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Re: Pitched Tapered Glu-Lam

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This didn't go through when I tried this morning so here goes again.
> 
> Bdpooley(--nospam--at)aol.com wrote:
> >
> > Indeed the 15 psi is a low value for radial tension (tension perpendicular to
> > grain) for Western Species (includes Douglas Fir -Larch, Hemfir, etc.) glulam.
> >
> > However, I disagree with the statement that it is a catastrophic failure.
> > Double pitched and tapered (DPT) glulam beams will sag, but I have yet to hear
> > of a beam that has fallen to the floor/ground. I investigated one situation
> > where the DPT beams sagged two feet under a snow load of 60 or more psf that
> > were designed for 30 psf. One of the beams even fractured to the extent that
> > the bottom tension lamination was broken, but it did not fall. If you know of
> > a failure, I would appreciate hearing from you.
> >
> >  AITC now has a recommendation for designing DPT glulam beams for Western
> > species. It shows how to design reinforcement (steel rod or rebar in epoxy)
> > to prevent the "smile" that can occur due to the radial tension. Southern Pine
> > has a much better value for radial tension and many of those designs do not
> > require reinforcement.
> >
> > Contact AITC at 303-792-9559 for more information.
> >
> > Bruce Pooley, P. E.
> >
> Bruce,
> 
> I observed several glulams which failed during the 1996-1997 winter snow
> in the Yakima Washington area.  Overall I was amazed that the beams were
> still "in place" after the snow.  Several truss chords had broken
> completely in to but the truss did not fall.
> 
> Specifically regarding radial tension.  There was one beam in a CA
> storage room that did fail and collapse onto the bins of fruit.  Several
> of the others in this structure had severe cracks but did not fall.
> This was a situation where the combined bending moment and the begining
> of the  curved section in radial tension combined to cause the failure
> of the beam under record snow loads.
> 
> Sincerely
> 
> Jill T. Shuttleworth, P.E., S.E.
> Sunnyside, WA