Stress-strain modeling of concrete columns with localized failure: An analytical study

Axially-loaded concrete columns with postpeak strain-softening suffer large inelastic deformation only in a localized failure zone, leading to nonuniform deformation along the height of the columns. Therefore, calculation of axial deformation of such a column is more complicated and involves the concept of compressive fracture energy. No model of compressive fracture energy and the relevant stress-strain relationship has been developed in the literature for fiber-reinforced polymer (FRP) confined concrete columns. Different definitions of the fracture energy have been adopted in extant literature, which has caused inconsistency and difficulty in application of the models. This analytical study involves the development of a more rational and general framework for stress-strain modeling of axially-loaded concrete columns involving failure localization. Modeling of the postpeak inelastic deformation and its associated compressive fracture energy is studied and its parameters are scrutinized and evaluated. A unified relationship is formed to relate different definitions of the fracture energy so that they can be compared with each other. The new stress-strain model shows good agreement with experimental results, and can be used for design of axially-loaded FRP-confined concrete columns.