Shear performance of damaged concrete T-beams strengthened with diagonal NSM Fe-SMA bars

The demand for active repair and efficient performance enhancement of concrete structures has been rapidly increasing, particularly in the area of shear strengthening, where the integration of prestressing is urgently needed. However, current prestressed shear strengthening techniques face significant challenges, including complex procedures, high friction losses, and the high cost of anchors. Fe-SMA offers a promising solution, as they can generate self-prestressing quickly through activation. The main goal of this study is to investigate the effectiveness of Fe-SMA bars for shear strengthening of T-beams, with a focus on the influence of different spacings, arrangements, and activation conditions. In this study, Fe-SMA bars were embedded diagonally for shear strengthening of T-beams. The results indicated that the stiffness, strength, and crack development were all enhanced. Notably, the failure mode with diagonal Fe-SMA bars strengthened beams transitioned from brittle failure to ductile failure. Compared to vertically strengthened specimens, the diagonal Fe-SMA bars were oriented such that the force and prestress directions were perpendicular to the crack propagation direction, which more closely aligned with the force characteristics of the truss-arch model. This resulted in more stable load-bearing behavior, effectively inhibiting the development of diagonal cracks. The load at which the critical shear crack developed was increased by 77 %. A comprehensive comparison of failure modes, load-displacement curves, characteristic values, and crack widths confirmed the superior performance of the diagonal Fe-SMA bars. Finally, a novel method for calculating the shear bearing capacity of T-beams strengthened with Fe-SMA bars was proposed. This method is the first to account for the self-prestressing effects of Fe-SMA reinforcement, providing a more accurate and reliable prediction of shear capacity compared to traditional methods. The theoretical values showed good agreement with experimental data, and the method was further used to predict the shear performance under various parameters, providing valuable insights for future research.