It is very weird. I just did the below cable tray support design. Both the members highlighted below are same length and have same load. The top member fails due to slenderness but the bottom is okay. Has anyone ever come across the similar situation?
Please attach the STAAD model here
Cable Tray 5m.STD
Attached is the file. The channels have the same vertical load
The member 21 is failing in slenderness because the nature of force in the member is compression for which the allowable slenderness is 200 and the actual slenderness for the member is around 280. The member 22 has the same actual slenderness but the allowable slenderness limit for that member is 300 as the nature of axial force in it is tensile. So the former fails the slenderness check while the later passes.