Integrating soil-structure interaction along basement walls in structural analysis programs

Recent field and laboratory studies have shown that the effect of Soil-Structure Interaction (SSI) can be not conservative to a structure if not considered. In evaluating the SSI effect along basement walls on the seismic response of moment-resisting frame buildings with multiple basements, a parametric study is performed on multiple story buildings resting on flexible grounds. The number of basements is varied and UBC suggested site conditions are considered. Comparing results obtained by Plaxis that considers SSI along basement walls and Robot that consider it only at foundation level (by mean of springs), one can observe that SSI along basement walls greatly affects the seismic performance of buildings subjected to ground movements. Results obtained from Plaxs and integrated into the Robot model by means of springs along basement walls with specific extracted stiffness values proved the accuracy of the method. These stiffness values are calculated using force-displacement relationships, and charts that relate stiffness to depth of basements are generated.