Seismic response of RCC buildings on strap footings under structure-soil-structure interaction

The rapid population growth and limited land availability in urban areas have led to buildings being constructed closer to property lines. In such situations, eccentrically loaded footings are commonly adopted at property lines, where settlement and rotational effects become significant. To mitigate these effects, strap beams are provided, connecting the edge footings to an adjacent interior footing and thereby improving overall stability. Conventional analysis assumes column bases to be resting on unyielding support for simplicity and computational efficiency; however, deformable soil conditions necessitate soil-structure interaction (SSI) and structure-soil-structure interaction (SSSI) analyses for realistic and rational solutions. This study investigates a three-storey, 4x4 bay RCC building with eccentrically loaded footings near the property line. Rotation and settlement of footings with and without strap beams are examined under gravity and seismic loading (IS 1893:2025) using ABAQUS software. Four distinct cases are ana-lysed to evaluate the effects of strap beams and SSSI: SSI-E (SSI without strap beam), SSI-S (SSI with strap beam), SSSI-E (SSSI without strap beam), and SSSI-S (SSSI with strap beam). The comparative analysis quantifies the influence of strap beams and SSSI effects on footing rotation and settlement. The results demonstrate that strap beams significantly reduce footing rotation and settlement. Compared to SSI, SSSI leads to increased rotation and settlement at edge footings near the adjacent building. However, incorporating strap beams under SSSI conditions yields a more realistic and reliable prediction of actual footing behavior.