A new computational method has been developed to predict the full torsional response of reinforced concrete (RC) beams strengthened with FRP (fiber-reinforced polymer) materials. The proposed model was a modification of the softened membrane model for torsion (SMMT) for RC members. It accounts for the confinement effect of FRP strengthening on the softened compressive and tensile behavior of concrete, improving predictions of torsional response (MSMMT-FRP). Then, a trial-and-error algorithm was developed in the MATLAB environment. A total of 25 RC beams, including 20 experimental specimens previously strengthened with FRP material and five new test beam specimens in this study, were used to evaluate the applicability and reliability of the proposed model. In addition, the predictions of torsional strength from the theoretical fib Bulletin 90 were compared with both analytical predictions and experimental results. The experimental and analytical results showed good agreement in predicting the overall torsional behavior of strengthened RC beams. Comparisons show that the MSMMT-FRP model provides better predictions of torsional strength than fib Bulletin 90. Finally, a parametric study was performed, and the results demonstrated that torsional strength could be improved by increasing the concrete compressive strength, modulus of elasticity of FRP, and its ratio.
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