KINEMATIC SOIL-STRUCTURE INTERACTION FOR LONG-SPAN CABLE-SUPPORTED BRIDGES

A general procedure is presented to study the dynamic soil-structure i nteraction effects on the response of long-span suspension and cable-s tayed bridges subjected to spatially varying ground motion at the supp orting foundations. The foundation system is represented by multiple e mbedded cassion foundations and the frequency-dependent impedance matr ix for the multiple foundations system takes into account also the cro ss-interaction among adjacent foundations through the soil. To illustr ate the potential implementation of the analysis, a numerical example is presented in which the dynamic response of the Vincent-Thomas suspe nsion bridge (Los Angeles, CA) subjected to the 1987 Whittier earthqua ke is investigated. Although both kinematic and inertial effects are i ncluded in the general procedure, only the kinematic effects of the so il-structure interaction are considered in the analysis of the test ca se. The results show the importance of the kinematic soil-foundation i nteraction on the structural response. These effects are related to th e type, i.e. SH-, SV-, P- or Rayleigh waves and to the inclination of the seismic wave excitation. Moreover, rocking components of the found ation motion are emphasized by the embedment of the foundation system and greatly alter the structural response.