A Method Of Seismic Capacity Evaluation For Bridges Based On Push-over Analysis

Bridges hold the key positions in the communication and transportation system. Once they are destroyed in earthquakes, there will be great difficulties for the emergency managements and bridges restoration. By evaluating the seismic capacity of existing bridges, the destruction process of every member of the bridge structure may be grasped wholly, and the weak positions of the structure may be found so that the bridge will be strengthened before earthquakes. Estimation of the bridges offers a basement for both the reliability analysis, damage assessment and retrofit of the bridge structures and the emergency responses after earthquake. It is one of the basic works for earthquake prevention and disaster reduction in the city areas.This dissertation focused on the push-over analysis method, the seismic damage model and the bridge damage analysis, and an evaluation method of seismic capacity of bridge structures is developed based on push-over analysis, studies presented in this thesis can be summarized as follows:1. The methods of seismic capacity evaluation for bridges are researched, most of these methods establish on the basis of empirical analysis, and cannot accomplish probably the exact estimation for seismic capacity of the structures.2. The basic principle and concepts of the push-over analysis method are systemically discussed. First of all, the distributing patterns of lateral loads are researched, and some push-over methods are provided, especially the capacity spectrum method is emphasized. Then a simplified procedure is presented to computer the stiffness of the equivalent bilinear system of a capability curve, and two simplified capacity spectrum methods, the simplified capacity spectrum method developed by Chopra and the strength coefficient reduction method, are briefly discussed. Finally numerical examples are used to demonstrate the rationality of the distributing patterns of lateral loads chosen in this study by comparing the results of push-over analysis with those of nonlinear time -history analysis.3. Seismic damage models are studied from both member level and system level. The principle is discussed for determining the grades of seismic damage of structures, and the relationship is recommended between the damage index and the seismic damage grades of the structure for bridges.4. Based on push-over analysis, a method of evaluation of seismic capacity isdeveloped for bridges. The basic principle of this method and the selection of the seismic performance parameter and the seismic damage model are researched, and the procedure for applying this evaluation method is provided.5. Two practical bridges are utilized for numerical illustration, each of them is assessed by the method presented in this thesis and the nonlinear time-history analysis procedure, and the results derived from the two methods are compared. The influences of different eminent period and site conditions are also studied from the two numerical examples.