Soil–Structure Interaction in Seismic Design Code: Risk-Based Evaluation

This paper puts forward a risk-based approach to investigate the consequences of practicing soil–structure interaction (SSI) provisions of modern seismic design codes. The proposed approach computes the probability that practicing SSI provisions increases or reduces the monetary loss due to structural and nonstructural damage compared with fixed-base systems. This in turn determines the probability that the SSI provisions yield unsafe, optimal, or overly conservative designs based on the premise that alternative design solutions suggested by the code must lead to the same level of risk. The proposed approach accounts for prevailing uncertainties in the ground motion and in the properties of the soil–structure system. The analyses cover a wide range of structures with various properties on different soil types. It is concluded that the soil type and the flexibility of the structure are more influential than other properties of soil–structure systems on the studied probabilities. It is also concluded that practicing SSI provisions is likely to result in optimal designs for buildings on moderately soft soils. However, as the soil becomes softer or the structure becomes stiffer, the chance that practicing these provisions yields either unsafe or uneconomic designs increases.