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Fwd: Lateral Stability of Wood Beams

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Re:   Lateral Stability of Wood Beams

Ref:  1.)   1991 NDS
      2.)   "Lateral Stability of Glue Laminated Beams," by R. F.
      Hooley and B. Madsen, ASCE Structural Journal, June, 1964, p.

Is there a problem with the lateral stability requirements for
unbraced wood beams in the 1991 NDS?

A while back, I was designing a wood beam that had what I considered a
rather large unbraced length (it was a beam supporting an exterior
bearing wall at a stairwell) and was getting very small reductions in
allowable stresses using the provisions of Section 3.3.3, so I decided
to check R(B) (Eq.  3.3-5) to see what would an effective length be
for R(B) = 50.  Assuming a 2 X 12, it would have to be *42'-8"* long
before R(B) would be equal to 50!

A footnote to Table 3 of reference (2) states that critical stresses
were determined by using E (Modulus of Elasticity) and G (Shear
Modulus) from Table 2, *however*, Table 2 has the Shear Modulus and
the Modulus of Elasticity listed with the *same order of magnitude*
instead of the Shear Modulus being about 1/16th of the Modulus of

I called this to the attention of AFPA when I discovered it, but
never received any response.  I would appreciate any comments and
thoughts that you might have on this.

A. Roger Turk, P.E.
A. R. Turk, Consulting Engineer
Tucson, Arizona

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Subject: Lateral Stability of Wood Beams
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Richard Lewis, P.E.
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