Experimental Investigation of Effect of Soil Structure Interaction on Buildings

Abstract

In the conventional analysis and design, buildings are generally considered to be fixed at their bases, but in actual practice, the support condition depends on the type of soil on which it is founded. The flexibility of the soil medium allows the movement of soil and foundation, which decreases in the overall stiffness of building frames and results in a subsequent increase in natural periods of the system. Thus, the response of the entire structure is altered. However, when the foundation of the structure rests on hard strata, these movements due to seismic activities become insignificant. Nonetheless, hard strata are not always available at a reasonable depth. Thus, the construction of structures on soft soil becomes inevitable, and ground motions due to seismic activities modify the behavior of a structure. The structure resting on soft soil becomes more flexible and has a longer time period as compared to the same structure resting on hard strata. This effect of soil and structure on each other is called Soil-structure Interaction (SSI). In this paper, SSI is studied for a three-story scaled-down model on soft soil block of various depths. The experimentation work was conducted on a shake table, and a ground motion was applied in terms of harmonic excitation. The story displacements of structure with soil block (flexible base) are compared with story displacements of the structure without soil block (fixed base).