Effect of Column Parameters on FRP-Confined Concrete

Confinement effectiveness of fiber reinforced plastic (FRP) jackets (shells) in concrete columns depends on several parameters, including concrete strength, types of fibers and resin, fiber volume and fiber orientation in the jacket, jacket thickness, shape of cross section, length-to-diameter (slenderness) ratio of the column, and the interface bond between the core and the jacket. In this paper effects of shape, length, and bond on FRP-confined concrete are studied. Square sections are shown to be less effective in confining concrete than their circular counterparts. Their effectiveness is measured by a modified confinement ratio that is a function of the corner radius and the jacket's hoop strength. Length effect in short columns of up to 5:1 is shown to be similar to ACI provisions for tied columns, i.e., 10% eccentricity and 20% strength reduction in pure compression. While chemical adhesive bond does not change the confinement effectiveness of the jacket, mechanical shear connectors can enhance the load-carrying capacity of the column by providing an effective load distribution mechanism.