Cyclic Loading of Spirally Reinforced Concrete

The concept of the envelope curve which was based primarily on plain concrete is extended to confined concrete subjected to cyclic loading. Spirally confined normal weight and light weight concrete specimens were subjected to stress and strain cycling loadings at low as well as high strain rates. Analytical expressions were developed to predict the envelope curve as well as the peak strength and the corresponding strain. All analytical expressions are functions of plain concrete strength $\left(f_c^{\prime }\right)$ and the confinement index $\left(f_r\right)$ which is a measure of the effective confinement.