I am analyzing an existing armory drill hall roof for new loading. It was built in the 1950's and is located in Minnesota. The glulam beams (running top to bottom in the picture) are 5.25 inches x 9 3/4 inches with 1 5/8 inch lams, and the wood decking is just called out as 2 inch wood decking on the existing drawings. Does anyone have any information on the type of wood and properties that would have been used in this application in Minnesota in the 1950's? Thanks in advance!
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Historical Properties of Wood
- Thread starter Gopher13
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msquared48
Structural
Well, if this was an Armory drill hall, it was built by the low bidder. Be conservative whatever you choose.
May have to do some testing, or do some research at the University of Minnesota for typical building construction of the time for the area.
OI notice you also have to deal with GL Tudor Arches... Lovely... Wrestled with those by hand in school.
Mike McCann, PE, SE (WA)
May have to do some testing, or do some research at the University of Minnesota for typical building construction of the time for the area.
OI notice you also have to deal with GL Tudor Arches... Lovely... Wrestled with those by hand in school.
Mike McCann, PE, SE (WA)
1. it looks really good and that, of course, is really good
2. 1.625" lams, i think, pre 1970s, points towards western species lumber. The old timers at a your local (relatively) laminator can tell you when the industry changed on that.
3. no matter how accurately you assess the species, however, you still won't know the combination. So at some point, sine plans, i think you'll be doing some reverse engineering. Knowing the snow load at time of design would be helpful/interesting/informative i think. Wouldn't it be nice if the current local snow was less than the 19505s era snow load. Ok, i'm an optimist.
4. but also, no matter all of the above, you're almost certainly dealing with that other thing. That other thing is that it was at one time an article of faith in the industry that the allowable wood stress in tension equaled, at least, the allowable bending tension stress. Tests proved otherwise. Code reflected tests in the allowable tension reduction of almost 50% around 1970ish. The glulammers started adding tension laminations shortly thereafter when they realized that the previous beams were not as strong in bending as they thought.
2. 1.625" lams, i think, pre 1970s, points towards western species lumber. The old timers at a your local (relatively) laminator can tell you when the industry changed on that.
3. no matter how accurately you assess the species, however, you still won't know the combination. So at some point, sine plans, i think you'll be doing some reverse engineering. Knowing the snow load at time of design would be helpful/interesting/informative i think. Wouldn't it be nice if the current local snow was less than the 19505s era snow load. Ok, i'm an optimist.
4. but also, no matter all of the above, you're almost certainly dealing with that other thing. That other thing is that it was at one time an article of faith in the industry that the allowable wood stress in tension equaled, at least, the allowable bending tension stress. Tests proved otherwise. Code reflected tests in the allowable tension reduction of almost 50% around 1970ish. The glulammers started adding tension laminations shortly thereafter when they realized that the previous beams were not as strong in bending as they thought.
- Thread starter
- #4
Thanks for the info Triangled.
Original design snow load was shown on the drawings as 35 psf which matches the current code.
The original dead load, above the 2" wood decking, included 1" of rigid insulation and S.I.S. Roofing. Maybe 3 psf. New dead load, above decking will be around 12 psf. So there will be an increase in total load by about 25%. More than enough to make me nervous when I am unsure of the properties of the wood.
Original design snow load was shown on the drawings as 35 psf which matches the current code.
The original dead load, above the 2" wood decking, included 1" of rigid insulation and S.I.S. Roofing. Maybe 3 psf. New dead load, above decking will be around 12 psf. So there will be an increase in total load by about 25%. More than enough to make me nervous when I am unsure of the properties of the wood.
yep, i get it.
and i'm thinking your 5.25 inches x 9 3/4 inch beams are only good for 70%-80% of what they were originally thought to be.
I suspect either/both of these two industry organizations will be helpful to you as you wend your way through this project: AITC and APA-EWS. And I would suspect they have a considerable repository of data regarding the way it was when it was that way, back in your 1950s.
and i'm thinking your 5.25 inches x 9 3/4 inch beams are only good for 70%-80% of what they were originally thought to be.
I suspect either/both of these two industry organizations will be helpful to you as you wend your way through this project: AITC and APA-EWS. And I would suspect they have a considerable repository of data regarding the way it was when it was that way, back in your 1950s.
Other worries about glulam from that era:
...They used casein glue (AKA Elmer's) which can deteriorate over time or moisture exposure.
...Ends of lams were often scarf jointed (before finger joints were used), these often separate due to lack of glue penetration in end grain, misalignment during gluing, or deterioration of the glue.
A major producer of glulam at the time was located in Albert Lee, MN. Onetime owned by Weyerhaeuser, but now spun off. Maybe they might have some info??
Another thing to check is radial tension in the arches. In the picture attached they look good, but with increase of dead load, it might be a problem.
...They used casein glue (AKA Elmer's) which can deteriorate over time or moisture exposure.
...Ends of lams were often scarf jointed (before finger joints were used), these often separate due to lack of glue penetration in end grain, misalignment during gluing, or deterioration of the glue.
A major producer of glulam at the time was located in Albert Lee, MN. Onetime owned by Weyerhaeuser, but now spun off. Maybe they might have some info??
Another thing to check is radial tension in the arches. In the picture attached they look good, but with increase of dead load, it might be a problem.
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