A NEW DESIGN PROCEDURE FOR BRACED REINFORCED HIGH STRENGTH CONCRETE COLUMNS UNDER UNIAXIAL AND BIAXIAL COMPRESSION

This paper presents a design procedure for braced high-strength reinforced concrete columns under the action of uni-axial and biaxial loading. The paper has two phases; the first phase represents the design procedure of such columns under the action of uniaxial bending, while the second phase shows the implementation of the design procedure on the columns under biaxial bending. Due to the lack of uniformity in the conceptual treatment of the upper slenderness limit for short columns in different codes and the unclear definition of the maximum slenderness limit for slender columns as well, a new approach has been presented. Proposed expressions for the flexural rigidity have been presented based on the mode of failure of such columns. In addition, the equivalent column concept has been implemented to reduce the uni-axially loaded column to an axially loaded one, hence, the upper slenderness limit for the short column condition can be checked properly. As a consequence, a design procedure for the uniaxially loaded column is presented using a strength interaction diagram. Furthermore, the adequacy of the proposed procedure for predicting the second order effect has been verified against the experimental results. The same proposed design procedure in the first phase has been implemented in each direction of the column cross-section then the load contour equation can be used to check the strength of such column under biaxial loading. Finally, two worked examples have been presented covering different curvature modes: single and double. The proposed design procedure shows its competence against the experimental test results and well-designed columns according to the provisions of the current codes as ECCS 203-2001 and ACI 318-05 for braced systems.