Strengthening Concrete Structures with Smart Materials

钢筋混凝土（RC）结构的恶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用加固技术和高性能的先进材料。最近，一类新的智能材料形状记忆合金（SMA）因其优异的性能而引起了不同领域研究人员的关注。SMA是一类独特的合金，具有承受大变形并通过消除应力恢复其原始形状的能力。除了具有超弹性、耐蚀性和疲劳电阻性外，sma的主要特点是其独特的热机械性能所继承的形状记忆效应（SME）现象。SME表示sma在加热后变形超过弹性极限后恢复其原始形状的能力。具有SME特性的sma可以作为外部预应力钢筋，为RC构件提供主动加固。***最常见的SMA由镍和钛（NiTi）制成。由于其相对较高的成本，niti - sma在土木工程应用中的使用受到限制。然而，最近开发的耐腐蚀铁基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。这项研究的动机是由铁- sma在钢筋混凝土梁和柱的加固中尚未得到解决的事实所驱动的。***本研究的主要目的是实验和分析两种主动加固技术的有效性和可行性，而不需要任何机械锚固/顶升系统进行预应力操作。提出的两种技术是：一种是用铁- sma钢丝约束RC柱，一种是用铁- sma钢筋加固RC梁。这两种技术都依赖于Fe-SMA在加热时转变为恢复（未变形）状态时产生的恢复应力。SMA对温度敏感，因此研究环境暴露对SMA加固RC构件性能的影响具有重要意义。循环加载和卸载的影响对于研究它是否影响SMA的活性应力也很重要。利用铁- sma的独特性能，利用铁- sma钢丝主动约束钢筋混凝土柱，利用铁- sma钢筋主动加强钢筋混凝土梁的弯曲，有望产生具有显著延性的结构构件。***本研究结果有望为该领域增加宝贵的知识，并扩大Fe-SMA在钢筋混凝土结构加固方面的潜在应用。***我的研究明确优先考虑HQP的教育/培训，寻求促进更多的网络互动/合作，并为研究界带来即时和长期利益的潜在技术影响。

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.