Effect of soil and foundation stiffness on the seismic behavior of mid-rise RC buildings

For a more realistic approach, the effect of soil-structure interaction on the behavior of reinforced concrete buildings should not be neglected. In this study, nonlinear static pushover analysis is applied to the twenty-five 4-storey reinforced concrete frame buildings with different foundation types (raft and continuous foundation) and soils having different bearing coefficients. The foundation type and foundation sections were changed by keeping the reinforced concrete frame system constant. The stiffnesses of the models are observed to be significantly affected by the foundation dimensions and the soil bearing coefficient. Period increase up to 44% is observed per fixed base case. The lateral strength and damage distribution of buildings, seems to be less affected by foundation and soil conditions. The shear force in smaller columns becomes 8% to 24% more than anticipated by a fixed base model. The building displacement demand values with significant changes according to the fixed base case are observed. Amplifications around 40% seems to be possible per fixed base case. Additionally, an equation is established trying to answer the question of “How stiff the foundation should be for a given soil condition?”. If the allowable displacement increase per fixed base case and soil stiffness is known, dimensions of structural members of the foundation may be decided by given equation.