Effect of Soil-Foundation-Structure Interaction on Seismic Structural Response Using Dynamic Centrifuge Test

Abstract eng:
Earthquake is a life-threatening and destroying natural hazard causing loss of lives and properties, leading to significant socio-economic crisis. In recent decades, an extensive research was done for the investigation and prevention of earthquake hazards, leading to the conclusion that careful consideration of soil-foundation-structure interaction is a crucial part in seismic assessment of structural systems. However, in current practice the seismic load on structure is determined from the ground motion assuming fixed base boundary conditions. In particular, majority of the previous studies were focused on the investigation of specific responses of superstructure or foundation only. Consequently, an experimental investigation assessing the behavior of foundation and superstructure and soil-foundation-structure interaction on it is still needed for better understanding of the phenomena behind it. Therefore, an experimental program was carried out to evaluate the effect of soil-foundation-structure interaction, namely the influence of foundation rocking, on seismic response of structures. The test set-up consisted of single degree of freedom structure model, shallow foundation and medium dense subsoil deposit in centrifuge container. Main test parameters were the dynamic period of the structure model and mass of foundation; in addition, the type and level of input earthquake accelerations served as secondary parameters in order to fully assess the seismic response of the system. Accelerometers, LVDT and earth pressure sensors were installed in soil, foundation and structure for capturing the seismic responses, settlements, moment-rotations and distribution of earth pressures beneath the foundation, respectively. The superstructure response obtained from centrifuge testing were compared with fixed base case and the difference between these responses can be regarded as soil-foundation-structure interaction effect. Furthermore, the rocking of foundation is an important phenomena, dissipating energy coming from the earthquake. Accordingly, seismic response of structures sitting on lighter and heavier foundations were compared when subjected to different types of earthquakes with varying intensities. As observed from the experiment, in lower intensity earthquakes rocking is not largely influenced by its weight, however in higher intensity ones rocking is more significant in lighter foundations due to difference in ultimate moment capacity. Through LVDT, dynamic and permanent settlement of foundations were measured. Representative results are presented in this paper. To sum up, this study provides an experimental evidence on influence of rocking of shallow foundations on seismic response of structures and reduction of ductility demand of structures.

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