Study Of Strength Reduction Factor For Seismic Design Of Bridge Structure Considering MDOF Effect

Strength reduction factor (SRF) is an important parameter in seismic design and a key index in determining the inelastic strength demand of structures. The reasonable selecting of SRF is significant for seismic design and improving security and economicalefficiency of engineering structure.In recent years, the study of SRF based on single degree of freedom (SDOF) has achieved remarkable progress. Related seismic codes of many countries have applied it to structural seismic design. However, because of multiple degrees of freedom (MDOF) effect, there will be an error when applying SRF basing on SDOF to MDOF structure, and the related studies mainly focus on architectural structure. So the research of SRF considering MDOF effect for bridge structure is essential.Because of the above problems, amplification factor considering MDOF effect on SRF was proposed based on theoretical analysis. Equivalent pier models of bridge were introduced for analysis and earthquake records from four soil sites were selected as input. The effect of displacement ductility, structural period and site on fixed-based amplification factor was quantitatively analyzed, as well as the SSI-based and performance-based amplification factors. A seismic design method for bridge structure was suggested, which is based on SRF considering MDOF effect. The content is as follows:1. An analytical method of SRF considering MDOF effect of bridge structure was put forward. The definition and calculation method of amplification factor were proposed. Calculation programs were compiled to analyze various equivalent pier MDOF model of bridge through the combination of finite element software and VB.2. Records from four types of soil sites were selected for nonlinear dynamic time history analysis of fixed-based model. The effect of ductility, period and the type of soil sites on amplification factor was is cussed. And a multi-parameter formula was suggested for fixed-based amplification factor.3. Another kind of models considering the effect of SSI was built. The influence of SSI on SRF was comparatively studied, and a multi-parameter formula was proposed for amplification factor considering SSI.4. Damage index was introduced to discuss the effect of cumulated damage on amplification factors. Then a multi-parameter formula was suggested for calculating damage-based amplification factor.5. Based on above achievements, a seismic design method of bridge structure was developed based on SRF including MDOF effect. The rationality and necessity were checked by two design examples.