The use of Fiber Reinforced Polymer (FRP) as an external reinforcement could effectively upgrade the strength of the reinforced concrete members subjected to torsion. However, insufficient information is available to evaluate the contribution of the FRP strengthening techniques on the torsional behavior of RC members. In this paper, the torsional behavior of RC beams strengthened with externally bonded Glass FRP (GFRP) and Carbon FRP (CFRP) sheets is presented. A total of seventeen beams were tested. One beam was designated as a control specimen and sixteen beams were strengthened using FRP sheets of different configuration then tested. All the beams were subjected to pure torsion till failure. The load, twisting angle of the beam and the strains of steel stirrups and FRP strips are recorded. The variables considered in the experimental study include the fiber type, the number of fiber layers, the spacing between FRP strips, the fiber orientation and the effect of adding longitudinal FRP strips. Experimental results reveal that using externally bonded FRP sheets can significantly improves the torsional resistance of the tested RC beams. In comparison with control beam, the ultimate torsional moment increased up to 132 % for beams strengthened with GFRP, and up to 163 % for beams strengthened with CFRP.
Based on the empirical equations reported in FIB (CEB-FIP) [15], an analytical model was proposed and applied to predict the torsional strength of the tested RC beams. For beams strengthened with CFRP strips, the predicted strengths were found to be in good agreement with the experimental results. However, the predicted torsional capacities of the tested RC beams strengthened with GFRP strips were lower than the corresponding experimental values. |
