Experimental study and analysis of RC beams shear strengthened with FRP/SMA composites

In practice, the prestressing is difficult to apply to achieve shear reinforcement of reinforced concrete (RC) beams due to the limited operating space used for installing mechanical tensioning equipment. So, how to efficiently introduce prestressing into RC beams is a practical problem. In this study, the authors utilized the recovery effect of shape memory alloys (SMA) wires to successfully introduce prestressing into RC beams and externally bonded with fiber reinforced polymer (FRP) sheets, forming a FRP/SMA composite shear reinforcement technology. After that, shear behavior of RC beams strengthened with FRP/SMA composites was investigated by a series of experiments. In order to further illustrate the effect of FRP/SMA composite shear reinforcement on RC beams, other reinforcement materials, such as SMA wires and FRP sheets, have also been separately applied in shear reinforcement experiments. Moreover, carbon fiber reinforced polymer (CFRP) and basalt fiber reinforced polymer (BFRP) are respectively applied to prepare FRP/SMA composites. For beams strengthened with FRP/SMA composites, the prestressing generated by the recovery effect of SMA wires can effectively suppress the formation of diagonal cracks in RC beams. The ultimate load and the corresponding displacement of strengthened beams significantly increased due to the constraint effect of FRP on the propagation of shear cracks. The shear capacity of CFRP/SMA composites strengthening beams was higher than that of BFRP/SMA composites strengthening beams, as CFRP/SMA composites better limited the propagation of cracks. Based on the test results, an analytical model has been proposed to predict the shear capacity of strengthened beams, and its effectiveness has been confirmed through comparison with experimental results.