| The steel bridge has unique advantages in terms of bearing performance,manufacturing and construction,and has been widely used in practical engineering applications at home and abroad.However,with the increase of service time of steel bridges,fatigue crack initiation and cracking continue to occur.Among them,the welding details of longitudinal ribs and diaphragms are typical fatigue details in orthotropic steel bridge decks.Because of its complex structure and large number of welds,it is difficult to completely avoid the manufacturing error of the structural details.The local stress field changes caused by this may accelerate the fatigue cracking,or cause the cracking mode to change,and thus increase the engineering risks,bring unnecessary losses in all aspects.At present,the study of manufacturing error of steel bridges on fatigue is still scarce.Therefore,it is of great significance to study the manufacturing error of steel bridges for the fatigue deterioration effect of longitudinal rib and diaphragm welding details.The research work carried out for this purpose and the main conclusions drawn therefrom are as follows:(1)By investigating the fatigue cracking cases of steel bridges at home and abroad,the importance of studying the fatigue properties of welded details of longitudinal ribs and diaphragms was analyzed.The development of linear elastic fracture mechanics(LFEM)is summarized,and the advantages of the extended finite element method(XFEM)compared to traditional finite element methods are compared.The research status of the current domestic steel structure manufacturing error was investigated,and the importance of studying the influence of steel manufacturing error on the structural fatigue performance was described.(2)Summarizes the current manufacturing technology of steel box girders at home and abroad,and manufactures the production flow chart of each component of the steel box girder.Through the investigation and summary of the specifications,the accuracy requirements of the steel box girder components in the cutting and assembly process are given.(3)The theory and method of numerical simulation of crack propagation in XFEM are introduced.The finite element plate with semi-oval surface crack is solved by XFEM and the stress intensity factor is compared with the calculated values in the traditional finite element method and the stress intensity factor manual.(4)The type of the cutting error of the diaphragm in the test piece and the cause of the error are analyzed,and the relevant data of the cutting error are obtained.The first principal stress field was analyzed in the area where the cutting error occurred,and the numerical formulae of the XFEM crack propagation at the opening of the diaphragm and the related formulas and relevant parameters of the fatigue life prediction were given.Through the numerical simulation of crack propagation in XFEM,the variation law of stress intensity factor amplitude,crack growth rate and fatigue life of fatigue cracks in structural details are obtained.Then,the fatigue deterioration effect of the cutting error of diaphragm is analyzed.(5)The Abaqus Dload subroutine was written using the Fortran language.Through the stress history curve of the horizontal most unfavorable loading position,the variation of the stress field under the welding is analyzed.Through the numerical simulation of the XFEM crack propagation of the assembly error model under different working conditions,the variation law of the magnitude of the stress intensity factor and the crack growth rate curve of the fatigue crack cracking in the structural details are obtained.The results are compared under the four typical assembly error conditions.The fatigue life of the crack cracking gives the fatigue deterioration effect of the assembly error of the diaphragm. |
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