| Under the action of vehicle load,crowd load,wind load and earthquake load,steel bridge produces variable amplitude fatigue stress.Fatigue damage occurs when the amplitude fatigue stress is repeated to a certain number of times.Fatigue damage will reduce the service life of steel bridge and even cause safety accidents.Therefore,it is urgent to study the fatigue life of steel bridges.Although a lot of research has been done by scholars at home and abroad,many achievements have been made,but there,is not much research on prolonging the fatigue life of steel bridges.In view of the shortage of fatigue life research on steel bridge,this paper takes a(45+60+45)m 3 span steel box girder brudge as an example to evaluate its fatigue life under the load of fatigue vehicle.At the same time,the effect of tuned mass damper(TMD)system on the vibration reduction and prolonging the life of steel box girder bridge is studied.The main results are as follows:(1)The theory based on the nominal stress method,local stress strain method,linear elastic fracture mechanics method,damage mechanics method and reliability fatigue life evaluation method are expounded.The analysis and comparison of them are carried out,and the characteristics of a 3 span steel box girder bridge adopted in this paper are combined,and the nominal stress method is finally decided to carry out fatigue.Life assessment.(2)Using Midas FEA to establish a 3 span steel box girder bridge model,through static analysis,find out the control points of fatigue life evaluation for steel box girder bridge.Referring to the design specification of highway steel structure bridge(JTG D64-2015),the fatigue vehicle load model is determined.Referring to the British BS5400 code and the AASHTO code of the United States,the influence of fatigue vehicle impact and multi vehicle effects is considered.Based on 3 different S-N curve correction methods,the fatigue life of steel box girder bridge is evaluated,and the best S-N curve correction method is selected according to the evaluation results.(3)The Midas civil analysis is used to obtain the optimum vibration damping effect of the tuned mass damper(TMD)system,the mass ratio of the TMD system,the damping ratio and the frequency ratio parameters,and compare the results with the results calculated from the theory.(4)The life extension effect of the TMD system under the optimal parameters is analyzed.After setting up the TMD system,the life prolonging rate of the steel box girder bridge is more than 21.36%. |
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