Effects of soil-structure interaction on distribution of seismic vulnerability in RC structures

Seismic vulnerability analysis of structures is usually accomplished without regard for soil-structure interaction (SSI). This is while accounting for SSI can result in variation of intensity and distribution of seismic vulnerabilities especially when a more rigorous analysis is implemented by nonlinear modeling of both structure and its underlying soil. This study moves in the same direction. Reinforced concrete buildings being 3, 5, 6, 8, 9 stories high, resting on soft and very soft soil types, once with moment resisting and once with concrete shear walls are considered. Twenty suits of 10 ground motions (200 records) consistent with 5 buildings with two different lateral load bearing systems on two types of soils are selected and scaled for nonlinear dynamic analysis of buildings. The analysis is once implemented for fixed-based and once for flexible-base buildings. The results show that contrary to the common belief, with a flexible-base, the location of maximum drift shifts to the first story where the most intensive vulnerability is observed. SSI changes the pattern of distribution of vulnerability especially for the beams of shear wall buildings and intensifies the seismic vulnerability on soft soils.