Seismic Response of Structure-Foundation Systems

A method for investigating the seismic response of single-story elastic structures situated on elastic foundation media which are represented by an elastic half-space is presented. The dynamic properties of the half-space are defined only for steady-state motion. This requires a solution of the equations of motion for the structure-foundation system subjected to a psuedo strong motion earthquake by a method similar to harmonic analysis, with the foundation properties redefined for each harmonic component. By inspecting the frequency dependent nature of these properties, it is found that good approximations to the seismic response of the interaction system may be obtained by taking the average values for the foundation properties in the range of the harmonics frequencies of the earthquake excitation. The results indicate that the response of the structure may be increased or decreased when compared to the response of the same structure on rigid foundation. An interpretation of this behavior is offered by means of the spectral velocity curves.