Smart Structures using Shape Memory Alloy and Carbon Nanofibers Ultra-High Performance Concrete

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Smart structures are adaptive structures that can understand their conditions or surroundings and react beneficially to changes using sensors. They require materials that can change on demand. Iron-based-shape memory alloy (Fe-SMA) and Carbon Nanofiber (CNF) Ultra-High-Performance Fiber Reinforced Concrete (UHPFRC) are two emerging materials that could hold the key to bringing structures to life. Fe-SMA has a unique ability to change and revert-back to recover its original shape on-demand through heating, a phenomenon known by the Shape Memory Effect (SME). This SME unique feature makes Fe-SMA an ideal and suitable candidate for serving as an actuating (self-prestressing) mechanism in smart structures. CNF-UHPFRC is a new generation of UHPC with outstanding mechanical properties capable of "self-sensing" changes in strain based on electrical resistance changes. Evolving to smart structures has substantial benefits. How smart structures function in real-life situations? During the service life of a concrete bridge, once the reported stress (from the CNF-UHPFRC self-sensing ability) in one of the girders exceeds predefined threshold stress, a signal is sent to a computerized control unit, which sends a warning to an operations center indicating the structure requires strengthening. After experts review the data and confirm the need for strengthening, the bridge can be closed remotely to stop traffic, thus, removing the load from the deficient girder. Once the bridge is closed, an automatic switch is turned on to reactivate the pre-strained Fe-SMA strips anchored at both ends to the girder by heating it to the desired activation temperature, then allowing it to cool. Thus, a smart self-prestressing force generated in the girder alleviates the excess flexural stress resulting in closing the existing cracks and reducing the beam's deflection. Hence, restoring the structural integrity of the system. The bridge is then opened, and traffic is allowed to cross. In the future, whenever the smart system detects stress exceeding the threshold stress, the strengthening cycle is repeated. The threshold stress can be predefined and tailored based on the smart structure's unique deflection or stress limits. The proposed research aims at developing an innovative smart, adaptable CNF-UHPFRC beam with pre-strained Fe-SMA strips anchored to the underside. Fe-SMA's ability as an actuating (self-prestressing) system will be demonstrated to counteract the stresses induced in the smart beam due to the effect of the applied gravity load. The effectiveness of the self-sensing ability of CNF-UHPFRC to changes in strain/damage will be demonstrated. The performance of the smart beam at the service load will be examined under quasi-static monotonic and cyclic loadings. The findings of this research will add valuable knowledge to the field of smart structures, widen the use of Fe-SMA in structural engineering applications, and employ the self-sensing ability of CNF-UHPFRC.