Experimental and numerical analysis of soil motions caused by free vibrations of a building model

Effects of vibrating structure on the free-field motion are presented through a field experiment at the Euro-Seistest and a corresponding numerical simulation. Ground motion has been recorded by a dense temporary three-component (3C), two-dimensional (2D) seismic network installed at increasing distances from a model building forced into vibration by pull-out tests. The building is a five-story RC structure at a one-third scale, resting on the soil through surface square footing. A traction force, F-0, applied at the building top and suddenly released forced it into vibrations. Two sequences of a pull-out test (POT) have been performed, each one made of two vibration tests in the two horizontal directions of the building (longitudinal and transverse). The experimental data are then compared to the results of the numerical simulation. The soil-structure system is modeled by a three degree of freedom (3DOF) system. The soil-structure interaction (SSI) is accounted for through the help of impedance functions, and the motion induced by POT are estimated together with the base force and moment developed at the soil-structure interface. By representing the base forces by surface point seismic sources, the induced wavefield radiated in the surrounding free field is then computed by numerical Green's functions. The results presented here do validate the numerical computation method, which gave distant motions in close relation with the experimental data, from a qualitative and quantitative point of view. The spectral analysis does also exhibit surface waves trapped in the topmost layer. Results confirm the significant contamination of ground motion due to building vibration.