Abstract
In the real world, the main cables of suspension bridges are commonly inspected by conducting a periodic visual inspection of the exterior cover of the cable. Although there is a need to conduct a nondestructive evaluation (NDE) of the damage of the main cable, a suitable NDE technique has not yet been developed due to the large diameter and low accessibility of the cable. This study investigates a magnetic sensing cross-sectional loss quantification method that can detect internal and external damage to the main cables. This main cable NDE method applies an extremely low-frequency alternating current (ELF-AC) magnetization method and search coil sensor-based total flux measurement. A total flux sensor head consists of a magnetization yoke and a search coil sensor. To magnetize the main cable, a magnetic field was generated by applying a triangular ELF-AC voltage to the electromagnet yoke. The sensing part measures the magnetic flux that passes through the search coil, and the B-H loop was then obtained using the relationship between the ELF-AC voltage that has been input and the total flux that was measured. Also, the cross-sectional loss can be quantified using a variation of magnetic features from the B-H loop. To verify the feasibility of using the proposed NDE technique, a series of experiments were performed using a main cable specimen with a gradual increase in the cross-sectional loss. Finally, the relationship between the cross-sectional loss and extracted magnetic feature was determined and used to quantify the cross-sectional loss via the proposed method.
Highlights
In suspension bridges, steel cables are the core supporting materials that suspend most of the load of the structure
This research proposes a noncontact nondestructive evaluation (NDE) technique incorporating magnetic sensing technology to exploit the ferromagnetic characteristics of steel cables
A power amplifier to generate the extremely low-frequency alternating current (ELF-AC) to the wired coil at the magnetization yoke, a fluxmeter to determine the integral of the total flux signal from the search coil sensor, a DAQ, and a controller comprised the measurement system to obtain the B-H loop from the specimen
Summary
Steel cables are the core supporting materials that suspend most of the load of the structure. It is difficult to diagnose cables since the damage in cable can be invisible and inaccessible To overcome these limitations, this research proposes a noncontact NDE technique incorporating magnetic sensing technology to exploit the ferromagnetic characteristics of steel cables. The magnetic flux leakage (MFL) method is an optimal technique for use with continuum structures that have a constant shape in their cross-section, such as railroads and pipelines, and it has been utilized to inspect steel wire ropes for elevators and cranes and for other applications [11,12,13,14,15,16]. Research and development to replace conventional visual inspection methods have not been actively conducted due to the large size of the main cables To overcome such limitations, a new method was proposed to inspect the whole cross-section, including the internal and external section. The feasibility of the proposed main cable NDE technique has been verified through a series of experimental studies using a large-diameter cable specimen with inflicted artificial loss of strands
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