Effectiveness of Carbon Fiber-Reinforced Polymer Sheets for Torsional Strengthening of Reinforced Concrete Beams

This paper presents the torsional behavior of reinforced concrete beams strengthened with carbon fiber-reinforced polymer (CFRP) sheets. Assorted retrofit schemes are implemented with variable widths and number of single- and double-layer CFRP U-wraps. After loading 27 beams (three unstrengthened and 24 strengthened), test data were collected to investigate the efficacy of those U-wrap configurations. The width and layer of the bonded sheets dominate the capacity of the beams, whereas the number of the U-wraps in the longitudinal direction is an insignificant attribute. Although the CFRP retrofit decreases structural ductility, the placement of the U-wraps impedes stiffness-reduction rates, reduces twist angles, and redistributes torque-induced stresses. The identified characteristic effective shear modulus of the strengthened beams demarcates the pattern of energy drops, which are related to the degree of brittleness in failure. As far as effective strains are concerned, the applicability of existing equations is appraised, and a new expression is proposed through reliability theory and stochastic simulations.