Research On Fatigue Life And Prolong Life Method Of Steel Bridge Under Fatigue Loads

Under the long-term effects of wind loads and vehicle loads, the fatigue damage ofsteel bridge may happen at any time. The accumulation of fatigue damage will endangerthe safety and shorten the service life of bridge. At present, fatigue life prediction of steelbridge has been widely studied by domestic and foreign scholars, and some achievementshave been gained, but some deficiencies and gaps still exist in prolong life method andeffect of lifespan extending. In view of the deficiency of fatigue research in our country,this paper evaluates the fatigue life of steel bridge under fatigue vehicle loads and studiesthe mitigating vibration performance and prolonging life performance of Tuned MassDamper system (TMD system) on the case of a (55+82.5+55)m steel-box girder bridge.The main research contents and the results are as follows:(1)The assessment steps and fundamental theory of two estimating methods offatigue life have been discussed. One is nominal stress method, the other is a method offracture mechanics. Nominal stress method is chosen to predict the fatigue life of structurebased on the characteristic of the (55+82.5+55)m steel-box girder bridge.(2)The fatigue-loaded vehicle model, multi-vehicle effect, impact coefficient andcorrected S-N design curves are developed. And on this basis, fatigue life estimation ofsteel-box girder bridge is made with different parameters for the fatigue life estimation. Bycomparing the evaluation results of fatigue life, the defects and improving methods offatigue life estimation in our country are pointed out.(3)The mitigating vibration performance and optimum parameters design of TMDsystem are studied. And the influence of mass ratio, damper ratio and frequency ratio onthe mitigating vibration performance of TMD system is analyzed. The experimentalresults illustrate that: the mitigating vibration performance of TMD system increases asmass ratio increases, it increases firstly and then decreases with the increasing in damperratio and frequency ratio. (4)The prolonging life performance of TMD system under optimal parameters isanalyzed. It is found that the prolonging life ratio of TMD system under optimalparameters is344.3%through comparing the fatigue life of steel-box girder bridge in twosituations: setting TMD in the structure, and without TMD in the structure.