Multiple support excitation of a bridge based on bem analysis of the subsoil-structure-interaction phenomenon

This study presents a numerical investigation of the influence of spatial variability of earthquake ground motion, site effects and Soil-Structure Interaction (SSI) phenomena on the inelastic dynamic analysis of bridge structures, considering a 2D analysis of the soil profile via Boundary Element Method (BEM). First, seismic waves propagating through complex geological profiles are modeled, so as to recover ground motion records that account for local site conditions. To that purpose, the BEM is employed for computing time-history records for four different geological profiles considering (a) canyon topography, (b) soil layering and (c) material gradient effect. Then bridge support-dependent ground motions and equivalent dynamic impedance matrices at the soil-foundation interface are generated for each support point of a bridge along the canyon. More specifically, a reinforced concrete, straight bridge with monolithic pier-deck connections is adopted as a case study. Next, a series of time history analyses considering local nonlinearities is conducted for the bridge using the Finite Element Method (FEM) taking into account subsoil-structure-interaction phenomena. To emphasize the relative importance of the topographic effects and the asynchronous motion, bridge response is determined under both synchronous and asynchronous earthquake input. In sum, the numerical results of this study show that the effect of spatially variable earthquake ground motion on the seismic response of the bridge studied depends on the interplay between the dynamic characteristics of the structure, the variability in space of soil and the properties of the incoming wavefield itself. It is also demonstrated that the detrimental or beneficial effect of spatially variable earthquake input is primarily dependent on the interplay of all the above mentioned key parameters.