Ultimate Strength And Reliability Design Of Steel Tubular Space Joints In 750kV Lattice Truss

With the rapid development of China's electric industry, the large span and high-rise steel tubular structure have become more and more widely applied. Compared to angle steel structure, the steel tubular structure has better mechanical performance,including small fluid resistance and good stability. Therefore, it has been widely used.In the large lattice truss of substation, the tube-gusset joint type is generally applied. It's convenience of production and construction, but a waste of steel. In order to save costs,a new type of space joint was produced, which is intersected welded on the side, and gusset plate connection on the other side of the joint. At present, there is few scholars on this kind of joint home and abroad. In view of the situation, this paper has carried out a series of research on this new kind of joint, and the concrete work is as follows:(1) a new type of column joint was applied in lattice truss of 750 kVsubstation in Youning,Qinghai. The column joint is intersected welded on the equal width side, and gusset plate connection on the variable width side. At the same time, a new type of beam joint was also applied, which is intersected welded on the upside and bottom,gusset plate connection on the front and back. Full-scale tests were carried on for the column joint and beam joint to analyze the stress performance, failure modes, ultimate strength and load- Strain response curves, and get the load- displacement response curves.(2) Use the finite element software ANSYS to set a proper model. Comparing the computed result of the software with the test result to confirm the model's compatibility by which it can be seen that the test result and the fitting result are in basic consistence.(3) Several parameters which affects the supporting capacity were obtained through the analysis of the test results, such as the ratio of diameter to thickness, the ratio of braces' diameter to chord's diameter, and the ratio of braces' thickness to chord's thickness. Analyze the influence of the different parameter on the bearing capacity with the finite element model.(4) Propose a concept design method based on reliability of complex joints. First of all, Split joint and use the codes and regulations to design the bearing capacity at limit condition of chord, braces and gusset plates. Analyze the reliability of joints through ANSYS probability analysis of PDS module and obtain the reliable index of the chord,the weakest brace and the weakest gusset plate. According to the caparison between the reliability index and target reliability index, a second design was carried onand a coefficient was proposed which could be used to design other braces and gusset plates. Eventually, the strength of joint must be greater than the strength of the chord.And the strength of chord must be greater than the strength of the braces. the reliability index should be greater than or equal to the target reliability index, to ensure the safety and economy of the joint.