Prestress Tension Measurement Using a Single Electromagnetic Sensor

Elasto-magnetic sensors are widely used to measure the tensile force of cable structures. Generally, the size of current elasto-magnetic sensors is designed to be large enough to measure the tensile force of the entire cable. Therefore, the tensile force of a single steel strand in cables cannot be measured, which causes some engineering problems, such as that the uniformity of prestress tension and forces within steel cables cannot be determined. In this study, a single-strand elasto-magnetic sensor, called the EM17 sensor, is proposed to detect and monitor the tensile force of single steel strands. EM17 is the smallest sensor developed to date, with an inner diameter of 17 mm. In addition, a series of experiments were conducted to investigate the effects of temperature, position, shielding environment, strand relaxation, strand fatigue and sensor sealing performance on sensor accuracy. The field tests show that the EM17 sensors can accurately measure the tensile force of steel strands. The results show that the uniformity of the prestressed steel strand and the error between measurement and target values are within the range of 5%, which is considered satisfactory.