Impact of elevated temperatures on the torsional behavior of thin-walled tubular RC structures strengthened with CFRP sheets

Different structural strengthening techniques have been used extensively in the last decades for flexural and shear strengthening purposes, such as the Carbon Fiber Reinforced Polymer (CFRP). However, the efficiency and performance of torsional strengthening for thin-walled Reinforced Concrete (RC) beams have not been previously considered under the combined effect of sensitive parameters (high temperature and wrapping configurations under torsion). Therefore, this study examines the behavior of CFRP-strengthened thin-walled RC beams under the torsional loading effect using the Nonlinear Finite Element Analysis (NLFEA) method that is first validated using available experimental data, followed by a parametric study. The parameters investigated were the temperature value (23°C, 400°C, 600°C, and 800°C), and the center-to-center spacing between the 50 mm width CFRP composites sheets (0, 200 mm, 100 mm, and 50 mm) corresponding to wrapping ratios of (0.00, 0.30, 0.55, and 1.00). The various component strains (stirrups, longitudinal steel, and CFRP), failure modes, torsion vs. twisting angle behavior, the ultimate capacity in torsion and twisting, stiffness, and energy absorption were introduced for all of the simulated beams. It was found that using the externally bonded CFRP strengthening laminates increases the structural performance characteristics under the torsional loading effect (i.e., load, deformability, and cracking propagation). In addition, increasing the spacing of the strengthening laminates or increasing the exposure temperature decreases the resulting enhancements.