Theory Analysis And Testing Study On Fatigue Properties Of The Steel Pipe-Welded Hollow Spherical Joints In Space Latticed Structure

As the paragon of space latticed structure, the plate space gird structure is widely used in the field of public and industrial constructions, especially in industrial buildings with hanging cranes. Currently, both engineering circle and academic community pay much attention to fatigue problem of space gird structure loaded by hanging cranes. The fatigue of joint connection is the main kind of fatigue of space gird structure. On the one hand, due to the lack of theory study and shortage of quality and quantity of fatigue test data, fatigue design methods of plate space gird structure has not been ruled officially. On the other hand, it is hard for designers to find proper proof when they have difficulties in space gird fatigue problems, which stops the application of plate space gird structure in the field of industrial buildings.Therefore, taking the steel tube-welded hollow spherical joint as research object (the tube-sphere joint, for short), this thesis goes as follow.(1) With the help of finite element analysis software, according to model of tube-sphere joint, the stress distribution law of tube-sphere joint loaded by axial tension was obtained. Besides, the change law of stress concentration factor was obtained by changing related parameters, such as D and T of hollow sphere, d and t of steel tube and w, A formula of stress concentration parameters of tube-sphere joint was proposed.(2) On the basis of finite element analysis, the stress of key parts of tube-sphere joint can be tested by static tensile test of tube-sphere joint, getting the measured stress distribution curve of tube-sphere joint, knowing the stress concentration parameters and do a comparison of testing results.(3) Respectively,29full-scale specimen of tube-sphere joint are used in both constant amplitude and variable amplitude tests, during which process, S-N curve of tube-sphere joint can be got by using AMSLER fatigue testing machine and three kinds of loading.(4) Use the Magnifying glass and the scanning electron microscope to analysis the fatigue fracture of tube-sphere joint macroscopically and microcosmically, revealing the fatigue mechanism of tube-sphere joint. In addition, proposed the effective solution to improve fatigue strength by analyzing related factors.(5) According to the fatigue curve from test, determine the fatigue calculative parameters C、β and [△σ], established the practical fatigue designing methods of tube-sphere joint, in which the hot spot stress amplitude is seen as the basic parameter. The creative points in this thesis lie in:Design a loading device used in space gird structure joint test on fatigue, which can be useful in steel tube-welded hollow spherical joint fatigue test, with3different loading methods to choose.Revealed the fatigue mechanism of tube-sphere joint by analyzing the fatigue fracture of tube-sphere joint macroscopically and microcosmically.Proposed a formula for stress concentration parameters of tube-sphere joint by static tensile. Established the practical fatigue designing methods of tube-sphere joint, in which the hot spot stress amplitude is seen as the basic parameter.The research achievement of this thesis will be the proof of reformulating related code on steel tube-welded hollow spherical joint design in our nation. In theory, it breaks the traditional design concept, proposed a formula for stress concentration parameters of tube-sphere joint. In practice, it also provides proof of designing and dealing with the problems in programs, promoting the development of plate space gird structure in the field of industrial construction.