Performance of high-modulus near-surface-mounted FRP laminates for strengthening of concrete columns

Abstract

This study investigates the performance of high-modulus near-surface-mounted (NSM) fiber-reinforced polymer (FRP) laminates in strengthening of existing concrete columns. The focus of this study is on the compressive and buckling characteristics of carbon FRP (CFRP) laminates installed on short columns for strengthening to validate their sufficiency for further studies on slender columns. In this paper, an experimental study was designed to consider the effect of eccentric loading on short concrete columns (500 × 150 × 150 mm3) strengthened with four longitudinal NSM CFRP laminates (1.2 × 10 mm2). All specimens were tested symmetrically under the eccentricity to width ratios of 0, 10, 20, and 30% to give a single curvature bending combined with axial load. The experimental results showed no buckling/debonding failure of CFRP laminates, while some of the CFRP laminates reached to crushing points long after the peak load. Moreover, material coupon tests showed that the strength and elastic modulus of the CFRPs in compression were 34% and 86% of those in tension, respectively. The average compressive strain of NSM CFRP laminates for all column specimens under eccentric loading at peak load and after 15% drop from the peak load was 41% and 84% of their ultimate compressive strain obtained from compression coupon tests, respectively. Furthermore, a robust analytical model was developed considering the material and geometrical nonlinearities and it was verified against experimental results. Overall, the results indicated that strengthening short concrete columns with NSM CFRP laminates improved the capacity of the columns without any premature buckling, debonding, or crushing of CFRP laminates. The results will open new avenues in the FRP strengthening of concrete columns, especially slender columns, where the high-modulus NSM system can also enhance the lateral stiffness of the columns for buckling control.