Code Check Using AISC 360-05 1

[eit09]

I have two questions concerning the envelope ASD Steel Code Check.

1. For a few members I am receiving L/r> 300 for tension member.
A few of the members are for monorails and the majority are horizontal braces which are marked tension only.

2. For a couple of beams but mostly double angle vertical braces I am receiving KL/r > 200 for compression members. The vertical braces are marked Euler buckling.

Q1.Why are these warning coming up in the code check versus the stress ratio?

Q2. On double angle vertical braces we provide a minimum of two tie plates. For the double angles I leave the unbraced length as full length but if I change it to the tie plate spacing I do not get the warning. Should I be changing the unbraced lengths to tie plate spacing in RISA?

 

[JoshPlumSE]

EIT -

There is a Tools - Preferences setting where you can prevent the KL/r > 200 limit from negating your ability to get a code check.

If these members are acting purely as tension members, then you may be able to ignore these limits. After all, the code gives these as a recommended limit rather than a hard limit. That being said, I would be cautious. You might want to pull open that section of the AISC code or the corresponding commentary to get a better feel for why the code committee doesn't like this level of slenderness.

 

[eit09]

I did read chapter E & D for both and to me it reads a constructability issue. Take care of that with tie plates but wanted to make sure there isn't somthing RISA is trying to tell me besides the kl/r rule of thumbs.