In case of square or rectangular pipes the section wall is treated as flange or as web depending on the method of loading the section (it has effect on the section class).
For walls of such a section the code allows for
2 possible design situations (Table1):
A. A flange subjected to compression for which: KL1 - 420/sqrt(Fy), KL2 - 525/sqrt(Fy), KL3 - 670/sqrt(Fy)
B. A web subjected to compression and(or) bending: KL1 - 1100/sqrt(Fy)*(1-039*Cf/Cy), KL2 - 1700/sqrt(Fy)*(1-061*Cf/Cy), KL3 - 1900/sqrt(Fy)*(1-065*Cf/Cy).
Thus the following design situations may be distinguished:
- Pure compression (N > 0.0, My = 0, Mz=0); in such a case, all the walls are treated as flanges applying conservative limit values according to point A
- Compression and bending with respect to Y axis (N > 0.0, My > 0, Mz=0); in such a case, vertical walls are treated as webs applying to them limit slenderness values according to point B and horizontal walls as flanges following the rules as in point A
- Compression and bending with respect to Z axis (N > 0.0, My = 0, Mz>0); in such a case, horizontal walls are treated as webs applying to them limit slenderness values according to point B and vertical walls as flanges following the rules as in point A
- Compression with bi-axial bending (N > 0.0, My > 0, Mz>0); in such a case, all the walls are treated as webs applying limit values according to point B.