UBC Theses and Dissertations
Evaluation of the effects of nonlinear soil-structure interaction on the inelastic seismic response of pile-supported bridge piers Ghalibafian, Houman
This dissertation presents an evaluation of the effects of nonlinear soil-structure interaction (SSI) on the inelastic seismic response of pile-supported bridge piers on soft soil. The research was carried out by studying the dynamic responses of prototype soil-foundation-bridge pier systems subjected to earthquake ground motions. The responses were obtained by performing nonlinear dynamic analyses using a commercial finite difference program. The nonlinearities of the soil, the structure, and the soil-structure interface were all accounted for. The numerical analysis method was carefully validated by verifying the modeling of each component of the system and by verifying the modeling of the system as a whole through analyzing an instrumented bridge pier subjected to an actual earthquake. The dynamic responses of the prototype bridge piers were computed with and without consideration of SSI (i.e. flexible-base versus fixed-base piers), and with and without consideration of the inelastic behaviour of the piers. This work explores the efficient implementation and practical application of the direct methods of SSI analysis with a system approach. It presents the seismic demands of the prototype piers and foundations, and provides a quantified picture of the effects of SSI on the ductility and the total displacement demands of the piers as functions of their natural period. This study investigates the effects of the modeling assumption of the structural elements (i.e. elastic versus inelastic behaviour) on the estimated demands, and demonstrates that SSI analyses with elastic structures cannot always provide plausible predictions of the inelastic responses. The effects of SSI on the seismic demands of the bridge piers are also studied probabilistically in order to consider the uncertainties in the system parameters and to account for the dispersions introduced by the variability of input ground motions and soil conditions. Subsequently, SSI modification factors are proposed to estimate the demands of the flexible-base piers from their corresponding fixed-base demands. The proposed method is probabilistic and quantifies the uncertainties involved in computing the modification factors. Finally, this work demonstrates the shortcomings of the nonlinear static pushover analysis for seismic demand estimation of pile-supported bridge piers when SSI is significant.
Item Citations and Data