Strengthening Concrete Structures with Smart Materials

钢筋混凝土（RC）结构的劣化是一个永无止境的问题，激励着世界各地的土木工程师寻求创新的耐久加固技术和高性能先进材料。近年来，一类新型的智能材料形状记忆合金（SMA）由于其上级性能而引起了不同领域研究者的广泛关注。SMA是一种独特的合金，能够承受大变形并通过应力消除恢复其原始形状。除了它们的超弹性、耐腐蚀性和抗疲劳性之外，SMA的主要特征在于通过其独特的热机械性能继承的形状记忆效应（SME）现象。SME表示SMA在加热时变形超过弹性极限后恢复其原始形状的能力。SMA具有SME特性，可作为体外预应力筋，对钢筋混凝土构件进行主动加固。 最常见的SMA由镍和钛（NiTi）制成。NiTi-SMA在土木工程应用中的使用由于其相对较高的成本而受到限制。然而，最近开发的耐腐蚀的铁基Fe-SMA具有相当低的成本和高恢复应力，使其成为结构应用的选择。这项研究的动机是驱动的事实，铁形状记忆合金加固钢筋混凝土梁和柱尚未得到解决。 本研究的主要目的是调查实验和分析的有效性和可行性的两个主动加固技术，而不需要任何机械锚固/千斤顶系统的预应力操作。建议的两种技术是：一个用于限制钢筋混凝土柱使用Fe-SMA线和一个用于弯曲加固钢筋混凝土梁使用Fe-SMA棒。这两种技术都依赖于Fe-SMA在加热时转变为其恢复（未变形）状态时产生的恢复应力。SMA具有温度敏感性，研究环境暴露对SMA加固钢筋混凝土构件性能的影响具有重要意义。循环加载和卸载的影响也很重要，以调查它是否影响SMA中的主动应力。由于Fe-SMA的独特性能，使用Fe-SMA丝主动约束RC柱和使用Fe-SMA棒主动加固RC梁，预计将产生显著的延性结构构件。 本文的研究成果对该领域的研究具有一定的参考价值，并拓宽了Fe-SMA在钢筋混凝土结构加固中的应用前景。 我的研究明确优先考虑HQP的教育/培训，旨在促进增加网络互动/合作，并有可能对研究界产生直接和长期的技术影响。

Deterioration of Reinforced Concrete (RC) structures is a never-ending problem that incites civil engineers around the world to seek innovative durable strengthening techniques and high performance advanced materials. Recently, a new class of smart materials called Shape Memory Alloys (SMA) has been attracting the attention of researchers from different fields due to their superior properties. The SMA is a unique class of alloy with the ability to undergo large deformations and return to its original shape through stress removal. Besides their super-elasticity, corrosion and fatigue resistivity, SMAs are mainly characterized by the Shape Memory Effect (SME) phenomenon that is inherited through their unique thermo-mechanical properties. The SME represents the ability of the SMAs to recover their original shape after being deformed beyond the elastic limits upon heating. SMAs with the SME property can be used as external prestressed reinforcement by providing active strengthening to RC members. The most common SMA is made of Nickel and Titanium (NiTi). The use of NiTi-SMAs in civil engineering applications was limited due to their relatively higher cost. However, the recent development of corrosion resistant iron-based Fe-SMA with considerably lower cost and high recovery stress, have made it to be the choice for structural applications. The motivation of this research is driven by the fact that Fe-SMA in strengthening RC beams and columns has not yet been addressed. The main objective of this research is to investigate experimentally and analytically the effectiveness and feasibility of two active strengthening techniques without the need of any mechanical anchorage/jacking systems for the prestressing operation. The proposed two techniques are: one for confining RC columns using Fe-SMA wires and one for flexural strengthening of RC beams using Fe-SMA bars. Both techniques rely on the recovery stress generated as the Fe-SMA transforms to its recovery (un-deformed) state upon heating. The SMA is temperature sensitive, and thus, it is important to investigate the environmental exposure effect on the performance of RC members strengthened with SMA. The effect of cyclic loading and unloading is also important to investigate if it affects the active stress in the SMA. With the unique properties of Fe-SMA, actively confining RC columns using Fe-SMA wires and actively strengthening RC beams in flexure using Fe-SMA bars is expected to produce a significantly ductile structural member. The findings of this research are expected to add valuable knowledge to the field and widen the potential applications of the Fe-SMA in strengthening RC structures. My research gives explicit priority to the education/training of HQP, seeks to promote increased network interactions/collaborations, and has the potential for technological impact for both immediate and long-term benefits to the research community.