Research On Safety Assessment Method For Jib Structure Of Tower Crane

In the tower crane,the jib structure is the main part of the bearing,and it withstands long-term alternating loads.In combination with the safety accidents of the tower crane in recent years,the jib structure is the high-risk area where tower cranes break down.The jib structure of the tower crane is mainly a welded truss structure,so there are initial welding defects.In addition,the work is often performed in a high-intensity cyclic random load,which is prone to fatigue failure,so there is a safety hazard in the work of the jib structure.Therefore,the research on the structure safety of the jib structure is particularly important.Taking the TC6020 tower crane serving on a building construction site as the research object,according to the theory of structural integrity assessment,and based on fracture mechanics theory,reliability theory,damage evolution criterion and fatigue damage theory,a research on the method of evaluating structural Integrity of jib structure has been done combined with finite element analysis results and numerical analysis and other technical means.The main content of the research in this paper includes the following aspects:(1)Based on the theory of structural integrity,the safety assessment process and methods for the jib structure are studied.From two aspects of fracture assessment and fatigue damage,a set of processes and methods that are more suitable for structural safety assessment of the jib structure are formed combined with the structural characteristics and working environment of the jib structure.(2)Research on the fracture safety assessment of the jib structure.Taking the jib structure of a TC6020 tower crane as an example,the finite element analysis is carried out.At the same time,take the British standard BS7910 three-level fracture assessment criteria as a reference,combining the finite element analysis result of the jib structure and the position parameter of the crack defects,the fracture safety assessment is carried out.Thus,the result of the safety assessment of the jib structure is obtained.(3)Research on the fatigue safety assessment of the jib structure.Taking the jib structure of a TC6020 tower crane as an example,analyzing the advantages and disadvantages of nominal stress fatigue life analysis method and fatigue crack propagation assessment method combining with the actual fatigue loading conditions and crack defect characteristics of the jib structure.The fatigue life of the jib structure is predicted combined with the results of the finite element analysis of the structure.And the influence of various parameters on fatigue assessment results is also discussed.(4)Research on the crack propagation analysis of the jib structure.Taking a finite plate with a large defect as an example,the interaction integral method and the extended finite element method are used to solve the force intensity factor respectively.And the accuracy of the two methods for crack simulation is compared and analyzed.Combined with the finite element analysis results of the tower crane boom structure,the local finite element model of the crack region is established.The crack propagation simulation analysis is carried out on the defect jib structure,and the fracture parameters of the defect jib structure and the propagation direction and state of the crack cell are obtained.