RESEARCH ON STRESS MONITORING OF CRACKED STEEL BOX GIRDER BASED ON SELF-MAGNETIC FLUX LEAKAGE

Hu Ma, Shangkai Liu , Tao Tang, and Runchuan Xia

Keywords

Steel box girder, self-magnetic flux leakage, stress monitoring, crack

Abstract

Steel box girder components of long-span bridges inevitably suffer from cracks. The present experimental study of a steel box girder was carried out based on the self-magnetic flux leakage technology. The variation of self-magnetic flux leakage signals during the loading of the cracked steel box girder was obtained, and the influence of the crack size on magnetic flux leakage signals was analysed. It was noticed that the bearing capacity of the steel box girder was affected by cracks and the strain near the crack was larger than those in other areas. The tangential and normal components and the corresponding gradient values of magnetic signals varied with the crack size. The obtained stress and magnetic signal curves manifested a prominent inflection point when the stress was30–50 MPa. The magnitude of the magnetic signal strength decreased when the stress value exceeded 30–50 MPa. The method was verified to determine the location and size of cracks and the stress state of the steel box girder.

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