Kim Junkyeong, Kim Ju-Won, Lee Chaggil, Park Seunghee
2066, Seobu-ro, Jangan-gu, Suwon-si, Gyonggi-do 16419, Korea.
School of Civil & Architectural Engineering, Sungkyunkwan University 2066, Seobu-ro, Jangan-gu, Suwon-si, Gyonggi-do 16419, Korea.
Sensors (Basel). 2017 Aug 30;17(9):1989. doi: 10.3390/s17091989.
The tensile force of pre-stressed concrete (PSC) girders is the most important factor for managing the stability of PSC bridges. The tensile force is induced using pre-stressing (PS) tendons of a PSC girder. Because the PS tendons are located inside of the PSC girder, the tensile force cannot be measured after construction using conventional NDT (non-destructive testing) methods. To monitor the induced tensile force of a PSC girder, an embedded EM (elasto-magnetic) sensor was proposed in this study. The PS tendons are made of carbon steel, a ferromagnetic material. The magnetic properties of the ferromagnetic specimen are changed according to the induced magnetic field, temperature, and induced stress. Thus, the tensile force of PS tendons can be estimated by measuring their magnetic properties. The EM sensor can measure the magnetic properties of ferromagnetic materials in the form of a B (magnetic density)-H (magnetic force) loop. To measure the B-H loop of a PS tendon in a PSC girder, the EM sensor should be embedded into the PSC girder. The proposed embedded EM sensor can be embedded into a PSC girder as a sheath joint by designing screw threads to connect with the sheath. To confirm the proposed embedded EM sensors, the experimental study was performed using a down-scaled PSC girder model. Two specimens were constructed with embedded EM sensors, and three sensors were installed in each specimen. The embedded EM sensor could measure the B-H loop of PS tendons even if it was located inside concrete, and the area of the B-H loop was proportionally decreased according to the increase in tensile force. According to the results, the proposed method can be used to estimate the tensile force of unrevealed PS tendons.
预应力混凝土（PSC）梁的拉力是维持PSC桥梁稳定性的最重要因素。该拉力通过PSC梁的预应力（PS）筋束产生。由于PS筋束位于PSC梁内部，施工后无法使用传统无损检测（NDT）方法测量拉力。为监测PSC梁的拉力，本研究提出了一种嵌入式电磁（EM）传感器。PS筋束由铁磁材料碳钢制成。铁磁试件的磁性能会根据感应磁场、温度和感应应力而变化。因此，可通过测量PS筋束的磁性能来估算其拉力。EM传感器能以B（磁通量密度）-H（磁力）回线的形式测量铁磁材料的磁性能。为测量PSC梁中PS筋束的B-H回线，需将EM传感器嵌入PSC梁。通过设计与护套连接的螺纹，可将所提出的嵌入式EM传感器作为护套接头嵌入PSC梁。为验证所提出的嵌入式EM传感器，使用缩尺PSC梁模型进行了试验研究。制作了两个嵌入EM传感器的试件，每个试件安装三个传感器。即使位于混凝土内部，嵌入式EM传感器也能测量PS筋束的B-H回线，且B-H回线的面积会随着拉力的增加成比例减小。根据结果，所提出的方法可用于估算未外露PS筋束的拉力。
