Experimental study on flexural behavior of RC beams strengthened with FRP/SMA composites

Fiber reinforced polymer (FRP)/shape memory alloy (SMA) composites are disclosed that can be used to repair cracked members and improve the mechanical behavior of concrete structures. This work aims to synthetically investigate the flexural behavior of reinforced concrete (RC) beams strengthened with FRP/SMA composites through both experimental study and finite element analysis. Five beam specimens are prepared to investigate the effect of important parameters on the flexural behavior of RC beams strengthened with FRP/SMA composites, including the different strengthened materials (i.e., SMA wires, CFRP sheets, and FRP/SMA composites) and different types of FRP/SMA composites (i.e., CFRP/SMA composites and BFRP/SMA composites). The test results showed that the flexural stiffness and capacity improvement of the beam strengthened with only SMA wires were not significant, but the ductility was not reduced. The flexural capacity of the beam strengthened with CFRP sheets was effectively improved, but the stiffness improvement was limited. However, the flexural stiffness and capacity of the beam strengthened with FRP/SMA composites significantly increased. At the same time, the service performance was also improved, FRP/SMA composites could effectively reduce the strain of longitudinal rebars and constrain crack development. Compared to the control beam, the capacity of the beam strengthened with the FRP/SMA composites improved from 17.52% to 40.23%, and the stiffness improved from 9.95% to 17.65%. In addition, the CFRP/SMA composites could more effectively improve the capacity and stiffness of strengthened beams than the BFRP/SMA composites because of the higher elastic modulus of CFRP sheets. The strength of BFRP sheets of the BFRP/SMA composites can be fully utilized after reinforcement. Finally, an iterative method for calculating the recovery stress of SMA wires for reinforcement was proposed and incorporated with finite element method for simulation, which was verified by experimental results.