Research On Out-of-plane Bending Stiffness For Directly Welded T-type RHS Joints

The directly welded T-type RHS joints are commonly used in vierendeel truss.When branch is subjected to out-of-plane moment loading, and the branch-to-chordwidth ratio β is less than0.85, T-type RHS joints show semi-rigid nature. In order tobuild the entire structural model accurately, determine the effective length of the branchand analyse the stability of the structure, a quantitative analysis of initial stiffness, yieldstiffness and yield load of T-type RHS joints which is subjected to out-of-plane momentloading was conducted in this paper, and the corresponding formulas were concluded，which will gain a lot of convenience for the engineering application. Specific details areas follows:(1) A plastic hinge model was built for T-type RHS joints under out-of-planemoment loading, which means the supporting plates of the joints are equivalentlyreplaced by six rigid variable-section rods. Based on the essential mechanical theory,and the application of structural mechanics, we derived the formula of out-of-planebending stiffness from the perspective of theoretical model.(2) Four node shell element shell181was used in building the ANSYS FE model.Meanwhile, the factors of boundary conditions, geometric nonlinearity, materialnonlinearity and the fillet effect were considered, and then modeling method wasvalidated. On that basis, we conducted a parameter analysis on the T-type RHS joints.Univariate parametric analyzing method was applied in analyzing the dimensionlessparameters, which include=10,=10,=020,=10(amongwhich the parameters0and0determine the geometrical size of the joint), mainlyto explore the influence of these parameters on the out-of-plane bending stiffness andyield load. At the same time, simple mechanical model was built to explain it.(3) Based on the plastic hinge model, with the application of multiple regressionanalytical method, formulas for out-of-plane bending stiffness and yield load areconcluded. For different yield-point steel，plasticity comes much earlier for steel oflower yield point when joints under out-of-plane moment loading, and it will lead to adecrease of post-yield stiffness. Therefore, correction factor was proposed in thepost-yield stiffness formulas.(4) The out-of-plane bending performance of T-type RHS joints under complexloading was analyzed, complex loading situations including the chord subjected to axialloading, the chord subjected to in-of-plane moment loading, the chord subjected toout-of-plane moment loading and the branch subjected to axial loading, their influenceon post-yield bending stiffness and yield load are considered respectively. Researchshows that, the branch subjected to axial loading has influences on initial bending stiffness. The chord under out-of-plane moment loading, the chord under in-planemoment loading, branch under axial loading show on obvious influence on post-yieldbending stiffness. The influences of complex loading situations were considered byproposing relevant correction factor to the formulas which were derived when thebranch under pure bending.