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 sh ort and slender concrete-encased square and rectangular composite colu mns under uniaxial or biaxial bending moments and axial load. The prop osed 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 structur al stability. The second order effects on slender columns are consider ed by incorporating a moment magnification factor similar to the one u sed by the ACI for reinforced concrete columns, with the appropriate a djustments for rectangular composite columns. The proposed design equa tion 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 un der uniaxial oh biaxial bending moments and axial load confirms the va lidity of the proposed design equation.