| Due to the advantages of mature technology,good integrity and easy prefabrication and assembly,there are more and more new long-span steel bridges using integral joints as the main beam structure.However,there are many members and welds in the integral joint,and the structure is complex,so it is easy to cause fatigue failure under the alternating action of vehicle load.Therefore,the fatigue performance of integral joints has been paid more and more attention.In this paper,based on the Baiyang Yangtze River Bridge in Hubei Province,the most unfavorable integral joints of steel truss are studied by numerical simulation.Firstly,the finite element software MIDAS / civil is used to build the whole bridge model.The 482 k N standard fatigue vehicle derived from the actual predicted traffic volume of Baiyang Yangtze River Bridge is used as the fatigue vehicle to load on the outermost lane,and the most unfavorable position of various members is obtained.The node 881,which is 412.5 meters away from the midspan,is the most unfavorable node.Based on the traffic volume regulations of BS5400 and miner’s linear cumulative damage theoretical formula,the equivalent axial force amplitude of 2 million times of the top chord,vertical web member and diagonal web member is calculated to be 3293 k N,778 k N and 2037 k N respectively.Secondly,a 1:4 scale model of steel truss beam and corresponding tooling are designed.The fatigue test scheme of single node loading is proposed.The segment model is established by MIDAS / civil,and the test loading amplitude is determined to be 500 kn.The finite element software ANSYS Workbench was used to carry out the numerical fatigue test.The axial force amplitude is divided into 15 load cases to simulate the hierarchical loading,and the equivalent stress values of 6 typical test points are extracted and the stress law is analyzed.The results show that the joint model keeps elastic state during loading and unloading,and the von Mises stress of H8 measuring point is the largest,which is 128.14 MPa.It is located at the joint between the joint plate and the right diagonal web member,and the static calculation results meet the requirements.The fatigue tool is inserted into the static calculation results,the Goodman model is used to analyze the fatigue life and fatigue safety factor of the integral joint,and the fatigue damage degree of the member is calculated.The results show that the minimum fatigue life of the whole joint is 2 million times,the minimum fatigue safety factor is 1.26 > 1,and the fatigue damage degree of each member is less than 1,which shows that the fatigue performance of the whole joint meets the requirements,and the whole joint of Baiyang Yangtze River Bridge will not have fatigue damage in the design life.Finally,by selecting different average stress correction model and stress ratio,the change rule of the overall joint fatigue safety factor is studied.After comparison,it is found that the fatigue safety factor values of the structure are reduced after the three models are modified.It is reasonable to select Goodman model to carry out the fatigue analysis of the whole node,and the analysis results are relatively conservative.For the same fatigue load amplitude,with the increase of the stress ratio,the value of the fatigue safety factor of the structure also increases,which is beneficial to the fatigue performance of the structure.Aiming at the failure of high-strength bolts in practical engineering,the models of bolt missing of diagonal web member and vertical web member are established respectively.The analysis shows that the lack of high-strength bolts in integral joints will increase the stress value of members and reduce the fatigue safety factor.The fatigue safety factor will be reduced by 6.44% if the diagonal web bolt is missing,and 7.28% if the vertical web bolt is missing,which is not good for the normal use of the bridge. |
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