Pakistan’s high seismic risk, accompanied by dense urbanization and active faults, necessitates accurate seismic assessment of low-rise reinforced concrete (RC) buildings, which dominate its housing stock. This study evaluates the influence of soil-structure interaction (SSI) and foundation embedment on the seismic performance of a typical low-rise RC residential building, addressing critical gaps in conventional fixed-base analyses. By quantifying SSI effects on key response parameters (accelerations and drifts), the research aims to improve seismic design practices for such structures in vulnerable regions.
A 3D time-history analysis was performed on a low-rise RC building using five spectrum-compatible artificial ground motions. Three foundation conditions were modeled: fixed-base (FF), SSI without embedment (SSIwo) and SSI with embedment (SSIem). Nonlinear soil behavior was simulated via the equivalent linear method (ELM), while radiation damping was accounted for using viscoelastic artificial boundaries. Key parameters, i.e. peak horizontal/vertical accelerations, inter-story drift ratios (IDR) and lateral displacements, were compared across models to isolate SSI and embedment effects.
SSI significantly altered the structural response. Horizontal drift response amplification factor (RAF) values were nearly identical for both SSIwo (1.07 ± 0.03) and SSIem (1.06 ± 0.02), with only a marginal increase compared to the fixed-base condition. Horizontal accelerations decreased by a response amplification factor (RAF) value of (0.76 ± 0.27) for SSIwo and (0.70 ± 0.22) for SSIem, relative to the FF model. Vertical accelerations increased by RAF (1.32 ± 0.24) for SSIwo and (1.35 ± 0.20) for SSIem. Foundation embedment reduced peak horizontal acceleration (0.93 ± 0.04) and drift (0.99 ± 0.01) in the SSIem as compared to the SSIwo case. However, it also increased peak vertical acceleration (1.03 ± 0.07), likely from greater soil-structure contact. These results suggest that SSI amplifies drift while reducing accelerations, with modest improvements from foundation embedment. The findings emphasize the importance of including SSI in seismic design.
This study enhances the understanding of soil–structure interaction (SSI) in a domain that has been largely overlooked: low-rise RC residential buildings, which represent a substantial share of Pakistan’s building stock and are highly vulnerable to seismic hazards. Unlike prior research that has concentrated on high-rise or idealized symmetric structures, this work investigates a realistic low-rise configuration with both plan and vertical irregularities. It further incorporates foundation embedment effects with vertical seismic excitation alongside horizontal motion. By employing 3D time-history analyses with layered soil profiles, nonlinear soil behavior and viscoelastic boundaries, the study provides robust evidence of how SSI and embedment alter seismic demands. The findings underscore the limitations of conventional fixed-base assumptions and offer practical insights for refining seismic codes and enhancing the resilience of residential structures in earthquake-prone regions.
