Shear strengthening of rectangular and T-shaped reinforced concrete beams with iron-based shape memory alloy (FeSMA) strips

In this paper, a comprehensive experimental investigation was performed to understand the behavior of shear critical beams strengthened with iron-based shape memory alloy (FeSMA) prestressing. The influence of the FeSMA activation process on the prestressing behavior of the material was investigated, a comparison between rectangular and T-beams shear strengthened with FeSMA was made, and the combined effects of the transverse reinforcement configuration (including both internal stirrups and external FeSMA strips) and the anchoring method was studied. First, the elastic modulus, yield stress, fracture stress of passive FeSMA and the recovery strain and recovery stress of active FeSMA was determined. The effects of heating approach, prestrain level, activation temperature, and the portion of the FeSMA length that is activated on the recovery stress of FeSMA were studied. Second, twenty shear critical RC beams were tested, including eight rectangular and twelve T-beams. The following variables were investigated in these beam tests; namely, the stirrup spacing, FeSMA spacing, number of FeSMA layers, use of passive or active FeSMA, and the method used in installation of FeSMA. For all beams, the crack patterns, failure modes, shear force-deflection responses, and strains in the stirrups and FeSMA were analyzed. The results demonstrated that for both rectangular and T-beams, the failure modes of beams strengthened with FeSMA strips shifted from shear to flexure; further, the beams strengthened with active FeSMA strips exhibited fewer and narrower cracks than beams strengthened with passive FeSMA strips. Compared with the control specimen, both the peak shear force and the deflection at peak force of rectangular and T-beams increased after strengthening with FeSMA strips.