The influence of anchored CFRP on the torsional and bending behavior of sulfate damaged RC beams

Reinforced Concrete (RC) structural elements are subjected to continuous capacity deterioration due to different overloading situations or environmental conditions, such as sulfate attack, steel corrosion, and alkali-activated binders. Therefore, ensuring the system's integrity is a challenging issue faced by municipal and governmental agencies. This raises the need to upgrade the structural capacity by the utilization of strengthening materials of different material types, such as the externally bonded Carbon Fiber Reinforced Polymer (CFRP) that proves efficiency in increasing the flexural and shear capacities of the strengthened system along with maintaining their ductile type of failure. In contrast, a major deficiency exists in the externally bonded technique, the debonding failure, limiting the benefits from the FRP material's high tensile strength and could be solved using a proper and efficient anchoring method. A new and novel use for the CFRP anchored strengthening system was proposed in this study to upgrade the beam's capacity against the effect of sulfate attack damage. The behavior of simply supported strengthened beams was examined in this study under the effect of combined torsional and bending stresses using the Nonlinear Finite Element Analysis (NLFEA) technique using twenty-two models that are divided into six main groups. The investigated parameters were the depth of the anchored CFRP (wfa) (0.00 hf, 0.25 hf, 0.50 hf, 0.75 hf, and 1.00 hf) and sulfate damage cycles (0 (without), 60, 90, and 150 cycles). The structural efficiency of the modeled beams was examined using the torsion-twist curves, the torsion and twist capacities at the ultimate stage, failure mode, stiffness (pre and post-cracking), steel, stirrups, and CFRP strains, and finally, the energy absorption. It has been found that the resulting improvement percentage has a directly proportional relationship with the depth of the anchored CFRP. In contrast, an inversely proportional relationship exists between the improvement percentage and the number of exposed sulfate damage cycles. In conclusion, applying externally boned anchored CFRP has a superior contribution to the RC beams structural performance.