Most of the current seismic design specifications are based on traditional fixed-based or simplified soil–structure interaction (SSI) approaches, which often fail to estimate the accurate response of foundation systems during seismic events, leading to overly conservative or potentially unsafe designs, especially for deep foundations on soft or highly variable soils in seismically active regions. In contrast, three-dimensional (3D) SSI risk-based analysis offers a more robust, cost-effective, and rational framework by explicitly accounting for SSI, spatial variability of soil properties, and nonlinear behavior of the system, while evaluating the likelihood of seismic demand and severity of resulting damage levels, enabling engineers to make informed, risk-based design decisions. The present study provides a 3D SSI risk-based analysis framework by conducting a comprehensive site-specific seismic risk assessment of concrete pile groups supporting highway bridges in the Charleston, South Carolina, area. The finite-element-based application ABAQUS (version 2023) was used for numerical modeling and analysis. The stress–strain behavior of the soil was modeled using the Drucker–Prager model, providing a realistic representation of the soil response. The behavior of the pile was represented by a linear elastic model. A total of 264 simulations were performed with 22 site-specific ground motions using incremental dynamic analysis. Additionally, analytical fragility curves were estimated for three damage states: slight, moderate, and collapse. Results indicate that the pile group is vulnerable to slight and moderate damage at the functional evaluation earthquake with a peak ground acceleration (PGA) of 0.11g and at the safety evaluation earthquake with a PGA of 0.22g hazard level. Results also suggest that incorporating SSI increased the PGA of the structure by approximately 36% compared to the fixed-based model, demonstrating a significant role of SSI in seismic design. These insights contribute to improved seismic design and greater resilience of foundation systems.
Bahuguna et al. (Tue,) studied this question.