QUASI-KINEMATIC RESPONSE OF EMBEDDED FOUNDATIONS: EVIDENCE OF FOUNDATION MASS EFFECT FROM NUMERICAL ANALYSES AND INSTRUMENTED STRUCTURES

Abstract eng:
Experimental and theoretical studies on soil-structure interaction (SSI) have demonstrated that the seismic motion imposed at the foundation of a structure may be different from the free-field motion due to the filtering action exerted by the foundation. In the realm of the substructure approach, the above kinematic interaction effect is investigated by disregarding the foundation mass. However, in the case of massive foundations supporting high-rise and/or wide plan view buildings or large monumental structures, foundation mass may contribute to the final input motion. This paper investigates the role of the foundation mass on the filtering action of embedded foundations by means of FDM numerical analyses. New analytical expressions of quasi-kinematic interaction factors are proposed, allowing for a direct implementation in analysis or design of massive foundations. The role of salient model parameters, such as the soil-to-foundation mass density ratio, the dimensionless frequency of the input motion and the aspect ratio of the foundation, is explored. The proposed analytical model is then compared with earthquake recordings from two accelerometric stations, maintained by ITSAK, that are installed at the free-field and at the basement of a nearby instrumented building with a massive embedded foundation.

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