Experimental study on the force-magnetic relationship of steel box girder based on metal magnetic memory

Metal magnetic memory testing (MMMT) is a nondestructive testing method for the early diagnosis and prevention of ferromagnetic metal components. Many scholars have studied the effect of uniform stress on the self-magnetic-leakage field (SMLF) strength of ferromagnetic materials. However, there are still insufficient studies on stress concentration caused by uneven force under the combined action of bending and shear. In this study, MMMT applied to bridge steel structures and its applicability in monitoring damage to steel structures under complex stresses was explored, and a static loading test was carried out on a steel box girder model. We studied the distribution law of the SMLF on the surface of the top flange, bottom flange, and web of the steel box girder and the force-magnetic relationship of magnetic signal measuring points that were symmetrical with the strain measuring points. Furthermore, we analyzed the magnetic parameters from the statistical point of view to characterize the critical yield state at different force parts of the steel box girder. The results indicated that the stress concentration position at different force parts of the steel box girder could be determined by the peak value of the distribution curve of the normal component H p ( y ) of the SMLF intensity. Thereafter, the yield strength of different stressed parts could be accurately determined by the peak value of the force-magnetic relationship curve to identify the safety state limit of the steel box girder structure and issue an early warning before the steel box girder was damaged. Finally, the reliability of the force-magnetic relationship between different force parts of the steel box girder and the imposed load F was further verified by the SMLF strength average Δ H p ( y ) a . This study can provide an experimental reference for the application of MMMT in the early warning of the state of damage of steel box girder.