The Theoretical Study Of Fatigue Loading Spectrum Of Grid Structure With Welded Hollow Spherical Joints And Fatigue Life Estimation Of Key Joints Under Variable Amplitude Loading

It is well known that the gird structure with the welded hollow spherical joint is widely used in the field of structure.The fatigue of the structure under the action of suspension crane has become one of the hottest topics in academic and engineering field.Corresponding to provisions on establishment of fatigue loading spectrum and fatigue life estimation of key joints,which are keys to the fatigue research of grid structure,are not given by Current national codes or standards.Under the co-funding of the project of National Natural Science Foundation of China(51578357)and Shanxi Natural Science Foundation(2015011062),taking roof reconstruction project of structural laboratory of TYUT as research objects,the design of steel roof structure is carried out by using 3D3 S and MIDAS software;Based on the finite element analysis software ABAQUS,the numerical simulation of the grid is carried out under different loadings and different working conditions.The main work and conclusions of this paper are as follows:1.The grid structure with welded hollow spherical joints was designed by using the software 3D3 S and MIDAS;2.Using the technique of element birth and death to simulate the grid structure effect under five different loadings(3t,5t,7t,10 t,12t),seven different conditions(hoist stilling in the line 3、line 2、line 1;crane braking;hoist braking in the line 3、line 2、line 1)total 35 different conditions;Obtaining the mechanical rules(the web member is equal or greater thanthe lower chord)of different bars of the same lower chord joint in single cycle load and the position of key joint(joint 5 and joint 13);Contraposing joint 5 and joint 13,establishing stress spectrum in a single cycle load,and forming stress spectrum in one year based on the combination of working conditions.3.Based on the rain flow counting method,the theoretical fatigue stress spectrums of key joint 5 and 13 were obtained.The formula of fatigue loading spectrum was provided.4.Based on the linear cumulative damage theory(Miner theory and relative Miner theory),combined with current S-N curve of steel pipe-welded hollow spherical joints by experimental study and theoretical fatigue stress spectrum analyzed above,fatigue lifeestimation of key joint of grid structure;Different lifting weights and different conditions make different degree of damage to the key joints,especially on the condition of lifting weight 10 t and the hoist stilling in 1/4 of crane.Based on theoretical Fatigue loading spectrum,the fatigue strength of grid structure is checked.Adjusting the cross section specification of hanging point,ensuring the safety of the grid structure.