Probabilistic Approach to Account for Soil-Structure Interaction in Seismic Design of Building Structures

This paper proposes a novel probabilistic approach to account for soil-structure interaction (SSI) in the seismic design of building structures. In this approach, an SSI response modification factor, $R_{\mathit{SSI}}$, is introduced to capture SSI effects on the seismic performance of structures. The proposed procedure quantifies $R_{\mathit{SSI}}$ such that the probability distribution of the collapse capacity of the structure designed to account for SSI concurs with that of the structure designed using the default fixed-base provisions. The proposed approach considers prevailing uncertainties in the properties of the soil-structure system and in the seismic loading. It is employed for special steel moment frame buildings with surface foundation. The results indicate that no reduction in the design base shear is advisable for structures located on moderately soft to firm soils with shear wave velocities above $150\mathrm{m}/\mathrm{s}$. This conclusion is at odds with the current prescription of SSI provisions of seismic design code, which allow some reduction in the design base shear for such buildings. A thorough assessment of the design base shears obtained through current codified SSI provisions reveals a nonuniform risk of collapse for different soil-structure systems. In comparison, the median $R_{\mathit{SSI}}$ values computed through the proposed approach lead to a uniform risk of collapse and can be considered for the seismic design of special steel moment frames.