EFFECTS OF SOIL-PILE-STRUCTURE INTERACTION ON SEISMIC RESPONSE OF STRUCTURES

The interaction between soil, foundation and structure is a complex phenomenon in which several mechanisms are involved. Usually the soil structure interaction (SSI) is considered formed by two main mechanisms: the kinematic and the inertial interaction. Theoretical studies on the subject abound in the literature show that the effects of SSI on the earthquake response of structures included primarily the period elongation and the increase of equivalent viscous damping. Nonetheless, the experimental validations of such studies are still scarce. Such validations can be efficiently investigated with physical scaled model in 1-g or n-g devices. In the present paper the SSI is investigated by utilizing the set of data selected from a comprehensive experimental test program carried out on 1-g shaking table tests. The scaled model adopted in the shaking table tests comprises a group of five piles embedded in a by-layer deposit with or without a single degree of freedom connected to the piles with and without a rigid connection between them. The present work focused on the response of the scaled model when subjected to the strong motion recorded at Tolmezzo Station during the 1976 Friuli (Italy) earthquake. The experimental outcomes are compared with analytical results derived from well-established theoretical formulations existing in the literature for both the period elongation and the variation of the damping ratios. It is found that: (i) the SSI effect are, as expected, more evident in the system without connection between piles and (ii) the theoretical formula are not able to predict in an accurate manner these quantities due to the hypotheses at their base.