Nonlinear Finite Element Analysis for Cyclic Behavior of Thin-Walled Stiffened Rectangular Steel Columns with In-Filled Concrete

Abstract

The strength, ductility, and energy dissipation capacity of thin-walled, stiffened rectangular concrete-filled steel columns (thin-walled stiffened RCFT columns) subjected to cyclic loads are significantly upgraded by filling with concrete the internal hollow space of rectangular steel tube with longitudinal stiffeners and diaphragms. However, because of the accumulation of plastic strains and the high tensile stress concentration in thin-walled steel columns, metal fracture sometimes occurs before the columns develop their high strength and ductility. To elucidate the behavior of CFT columns and prevent the premature failure resulting from metal fracture, it is necessary to develop some geometrically and materially nonlinear finite element (FE) models that can accurately take into account important factors such as cyclic local buckling, stress and strain concentrations in the steel tube, confinement of the in-filled concrete, and interface action between steel tube and in-filled concrete. In this paper an accurate and yet, numerically stable FE model, which fully includes these important factors, is proposed. The accuracy of the proposed model is confirmed by comparison with the existing cyclic-loading tests on thin-walled stiffened RCFT columns. By utilizing the numerical results obtained by the proposed FE model, the upgrading mechanism and metal fracture of thin-walled stiffened RCFT columns are discussed in detail.