Impact of soil structure interaction on the seismic design of reinforced concrete buildings with underground stories

Abstract

Current building codes lack explicit recommendations on how to simulate the seismic performance of high-rise buildings with multiple underground stories. Designers are typically basing their analyses on subjective engineering judgments and experience. Some model and analyze the buildings cropped at the ground floor level, others include a partial number of basement floors, while a few include all the underground floors. This paper studies the seismic behavior of reinforced concrete buildings with multiple underground stories. It seeks to provide recommendations on the number or percentage of underground stories to be accounted for in the analysis of reinforced concrete shear wall buildings. A sensitivity analysis is conducted to evaluate the nonlinear seismic response of 5, 10 and 15 story buildings. A base-case where the buildings are modeled with a fixed condition at ground level is adopted, and then the number of basements is incrementally increased to investigate changes in performance. Two site conditions are considered in modeling subsurface soil conditions: stiff sands and loose to medium dense sands. In addition, 3 ground shaking levels are used in the study. The base shear is evaluated in order to quantify the effects of soil structure interaction on the design process. The results showed that incorporating the underground floors in the analysis models are significant for low rise stiff structures since the base shears at ground floor level increased when compared to the standard practice analysis model. For taller less rigid structures, it was found that engineers are currently overestimating when designing buildings with basements.