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RE: LIGHTWEIGHT STEEL/COLD-FORM METAL FRAMING

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It is correct that calculating the allowable stresses on light gauge
sections can be complicated as others have stated. Depending on the tables
you are working from, if they give you the effective section modulus at Fy,
then you can use Fy*Se=Mn. To get to allowable stress design levels, you
would then divide by gamma which for bending is 1.67. This is all based on
the assumption that the section is restrained from lateral torsional
buckling and that the compression flange is laterally stabilized. If this
assumption is incorrect, Fs<Fy. If your tables do not give you Se, you must
check the width to thickness (w/t) ratio of the compression flange as well
as the depth to thickness (d/t) of the web and subtract the "ineffective"
portions of those elements and then calculate the effective section modulus
neglecting the ineffective portions of these elements.

The 1996 Cold Formed Steel Design Manual is an excellent publication with
the specifications and extremely clear examples on calculating effective
section properties and allowable stresses. From there, it is fairly simple
to set up a spreadsheet to do the work for you. It's painful the first time,
but well worth it the second time. You can call AISI at 1-(800) 79-STEEL or
go to their website:

http://www.steel.org

Regards,
Bill Allen

-----Original Message-----
From: TahirQ(--nospam--at)aol.com [mailto:TahirQ(--nospam--at)aol.com]
Sent: Tuesday, August 04, 1998 4:12 PM
To: seaint(--nospam--at)seaint.org
Subject: LIGHTWEIGHT STEEL/COLD-FORM METAL FRAMING


STRUCTURAL STEEL DESIGNERS:

For 33 Ksi LIGHTWEIGHT STEEL (10SW16) what to use as allowable stress in
calculating Sx.  I have been thinking to use 0.667(33 Ksi) = 22 Ksi as was
done for 36 Ksi (0.67X36ksi=24ksi)
A speedy reply would be great.

Tahir