| In recent years,with the rapid development of China’s railway bridge industry,more than30000 railway bridges have been built.According to the investigation,only 7.6% of the steel beams in Beijing Handan section of Beijing Guangzhou railway have fatigue cracks.It can be seen that the research on the fatigue failure problem is still insufficient.For steel truss bridge,there are dozens of bolt holes in each joint,and the stress concentration is coupled with each other,so it has a great potential fatigue failure.On the other hand,with the rapid development of economy and technology,people have higher and higher requirements on saving materials,environmental protection and safety,so the quantitative evaluation of bridge fatigue problem will become an inevitable trend.However,the current bridge steel structure design code only gives the fatigue limit of infinite fatigue life,and can not achieve specific quantitative fatigue evaluation.Therefore,it is of engineering significance to carry out the research on fatigue life evaluation of steel bridge,and provide theoretical reference for related research.Based on the steel truss railway bridge,this paper studies the finite element simulation analysis of fatigue life.The main research contents and results are as follows(1)ANSYS software is used to model the whole bridge and carry out the static strength analysis.The results meet the engineering design requirements given in the design specification and the dynamic and static load test conclusions,which verify the rationality of the model built in this paper.On this basis,the bridge joints with potential fatigue damage are further analyzed and determined.The results show that the end and the middle of the bridge are the potential dangerous parts of fatigue failure.(2)A refined finite element model for fatigue life analysis of steel truss bridge is established.The contact conditions of 55 contact pairs including 48 bolts are set in the model,and the mesh density is divided according to the stress concentration of bolt holes.In order to compare the influence of the bottom chord connected with the node,the model is divided into two types: the model with bottom chord and the model without bottom chord.The internal force of each member on the fatigue dangerous joint calculated in(1)is applied to the refined model by means of equivalent loading.The results show that the calculation results of the model without bottom chord are the same as those of the model with bottom chord;The maximum principal stress of the end joint is located on the web plate;The location of the maximum principal stress of the mid span joint is located in the connection plate and a certain distance away from the edge of the bolt hole.(3)Under the condition of bolt preload loss of 1 / 3 and 1 / 2 respectively,the influence of bolt preload loss on fatigue life of bridge joints is studied by using metal fatigue theory and method.The results show that the preload loss has little effect on the fatigue life of mid span joints;When the preload loss is 1 / 2,there is a risk of fatigue failure,and the fatigue life is1.94 million times.(4)The results of fatigue life analysis based on metal fatigue theory and method are compared with the fatigue checking method in design code.The results show that in the case of bolt preload loss,the standard method is conservative for the fatigue limit of bridge,and the standard method can not be used for the quantitative evaluation of fatigue life;The evaluation method of metal fatigue theory can be used for the quantitative evaluation of fatigue life of steel truss bridge,but it needs to accumulate a large number of relevant data of bridge fatigue life design in the future. |
