Analytical modelling of confined HSC columns under flexure and axial load

Existing models for high strength concrete (HSC) confined by rectilinear ties have ignored the effect of axial load eccentricity (strain gradient). An empirical stress-strain model for confined HSC developed by the writers using 108 large-scale specimens tested under uniaxial compression is further verified against recent test results and subsequently extended to include the influence of strain gradient on ductility. This was achieved by introducing the ratio of confined section depth to the neutral axis depth into the equation determining the slope of the descending branch of the stress-strain curve. The effects of the concrete compressive strength, volumetric ratio of transverse reinforcement, yield strength of ties, tie spacing and tie pattern are all explicitly accounted for. The new proposal is found to yield better agreement with experimental results than existing models for uniaxial compression.