Abstract
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.
Highlights
Civil structures and their behaviors have become more complicated due to the development of materials, design, and construction technology
The EM sensor should be located inside a pre-stressed concrete (PSC) girder to measure the magnetic responses of the PS tendons because the tendons are built into the PSC girder and could not approach after casting concrete
An embedded EM sensor based tensile force monitoring for PSC girders was proposed in this research
Summary
Civil structures and their behaviors have become more complicated due to the development of materials, design, and construction technology. A magnetic sensor is a reliable method for stress estimation of steel specimens, due to its outstanding superiorities including corrosion resistance, actual-stress measurement, nondestructive monitoring, and long service life [23]. The previous magnetic sensors should located closely to specimen and it cannot be applied actual PSC girder that the PS (pre-stressing) tendons did not expose to outside of girder. To overcome this limitation, this research proposed an embedded EM sensor that can embed into the PSC girder and measure the magnetic responses of internal PS tendons to improve field applicability. For this purpose, embedded EM sensors are developed for measuring the magnetic hysteresis loop variations in pre-stressing tendons and a test was carried out using a 6 m down-scaled PSC girder beam in order to verify the proposed method
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