A constitutive model for concrete confined with carbon fiber reinforced plastics

Uni-axial compression tests on three different strengths of concrete cylinders confined with different number of layers of carbon fiber reinforced plastics (CFRP) were used to develop a constitutive model for confined concrete in the use of retrofitting and strengthening reinforced concrete structures. The peak strength of this constitutive model (named L-L model) is derived from the Mohr-Columb failure envelope theory and can be explicitly expressed as a function of the unconfined concrete strength, the lateral confining stress and the angle of internal friction of concrete. The strain at the peak strength in this model is obtained from the regression analysis of the experimental results. A second-order polynomial equation is used to present the stress-strain curve of the L-L model. In the L-L model, the lateral confinement of the concrete came from the CFRP composite material. Test results of 108 concrete cylinders confined by CFRP material were recorded to show the accuracy and effectiveness of the L-L model. For concrete confined by steel reinforcement and CFRP material, a modified L-L model was also proposed. And 18 concrete cylinders with a dimension of ø30 × 60 cm were tested to verify the accuracy of the modified L-L model.