AISC 360-05, Tees in flexure queries

[12345abc6ttyui67]

Hi everyone,

Been browsing for awhile (thanks for all the tips I've picked up anonymously!), but now it's time for my own question.

I am using AISC 360-05 for the design of a tee in flexure, as per Chapter F9.

I understand sections F9.1 and F9.2 but am having trouble confirming what F9.3 does / doesn't cover.

Firstly, "Sxc is the elastic section modulus referred to the compression flange". I don't really understand the phrase "referred to the compression flange" but presume this is meant to mean bending in such a way that the flange is in compression (e.g. Sxc is the 'larger' value of the elastic modulus, as the 'smaller' value would be the toe in compression). Is that right?

Secondly, does F9.3 only apply when the flange is in compression? The fact we are talking about 'flange local buckling' would suggest this is the case, but I don't see any statement along the lines of "for flanges in tension, F9.3 does not apply" which I might expect to see if this were the case? Can anyone confirm if this check is required for flanges in tension?

Thirdly, what about cases where the stem is in compression. I would have thought local buckling of the stem is more critical than flanges in compression, but I don't see it covered anywhere except with +/-B in F9.2? The commentary (p. 16.1-277) mentions the stem is covered by setting Cb = 1.0 and is 'built into' equations F9-4 & F9-5. Am I interpreting correctly that cases with stems in compression are already suitably covered by F9.2 and do not require any further consideration of buckling?

Thanks in advance!

 

[cal91]

Firstly, "Sxc is the elastic section modulus referred to the compression flange". I don't really understand the phrase "referred to the compression flange" but presume this is meant to mean bending in such a way that the flange is in compression (e.g. Sxc is the 'larger' value of the elastic modulus, as the 'smaller' value would be the toe in compression). Is that right?

My = Fy* Sxc.
Sxc = Ix/c

If the stem is in compression, c = distance from neutral axis to tip of stem, and F9.3 is used.

If the flange is in compression, c = distance from neutral axis to tip of flange.

Secondly, does F9.3 only apply when the flange is in compression? The fact we are talking about 'flange local buckling' would suggest this is the case, but I don't see any statement along the lines of "for flanges in tension, F9.3 does not apply" which I might expect to see if this were the case? Can anyone confirm if this check is required for flanges in tension?

Yes, flange buckling only occurs when the flange is in compression. F9.3 does not apply when the flange is in tension.

Thirdly, what about cases where the stem is in compression. I would have thought local buckling of the stem is more critical than flanges in compression, but I don't see it covered anywhere except with +/-B in F9.2? The commentary (p. 16.1-277) mentions the stem is covered by setting Cb = 1.0 and is 'built into' equations F9-4 & F9-5. Am I interpreting correctly that cases with stems in compression are already suitably covered by F9.2 and do not require any further consideration of buckling?

Stem Local Buckling is covered in F9.4 ; F9.4 is not applicable when the stem is in tension.

 

[12345abc6ttyui67]

Thanks cal91, all makes sense. I've since picked up a copy of 360-10 which has the stem check you reference above (F9.4). It's not (explicitly) covered by 360-05.