Some experimental evidences on dynamic soil-structure interaction

Due to dynamic soil-structure interaction (DSSI), the foundation soil experiencesan additional motion which is added to its free-field response and DSSI is ruled by the soilcompliance and by the vibration of the structure. In this framework soil non-linear behavior,as well as soil-foundation interface non-linearity, can represent crucial aspects and may governthe seismic response of the overall soil-structure system. Experimental tests on physicalmodels allow identifying the interaction mechanism and also provide a benchmark for theoreticaland/or numerical analyses. The present paper describes some experimental evidencesconcerning dynamic soil-structure interaction. Specifically, the paper deals with the results oftwo shaking table tests performed on a physical model consisting of a one-storey steel frameand a sand deposit. The steel frame (1.3 x 0.95 x 1.3 m) represents a 1:6 scaled model of aone-storey reinforced concrete building prototype. To reproduce the effects of the foundationsoil on DSSI, a special laminar box (5m x 1m x 1.2m) was placed over the table, fixed to itand then filled with dry Leighton Buzzard sand up to a depth of 90 cm. During the tests sinedwellexcitations, with different acceleration amplitudes and frequencies, were applied as inputmotions and the overall model response was monitored through a large set of accelerometersand displacement transducers. Selected experimental results are presented and discussedin the paper using both time- and frequency-domain representations of the acceleration responses.The obtained results highlight the influence of the frequency and of amplitude of theinput motion on the coupled and/or uncoupled response of the considered soil-structure system.In some cases an uplifting of the foundation was clearly observed during the tests andrepresented a natural isolation for the system; accordingly, the accelerations recorded in thesoil underneath the foundation are not completely transmitted.