Nonlinear Analysis on Ultimate Flexural Bearing Capacity of the N-shaped Steel Tubular Joints

As the author has discovered in the pratice of the project design, the steel pipe size in the truss structure will increase with the expanded span of the spatial structure, far exceeding its original range of application. Therefore, the resulting effect of the joint additional moment on the steel pipe crossing nodes should not be ignored, and how to calculate the ultimate flexural capacity of the steel tubular joints has become an urgent problem to be solved in the joint design. However, the research on ultimate load-carrying capacity is mainly restricted in utilizing the current data and Code for Design of Steel Structures to analyze the axial load-carrying capacity, and the research on ultimate load-carrying capacity of the joint under additional moment is still inadequate. This paper, from the joint stiffness perspective, initiates with brief analysis of the effect of steel pipe size on the joint additional moment so as to illustrate the rationale and necessity for taking into account the joint additional moment in the steel pipe structure, and follows with the adoption of both three-dimensional four-joint 181 elastoplastic shell element and the finite element model (by which N-shaped circular steel pipe crossing nodes is established for the ideal elastoplastic material in ANSYS finite element program) to fit the formula for the flexural capacity of the N-shaped joints based on orthogonal test method and regression technique with geometric nonlinearity and material nonlinearity taken into consideration. It is designed to provide some reference for the design and application of steel tubular intersecting joints in the future.