Investigation of Steel I-Beams Strengthened Using CFRP and BFRP Sheets under Torsion

Torsional demand acting on beams can significantly effect structural behavior and cause high-local stresses. The torsional resistance of beams can be potentially increased by using fiber-reinforced polymer (FRP) sheets. In this study, basalt (BFRP) and carbon (CFRP) fabrics with different layouts are used to strength the steel I-beams, and the enhancement in the torsional strength is investigated experimentally and numerically. First, 12 specimens are reinforced using BFRP and CFRP fabrics bonded to the web of steel I-beams in three different layouts to carry out the experimental study. In total, 14 specimens are tested under torsion including two reference beams. Second, a numerical model is developed to capture the torsional behavior of web-reinforced steel beams. After the numerical model is verified satisfactorily, a parametric study is conducted to evaluate the effect of FRP strengthening on steel beams for flange-only and full reinforcement alternatives. In the experiments, fully web-bonded FRP strengthening configuration achieved 18% and 14% increase in torsional capacities for BFRP and CFRP sheets compared to reference, respectively. In last, it is discovered by the parametric study that the full reinforcement using FRP on the web and flanges can achieve up to 43% increase.