Method For The Inelastic Seismic Response Analysis Of Bridges Based On Strength Reduction Factor Spectrum

In performance-based seismic design theory of bridges, it's very important to find a simple and relatively accurate method to analyze inelastic seismic responses of structures. Based on strength reduction factor spectra and pushover analysis, a relative simple nonlinear method for seismic analysis of regular and irregular bridges is presented in this dissertation. The studies reported in the dissertation are summarized as follows:1. The strength reduction factor spectra proposed by others are compared. The influences of some factors on strength reduction factor are discussed, including natural period, damping ratio and site conditions.2. A simplified method for determining maximum inelastic response of regular bridges directly by elastic response spectra analysis and strength reduction factor spectra is proposed. In the proposed method, regular bridges are transformed to equivalent SDOF systems directly, and the force-displacement relationship of the SDOF system is constructed using moment-curvature analysis of the plastic region section of bridge piers. The soil-foundation interaction is considered in the method. The maximum pier top displacement of a equal-span continuing bridge which can be simplified to SDOF subjected to rare earthquakes are calculated using the proposed simplified method and nonlinear time history analysis method, and results show that the proposed method is effective.3. A simplified method for determining maximum inelastic response of irregular bridges using pushover analysis and strength reduction factor spectra is proposed. In the proposed method, irregular bridges are transformed to equivalent SDOF systems by pushover procedure firstly, then the inelastic seismic demand of the equivalent SDOF system is determined by elastic response spectra analysis and strength reduction factor spectra. Nonlinear response of a continuous girder bridge which can not be simplified to SDOF subjected to rare earthquakes is calculated using the proposed simplified method and nonlinear time history analysis method, and results show that the proposed method is effective.