Experiments to study the effect of foundation rotation on the seismic building torsional, response of a reinforced concrete space frame

Results of an experimental research conducted to study the effect of foundation rotation on a two-story reinforced-concrete space frame subjected to harmonic excitations are presented. The frame torsional response is analyzed in terms of the dynamic story torsional moments estimated from test results. Since the structural responses computed with and without soil-structure interaction may be different, an unanticipated high torsional response can be obtained when the flexibility of the foundation-soil system is neglected at the building design stage. In this study, which is limited to the linear-elastic behavior, emphasis is given to study the torsional response of a reinforced concrete frame when excitation frequencies are close to the modal frequency associated with the first torsional mode of the system (buildings + soil). Results suggest that building codes should include specific provisions to anticipate high torsional response of regular buildings located at soft soils.