Friday, 3 August 2018

Global buckling analysis

Stability is one of the most important, but also the most complicated design situation. Design standards are covering the most conventional structural designs, but what can you do in case of complex buckling problems that are not covered by code rules?

To automatically calculate the complex global stability failures (flexural buckling, torsional buckling, lateral-torsional buckling and any interactions of these) ConSteel introduced 7 degrees-of-finite element (7 DOF) for steel members.

The 7DOF element is specially developed for thin-walled members where the warping of the cross-section is of high importance in the behavior, this effect is considered by the 7th DOF. In the following figure the considered nodal displacements are illustrated:

The first 6 DOF are the conventional displacements (Ux, Uy, Uz) and rotations (Φx, Φy, Φz), but 7th DOF needs more explanation. Mechanically it represents the warping of the section which is straight consequence of torsion on thin-walled members. The next figure illustrates the warping effect of I shaped cross-section when the flanges step out of the original plane of the section.

In this case, the warping DOF can be considered as a dual and opposite rotation of the flanges about the axis perpendicular to their width.

Based on the advanced 7 DOF finite element and global buckling analysis, ConSteel is able to automatical perform the stability design for the global model, including the irregular structural members such as tapered members, haunched members, and built up members.