Slenderness effect of circular concrete specimens confined with SFRP sheets

Experimental investigation of Fibre Reinforced Polymer (FRP) confined concrete is normally conducted on relatively small-scale specimens, where the scaling effects of the specimen size are usually ignored. Few researchers investigated the scaling effects of confined concrete with Carbon FRP (CFRP), Glass FRP (GFRP) and Aramid FRP (AFRP) sheets. However, based on the authors' knowledge, there is no information available in the literature on the slenderness effects of confined concrete with Steel FRP (SFRP) sheet. The SFRP sheet is a new type of material recently introduced for strengthening applications of concrete structures. Thus, the main aim of this investigation is to quantify and access the axial strength, axial strain, hoop strain, dilation and ductility performance of SFRP confined concrete with the increase in the slenderness of the specimens. The experimental program included eighteen specimens with varying slenderness ratios (height-to-diameter ratio) of 2 (150 mm x 300 mm), 4 (150 mm x 600 mm), and 6 (150 mm x 900 mm). Six specimens were constructed in each size, where three specimens were left unwrapped as control specimens and three specimens were wrapped with SFRP sheets. All specimens were loaded in uniaxial compression until failure. The specimens were also instrumented with a photogrammetric method termed Digital Image Correlation Technique to measure the hoop strains from the surface of the SFRP confined concrete specimens. The experimental investigation showed that the effectiveness of the SFRP sheets, measured in terms of the percentage increase in the ultimate axial strength, axial and hoop strains, and the ductility was significantly enhanced compared to the unwrapped specimens. The results also indicate that the overall performance of the SFRP wrapped concrete specimens was reduced with the increase in the slenderness of the specimens, when compared to the standard size cylinders. The study of three major design codes/guidelines to predict the ultimate SFRP-confined concrete compressive strength revealed that the FRP Building Code has the best confinement model when compared with the experimental results. (C) 2012 Elsevier Ltd. All rights reserved.