves shows that bearingwas more likely to damage than the pier; The overall fragility curves of bridge systemcan be obtained by using grace method to analyze the fragility dates of piers andsupports and the curves shows that it was more reasonable to determine the seismicperformance of the bridges;(3).The analysis on Seismic financial risk of offshore isolated bridges:Considering the differences of the seismic hazard characteristics between differentregions, different shape parameter k were taken in different regions to draw seismichazard curves of the seismic intensity of8degrees in southeast coastal areas. Then theannual probability of exceedance can be calculated when the bridge encounterdifferent intensities. The seismic financial risk can be expressed in the form ofexpected annual loss by the research results on Vulnerability、risk and the economicloss ratio of isolated bridges on the basic of the framework of PerformanceEngineering (PEER)performance-based earthquake economic risk analysis.