Stress–strain curve of laterally confined concrete

The objective of this study is to present a stress–strain relation of confined concrete from an empirical study of 65 columns. Experimental parameters include the strength of concrete, the volumetric ratio, strength, and confinement type of rectilinear ties, and the distribution of longitudinal bars. For the purpose of investigating confinement effects, an effectively confined distance ratio was introduced and the effects according to each parameter were analyzed. This paper provides an equation to determine the tie stress caused by lateral concrete pressure as an important index to measure confinement degree. Analyzing the experimental data by nonlinear multiple regression method, this study provides the empirical equations to determine the peak stress and its corresponding strain of confined concrete expressed by the tie stress, the effectively confined distance ratio, the strength of concrete, and the configuration of ties. Starting from the model proposed by Popovics, an empirical model for stress–strain curve of laterally confined concrete is developed by three coordinates, (fcc,εcc), (0.85fcc,ε0.85), and (0.3fcc,ε0.3). Comparison with other stress–strain curves illustrates the validity of the proposed relation.