Research On Practical Design Method Of Circular Steel Tubular X-joints With Stiffener

Simple tubular joints (also known as direct welded joints) are widely used in the steelstructures.Internal stiffeners are commonly employed to enhance the strength and stiffness of simpletubular joints. Ring-stiffened tubular joints are widely used in modal structures as they havemany advantages such as high bending capacity, high rigidity and not affect the appearance ofbuildings.At present, abundant research results of simple tubular joints were achieved and theformula expressions for the strength of simple joints are provided in existing major codes anddesign guides. Part of codes suggest the forms of ring-stiffened joints, but lack of detaileddesign guidance on the determination of their strengths. Experiments and FEM analysis werewidely used in recent actual projects.In this paper, finite element analyses of axially loaded X-joints with plain ring stiffenershave been carried out to provide a practical design method and formula expressions. A groupof studies were carried out in this paper:1) Compare the loading-carrying capacity improvements of the ring-stiffened X-jointswith stiffeners set in different positions under axial brace force.2) FEM analysis of saddle-stiffened joints and crown-stiffened joints were carried out,different theoretical models based on the observed failure mechanism were presented, theinfluence of dimensionless parameters (such as β,b_w/d,t_w/t) to the/was studiedand the formula expressions based on the six-hinges (or four-hinges) loop medal and six-hinges (or four-hinges) link modal were derived.3) The influence of effect of axial stress of the main pipe on the ring-stiffened joints werestudied, combined with formulas of unstiffen X-joints provided by <Code for design of steelstructures> GB50017-2003, the practical design method and formula expressions for saddle-stiffened and crown-stiffened orthogonal X-joints were provided in this paper.4) According to the literature review and numerical analysis results, based on theexpression of “strength of ring-stiffened joints=strength of unstiffened joints+strength of stiffeners”, the strength of stiffeners were grouped into10basic mechanical models. Under theguidance of this design idea, the strength formula expressions and practical design method foroblique ring-stiffened X-joints were provided.