Experimental And Theoretical Study On Static And Constant Amplitude Fatigue Behavior Of Pipe-hollow Sphere Suspension Joints In A Space Frame Structure

Welded hollow sphere joint grid structure,which is due to its large span,reasonable load and convenient construction,is widely used in industrial architecture,especially in industrial plant with suspension crane.Repeated alternating load caused by function of suspension crane leads to the possibility of fatigue failure in grid structure and suspension joints.The research on grid structure is mainly focused on its static behavior and so on,but is immature on its fatigue property,which caused that the current relevant codes are imperfect.This paper is supported by national natural science foundation project(51578357)and natural science foundation project of Shanxi(2015011062),aiming at commonly used suspension joints— “pipe-sphere” joints,experimental and theoretical study on static and constant fatigue behavior is conducted,the main research work and conclusions are as follows:(1)Based on field investigation around Taiyuan,combining with design code and manual related to suspension joints,adopting orthogonal experimental design method,using welded hollow sphere diameter D,welded hollow sphere wall thickness T,pipe diameter d and wall thickness t as variables,which were considered at three values,9 joint specimens were designed and finished.(2)Based on MTS testing machine,static tests of 8 specimens of joints were conducted,static finite element analysis of 9 joints were analysed by ANSYS and ABAQUS,stress distribution and location of hot spot stress in the joint were presented;aiming at “pipe-sphere” joints,main factors related to stress concentration were discussed,influence degree and correlation of different factors were presented;formula of hot spot stress concentration factors considered reduced factor by leg size of fillet weld was established.(3)Fatigue behavior testing with constant amplitude in higher stress range of 8 “pipe-sphere” joints were completed by MTS testing machine,through which 8 effective constant fatigue testing data were obtained;and nominal allowable stress amplitude of joint was calculated,namely [ ]62 10?100.02MPa?(35)(28).(4)Constant amplitude fatigue life of “pipe-sphere” joints were estimated through fracture mechanics method,which was lower than fatigue life by test;emphasis on discussing the influence of different initial crack length on the crack propagation life,concluded that if the initial crack size increases ten times,the fatigue life of the crack propagation is reduced by about 80%.(5)Finite element analysis of representative “pipe-sphere” joints was analyzed by XFEM technology of ABAQUS,acquired crack initiation and propagation direction in single cycle;compared with test results,the suggested values about the key control parameters of this kind of joint with the constant amplitude fatigue test were presented: recommended displacement value of joint with crack initiation is 5%(35)U;displacement value of specimen failure is 10%(35)U.