Research On Probabilistic Safety Assessment Method And Fatigue Life Prediction For Box Girder Of Bridge And Gantry Crane

Lifting machinery,one of the most important categories of special equipment,plays a crucial role in reducing worker's heavy manual labor,realizing automation,and improving labor productivity,which has been widely used in various fields of human production and life.As crane metal structure is a large welding structure,crack defects inevitably happen in the process of production,assembly and operation.The existence of these cracks brings hidden troubles to the work safety of the crane.Unpredictable accidents should be caused once the crack growths render the structure useless for fracture while the crane is working.Therefore,it is of great practical significance to evaluate the safety of crane with crack defects from a work safety prospective.Taking an in-service 36t gantry container crane of some Railway Bureau as the research object and according to the British standard BS7910 guide to methods for assessing the acceptability of flaws in metallic structures,a research on the crane box beam with cracks has been done based on the theory of Linear Elastic Fracture Mechanics(LEFM),reliability theory and fatigue damage theory.The research contents include the probabilistic safety assessment and fatigue life prediction by using the theoretical analysis and finite element numerical simulation.The main work of the research in this paper includes:(1)Based on standard BS7910,this paper project mainly elaborates Failure Analysis Diagram(FAD)and three assessment levels of BS7910.It also is a summary of the common types of distribution in reliability analysis and common methods to solve reliability index.(2)The finite element model and the crack sub model of the box girders for cranes were established by ABAQUS software,meanwhile employing interaction integral method to solve the stress intensity factor(KI)of actual oblique crack tip and corresponding simplified equal length crack tip where the bottom plate and web plate.By comparing calculation results,simplifying actual oblique crack as equal crack is feasible in the crane box beam.(3)Based on the basic theory of reliability and FAD,the method and process of probability safety assessment for the crane box beam structure were established.A case of box girder structure of a 36t container gantry crane with crack defects was studied using the finite element analysis results and the Monte Carlo random sampling method.Example analysis shows that this method of probability safety assessment is feasible.Through parameter sensitivity analysis,some parameters including the fracture toughness,yield strength and Primary membrane stress have an important effect on the structural failure probability.These parameters should be prioritized during the assessment process.(4)In view of the crane box beam structure and its stress distribution characteristics of complex,an equivalent crack method based on fatigue test data was presented to estimate fatigue life.By comparing estimation results with fatigue test results in the literature,the proposed method is effective and feasible to estimate the fatigue life under constant amplitude loading,but it needs to be further researched for estimation fatigue life under variable amplitude loading.The estimation method provides certain references for the crane design and manufacture.