EXPERIMENTAL ASSESSMENT OF FRP-CONFINED CONCRETE COLUMNS WITH DAMAGED JACKETS

Abstract

Axial compressive strength of circular concrete-filled fibre-reinforced polymer (FRP) tubes (CFFTs) benefits greatly from significant concrete confinement by the tubes. Accidentally or deliberately induced damage to the tube would undermine the CFFT strength. In this study, 33 CFFT short columns of 144-168 mm outer diameter and 420-460 mm height were tested under concentric loading to failure. Tube damage was artificially induced in the form of through-thickness linear cuts at mid-height. The cut length and orientation angle with respect to the longitudinal axis were varied. Two types of Glass-FRP (GFRP) tubes were studied, namely a nominal [±55o] angle-ply tube with diameter-to-thickness ratio (D/t)=35 and a [86o/-12o] near cross-ply with D/t=48, to investigate two commonly available but distinctly different tubes. The effect of cuts in the two tubes studied was very similar. Vertical and diagonal cuts significantly affected strength, whereas horizontal cuts had insignificant effect on strength. A nonlinear descending trend can be seen in axial strength ratio, relative to the intact CFFT strength, as vertical cut length increase. Initially, a rapid descent occurs up to a 40% reduction of strength, at cut lengths of 20% of the height, followed by a lower rate decline. Strain measurements revealed stress concentrations at the tip of the cut, where crack propagations occurred in the tube. A design-oriented simple model is presented to capture the strength reduction of the damaged CFFT column. Concepts of models for partially confined columns were adapted to the conditions of CFFTs with linear damage. Different assumed conditions regarding the FRP volume and idealized parabola on the concrete at the level of the cut were assessed to establish the expressions that best predict the reduced strength of damaged CFFTs. By idealizing the cut length projection on the longitudinal axis as the gap between two bands of FRP with the same properties as the intact jacket, the strength of damaged CFFT columns can be calculated using this method based on the model proposed by Wang et al. (2018).