Stress—strain behaviour of laterally confined concrete columns

An empirical formulation of the stress–strain relationship of laterally confined concrete columns is derived from axial compression tests on short concrete columns, reinforced only with lateral layers of orthogonally placed HTS (high–tensile steel) bolts. Several factors considered likely to influence the behaviour of the columns were studied. It was found that the longitudinal tangent stiffnesses of the columns degraded as the columns were loaded, with the relationship between stiffness degradation and axial strain of a bilinear form, with gradients governed by the type of confinement. Empirical relationships were developed which allowed the stress–strain relationship for each column to be predicted. For the set of data analysed, the predicted curves fitted well with the experimental curves. The two–stage stiffness degradation in the columns demonstrated a general two–stage deformation in the concrete—the first at low loads when the concrete was relatively intact, and the second at higher loads and up to ultimate, when the concrete had suffered extensive internal damage with confinement from mobilization of the lateral reinforcement.