Seismic Performance Research For Bridge Structure Based On Pushover And Capacity Spectrum Method

China is a frequently earthquake-attacked nation. As life-line engineering projects, bridges play a paramount important function in modern society. Researches on bridge performance under earthquake are also important topics facing Chinese engineers as to improve bridge seismic performance. With the concept of performance-based design of structures, this paper studies the Pushover analysis method and the Capacity Spectrum method. In application the presented methods to real bridge engineering, the following aspects have been dealt with in detail.(1) The principles, solving procedures, as well as reasonable selection of cross-section stiffness on nonlinear analysis of reinforced concrete cross section have been studied. In order to perform nonlinear analysis of reinforced concrete cross section, a computer code is developed based on the FORTRAN language. For a real long-span bridge, the M-N-φcurves of reinforced concrete cross section are obtained, which will be employed in Pushover analysis.(2) The principle and procedures of Pushover method are introduced in detail. The factors affecting the accuracy of this method are discussed. For a real long-span bridge, the influence of lateral loads distribution on the accuracy of Pushover method is also discussed. It is found that the Pushover method can effectively predict the seismic response of bridge structures, if their responses are dominated by their first vibration mode. It is also found that the lateral load distribution, obtained from the spectrum analysis method, is an ideal distribution form, since higher order vibration mode can be considered.(3) The basic ideas of the ATC-40 Capacity Spectrum, the Chopra Improved Capacity Spectrum, as well as the Simplified Capacity Spectrum are introduced. By using the three methods based on the Pushover analysis, seismic analysis of a real long-span bridge is carried out, with results compared with those from the inelastic time history analysis. It is found that the Chopra Improved Capacity Spectrum is easy to understand and perform with relatively high accuracy, hence it is an effective inelastic analysis method to predict seismic response of bridges.(4) Based on the Pushover analysis and the Capacity Spectrum method, performance-based seismic analysis has been carried out to a real long-span bridge. It is shown that under fine anti-earthquake desired levels, performance-based seismic analysis can present more detailed performance information, which will be more helpful for engineers to understand the performance of bridges under earthquake attack.