Comparing response spectrum analysis and time history analysis for structure–soil–structure interaction on adjacent buildings

This study investigates structure–soil–structure interaction (SSSI) effects on adjacent reinforced concrete buildings through systematic comparison of response spectrum analysis (RSA; Indian standard IS 1893:2016) and time history analysis (THA). Three-dimensional finite-element models of identical three-storey buildings separated by 50 mm were analysed in the SAP2000 software program for non-interaction analysis, soil–structure interaction (SSI) and SSSI scenarios using four Indian earthquake records. Results reveal SSSI causes force redistribution from −7% to +16% compared to SSI analysis, with maximum amplification at interface footings. Settlement increases up to 15.8% under gravity and 10.2% under seismic loading were observed. SSSI/SSI interaction ratios from THA exhibit ground motion-dependent variability (1.022 to 1.110), compared with 1.050 from RSA, indicating frequency-dependent SSSI amplification. RSA provides a reasonable envelope of SSSI force amplification but cannot capture duration-dependent settlement effects. Design recommendations include 15% force amplification for interface footings and increased seismic gaps based on soil conditions.