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RE: Laminated, curved stair stringer

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Actually, Section 5.5 of the Fourth Edition of the Timber Construction
Manual says "Until further research is done in this area, it is recommended
that the design value in torsion, Fs, be limited to the same value
recommended for radial stress".  Those values may be found in Section 5.11.3
of the same manual.  The values are very low...15psi for Douglas Fir-Larch.

J. Grill

-----Original Message-----
From: Casey K. Hemmatyar [mailto:khemmatyar(--nospam--at)hotmail.com] 
Sent: Monday, April 19, 2004 9:31 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Laminated, curved stair stringer

Dmitri:
The "Shear Parallel to Grain" (Fv) property, is used for the torsional 
analysis of Sawn Lumber.

Casey K. Hemmatyar, P.E.

===========================================
I have been asked to design a stair stringer for a curved stair that will be
constructed of microlam or versalam material.  The stringer(s) will have no
intermediate support (this is not a spiral stair), so the loads will be
significant.  My primary concern is torsion stress in the stringer.  I have
not been able to locate any method for determining the allowable torsion in
a wood member.  Do I simply use the values for allowable shear?
Any comments or advice would be greatly appreciated.

Dmitri Wright, S.E.

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