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

智能结构是一种自适应结构，可以理解其条件或环境，并使用传感器对变化做出有益的反应。他们需要的材料可以根据需要改变。铁基形状记忆合金（Fe-SMA）和碳纳米纤维（CNF）超高性能纤维增强混凝土（UHPFRC）是两种新兴材料，可能是使结构焕发生机的关键。Fe-SMA具有独特的改变和恢复能力，通过加热按需恢复其原始形状，这种现象称为形状记忆效应（SME）。这种SME独特的功能使Fe-SMA成为智能结构中用作致动（自预应力）机制的理想和合适的候选者。CNF-UHPFRC是新一代UHPC，具有出色的机械性能，能够根据电阻变化“自感知”应变变化。智能结构的发展有很大的好处。智能结构如何在现实生活中发挥作用？在混凝土桥梁的使用寿命期间，一旦报告的应力（来自CNF-UHPFRC自感知能力）在一个梁超过预定义的阈值应力，信号被发送到计算机控制单元，该单元向操作中心发送警告，指示结构需要加强。在专家审查数据并确认需要加固后，桥梁可以远程关闭以停止交通，从而消除缺陷梁的负荷。一旦桥被关闭，自动开关被打开，以通过将其加热到所需的激活温度，然后允许其冷却来重新激活锚固在梁两端的预应变Fe-SMA条。因此，在梁中产生的智能自预应力消除了多余的弯曲应力，从而闭合了现有的裂缝并减小了梁的挠度。从而恢复系统的结构完整性。然后桥被打开，允许车辆通过。将来，只要智能系统检测到超过阈值应力的应力，就会重复强化循环。阈值应力可以基于智能结构的独特偏转或应力极限来预定义和定制。拟议的研究旨在开发一种创新的智能，适应CNF-UHPFRC梁与预应变Fe-SMA带锚定到底面。铁形状记忆合金的能力，作为一个驱动（自预应力）系统将被证明，以抵消在智能梁中引起的应力，由于施加的重力载荷的影响。CNF-UHPFRC应变/损伤变化的自感知能力的有效性将得到证明。在准静态单调和循环载荷下，将检查智能梁在使用荷载下的性能。本研究结果将为智能结构领域增加有价值的知识，拓宽Fe-SMA在结构工程应用中的应用，并利用CNF-UHPFRC的自感知能力。

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.