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dswag (Structural) (OP)
10 Apr 12 17:13
I am designing a roof with a 24' span using 4x15 beams (nominal-3-1/2" x 14" actual dimensions).  The beams are exposed to elevated temperatures 100-120 deg F throughout the entire year.

Which wood product is the best for elevated temperatures: Parallam (PSL), Glulam or regular sawn lumber?

Any thoughts welcome, Thank You
dik (Structural)
10 Apr 12 21:48
There are several threads regarding wood exposed to fire.  At 100 to 120F it's not likely a problem.  Best to check with the suppliers of glulam, PSL, or LVL material to see what the effects are on the adhesives.

The wood will dessicate, will become more brittle, and lose some of its toughness...

Dik
focuseng (Structural)
10 Apr 12 21:59
NDS has some good primer info on elevated temps. Beyond that check forest product lab.  Also Wood Handbook Chp 4.  As I understand it: at the cellular level, the wood looses strength at elevated temps (above 150 on more than an occasional basis it is not reversible).

Ct needs to be applied to for this temp range -see table 2.3.3 (NDS 2005 ed).  Generally all get the same treatment of the adjustment factor to all your proposed material and I don't think I could say that one will perform better at this temp range better than the other.  At that span though I would expect you to get better mileage out of EWP than sawn lumber.  If exposed for visual effects then that changes the equation.  It all depends on what you need it to be.

MAP
Helpful Member!  MiketheEngineer (Structural)
11 Apr 12 16:32
My recollection is that over 150F - you will get degradation.  Below that - OK.  Check w/ mfg!!
Helpful Member!  msquared48 (Structural)
12 Apr 12 14:27
Is there elevated humidity associated with the elevated temperatures?  If so, I'd be concerned with mold too with wood with a possibility of needing positive venting.

Under sustained load with elevated temperatures, plastic will creep.  So I wonder about the Parallams, not so much the Glulams or solid sticks.   

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
 

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