Seismic Vulnerability Comparative Analysis Of Isolated And Non-isolated Steel-concrete Composite Bridge

Bridge has become the most important structures in modern transportation system, it is serious consequences if bridges were damaged in the earthquake,So it is necessary to study bridges seismic fragility.At present,the bridges seismic vulnerability study is focus on non-isolated bridges and the Isolated bridges seismic fragility is lack of.There is very little comparison analysis between isolated bridges and non-isolated bridges.For decades, With the development of isolation technology, it is become more and more mature and gradually applied in bridge structures.There are more and more isolation bridges in our country.It is unknow how much improve of bridges ability to resistance earthquake after the bridges are isolated bridge.At moment,the experience of isolated bridge is very limited because of the randomness of earthquake damage.In order to know the probability of damage between isolated bridge with non-isolated bridge in each of damage state.It is necessary to compare the seismic vulnerability between isolated bridge with non-isolated bridge.In view of this, the paper mainly completed the work in the following areas:(1) Summarized the theories and methods of seismic vulnerability in our country and foreign country.And introduction the present situation of seismic vulnerability research in our country and foreign country.(2) Act the peak ground acceleration(PGA) as the earthquake intensity index and act displacement ductility factor as the bridge pier damage index and act bearing longitudinal displacement as the pot bearings damage index and act bearing shear strain as the LRB damage index.After knowing the bridge structural failure criteria,divided the damage of structure into five states(largely intact、slight damage、moderate damage、serious damage、completely destroyed) and calculate each damage index value by moment- curvature analysis.(3) Generated ground motion-site-bridge structure samples and do nonlinear dynamic time history analysis.Selecting 90 seismic waves and than generated 90 ground motion-site-bridge structure samples by using random Latin hyper-cube sampling in case ofconsidering the structural uncertainty and earthquake uncertainty.After do nonlinear dynamic time history analysis by software SAP2000 to isolated bridge and non-isolated bridge with samples that had generated and than get results.The piers and supports seismic demand of isolated bridge and non-isolated bridge can be got by linear regression.(4) The comparative analysis between isolated bridge fragility curve and non-isolated bridge fragility curve.Comparing analysis fragility curve of bridge piers and bearings as well as bridge system fragility curves between isolated bridge and non-isolated bridge than find out which structure is easier to damage.