A relative rigidity approach for design of concrete-encased composite columns

Abstract

Presented herein is a new design approach utilizing the concept of relative rigidity for the design of concrete-encased composite columns. The new approach takes into account the relative rigidity ratio (RRR) of the steel portion and the reinforced concrete (RC) portion in a composite column to calculate the axial loads shared by each of the participating materials. The proposed approach also adopts the concept of strength superposition to sum up the calculated flexural strengths of the steel and the RC portions in a composite column. By utilizing the concepts of "relative rigidity" and "strength superposition", it becomes feasible to combine the column design equations in the ACI-318 Code and the AISC-LRFD Specification to create a new design approach for composite columns. To evaluate the accuracy of this method, the column strengths predicted by the proposed approach are compared to the results calculated using a numerical fiber analysis and to the results of 28 composite columns tested by previous researchers. The comparisons show that the proposed new approach gives satisfactory predictions of the strengths of the composite columns.