CONSIDERING THE EFFECTS OF LOCAL UPLIFT AND SOIL ELASTIC PERFECTLY PLASTIC BEHAVIOR ON SOIL-STRUCTURE INTERACTION PROBLEM UNDER SEISMIC LOADING

Seismic response of an interacting soil-structure system has been studied by taking into account elastic perfectly plastic soil behavior and local uplift of the foundation. The structure was modeled by an equivalent flexible beam mounted on a rigid foundation that interacts with basement soil. This last was modeled by means of discrete Saint Venant's units mounted in parallel and distributed over the entire width of the foundation. Each unit consists of an elastic element which is connected in series with a plastic element having constant flowing stress. The rotation was considered to remain small. The equations governing the problem were derived by taking into account the equilibrium of the coupled soil-structure system where the mat of the structure was idealized as a single-degree-of-freedom. The obtained non-linear system of ordinary differential equations was integrated by using the Matlab command ode15s. A parametric analysis was then performed in order to evaluate the maximum response of the system under seismic loading as function of the selected soil model and key dimensionless parameters that include the slenderness ratio and the ratio of mat elastic resonance frequency to the vertical resonance frequency of foundation. The obtained results have shown that taking into account local uplift of the foundation under seismic loading yields smaller rotational angles than those obtained for a purely elastic analysis. Tip horizontal displacement can however be increased or decreased by considering the soil plasticity.