Measurement method of natural frequencies and tension forces for cables based on elasto-magnetic sensors calibrated by frequencies

Abstract

Vibration-based (VB) method and elasto-magnetic (EM) method are usually used to measure cable forces of cable-supported bridges. For the VB method, it is difficult to accurately identify each order natural frequency of the cable disturbed by random excitations, and there are also no precise selection criteria between the taut string model and the hinged beam model. For the EM method, it is not convenient to calibrate EM sensors on bridges in service due to unknown cable forces. To address these issues, a vibration-based elasto-magnetic (VBEM) method is proposed. In this method, a numerical model describing the tie between each order natural frequency and induced voltage was constructed first, and then, a new cable force formula with nominal flexural stiffness was derived. To verify the VBEM method, a steel strand experimental platform was built and the load applied to the steel strand was achieved by a jack. At 18 °C, the first three order natural frequencies of the steel strand and corresponding induced voltage were recorded for each load. According to the obtained experimental data, the VBEM method is tested and analyzed. The results show that the VBEM method exhibits the ability to identify each order natural frequency of the steel strand with high precision; the introduction of nominal flexural stiffness makes the hinged beam model cover the taut string model, resulting in tension force measurement with satisfactory accuracy; the constructed models do not contain tension forces, and this will make it very beneficial to calibration of EM sensors on bridges in service.

Research on an Intelligent Identification Method for Cable-Stayed Force with a Damper Based on Microwave Radar Measurements

“…In this study, Equation ( 14) was used to calculate the cable force of a cable-stayed cable, and the influence of the bending stiffness was not considered in the calculations. In order to reduce the deviation between the calculated cable force and the measured cable force, the bending stiffness of the 12 cables mentioned above was corrected according to Equation (15) in Section 3.4, and the calculations are shown in Table 7. After the coefficient correction, it was found that when the cable was long, the influence of the bending stiffness on the accuracy of the measured cable force was almost zero and could be ignored.…”

“…Jo, Hyeon Cheol et al [14] proposed a tension and tension range evaluation method based on multiple digital images that was able to obtain the cable force more economically and efficiently than traditional methods could. Xiaofeng Liu et al [15] proposed a vibration-based elastic-magnetic (VBEM) method that had a good ability to identify the natural frequencies of each order of steel strand. Hongbo Liu [16] conducted dynamic response tests on closed cables and high vanadium cables under prestress and proposed a deep learning model that could intelligently identify the cable force for construction based on test data.…”

Working Stress Measurement of Prestressed Rebars Using the Magnetic Resonance Method

“…According to the Joule effect and the magnetization theory of ferromagnetic material, there is a functional relationship between the stress of rebar and the change in magnetic permeability [30,31]. In Equation (1), µ is the permeability of rebar, µ 0 is the vacuum permeability, λ s is the axial deformation constant, M s is the saturation magnetization, K u is the uniaxial magnetic anisotropy constant, H R is the excitation magnetic field, and θ 0 is the angle between the magnetic field and the easy magnetization axis [32].…”