Design of biaxially loaded short composite columns of arbitrary section

In this paper, an iterative quasi-Newton procedure based on the Regula-Falsi numerical scheme is proposed for the rapid sectional analysis and design of short concrete-encased composite columns of arbitrary cross section subjected to biaxial bending. The stress resultants of the concrete are evaluated by integrating the concrete stress-strain curve over the compression zone. Exact integral expressions of the stress resultants for both polygonal and circular subsections are derived, and these are used to achieve an efficient and accurate analysis. The stress resultants of the encased structural steel and the steel reinforcing bars are obtained using the fiber element method. A particularly important feature of the present method is the use of the plastic centroidal axes of the cross section as the reference axes of loading in the iterative solution process. This ensures the convergence of the solution process for all cross-sectional conditions. Numerical examples are presented to demonstrate the validity, accuracy, and capability of the proposed method.