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RE: AISC k values for wide flanges

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>In Table 1-1 of the AISC LRFD 3rd edition,
>k values for wide flanges are now listed
>both as decimals and fractions. For example,
>W16x26 shows both 0.747" and 1-1/16" for the
>k value. W 14x90 shows 1.31" and 2". In
>every case the decimal value is less, sometimes
>by quite a bit.  My first question is this:
>why are the values so different?  

The fractional value is for detailing and is based upon the largest fillet
reported to AISC in the survey we do of steel producers. Thus, the steel
will fit up no matter from which producer it is purchased. The decimal value
is for design and is based upon the smallest fillet reported to AISC in the
survey. Thus, the steel will have the minimum strength predicted no matter
from which producer it is purchased.

The new T, k and k1 values were the subject of an advisory in Modern Steel
Construction that is accessible here:;

Long link. May have to cut and paste. Or go to Click News. Click
Advisories and Technical Bulletins. Click Changes to T, k and k1....

>Second question: Since the values are so different, when is it
>appropriate to use the fractional value and when is it appropriate to
>use the decimal value?

See above.

>I was going through the example on p. 14-18 of
>the manual, and I checked the R1 value used in
>checking local web yielding ... and found out that
>it is based on the FRACTIONAL value of k,
>not the decimal value as I would have thought.

That's a screw-up. It should be based upon the decimal value. We have this
corrected in an errata list that will be posted to the AISC web site.

>Bonus question (not related to k values): in the
>example on p. 5-13, about 3/4 of the way down the
>page, where the shear yielding design strength of
>a W18x40 is being checked, shouldn't there be a
>0.6 factor in the equation for Vn, as shown in Eq.
>F2-1 on p. 16.1-35?

Yes. You are a sharp screw-up identifier and this is also corrected in the
errata list I spoke of. And as I have said before, I never cease to be
amazed at how simple and obvious an error can evade the eyes that are
supposed to be finding these things before they see the light of day (most
notably mine).

Thank you.


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