Design Value of aspen

[jfl]

Hi everybody,

I ve been trying to build something (garage, workshot, toy box for adult... I have to call it a "agricultural machine shelter" to stay within the municipal bylaw...)

The best thing to give you an idea is a picture:


The other title I could as given to this post  is "The whole universe is against me!" because I've been looking for one information for the past 2 years and I always come very close but there is always a single missing element.  I'm trying to find out the proper size for the beams in the shelter if I use Aspen (Trembling aspen (populus tremuloides) or Largetooth aspen (populus grandidentata) mixed together).

I found many interesting documents, amongst other, the 1986 Wood Structural Design Data - with 1992 Revisions

http://www.awc.org/Standards/wsdd.html

Where you can get the tables for the load you can put on every standard size with every Fb value. On that site, I also found a lot of information on powerpoints.  In any way, I just found while browsing Forestry Forum a link to a calculator summarizing everything I took a long time to learn:


https://forestryforum.com/members/donp/beamclc06b.htm


Everywhere I look, I can find US values for for Aspen, in 2 to 4 inch thick... Ho! I realized I did not give much background on myself, so here I go:

I live in Quebec, Canada, close to Montreal.  Hence, here I have to consider snow, A LOT OF IT. Since I'm in the woods (a 25 acre lot) there is not much wind, so that should not be an issue, compare to building located in an open field.  Also earthquake is not an issue. (I've been reviewing a lot of powerpoints on the AWC...) Even if I'm Canadian, I still use imperial system when building. For most of the rest I use metric, all but the swimming water, which has to be in F. Anyway, I have found Aspen design values and grading rules on http://www.nelma.org/Page-9.html .  More recently I found the NDS 2005 Supplement at http://www.awc.org/pdf/2005-NDS-Supplement.pdf.

On all those references, aspen only exists at 2 to 4 inch thick lumber.  In Timber section (beam and stringer, and, post and timber in fact) there is no aspen.  In Canada, Aspen is classified in Northern Species. If you go to the Canadian wood council:

http://www.cwc.ca/NR/rdonlyres/6558C04A-F29E-41E4-BEF5-424B767CB58D/0/Timber.pdf

you'll find the canadian design value in MPA for 4 wood classifications, but the US design values of only SPF and Douglas fir larch(N).

I tried to convert MPa into psi by using 1 atmosphere = 14.7 psi = 0.1013 MPa, but the number just doesn't fit even with rouding.  If I take Select Structural SPF  Beam&Stringer = 1100 Psi.

1100 psi / 14.7psi * 0.1013 = 7.6 MPa
for no1: 900 psi => 6.2 MPa
for no2: 600 psi => 4.1 MPa

The actual number in MPa are (directly from the document):
SS: 13.6 MPa
no1: 11.0 MPa
no2: 6.3 MPa

So obviously I  do something wrong.  Maybe the ajustement factors are not the same and US values must be ajdusted according to NDS but Canadian values must be adjusted differently from CSA 086.  And I can't any usefull documentation on CSA 086 (compared to what I can find on US sites).

I could find some values from https://forestryforum.com/members/donp/logbeamcalc.htm but I think those are only valid for unsawn logs, isn't it?

I'm starting to think that I should take my 8x10 beams and cut them in 2 to make 4x10 beam (for which I know the strength), grade them and then just nail them together.  I just doesnt make any sense to me to do that.

Anybody has a suggestion?

Thanks,

jf

[Don P]

Hi jfl, welcome to the forum.

The beam calcs you stumbled upon are mine. I'm just a simple carpenter who ran into the same troubles you've been bumping into. I'm not a real math wiz so I programmed the beam formulas into javascript to keep me from making dumb mistakes. When other folks here were bumping into the same problems Jeff, the webmaster here, gave me space to put the calcs online. So there's the quick story from this end (don't look behind the curtain  :D).

The log beam calc was one of, if not the first one, the formulas are from Mackie and Hahney "Log Span Tables" and the drop down values came from every source I could scrape together. They had a very few species listed. So no I wouldn't call them gospel. I should redo that calc.

You've been busy checking sources and have found the right ones, the '05 supplement is the most up to date design value info published and aspen is not in the heavy timber table other than as northern species as you've found.

I'm no good at converting, hopefully a math wiz will pipe up with the conversion, but one thought would be to check the Wood Handbook which contains metric and imperial numbers, find your numbers under any species and then cross reference to find the converted number.
Should be chapter 4;
http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm

Another way to check a beam is to proof load it to 2.1x the design load.
Another thought is to call or email the awc help desk, contact info is on the front page of their site if I remember right.

[jfl]

Another way to check a beam is to proof load it to 2.1x the design load.

Hi Don,

By proof loading a beam, you mean putting 2.1 x the expected snow load?

That would mean in my case 10 ft x 9 ft by 45 lb/sqft *2.1 = 8505 lbs. 

I think I'll check the wood handbook first...

Thanks,

jf

[Don P]

2.1x the total load, live + dead load. If 45psf is your snow load and if it is typical construction then add 10-15 psf for dead load.

Yeah nobody would loan me their truck either  ;D