Experimental study of a simple reinforced concrete beam temporarily strengthened by SMA wires followed by permanent strengthening with CFRP plates

It has been proven that carbon fiber reinforced polymer (CFRP) sheets or plates are capable of improving the strength of reinforced concrete (RC) structures. However, residual deformation of RC structures in service reduces the effect of CFRP strengthening. In the past few decades interest in using shape memory alloys (SMA) as actuators has been gradually increasing due to SMA’s capability of generating recovery stresses when heated. SMA can be applied to potentially decrease residual deformation and even close concrete cracks because of its recovery forces imposed on the concrete. However, this technique can only be applied for emergency damage repair because SMA wires need to be heated continuously to generate recovery forces. To overcome the shortcoming of the previous two methods, a new method to strengthen RC structures through CFRP plates in combination with SMA wires is proposed in this paper. The strengthening effect of the proposed method is experimentally investigated in a test specimen of a simple RC beam. Test results indicate that SMA wire recovery forces can decrease deflections and even close cracks in the concrete. The more embedded SMA wires that are added into the specimen, the greater is the reduction in residual deformation. The main reinforcing steel bars prevent the reduction of residual deformation. The strengthened specimen with CFRP plates has a relatively large stiffness in the test when the residual deformation of the beam is reduced by activation of SMA wires in advance. In addition, this study shows that there is a linear relationship between the rate of change in electric resistance of the SMA wires and the mid-span deflection of the specimen, which can be potentially used for damage detection and deformation monitoring in civil structures.