Study On Bending Test Of Steel Box Grider With Corrugated Web Of Different Sections Based On Magnetic Memory Method

As a new non-destructive testing technology,the metal magnetic memory testing technology can identify the stress concentration and judge the damage of components.In the field of building steel structure,the sudden damage caused by stress concentration will have serious impact on the safty of the structure.In order to evaluate the stress concentration and stress state of the steel box girder,and study the variation of magnetic memory signal under complex stress,and prove and expand the applicability of metal magnetic memory detection technology in the field of bridge steel structure,the mechanical behavior and stress concentration of steel box girder with corrugated webs with different sections are studied on the basis of theoretical and experimental research.The main work and conclusion of this paper are as follow:（1）The four-point bending test of steel box girder with corrugated webs with different sections is carried out in order to analyze the law of normal magnetic memory signal changing with load under different stress states.The results show that the normal magnetic flux leakage signal can characterize the different stages of the whole loading process.The variation of normal magnetic memory signal with the increase of load under different kinds of stress is different.In addition,the yielding moment and the yielded detection point of the specimen can also be judged by observing the droping phenomenon and the trend after signal decreases.（2）The theoretical model of stress distribution under double concentrated loads considering the shear behavior of webs is derived.Then,the mechanical behavior of corrugated web steel box girder is theoretically deduced and simulated by finite element method.The theoretical results are in good agreement with the stress distribution of the finite element simulation,which indicates that the theoretical model has high accuracy and can be applied to the simple stress analysis of the flexural members.The stress distributions of beams with different cross sections are compared,and result shows that the shear capacity of inclined corrugated web is better than that of straight corrugated web.（3）To study the magnetic signal’s characterization of the stress distribution,the force distribution of corrugated web steel box girder with different sections is compared with the normal magnetic flux leakage signal distribution.The results show that the normal magnetic flux leakage signal can characterize the stress distribution.The absolute value of the magnetic signal detected at the place where the stress is greater is larger,and the shape of the curve is similar to that of the stress distribution.（4）The stress concentration location identification method based on normal magnetic flux leakage signal is studied.When the stress changes along the detection line,the stress concentration phenomenon needs to be compared with the change trend of the initial magnetic signal.For the flange,the position where abnormal peak/valley value generated by the normal magnetic memory signal curve can be preliminarily judged as the stress concentration position.For the web,the stress concentration position can be judged when the gradient curve produces abnormal peak value relative to the initial curve.（5）The characterization methods of stress concentration degree and stress concentration range were studied.The degree of stress concentration in contact stress concentration and non-contact stress concentration can be expressed byH_{co n}andK_con respectively.