Seismic Vulnerability Analysis For Concrete Continuous Rigid Bridge With High Piers

Seismic fragility curve of the bridge structure reveals the relationship between the damage probability of bridges and ground motion intensity; it is very important for the response plan after the earthquake, engineering repairs, estimating economic loss and performance assessment of transport systems in the post-earthquake. Concrete continuous rigid bridge with high piers is a kind of irregular bridge, and it is widely used in some trunk lines of the earthquake-prone areas. Its seismic vulnerability study is of great significance. The following work has been done in this thesis:(1) The process of the bridge seismic vulnerability analysis is sorted and the most important steps of the analysis of seismic vulnerability such as the selection and processing of seismic waves, the damage index selection, finite element analysis methods and the plotting methods of the vulnerability curve are systematically summarizes.(2) Seismic mechanical behavior of concrete continuous rigid bridge with high piers such as higher order modes effect and dynamic axial force effect are researched. The main piers and bearings of the transition piers are selected as the most vulnerable location under the earthquake according to both the damage investigations and theoretical calculations. A curvature damage index with the dynamic axial force effect considered is proposed to assess the damage degree of main piers under earthquake.(3) The spectral acceleration and peak ground acceleration are compared as ground motion intensity indicators used in the seismic fragility analysis of the concrete continuous rigid bridge with high piers. The results show that the results with spectral acceleration as ground motion indicator have smaller discrete, so it is more suitable for the seismic fragility analysis of the structures with longer period.(4) Seismic fragility analysis of the main pier has been performed, and the seismic vulnerability curves have been plotted. The results show that:the main piers have good seismic performance; the bottoms of the piers are more vulnerable than the top under the earthquake of the longitudinal direction of the bridge, but the difference is minor; Main Pier under serious damage state will quickly go to the complete damage state as the intensity of ground motion increased; the bottoms of main piers are more vulnerable under the earthquake of the transverse direction of the bridge than the longitudinal one.(5) Displacement damage index is used to perform the seismic vulnerability analysis of the transverse piers bearings and seismic fragility curves are also plotted. The results showed that:bearings are vulnerable under the earthquake of the transverse direction of the bridge than the longitudinal one if the devices which restrain the lateral displacement of the bearings and the anti-knock block are ignored, and this difference is obvious; bearings may have been damaged before the overall structure entered the strongly nonlinear stage.(6) The method of damage degree assessment of the reinforced concrete bridge piers under earthquake as the crack width with damage index, and example has been given. The main conclusions are close to which get from a curvature index as damage index.