Despite the key role of thin‐walled tubular reinforced concrete (RC) members in major critical infrastructure projects, for example, bridges, their torsional performance is still not well understood and the effectiveness of strengthening systems cannot be easily assessed, especially when using innovative strengthening materials. With a large part of critical infrastructure approaching its design service life, these issues are becoming more and more important. This paper examines the torsional behavior of thin‐walled tubular RC beams and evaluates the contribution of different strengthening configurations using carbon fiber reinforced polymer (CFRP) reinforcement applied according to the near surface mounted (NSM) technique. Six strengthened specimens are tested with different amounts of CFRP laminates in the longitudinal and transverse direction. Digital image correlation (DIC) is used to gain a deeper understanding of the contribution of the NSM CFRP laminates to the fracture process and overall deformation behavior of the RC elements. The crack mouth opening displacement (CMOD) of the critical crack is compared to those of the other cracks, and the torsional crack evolution is assessed against the strain evolution in the CFRP laminates. The results confirm the effectiveness of NSM CFRP strengthening solutions for thin‐walled RC members, and provide clear evidence that torsional performance can be improved in terms of torsional moment carrying capacity, torsional stiffness, torsional angle of rotation and limiting the crack width propagation, which improves the aggregate interlock shear resisting mechanism.

中文翻译：

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NSM技术对管状RC梁的扭转加固：利用DIC的结构性能和开裂过程

尽管薄壁管状钢筋混凝土（RC）构件在重要的关键基础设施项目（例如桥梁）中起着关键作用，但它们的抗扭性能仍未得到很好的理解，并且无法轻松评估增强系统的有效性，特别是在使用创新性增强技术时材料。随着关键基础设施的大部分接近其设计使用寿命，这些问题变得越来越重要。本文研究了薄壁管状RC梁的扭转性能，并评估了根据近表面安装（NSM）技术应用碳纤维增强聚合物（CFRP）增强材料进行的不同加固配置的贡献。使用不同数量的CFRP层压板在纵向和横向上测试了六个增强的样本。数字图像相关性（DIC）用于更深入地了解NSM CFRP层压板对RC元件的断裂过程和整体变形行为的贡献。将临界裂纹的裂纹口张开位移（CMOD）与其他裂纹的裂纹张口位移（CMOD）进行了比较，并针对CFRP层压板中的应变演变评估了扭转裂纹的发展。结果证实了NSM CFRP加固解决方案对薄壁RC构件的有效性，并提供了明确的证据，表明扭转性能可以在扭转承载力，扭转刚度，扭转旋转角度和限制裂纹宽度扩展方面得到改善，改善骨料联锁抗剪机制。