Experimental analysis of curved RC beams strengthened with carbon fibre for flexural and shear capacity enhancement

Abstract

Among the concrete strengthening applications, Carbon Fibre Reinforced Polymer (CFRP) systems offer better mechanical properties than other alternatives, such as stronger tensile strength, stiffness, and durability. Most of the studies have been focused on strengthening or retrofitting straight Reinforced Concrete (RC) beams using CFRP, fewer on the horizontally curved out of plane loaded RC beams, which are present in novel featured structures worldwide. In contrast to straight beams, the curved beam behaviour possess combined effect of bending, torsion and shear where CFRP application requires a careful selection based on the intended capacity enhancement. The experimental program includes total 6 nos. of RC beam specimens of fixed curvature casted, 2 beams weak under shear and 2 beams weak under flexure and their control beams. The CFRP strengthening was applied as relevant to evaluate the effectiveness of flexural and shear enhancement. The NSM CFRP plate application and end anchored NSM CFRP for flexure strengthening along with 450/1350 oriented CFRP fabrics at beam sides and increased area of fabric for shear strengthening was focused. The specimens were tested using four point bending test and the ultimate failure load, crack patterns, failure modes and deflection was observed. The experimental results under flexure concluded that NSM CFRP enhance flexural strength according to the initial cracking load observations. Where end anchored CFRP fabric provided it contribute to additional flexure strength and reduce overall deflection by 23%. Ultimate load carrying capacity of NSM CFRP retrofitted beams were enhanced by 12.1% and 8.4% for respective application. NSM CFRP retrofitted beams showed, lesser crack density and widths. Propagation of the crack which was in the direction of NSM CFRP plate corners is restrained with the use of end anchored CFRP, although its effect over shear capacity enhancement is insignificant. The experimental flexural enhancements are 28.8% and 29.3% less than the theoretically predicted values by ACI 440.2R-17 guide, respectively for NSM CFRP only and end anchored beams, which may have occurred due to the contribution of additionally induced torsional stresses. iv The experimental results under shear concluded that ultimate load carrying capacity of shear retrofitted beams were enhanced by 20 % and 30%. The influence of CFRP retrofitting is higher when the CFRP application area is increased at inner shear span. The experimental shear enhancements are 35.4% and 20.3% less than the theoretically predicted values by ACI 440.2R-17 guide, respectively for side laminated and extra side laminated beams. The intermediate debonding and induced additional torsional stresses may have caused this capacity reduction.