Nonlinear Analysis of Building Structures Resting on Soft Soil Considering Soil–Structure Interaction and Structure–Soil–Structure Interaction

Over the decades, various researchers have suggested that considering a structure fixed at the base predicts erroneous results in estimating the seismic response of soil–structure systems due to earthquake motions, potentially leading to faulty system designs. The magnitude of these errors may be attributed to variables such as soil type and modeling techniques. Improper modeling techniques are major factors contributing to erroneous responses of soil–structure systems. Selecting and implementing wave-transmitting boundaries are challenging tasks in finite element modeling techniques to simulate the infinite extent of soil and account for radiation damping in soil for solving soil–structure interaction (SSI) problems. This paper studies the effects of SSI and soil–structure–soil interaction (SSSI) on a four-storey steel structure with a raft foundation resting on soft semi-infinite soil. Here, the infinite domain of soil is simulated through an infinite element as a boundary condition after validating the modeling technique with experimental results found in the literature. The new modeling method, using ABAQUS, effectively handles soil–structure interaction (SSI) problems with acceptable accuracy, facilitating simulation of both SSI and SSSI scenarios for a four-storey steel structure. Using an infinite element (CIN3D8) in finite element method (FEM) analysis proves viable for SSI and SSSI simulations. Results show reduced storey drifts but varied floor shear forces across soil types (S1: a uniform soil system and S2: a two-layer soil system) compared to fixed base conditions. In SSSI analysis, higher storey levels experience increased drifts, while lower levels have decreased drifts compared to SSI scenarios. Base shear forces are consistently higher in SSSI analysis across all soil profiles, resulting in overall higher total floor displacements in both SSI and SSSI conditions compared to fixed base conditions.