On the Seismic Design of Ductile RC Buildings Considering Soil-Structure Interaction Effects

Abstract

Soil-structure interaction (SSI) may condition the seismic performance of buildings in different ways. Previous studies show that SSI effects on structural response parameters may be either beneficial or detrimental, depending on specific characteristics of the structure, the soil, and the demand. Despite the great efforts put over the last decades into developing performance-based seismic design (PBSD) practices, engineers still rely on prescriptive code requirements for design purposes. Considering SSI effects, ASCE-7, for example, allows determining a reduced design-shear demand ($\tilde{V }$) that obeys the interacting soil-structure system behavior. It is calculated by reducing the conventional shear demand, $V$, by a variation $\Delta V$, according to $\tilde{V }=V-\Delta V\ge \alpha V$; where $\alpha$ controls the magnitude of the reduced demand. $\alpha$ depends on the response modification factor ($R$), resulting in a more significant reduction for structures presenting limited inelastic responses than for more ductile ones. This study investigates the behavior of $\alpha$ in ductile RC buildings while exposing the need to reflect not only the beneficial effects of SSI but the detrimental ones in determining the design-shear demand. To this end, 729 3D soil-structure systems (SSS) with different plan aspect ratios, slenderness ratios, and soil shear wave velocities were designed and analyzed using OpenSeesPy. Linear and nonlinear analysis procedures (APs) recommended at ASCE-41 are used to evaluate the response of the designed buildings. Based on these responses, a machine-learning (ML) technique is used to generate an estimation model for $\alpha$, showing that the slenderness ratio, ${\lambda }_{str}$, the fixed-base period, $T$, and the wave parameter, ${\sigma }_{SSI}$ are key parameters to explain up to 90% of its variation.