VERIFICATION OF APPLICABILITY OF MACRO-ELEMENT IMPLEMENTATION IN A FINITE ELEMENT CODE FOR SHALLOW FOUNDATIONS

摘要

Practical design theory usually considers a fully uncoupled behavior of soil-foundation and superstructure and neglects the nonlinearities occurred at the foundation level. However, there is a growing awareness of considering soil-foundation plasticity in the seismic analysis and design. In this paper, the theoretical framework of a macro-element model for structures resting on shallow foundations is briefly introduced. Nonlinear constitutive law to represent the mechanical property of the soil-foundation-structure system is formulated in terms of a set of generalized force and displacement parameters. The evolution of ultimate loading surface of shallow foundations is governed by the combination of three independent nonlinear mechanisms (soil plasticization, uplift, and sliding of the footing). The mechanisms of sliding at the soil_ footing interface and of soil yielding in the vicinity of the footing are irreversible and dissipative; on the other hand, the mechanism of uplift is reversible and nondissipative. Bounding surface concept is adopted in line with the surface of ultimate loads of the foundation in the space of force parameters. The proposed macro-element model is implemented in a finite element program, SeismoStruct, which serves as a practical tool for dynamic analyses of structures with comprehensive illustration of all the nonlinearities including the one occurred at the foundation level. The validation of such macro-element implementation is carried out by comparisons with experimental results of large-scale cyclic laboratory tests within the framework of European research project TRISEE, as well as the numerical simulations conducted by a set of Matlab codes.