A rational model for the stress-strain relationship of circular hoop-confined concrete

A model for predicting the stress-strain relationship of circular spirally-confined concrete is presented. The model utilizes Boussinesq's approach to calculating the beneficial effect of hoop confinement on the strength of concrete. The lateral stress distribution due to each individual hoop is computed and superposition is used to obtain the lateral stress distribution across the height of the confined zone. The strength enhancement factor k is shown to decrease with increasing diameter of the concrete section, and increase with the height of the confined concrete section. This implies that the geometry of the confined section also effects the strength enhancement factor. Once the strength of the spirally-confined concrete is computed using the strength enhancement factor, non-linear elasticity is used in conjunction with a fractional equation to predict the entire stress-strain relationship. The predictions of the model are compared with experimental results reported in the literature and the comparisons are judged to be good.