Study on Direct Analysis and Design Method of Space Truss Structure with Steel Pipes

At present, many steel structure design standards at home and abroad recommend the direct analysis method as the preferred method for steel structure analysis and design. The simulation method of the rear member and the implementation details of the cross-section fiber division method are not described in detail. The displacement-based beam-column element is used to comprehensively consider the geometric nonlinearity, material nonlinearity, the overall initial defect of the circular steel tube space truss structure, the initial defect of the circular steel tube member and other factors that have an important influence on the structural stability and bearing capacity, and the nonlinear analysis of the structure is carried out. Based on the analysis and full stress optimization design, the direct analysis and design process of the circular steel tube space truss structure is proposed. Taking a main truss in an actual project of a three-center truss structure as an example, the structural orientations of different member equal fractions, different initial geometric defect application directions of different members, and different fiber division numbers of circular steel tube sections are compared. The maximum deformation of z-direction, the stress, the axial force and the bending moment of the member are studied. The influence of these three factors on the results of the direct analysis of the circular steel tube space truss structure is studied. By comparing the calculation results with the traditional first-order elastic analysis method, the applicability of the proposed direct analysis and design method of the circular steel tube space truss structure in engineering practice is verified. The results show that: under the combined working conditions of 1.3D+1.5L and 0.9D+1.5W, the calculated truss deformation and the stress of the members increase gradually with the increase of the equal fraction of the members; With the increase of the rotation angle of the maximum bending direction of the member around the biaxial direction of the member, the maximum z-direction deformation of the structure obtained by direct analysis and calculation, the stress of the member and the biaxial bending moment all show a decreasing trend, and the biaxial bending moment of the member is greatly affected with a change rate exceeding 80%; because the wall thickness of the round steel pipe is much smaller than the circumference, the change of the structural calculation results is very limited when the radial equal fraction increases from 2 to 4, and the change rates of deformation and stress are both less than 0.1%. Under the combined condition of 0.9D+1.5W, the maximum z-direction deformation of the structure when the hoop equal fraction is 32 is 15.9% different from that when the hoop equal fraction is 4, indicating that the number of section divisions has a nonnegligible effect on the structural stiffness; for the members with small slenderness in the circular steel tube space truss structure, the stress calculated by the direct analysis and design method and the traditional first-order elastic analysis method are relatively close, and the difference between the stress results under the two working conditions is less than 3%. For slender members, the difference between the calculation results of the two calculation methods is obvious, and the difference can reach 25.5%.