Soil amplification factor for multi-story concrete buildings

Recent earthquake observations have highlighted the significant influence of Soil – Structure Interaction (SSI) on the seismic performance of reinforced concrete (RC) buildings. Flexible foundation soils alter the dynamic response of structures by increasing the fundamental period and modifying the effective damping ratio compared with fixed-base conditions. This study investigates the effect of SSI on the seismic behavior of RC buildings with basements founded on different soil types, including dense, medium, and soft soils. Three-dimensional finite element models were developed in ABAQUS using the Concrete Damage Plasticity (CDP) model for concrete and the Mohr – Coulomb model for soil. The numerical models were verified against available experimental and analytical data to ensure reliability. The results demonstrate that soil flexibility leads to a noticeable shift in natural frequencies, changes in acceleration amplification across the soil layers, and redistribution of stresses within the structure. Buildings on softer soils exhibited greater lateral displacements and reduced base shear compared with those on dense soils. The findings emphasize the importance of accounting for SSI effects in seismic design to achieve a realistic evaluation of structural performance and safety.