Failure of a structural element under shear and torsion is brittle in nature and should be avoided as it compromises the ductile behaviour of the structure. Under various cases of loading and geometric configuration, concrete structural members are subjected to significant torsion accompanied by either bending, or shear and bending. A limited number of studies were conducted to study torsion and shear behaviour of reinforced concrete (RC) girders. Most of these studies were focused on rectangular girders. None were conducted to investigate the strengthening of RC T-girders under combined torsion and shear.; An experimental study was conducted to investigate the shear and torsion behaviour of RC T-girders. Three T-girders were tested while subjected to three different torque to shear ratios selected to cover a wide range of the torsion and shear interactions. In addition, the Shear and Torsion provisions of the North American Design Codes were assessed using the experimental data. It was found that code predictions are more accurate at low torque to shear ratios.; In most damage problems, strengthening using fibre reinforced polymers (FRP) is an effective and convenient solution. An experimental investigation to explore the strengthening of RC T-girders was conducted. Four strengthening schemes were proposed and implemented. The effectiveness of the proposed techniques was evaluated.; An analytical model capable of predicting the full behaviour (i.e. up to failure) of torsionally strengthened rectangular RC girders was proposed and validated using available experimentally observed behaviour and were found to be in good agreement with the experimental results.; An analytical model capable of predicting the behaviour up to ultimate strength for strengthened and un-strengthened RC T-girders subjected to shear and torsion was proposed and validated using the available experimental results.; A simplified strength model that can he used as basis for design code provisions was proposed for both strengthened rectangular and T-girders under torsion and/or shear. The model predicting the strength was verified using experimental results and was found to be in good agreement.
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