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，可以理解它们的条件或周围环境，并通过传感器对变化做出有益的反应。他们需要可以随需改变的材料。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，可能是将结构带入生活的关键。Fe-SMA具有独特的通过加热改变和恢复其原始形状的能力，这种现象被称为形状记忆效应（SME）。这种SME独特的特性使Fe-SMA成为智能结构中作为驱动（自预应力）机构的理想和合适的候选者。CNF-UHPFRC是新一代UHPC，具有优异的力学性能，能够根据电阻的变化“自感知”应变的变化。进化成智能结构有很大的好处。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，一旦其中一个主梁的应力报告（来自CNF-UHPFRC自感知能力）超过预定义的阈值应力，就会向计算机控制单元发送信号，计算机控制单元向操作中心发送警告，表明该结构需要加强。在专家审查数据并确认需要加强后，可以远程关闭桥梁以停止交通，从而消除缺陷梁的负载。一旦桥梁关闭，一个自动开关被打开，通过加热到所需的激活温度，重新激活固定在梁两端的预应变铁sma条，然后让它冷却。因此，在梁上产生的智能自预应力减轻了多余的弯曲应力，从而关闭了现有的裂缝并减少了梁的挠度。因此，恢复系统的结构完整性。然后桥被打开，车辆被允许通过。在未来，只要智能系统检测到应力超过阈值应力，就会重复强化循环。阈值应力可以根据智能结构独特的挠度或应力限制进行预定义和定制。提出的研究旨在开发一种创新的智能，适应性强的CNF-UHPFRC梁，其底部固定有预应变的Fe-SMA条。Fe-SMA作为驱动（自预应力）系统的能力将被证明可以抵消由于施加重力载荷的影响而在智能梁中引起的应力。将证明CNF-UHPFRC对应变/损伤变化的自感知能力的有效性。智能梁在工作荷载下的性能将在准静态单调和循环荷载下进行研究。本研究结果将为智能结构领域增加宝贵的知识，扩大Fe-SMA在结构工程中的应用，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.