Measurement Methods For Metal Cross-sectional Area Of In-service Cables

Cables are widely used in large-span bridges, large buildings and tour facilities. To ensure safe operation of the in-service cables, it is necessary to periodically test them. In this dissertation, for the cable's structure with large diameter and thick protecting layer, the metal cross-sectional area measurement methods and key technologies are studied systemically in depth. Precise measurement of the variation of metal cross-sectional area of cable and the position of metal cross-sectional area change are achieved.To measure the variation of metal cross-sectional area of cable, a magnetic measurement method based on lead-out magnetic flux is proposed. The analytical model of the reluctance for this method has been established, which reveals the variation rate of the Hall elements output voltage at the measurement point is proportional to the variation rate of the cable's metal cross-sectional area. Later, the model is verified by experiments. Analysis has been conducted systematically for the impacting factors to measurement accuracy, which include the calibration of the measuring system, the radial position of the cross-sectional area change, the magnitude of the magnetizing current, the number of the magnetic circuits, the placement of the Hall elements and the stress in cable.To determine the location of the cable's metal cross-sectional area change, a method based on magnetic flux discrete array model has been developed. The corresponding discrete array model of magnetic flux in metal cross-section and mathematic equations have been constructed. The model is verified by experiments. To meet the requirements of online real-time locating measurement, the particle swarm optimization algorithm has been introduced to optimize iteration calculation of the model parameters, achieving the fast solution of the inverse problem of locating measurement. The effectiveness of this inversion locating measurement method is verified by experiment.On the cable's features of large diameter and difficulty of being magnetized effectively, finite element simulation calculation is applied to analyze the impacts of the parameters such as the ratio of the length and diameter, number of layers of magnetization coil, etc. on the magnetic field distribution, and the demagnetization factors of cylindrical rod under the conditions of different ratios of the length and diameter, permeability, overall magnetization and local magnetization in non-uniform magnetization are achieved, and the effect of demagnetizing field is also studied. On this basis of the results above, by the equivalence analysis of local magnetization effect of the cylindrical rod and the wire bundle, the main road magnetization method has been obtained to optimize the cable local magnetizaiton. The method effectively reduces the weight of the magnetizer. Two crawler structures, namely separate and reconfigurable structures have been put forward to adapt to different application requirements. Climbing experiments have been carried in field. The crawler prototypes have strong loading capacity, small size and light weight, which is easy to dismantle and able to adapt to the testing of cables with different diameters in service. These two technologies are the key points to solve the problem of engineering testing of in-service cables.