Combined use of FBG sensors and SMA actuators for concrete beams repair

The combined use of sensing and actuating systems enables the development of intelligent structures, which can respond in a predetermined manner to changes in the environment or in the structural conditions. In this work, small-scale smart reinforced concrete beams with fibre Bragg grating (FBG) sensors and shape memory alloy (SMA) actuators are designed and tested. SMA wires placed within sleeves are added to the traditional steel reinforcement. The recovery stress developed in the SMA on heating provides the smart beam with a temporary restoring force, which decreases the residual midspan displacement and crack width. As the recovery stress relaxes on cooling of the SMA wires, the proposed method is effective to provide a temporary beam repair, while a long-term strengthening could be achieved by combining the SMA effect of crack closure with other techniques, such as carbon fibre reinforced polymer (CFRP) plating or resin injection. FBG sensors are used to monitor the deformation in the SMA wires and to determine the beam critical conditions. The effectiveness of both the sensing and the actuating methods is experimentally demonstrated, while the different factors influencing the amount of repair provided by the SMA actuators still need to be investigated

Temporary repair of concrete beams by embedded shape memory alloy actuators

The development of smart materials has paved the way to the creation of adaptive and self-healing structures. Shape memory alloys (SMA) embedded in a structure can provide crack closure and temporarily restore structural integrity. The active emergency repair should be followed by long term strengthening, which benefits from the reduced crack width. Here, small scale self-healing concrete beams are built and tested. Prestrained SMA wires are embedded in the beam, while fibre Bragg grating (FBG) sensors are used to detect a critical beam conditions and activate the emergency repair. The actuation of the shape memory alloy elements leads to a crack size reduction and to a decrease in the inelastic beam displacement. Further experimental investigation is necessary to determine the influence of beam ductility and other factors on the amount of repair provided by the SMA actuators