STUDY OF EARTHQUAKE RESPONSE OF BRIDGES USING DIFFERENT TYPES OF SOIL SPRINGS

Abstract

The flexibility of the soil-foundation leads to the significant modification in whole dynamic response of the bridge substructure. Various methods are in use for considering the soil flexibility in dynamic analysis of structure. The present study is based on five types of frequency independent soil-springs. Springs used are due to Wolf, Gazetas, Bycroft-Parmelee, Bycroft-Lin and Terzaghi. The response of the structure obtained on the application of five soil springs have been compared with Beredugo-Novak spring. For the numerical study purpose three bridges situated in seismic zone V in India are selected. Two of them are simply supported and the third one is a cantilever hammer head bridge. The simply supported bridges are analyzed in both longitudinal and transverse directions whereas the cantilever bridge is analyzed in transverse direction only, using the transfer matrix approach. From the numerical results, it has been observed that Terzaghi spring is the most flexible among the five springs used in the analysis. Flexible support conditions decrease the fundamental frequency of a structure. Flexibility of the soil springs reduces the shear force and bending moment, but it increases the deflection at top. Equivalent damping varies with frequency. Seismic. coefficient and acceleration are not constant through out the height of the structure.