Appraisal of reciprocal load method for reinforced concrete columns of normal and high strength concrete

Use of the reciprocal load method for evaluating the capacity of reinforced concrete (RC) columns under axial load and biaxial bending is suggested in concrete design handbooks and in commentaries to the design codes. The reciprocal load method interpolates such a capacity from the interaction diagrams obtained for the uniaxial bending cases. The adequacy of the reciprocal load method for short reinforced concrete columns of normal strength concrete has been verified in the literature. It is noted that the validity of this method for reinforced concrete columns of high strength concrete is rarely discussed, and that the characteristic of the stress-strain relation of normal strength concrete differs from that of high strength concrete. A numerical assessment of the adequacy of the reciprocal load method for short RC columns of normal and high strength concrete was presented in this study. Also, the possibility of using the reciprocal load method for slender reinforced concrete columns was investigated. The assessment was carried out by comparing the predicted capacities obtained using the reciprocal load method and those obtained by solving several nonlinear coupled governing equations that are established based on statics and considering the nonlinear stress-strain relations of concrete and steel.