Seismic Fragility Analysis Of Curved Continuous Girder Bridge

Our country is located in the place between the circum-Pacific seismic belt and the Eurasian seismic belt, and the “earthquake environment” is very harsh. The importance of the bridge, as the lifeline engineering, goes without saying. Because of the unique advantages, curved continuous girder bridges are increasingly widely applied in city overpass, highway ramp and so on. However, the study about the seismic capacity assessment of curved continuous girder bridges is limited. Seismic vulnerability analysis can get the probability of the structural response demand beyond the structural resistance when the intensity of earthquake is certain. Besides, it can also get the vulnerability curves of the four different damage states. So, it’s necessary to use this effective approach to evaluate the seismic capacity of curve continuous beam bridge. In this paper, a systematically vulnerability analysis about a practical curve continuous girder bridge was made on the most vulnerable parts, such as bearings and piers. Overall the major contents are as follows:(1) On the basis of summarizing bridges’ status quo about vulnerability analysis, this paper described its role in structural seismic performance evaluation. Then the method of probability seismic demand analysis and the principle determining the damage index were stated. And the procedure of the seismic vulnerability analysis of curved bridge was confirmed.(2) The curvature ductility ratio was taken as the damage index of the piers, and the displacement ductility ratio was used as the damage index of the bearings. The moment-curvature analysis of the piers’ plastic hinge section was made with the XTRACT, and calculated the damage index of each pier. Besides, the four limit damage state of the bearing and pier were respectively defined.(3) Considering the uncertainty of the compressive strength of concrete and the yield strength and ultimate strength of steel, the bridge samples was got by random sampling. Meanwhile, taking the PGA as the ground motion parameter, the 10 ground motion records were adjusted to different levels according to the IDA. Then, the 100 bridge-ground motion samples were formed randomly.(4) Based on the SAP2000 software platform, the elastic-plastic time history analysis of the 100 bridge-ground motion samples were conducted. As for the 100 sample points, logarithm linear regression analysis could give a better processing. The Vulnerability curve of the bearings and piers could be formed with the traditional reliability method. After that, the paper gave a detailed comparative analysis of the vulnerability curve of bearings and piers, and confirmed the main factors affecting the vulnerability curve.(5) The paper also considered the influence of the direction, and determined the most negative ground motion direction by the comparison of the vulnerability curve about the bearing, pier and the bridge system. What’s more, the effect of the use of isolation bearing in the curved bridge was verified.