Compressive Concrete Strain at Buckling of Longitudinal Reinforcement

Abstract

For the calculation of the ultimate strain of compressed concrete elements, a procedure is proposed that is based on the limit stability condition of longitudinal reinforcing bars. The analysis model is the one proposed in Papia et al. (1988), which provides the critical load of the bar with reasonable accuracy. Analogous precision in the values of the critical strain of the longitudinal reinforcement, assumed to coincide with the ultimate strain of the concrete element, is obtained here by not assuming a constant elastic modulus in the strain hardening region of the steel, and by adopting for the latter the constitutive link given in Park and Paulay (1975). The problem is reduced to the solution of an equation in the unknown strain, which depends on the slendemess of the bar of length equal to the spacing of hoops, and on the hoop stiffness. The most widely used steels are then considered with the variations in the parameters indicated above. On the basis of the results obtained, an approximate analytical expression is given of the ultimate strain to be used in practical ductility calculations. A comparison to the experimental results obtained by other authors confirms the validity of the theoretical approach proposed.