Nonlinear static and cyclic analysis of concrete-filled steel columns

This paper presents the formulation of a one-dimensional (1D) composite frame element for the nonlinear static and cyclic analysis of concrete-filled steel (CFS) beam–columns. A two-node frame element is formulated using the force interpolation concept, and the material nonlinearity at section level is taken into account by employing a total secant stiffness and modified fibre element approach. The size effect and steel tube confinement on the concrete strength and ductility are taken into account. Further, the effect of steel tube local buckling on the member strength is addressed. Concerning geometrical nonlinearities at the element level, the equilibrium equations are satisfied for the deformed element to take account of P–ΔP–Δ effects. The formulation accuracy and efficiency of the model are verified by some numerical examples of the static and cyclic analysis of CFS members.