Analysis And Prediction Of Fatigue Life Of Steel Crane Runway Girder

As a huge manufacturing country,there are still a large number of steel structure industrial workshops in China and meanwhile more are under construction.The steel crane runway girder,sustaining the alternating load,is an important component of the steel structure factory.The fatigue failure of the crane runway girder,if occurred,will bring about serious casualy and property loss.Since the special characteristic and restrictions of production activities in industry workshops,the fatigue fracture can not always be under monitoring and disposed during its working process just like other steel structural members.The fatigue failure of the steel crane runway girder,a prolonged process of fractures’initiation and extention,is always an unexpected incident without any apparent signs before final crack.Therefore,the prediction of fatigue life can provide clearly significant reference for the rational planning and maintenance of the steel crane runway girder.Furthermore,it can also help design and investigate the crane runway girder in steel structure workshop.The basic structures and classification of the steel crane runway girder as well as the fatigue mechanism will be presented in this thesis.Several finite element models were built through the software Ansys-Workbench,to simulate the whole running processes of the crane aboard the crane runway girder.Through the FE simulation,the distribution law of the stress,the time-history of the stess,the distribution law of deformation and strain can be obtained for further fatigue research.The maximum equivalent stress during the running process was detected at the support region of the end of the crane runway girder.The stress distribution hence can be processed by rain-flow counting method to work out the stress spectra of the steel crane runway girder which shall be adopted in the prediction of fatigue life.There have been several prediction methods already available including:S-N curve method,linear damage cumulation method based on the theory of damage mechanics,linear-elastic fracture mechanics method,probabilistic fracture mechanics method,DFR（detailed fatigue rating）method and the mthod in steel structure regulations.All these 6 methods shall be adopted in peddicting the fatigue life of the steel crane runway girder.And then the linear cumulation method and DFR method are picked out as the results of which seem close to the fatigue life expected.The structure style and loading property are the main research matters in this thesis among those mass of influence factors of the steel crane runway girder.About the support form of the crane runway girder,the fatigue life of that with rectangular mutational support seems larger than those with circular arc transition,trapezoid transition and angle seel plate.It can be concluded that the fatigue property of the rectangular mutational suppert shows optimized than others,manifested as the relatively smaller stress comcentration.The stiffening ribs at the support are also beneficial to the fatigue peoperty of the steel crane runway girder by cutting down the equivlent stress at the support.The section heights of the web at the support can also affect the fatigue life of the crane runway girder.When the value of ₁h/h is approximately equal to 0.5,the prediction of fatigue life will reach its maximum.The load position of the vertical load from the crane may has a physical impact on the fatigue life of the crane runway girder.The eccentric loading upon the top flange may result in the recession of the fatigue life.Essentially,it needs to be avoid as far as possibly that the crane load is applied biased on the crane runway girder.Moreover,several detail measures are explored to find out their optimal effects on the fatigue life of the crane runway girder.The width of the support rib stiffener can enhance the anti-fatigue behaviour and make the fatigue life increase.As well as the angle iron welded in the support region can increase the fatigue life with little spending enlarged.The fatigue life could be improved effectively through these reinforcement measures if technical and ambient condition permits.The main innovative points of the thesis are presented as follows:the prediction methods based on the damage mechanics and fracture mechanics are introduced into the field of the fatigue life prediction of the steel crane runway girder,as well as the DFR method traditionally applied in the life prediction of the civil aircraft.Furthermore,the fatigue life prediction values based on different theories are systematically analysed.Several structural styles such as the stiffening ribs at the support may have an impact on the fatigue life just according to the research in this thesis which can provide proposal on the design,regulation,maintenance and reinforcement of the steel crane runway girder.