Effect of foundation compliance on the earthquake stresses in typical tall buildings

Abstract

This paper shows the quantitative effect that foundation compliance has on the maximum base shear force, the maximum base moment, and the fundamental period of vibration in typical tall buildings subjected to strong-motion earthquakes. A study is made of 5, 10, and 15 story building models on the Electric Analog Computer, subjecting them to the ground accelerations of actual earthquakes. The base shear forces and base moments are measured with the foundation compliance of the models being changed through a very wide range. The properties specified for the building models are shown to be similar to the properties found in real buildings. The experimental results imply that the base shear forces and base moments in typical real buildings of 5 stories and higher during strong-motion earthquakes will be unaffected by any degree of foundation compliance that can be expected. The fundamental period of typical buildings will be increased by about 10 percent if the foundation compliance is the maximum that can be expected. It is shown, however, that even a doubling of the fundamental period does not significantly reduce the base shear forces.