Torsion of Carbon Fiber-Reinforced Polymer-Strengthened Inverted T-Beams under Combined Loading.

This paper presents the torsional behavior of inverted T-beams strengthened with carbon fiber-reinforced polymer (CFRP) sheets when simultaneously subjected to shear- and flexure-combined loading. Two types of CFRP bonding are tested: complete wrapping and side-bonding with single and double layers at variable coverage areas. The capacity of the beams with completely wrapped sheets is higher than that of the beams with side-bonded sheets, whereas such a tendency diminishes as the intensity of the combined loading increases. Moreover, the torsional stress of the test beams is in part relieved by the interaction with the flexural component. For the side-bonded beams, the cross-sectional area of the CFRP controls the load-carrying capacity. While the completely wrapped sheets enhance the ductility of the beams, the wide side-coverage of the CFRP benefits their polar moment of inertia that is concerned with the torsional rigidity and rotations. The degree of stress redistribution under the combined loading is not as significant as the case under pure torsion. Crack localization leads to the failure of the beams subjected to pure torsion, accompanied by partial delamination of the side-bonded sheets; however, torsional cracks spread over the loading span with the presence of shear and bending. The loading scheme affects the magnitude of the effective strain in the CFRP, and the applicability of existing equations is assessed. Based on the proposed effective confinement index, the influence of CFRP layers on the shear-flow path of the concrete section is examined. For design recommendations, analytical modeling with uncertainty simulations generates interaction envelopes, which demarcate the safe and unsafe regions of the strengthened beams under the combined loading. [ABSTRACT FROM AUTHOR]