NONLINEAR-ANALYSIS OF REINFORCED-CONCRETE FOUNDATION PLATES

A nonlinear analysis of reinforced concrete foundation plates resting upon ground, based on a finite element model, capable of simulating th e evolutive behavior up to rupture of the soil and/or of the RC plate, as well as of evaluating both the serviceability and the ultimate loa ds, is proposed. The contact problem between an RC plate and soil is s olved by a unilateral elastic-plastic Winkler type model, where the pl ate-soil bonds have tensile strength equal to zero and compressive beh avior described by a nonlinear curve, which is a function of geomechan ical properties, capable of simulating phenomena such as the softening after the pressure has reached the maximum strength, as well as the r esidual strength. Moreover, the model also takes into account friction forces which arise on the contact surface between plate and soil. The RC plate is modeled by materially nonlinear layered finite elements w here an orthotropic incrementally linear relationship and equivalent u niaxial concept are used to represent the behavior of concrete under b iaxial stresses, while a uniaxial bilinear elasto-plastic model with h ardening is employed for rebar. After cracking, the smeared orthogonal coaxial rotating crack model is adopted and tension stiffening, reduc tion in compressive strength and stiffness along the crack direction, and strain softening in compression are accounted for. The fundamental equations of the plate upon unilateral Winkler type ground are review ed and generalized. The problem is solved by adopting an incremental a pproach, and the modified Newton-Raphson iteration method is employed to ensure convergency of nonlinear solution. The proposed finite eleme nt model was tested by comparisons with another analytical model avail able in literature, showing a good agreement. Furthermore, parametric analysis was conducted in order to investigate the influence of reinfo rced concrete nonlinear behavior of friction forces between plate and soil, and of relative density or consolidation index of the soil, on t he nonlinear response of foundation plates. Copyright (C) 1996 Elsevie r Science Ltd.