| Welding hollow spherical grid is a common roof structure in large-span buildings in China,and welding is the main connection mode of this type of grid.The welding process is complex and the randomness is high.The uneven temperature field in the welding process will lead to a large number of residual stresses after cooling.In addition,the fine defects of the weld will lead to different degrees of stress concentration,which will have a great impact on the fatigue performance of the welding part.At the present stage,even the use of a variety of technical means cannot fully guarantee the fatigue strength of the welding material.However,fatigue failure is one of the common failure forms of steel structure.Therefore,it is important to study the fatigue performance of welded joints.Nowadays,most flat grid structures are equipped with suspended cranes.Therefore,this paper studies the fatigue performance of steel tube-end plate connection joints in the design of grid and crane track connections.The main research contents and results are as follows :1.In this paper,the constant amplitude fatigue tests of ten specimens were carried out for the steel tube-end plate connection joints in the welded hollow spherical grid under two stress amplitudes using the Amsler fatigue tester,and the S-N curve was obtained.2.Based on the theory of elastic mechanics,the initial residual stress of the specimen was measured by the blind hole method,and the weld toe was treated by an ultrasonic impact tool.Through the fatigue test of the treated specimens,it is found that ultrasonic impact can significantly improve the fatigue life of the specimens under the same stress amplitude.3.In this paper,the eccentric measurement method of welded hollow spherical joints is established,and the accuracy of this method is demonstrated from three different aspects:theoretical derivation,static test,and finite element analysis.In addition,the fatigue test results show that the fatigue life of the specimen under the same stress amplitude decreases significantly with the increase of the eccentric angle.4.In this paper,a weld fatigue design method based on hot spot stress amplitude is proposed,and the feasibility of this method is analyzed.5.In this paper,the relevant parameters of fracture mechanics are used to preliminarily estimate the fatigue life of the specimen,and the estimated results are in good agreement with the experimental results.In this paper,the fatigue performance of welded joint of the end-plate of the circular steel tube was studied experimentally,and the influence of residual stress and initial eccentricity on the fatigue strength of the weld zone was analyzed.The research results provide a reference for the revision of relevant national standards and engineering design. |
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