Seismic behavior of pile-supported bridges

An analytical technique of integrating a bridge structure and its soil-foundation system into the complete global model is proposed for seismic soil-structure interaction analysis of pile-supported bridges. A simple yet realistic model for single piles and grouped piles is developed based on dynamic beam-on-nonlinear-Winkler-foundation methods. Performance of the proposed single-pile and pile-foundation model in predicting static and dynamic response to vertical and lateral loads is validated through comparisons with both experimental results and analytical results from several other investigators. Performance of the integrated soil-foundation-structure model of the entire bridge is justified through comparisons with recorded responses of a road bridge in Japan. Parametric studies are also conducted to evaluate the sensitivity of the results to uncertainties in determining system parameters.; The presented modeling technique is applied for seismic analysis of an existing truss-arch bridge spanning across the Mississippi River in southern Illinois (the Cairo Bridge). The nonlinear time-history analysis is performed using input motions obtained from ground response analysis of bedrock motions artificially generated for the Cairo area. Comparison studies of dynamic characteristics and seismic response of the bridge obtained from the integrated model and those obtained from other foundation models (the fixed-base model, and the equivalent linear and nonlinear foundation spring models) are conducted. The results promote the use of the integrated model and emphasize the importance of the soil-structure interaction in seismic analysis of pile-supported bridges. The proposed model is applied to perform seismic performance evaluation of the Cairo Bridge for different excitation intensities and to identify an appropriate retrofit strategy for the bridge. Applications of the pile group model to investigate the behavior of retrofitted foundations and to develop a simple method of evaluating foundation characteristics are presented.