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Re: shear strength of WF

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Both the ASD and LRFD manuals develop their design equations based on
elastic flexural theory, i.e., fv = VQ/It.  In both cases, AISC wanted to
save the engineer the trouble of calculating Q for every design situation.
For W-shapes in strong-axis bending, fv (max) at the neutral axis is
approximately equal to the shear force V divided by the area of the web.
Thus the code simplification.  See Salmon & Johnson's 4th edition, chapter
7, for a good discussion of this.

Following the same philosophy, you could calculate the weak-axis bending
shear stresses using VQ/It.  the maximum stresses will of course be at the
neutral axis.  This assumes, that your weak-axis loading is applied in such
a way as to mobilize the entire cross-section.  If you weak-axis loading is
applied at one of the flanges, you may also have to include torsional shear
stresses in the flanges.  The LRFD Specification Section H2 gives
requirements for combining shear stresses that involve torsion.

Hope this helps.

Rick Drake, SE
Fluor Daniel, Aliso Viejo

Mark Pemberton <Markp(--nospam--at)> on 11/01/2000 09:01:47 AM

Please respond to seaint(--nospam--at)

To:   "'seaint(--nospam--at)'" <seaint(--nospam--at)>

Subject:  shear strength of WF

Can anyone direct me to useful provisions for
the shear strength of a wide flange beam in
weak direction loading?  (The key word in this
sentence is "useful" - the AISC ASD & LRFD
manuals do not seem to address this issue
in a usable manor)

Mark Pemberton, P.E..

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