VARIATION OF SEISMIC RESPONSE OF MID-RISE RC BUILDINGS DUE TO SOIL STRUCTURE INTERACTION EFFECTS

The seismic design of RC buildings requires determining the expected base shear, lateral drift at each story level and internal forces of the structural elements. In the analysis, it is common for the structural engineers to consider a fixed base structure which means that the foundations and the underlying soil are assumed to be infinitely rigid. This assumption is not proper since the underlying soil in the near field often consists of soft soil layers that possess different properties and may behave nonlinearly leading to drastic variation of the seismic motion before hitting the structure foundation. In addition, the mutual interaction between the structure, its foundation and the underlying soil during the vibrations can substantially alter the structure response. This response variation depends on the structure characteristics, the soil properties and the nature of the seismic excitation. Consequently, an accurate assessment of inertial forces and displacements in structures requires a rational treatment of soil structure interaction (SSI) effects.