Development of Compressive Fracture Energy Model for Confined Normal-Strength Concrete

The damage in reinforced concrete (RC) columns under concentric compressive load conditions tends to localize within certain regions. The softening branches of the stress -strain curves for confined concrete are gauge -length -dependent. The sizedependent confined model, when applied to numerical simulations, will bring in mesh -dependency problems. This paper develops a compressive fracture energy model for confined normal -strength concrete to predict the strain -softening behavior of RC columns. The compressive load -deflection response data of 47 normalstrength RC columns under concentric load conditions are collected to form a database. Then, an exponential function, with the best fit to the tested post -peak softening curves, is adopted to compute the compressive fracture energy. The effect of confinement on the compressive fracture energy is studied, and an empirical expression is proposed to predict the compressive fracture energy. For validation, the proposed compressive fracture energy model is introduced into a uniaxial concrete model to simulate the softening responses of RC columns under large deformations. It is found that the predicted force -displacement response without compressive fracture energy regularization is extremely brittle, which deviates significantly from the test results. While the proposed compressive fracture model provides an objective and accurate prediction of the softening responses of RC columns, it can also be used for collapse assessment of RC structures against extreme load conditions.