A NEW SEISMIC DESIGN METHOD FOR DEEPLY EMBEDDED FOUNDATIONS ACCOUNTING FOR SSI EFFECTS

Abstract eng:
A Seismic capacity design method for deeply embedded (or caisson) foundations is proposed based on 3D finite element analysis results. Emphasis is given on the influence of: (a) the kinematic constraints imposed by the superstructure, and (b) the nonlinear behaviour (due to both material and interface nonlinearities) of the foundation on the response of the SSI system. The method involves an analytical formulation of the load path at the caisson head level until complete failure. Interestingly, all load-paths display a particular “overstrength” in bearing capacity that is mobilized by the foundation, identified as the “inverted” pendulum failure mode, irrespective of the stiffness properties of the superstructure and constraints imposed at the foundation level. By exploiting this observation, the paper aims at presenting a flexible design methodology that allows the engineer to orient the seismic performance of the soil-foundation-superstructure system toward a predefined cost-effective failure mode, choosing between failure of the foundation, or failure of the above-ground structure, or a combination of both of them.

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