Confinement model for FRP-wrapped circular columns when the wraps are subjected to damage

Abstract

Fiber-reinforced polymer (FRP) wrapped concrete columns are vulnerable to accidental damage or vandalism, which may cause physical cuts or tearing of the jacket, thereby compromising the confined strength and ductility of the column. This paper aims at providing a simple tool to reassess the strength under a given level of damage. Finite element (FE) models were developed to examine a variety of cuts in the FRP jacket and develop a confinement model including the damage effects. After validation with 37 experimental tests from literature, the FE model was used in a comprehensive parametric analysis, examining different geometric and material variables, namely: cut orientation (longitudinal or circumferential); cut length and location, diameter-to-jacket thickness ratio, multiple cuts, concrete strength, and FRP elastic modulus. Results of the numerical models were analyzed using multiple nonlinear regression (MNR). New equations were developed to predict the reduction in axial strength and corresponding strain at ultimate. Reduction factors have been proposed, which are then easily implemented in commonly used confinement models in design guides such as ACI 440.2R.