Zhang Shenghan, Liu Han, Darwish Esam, Mosalam Khalid M, DeJong Matthew J
Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA.
Sensors (Basel). 2022 May 23;22(10):3957. doi: 10.3390/s22103957.
Distributed fiber-optic sensing (DFOS) technologies have been used for decades to detect damage in infrastructure. One recent DFOS technology, Optical Frequency Domain Reflectometry (OFDR), has attracted attention from the structural engineering community because its high spatial resolution and refined accuracy could enable new monitoring possibilities and new insight regarding the behavior of reinforced concrete (RC) structures. The current research project explores the ability and potential of OFDR to measure distributed strain in RC structures through laboratory tests on an innovative beam-column connection, in which a partial slot joint was introduced between the beam and the column to control damage. In the test specimen, fiber-optic cables were embedded in both the steel reinforcement and concrete. The specimen was tested under quasi-static cyclic loading with increasing displacement demand at the structural laboratory of the Pacific Earthquake Engineering Research (PEER) Center of UC Berkeley. Different types of fiber-optic cables were embedded both in the concrete and the rebar. The influence of the cable coating and cable position are discussed. The DFOS results are compared with traditional measurements (DIC and LVDT). The high resolution of DFOS at small deformations provides new insights regarding the mechanical behavior of the slotted RC beam-column connection, including direct measurement of beam curvature, rebar deformation, and slot opening and closing. A major contribution of this work is the quantification of the performance and limitations of the DFOS system under large cyclic strains. Performance is quantified in terms of non-valid points (which occur in large strains when the DFOS analyzer does not return a strain value), maximum strain that can be reliably measured, crack width that causes cable rupture, and the effect of the cable coating on the measurements. Structural damage indices are also proposed based on the DFOS results. These damage indices correlate reasonably well with the maximum sustained drift, indicating the potential of using DFOS for RC structural damage assessment. The experimental data set is made publicly available.
分布式光纤传感（DFOS）技术已被用于检测基础设施损伤数十年。最近的一种DFOS技术，即光频域反射测量法（OFDR），因其高空间分辨率和高精度，能够为钢筋混凝土（RC）结构的行为提供新的监测可能性和新见解，从而引起了结构工程界的关注。当前的研究项目通过对一种创新型梁柱连接进行实验室测试，探索OFDR测量RC结构中分布式应变的能力和潜力，该连接在梁和柱之间引入了部分槽口节点以控制损伤。在测试试件中，光纤电缆被嵌入钢筋和混凝土中。试件在加州大学伯克利分校太平洋地震工程研究（PEER）中心的结构实验室进行准静态循环加载试验，位移需求不断增加。不同类型的光纤电缆被嵌入混凝土和钢筋中。讨论了电缆涂层和电缆位置的影响。将DFOS结果与传统测量方法（数字图像相关法和线性可变差动变压器）进行了比较。DFOS在小变形时的高分辨率为开槽RC梁柱连接的力学行为提供了新见解，包括直接测量梁的曲率、钢筋变形以及槽口的开合。这项工作的一个主要贡献是量化了DFOS系统在大循环应变下的性能和局限性。性能通过无效点（当DFOS分析仪未返回应变值时在大应变中出现）、可可靠测量的最大应变、导致电缆断裂的裂缝宽度以及电缆涂层对测量的影响来量化。还基于DFOS结果提出了结构损伤指标。这些损伤指标与最大持续漂移有合理的相关性，表明使用DFOS进行RC结构损伤评估的潜力。实验数据集已公开提供。
