Iron-based shape memory alloys (Fe-SMA) have shown a strong potential for strengthening applications in concrete structures. This paper presents an experimental study on the bond strength and bond-slip behavior of ribbed Fe-SMA bars embedded in concrete. A total of nineteen pullout tests were conducted to study the bond behavior of 16-mm Fe-SMA bars embedded in concrete specimens with different levels of passive confinement. Prior to specimen fabrication, the bars were pre-strained (at 4% or 8%) and then activated by resistive heating after concrete casting. The experimental study considered different activation temperatures (160 °C, 300 °C, and no activation) to evaluate their effects on bond performance. Five specimens with conventional steel bars were also tested to establish a direct comparison with conventional reinforcement. Unconfined pullout specimens failed by splitting of concrete in most of the cases, while confined specimens presented pullout failures and higher bond strengths. In general, the Fe-SMA bars presented similar bond performance as conventional steel bars. However, the bond strength of unconfined specimens was reduced with the activation temperature. For confined specimens, the activation temperature had a minor effect on the bond strength. Local bond stress-slip relations derived from tests have also been compared with two analytical bond-slip laws available in the literature. Finally, the transfer length of Fe-SMA bars in prestressing applications has been estimated based on the experimental data and a simple analytical model of the bond stress distribution along the embedment length of a bar.

中文翻译：

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嵌入混凝土中的铁基形状记忆合金钢筋的粘结性能

铁基形状记忆合金 (Fe-SMA) 已显示出在混凝土结构中的强化应用的强大潜力。本文对嵌入混凝土中的带肋 Fe-SMA 钢筋的粘结强度和粘结滑移行为进行了实验研究。总共进行了 19 次拉拔试验，以研究嵌入在具有不同被动约束水平的混凝土试样中的 16 毫米 Fe-SMA 钢筋的粘结行为。在试样制造之前，钢筋经过预应变（4% 或 8%），然后在混凝土浇筑后通过电阻加热激活。实验研究考虑了不同的活化温度（160 °C、300 °C 和无活化）来评估它们对粘合性能的影响。还测试了五个带有传统钢筋的试样，以建立与传统钢筋的直接比较。在大多数情况下，无约束拉拔试件因混凝土劈裂而失效，而受限试件则出现拉拔失效和更高的粘结强度。一般来说，Fe-SMA 钢筋与传统钢筋具有相似的粘结性能。然而，无侧限试样的粘结强度随着活化温度的升高而降低。对于受限试样，活化温度对粘合强度的影响较小。来自测试的局部键应力-滑移关系也与文献中可用的两个分析键-滑移定律进行了比较。最后，基于实验数据和沿钢筋嵌入长度的粘结应力分布的简单分析模型，估计了预应力应用中 Fe-SMA 钢筋的传递长度。