| With the increase of the number of steel Bridges in China,the problem of fatigue damage of steel bridge is attracting more and more attention nowadays.Under the study of Chinese scholars,the standard fatigue load of steel bridge structure was put forward in the steel structure bridge design specification issued by China in 2015.In addition,the standard load of fatigue checking is given in the foreign BS5400 standard,the Eurocode standard and the AASHTO LRFD Bridge.And the research about the difference of these four standard fatigue vehicles when they act on steel bridges is less.To find out the difference of those standard fatigue cars in different standards,this article uses a double-deck road and railway steel structure bridge as the support of this research.To find out the most adverse joint which connects the crossgirder and the longitudinal beam in the lower deck of brige structure and the internal influence line of each lane under moving loads,a finite element model of the whole bridge was established by Midas Civil.After the influence line is reached,the most unfavorable lane of structure is determined through the entity model established by ANSYS.Then use the standard fatigue vehicle respectively according to BS5400 standard,AASHTO LRFD Bridge and the Eurocode standard to load onto the internal influence line of each lane,and standard loading of the most adverse joint under the action of various standard fatigue vehicles is obtained.The internal force cycle is calculated by using the rain flow counting method in standard loading of the fatigue vehicle.The Miner linear fatigue accumulation theory is used to stack the internal force cycle.To facilitate comparison,the results of stacking is equivalent to the test load of 2 million cycles.In order to compare the stress variation of each component under the equivalent load,a plate element model of crossgirder was established by ANSYS.Exert each standard fatigue car corresponding effectiveness on the model,and then extract the magnitude of stress of the vertical angle steel,th top angle steel and web steel in the the most adverse joint.Exert self-weight and constant load on the model and then extract the same thing.Exert self weight,constant load each standard fatigue car corresponding effectiveness on the model and then extract the same thing.Results shows that the effect of upper lane on the most adverse joint is relatively smaller than the lower lane.When the standard fatigue car acts on the lower lane,the Maximum internal force of the joint was caused by the car with the heaviest axle load,and the the minimum internal force was caused by the car with the lightest axle load.The reason of the internal force of the AASHTO fatigue car is smaller than the BS5400 one is that the BS5400 fatigue car acts on more lanes than the AASHTO fatigue car.When the function of the fatigue car is combined with rail lane,the Chinese fatigue car corresponds the maximum internal force equivalent,the BS5400 ranks second,the EUROPEAN ranks third and the AASHTO ranks fourth.The changes of mechanical stress of three parts in the most adverse joint in finite element model show that the stress variation of the three components under the effect of Chinese standard fatigue car is the largest.The corresponding mechanical stress results of the four specifications can be verified by their respective fatigue checking calculation,and the test results show that the Chinese standard is the most conservative and the most stringent in the fatigue checking calculation. |
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