I've got a situation where I am assigning LY = 5' to some C6x13 (ry = 0.524") girts of varying lengths that will have restraint from sag rods spaced around 5'. However, when running the code check (AISC Unified 2016), my girts continue to fail from Cl. D1 (my interpretation is this is the slenderness clause of the tension section) despite what should be a KL/r ratio of (1.0)(60")/.524" = 114.5. MAIN and TMAIN are at default values of 200 and 300 respectively.
My question is what is the difference between failing from slenderness and failing from Cl.D1? Why is the Cl.D1 code check unaffected by the assignment of any LY or LZ value. I can assign LY and LZ values of 1 to my members and still I'm getting a Cl.D1 failure...The KLR in postprocessing is even listed < 200 and still showing as a failed member. What am I missing here?
I can assign MAIN and TMAIN high enough to override this situation but I don't get why it's a situation at all...
It seems the member is failing in tension slenderness. can you please share the file so that I can investigate and let you know the exact reason? Please note we check tension slenderness case against allowable value 300.
Rail Car Building to Forum.STD
Abhisek,
File attached.
Understood that tension slenderness is checked against 300, but shouldn't the program be checking the member slenderness using the LY and LZ values assigned to it rather than member length? A C6x13 with length 15' but LY=LZ=5' should have a slenderness of (1.0)(60")/.524" = 114.5 which should not be failing... the program is even showing KLR as 114.5