Biaxially loaded concrete-encased composite columns: Design equation

The main objective of the work presented in this paper is to propose a design equation to predict and check the ultimate load capacity of short and slender concrete-encased square and rectangular composite columns under uniaxial or biaxial bending moments and axial load. The proposed design equation satisfies basic analysis and design parameters of both the American Concrete Institute (ACI) and the American Institute of Steel Construction (AISC). It is simple to use, and is compatible with the principles of equilibrium-consistent deformation and structural stability. The second order effects on slender columns are considered by incorporating a moment magnification factor similar to the one used by the ACI for reinforced concrete columns, with the appropriate adjustments for rectangular composite columns. The proposed design equation was used to predict the ultimate axial load capacity of more than 80 square and rectangular composite column specimens. The analytical results were compared with the actual test results and current ACI and AISC design methods. The accuracy obtained in predicting the ultimate axial load capacity and checking the design of a composite section under uniaxial oh biaxial bending moments and axial load confirms the validity of the proposed design equation.