FEM analysis for the behaviour of two-dimensional CHS joints with asymmetrical Full-Overlapped top-connection

Abstract

Circular hollow section steel profiles are often used for industrial purposes, like offshore structures or for aesthetical reasons. By welding two or more steel members with different inclination angles columns with a tree-shaped structure will be formed. Designers are using this column to get a natural optic for example in representative halls. Like in nature the connected members often have asymmetrical angles. To calculate the nodes of these structures is a complex part. Due to the geometrical and material heterogeneity, different stresses arise in the microstructure. Current standards have got limitations. These limitations are there for material, geometrical options or process in welding. The vertical column is defined as chord, the connected members as braces. The inclination angle is the horizontal imperfection between braces and chord. Standards have got limitations regrading this inclination angle. There is no definition for an angle smaller than 30°. Because of aesthetical reasons, there are steel joints with two or more braces, where the inclination angles are not equal. An example is the natural optic as the ideal of a tree. Columns with an on-top connection, together with a steel plate node is not included in the current standards. However, designing engineers often have to build their own models for complex structures or design it with the help of laboratory tests. In literature, it was figured out, that the inclination angle has got a large influence on the resistance of a steel joint. Due to the geometrical heterogeneity, internal bending moments can arise, which degrades the carrying capacity of the joint. This paper is about numerical case studies of tree-shaped columns with an asymmetrical shape. The full-overlapped node is made of circular hollow section profiles (CHS), which are welded in a three-dimensional way. The aim is to figure out the influence of the inclination angles on the stability of asymmetrical shaped columns in the ultimate limit state, when the angles are not equal.