Study of rectangular concrete columns reinforced with external FRP

Abstract

One of the most attractive applications of FRP (fibre reinforced polymers) is the confinement of concrete columns to enhance both its strength and ductility against axial compression loads. So far, many experimental studies have been conducted on circular cross-sections confined with FRP and subjected to pure axial compressive loading. Consequently, several design models have been proposed to describe the behaviour of FRP-confined concrete. There are two key parameters on the fitting of the models: the strain efficiency factor (the ultimate strain of the FRP jacket is lower than the ultimate strain obtained by the standard tensile test of the FRP) and the effect of confinement in non-circular sections. The curvature of the fibres in the jacket has been identified as one of the causes of the reduced value of the effective ultimate strain, which is particularly predominant in rectangular sections with rounded corners. It is well known that the confinement of square or rectangular sections is less effective, and design guides usually introduces a shape factor to account for the non-uniform confinement. However, the effect of the radius of curvature of the corners on the rupture strain of the fibers is not generally taken into account. The British guide TR55 propose to use a smaller strain efficiency factor for rectangular columns, but it is necessary to increase the experimental base in order to clarify this hypothesis. The aim of this work is to show the results of an experimental program that is being carried out in square and rectangular specimens in order to study the influence of the shape factor and the corner radius in the FRP effective ultimate strain. It is planned to use the results of the full experimental program to develop a model of behaviour of the composite system for square or rectangular columns.