The effect of soil–structure interaction on damage index of buildings

The effect of Soil–Structure Interaction (SSI) on Park and Ang Damage Index in a Bilinear-SDOF model is investigated under seismic loading. This is done through an extensive parametric study. Two non-dimensional parameters are used as the key parameters which control the severity of SSI: (1) a non-dimensional frequency as the structure-to-soil stiffness ratio index and (2) the aspect ratio of the structure. The soil beneath the structure is considered as a homogeneous elastic half space and is modeled using the concept of Cone Models. The system is then subjected to three different earthquake ground motions as the representative motions recorded on different soil conditions. The analysis is done directly in time domain using direct step-by-step integration method. The results are presented in the form of damage spectra for a wide range of key parameter variations. It is observed that generally SSI increases the damage index before a threshold period which is closely related to the predominant period of the ground motion. It means that the conventional fixed-base model underestimates the damages sustained by buildings having periods less than this threshold period. In particular, the SSI substantially increases the damage index of short-period buildings located on soft soils. It is also observed that increasing the aspect ratio of the structure increases this effect. However, the trend is reversed after the threshold period.