"h" value in calculating HSS nominal shear strength? 1

[RobertEIT]

I am looking at AISC-13th 16.1-68 sect.G4, it says in calculating rectangular HSS nominal shear strength, the area Aw=2ht, where h shall be taken as the corresponding outside dimension minus three time the thickness.

Now look at AISC Example G.4 (Example page G-8), "h" is taken as:

h=d-2*(3*tw)=6-2(3)0.349)=3.91 in. (note: there is a "2" multiplies 3 times of the thickness)

Look at another AISC Example H.5c(page H-15), "h" is taken as:

h=d-3*tw=6-3(0.233)=5.3 in. (note: there is just "1" multiplies 3 times of the thickness)

These two examples, which one is correct, which one is wrong?

Thanks.

 

[kslee1000]

Looked up on my 9th ed. structural tubing properties table, there is a foot note "Properties are based upon a nominal outside corner radius equal to two times the wall thickness". Look up the 13th, there shall have noted as well.

 

[nutte]

There does appear to be an inconsistency. The specification (page 16.1-68, section G5) says to use d-3t, which is what the example on page H-15 did. This is also consistent with specification section B4.2, whch says to take off 3t (1.5t twice) from the nominal dimension.

Page 1-5 says that this radius is assumed to be 1.5t, but that the tolerances of ASTM A500 allow it to be as much as 3t. Perhaps that is why the example on page G-8 took off 3t twice, using the upper bound for the radius. This would appear to be conservative and unnecessary, though, since section B4.2 says to use 1.5t.

If I were doing one of these calculations, I would follow H-15.

 

[RobertEIT]

Thanks nutte, you answered my question.

One more question to ask: if this kind of question showed up in SE I exam, which answer you think NCEES will accept as a correct answer?

Thank you very much.

 

[nutte]

They should accept either answer. How can they say one's wrong when it's in the specification that way?

If it's multiple choice, though, just hope both answers aren't there!