Research On The Fatigue Assessment Method For Crane End Girder Structures

Bridge crane is a kind of essential equipment in modern enterprises, which plays avery significant role in the normal production and safe operation for enterprises. Themetal structures of bridge crane are the main load-bearing components, consists ofplates and different section bars, which belongs to typical welding structures and themain failure mode is fatigue failure under cyclic loading. Thus researches on fatigueperformances of metal structures in bridge cranes have very important meaning to thedesign, manufacture, application and maintenance of bridge cranes. Generally speaking,the fatigue assessment of metal structures in bridge cranes is aimed at the main girder.However the fatigue cracking phenomena of end girder also occur sometimes in theengineering practices of recent years. In order to deepen the understanding of the endgirder’s fatigue performances on bridge cranes, the paper deeply studied the fatigueperformances of the end girder at several different dangerous positions with the fat igueassessment methods commonly used for welded structures. The main work includes:(1) The fatigue analysis methods in "Design rules for cranes " and "Code for designof steel structures" are organized and discussed, and with these methods the fatiguestrengths at middle span section and support sections are calculated for the six groups ofend girders structures in general bridge cranes, which have the same span(28.5m) anddifferent rated lifting weights (5t,10t,16/3.2t,30/5t,50/10t), and the related fatigueperformance analyses are conducted. At the same time, the fact that the aboverecommended methods have no engineering practicability when used to analyze thetapered cross section regions of end girder structures were found.(2) The theoretical basis, modeling methods and implementation strategies of hotspot stress method and equivalent structure stress method are studied, and with the twomethods separately the fatigue life calculations and analyses for end-coped girderstructure and saddle shaped end girder structure are conducted, and the conclusion thatthe equivalent structure stress method has a greater advantage in the fatigue assessmenton the metal structures of bridge cranes was proposed.(3) The basic principles of fracture mechanics are introduced, and for the specialobject, the metal structures of bridge crane, the determining rules of critical parameters(including fatigue propagation parameters C, m and initial crack length a0,critical crack length acand the correction coefficient of stress intensity factor) were discussed, and afatigue assessment method which combines SN curve method and fracture mechanicsmethod was proposed, the calculations for the two instances in item(2) were tried andsatisfactory results are obtained.