Dilation behavior of normal strength concrete confined by FRP wire jackets

The introduction of confining pressure is an effective method to improve both ductility and strength of concrete. To confine concrete, recently, fiber reinforced polymer (FRP) wire has been employed because of several advantages, such as corrosion resistance, cost-effectiveness, and the ability to control the tightness of jackets during the installation process. In addition to experimental researches, confinement models need to be studied; in which, a factor affects directly to the accuracy of the models is dilation. This study aimed to investigate dilation behaviors and the effects of FRP wire jackets confinement on concrete. For this purpose, the uniaxial compression tests were conducted on twelve specimens by changing the number of FRP wire layers and the compressive strength of concrete. Experimental results illustrated that the FRP wire jackets provided higher confinement effects on concrete than FRP sheets. The dilation developed through three stages of compressive behaviors of confined concrete, i.e., the elastic, hardening, and damaged stages. Moreover, the test results indicated that the effects of the stiffness ratio for FRP wire jackets were different from these for FRP sheets. Additionally, to estimate the lateral-axial strain relation of concrete confined by FRP wire jackets, a dilation model was developed on the basis of a secant dilation ratio, which is the percentage of the lateral strain to axial strain. The experimental results and the model estimation demonstrated in a good agreement.