Theortical And Experimental Research On Uniplanar X- And Multiplanar XX-joints Made Of Square Hollow Sections

This paper studies the static behavior of uniplanar X- and multiplanar XX-joints made of square hollow steel sections. As structural compents, square hollow steel sections have favourable properties for resisting compression, bending and torsion. The structures made of square hollow steel sections by using the directly welded joints without any reinforcement are fabricated easily and economically, which can be found in many applications all over the world. The key problem in the designing of this structure is the static behavior of the directly welded joints. Because the stress distribution around the joint is complicated, little information was available. In china, the research about the directly welded joints has been developed for a short time, and no mature designing specification can be observed, which leads to restrict its applications to some extent. This paper has the important theoretical and practical value. The main research woks are concluded as follows:1, Among the tubular analysis methods, the reasonable analytical study is a important and indispensable part. Firstly, a set of formula is developed for uniplanar X- and multiplanar XX-joints loaded with axial forces, in-plane bending moments and out-of-plane bending moments respectively. In china, it is the first time to develope a set of formula for full-width joints considering the membrane effect. 2, In the experimental study , 12 joints tests are completed, including 5 uniplanar X joints loaded with axial forces, 3 uniplanar X joints loaded with in-plane bending, 4 multiplanar XX-joints loaded with axial forces, with the emphasis on the influence of and the existence of the out-of-plane braces, of which the multiplanar XX-jointstests is the first experiment project in china.3, In the numerical study , a numerical model (finite element model) by using thecommercial FEM program named ANSYS and the shell element has been developedand calibrated with the results. The numerical modeling and calibration considers thefollowing aspects : the element types , the modeling of the weld, the modeling of themembers and the behavior of material and geometrical non-linearities.4, In the parameterical study , a amount of joints with the variable joint parametersunder different load-case are analyized. Based on the analytical formula and theexperimental and numerical results , design recommendation on the static strength forsuch connections are proposed.