Fiber-Reinforced Polymer Jacketed and Shape-Modified Compression Members: II – Model

This paper presents a confinement model for different types of fiber-reinforced polymer (FRP)-confined concrete, including bonded FRP composite jackets for square and rectangular column sections, and shape-modified circular and elliptical sections confined with post-tensioned FRP shells. The model uses a combined strength-based and strain-based method to describe the axial stress versus axial strain behavior of FRP-confined concrete. The model is based on a plasticity theory using the Willam-Warnke five-parameter concrete model and the Pantazopoulou-Mills theory of degradation of concrete elastic modulus. The Popovics concrete model for hardening behavior and the Saenz model for softening behavior are applied in the formulation. The confinement model is implemented by an incremental approach which accounts for the variable FRP confinement and dilation behavior as axial stress is increased. Medium- and large-scale tests of FRP-confined concrete compression members with bonded FRP jackets or post-tensioned FRP shells are used to verify the model. The proposed model is shown to perform better than existing models in predicting the axial strength of FRP-confined concrete for a wide range of effective confining stresses.