Nonlinear Analysis of Square CFT Columns with Fiber Beam/Column Element

Abstract

The use of concrete filled steel tubes (CFT columns) in seismically active regions is becoming more common and widespread due to numerous advantages they offer over steel and reinforced concrete columns, such as increased ductility, buckling delay and good cyclic performance. Since the behavior of CFT columns is highly nonlinear, a numerical model needs to consider different nonlinear effects. The model proposed in this paper adopts the nonlinear force based beam/column element that takes into account the nonlinear behavior of steel and concrete, confinement effects and geometrical nonlinearities. Through a parametric study, different material models for steel and concrete, widely available in commercial software programs, are evaluated and the constitutive model parameters that best approximate the behavior of CFT columns under static loading conditions are determined. This numerical model is then validated through a comparison with a number of experimental tests from the literature. Different types of loading (cyclic static and dynamic), types of structures with different slenderness of tested specimens and B/t ratio are considered. In addition, limitations of the proposed fiber element model for modelling CFT columns are emphasized.