Compilation Of Load Spectrum And Estimation Of Fatigue Life Of Bolted Spherical Joint Grid Structures Under The Action Of Suspended Cranes

In recent years,due to the production demand,the suspension crane under the grid structure of bolted spherical joints plays a key role in lifting and transportation of heavy objects.However,under the cyclic alternating load,with the increase of service time,the fatigue damage of the grid structure is like that of a thousand miles dike destroyed by ant caves.At present,little attention has been paid to the fatigue problem of suspension cranes under the grids at home and abroad,and there is no corresponding code in our country as a basis for designers,which leads to conservative tendencies in the process of grids design,resulting in a certain degree of waste of resources and hindering the future development of grids.Therefore,the fatigue problem of bolted ball space truss is urgently put forward to the design,manufacture and installation workers,which needs to be solved urgently.The contents,methods and results of this study are as follows:1.Through MIDAS finite element analysis software,the analysis and calculation of the grid structure with bolted spherical joints are carried out.The maximum stress amplitude of suspended suspension points is counted,and thesuspension points which are prone to fatigue damage are found out.After obtaining the load-time history curve of the key hanging point,it is converted into the stress amplitude-frequency histogram by rainflow counting method,which has a certain reference value for the compilation of the load spectrum in the future;2.Through the investigation of No.1 and No.2 workshop of bolted spherical joint grid structure,the general situation of workshop engineering and crane operation are known.According to the actual operation of crane,the key hanging points of No.1 and No.2 high-strength bolted spherical grid structure workshop are analyzed and calculated,namely No.6,No.16,No.37 and No.45 of No.1 workshop,No.6,No.16,No.37 and No.45 of No.2 workshop.Based on the linear cumulative damage theory-Miner theory and modified Miner theory,and combined with the constant amplitude fatigue S-N curves of M20 and M30 high strength bolts obtained from the experiment of Institute of Steel Structure and Spatial Structure of Taiyuan University of Technology,the annual cumulative fatigue damage of suspension bolts was calculated,and the residual fatigue life of two workshops was estimated.The fatigue life of No.1 workshop is 21.47 years and that of No.2 workshop is 57.41 years;3.Taking the lifting weight and initial acceleration as variables,the influence of crane lifting on dynamic response of bolted spherical space truss and the relationship between stress diffusion range and initial acceleration are explored;4.Some factors affecting the fatigue of space truss are discussed,such as crane lifting,load sequence,small load selection and under-load overloading;This paper discusses the compilation of fatigue load spectrum theory for suspension point of bolted spherical space truss structure under suspension crane action,which can provide reference for fatigue life estimation by cumulative damage theory and determination of fatigue reliability index.