Load Calculation? - Using Don P's Calculator

[jander3]

 

 

Thursday, I am going to the Stump Ranch to cut down the trees and mill up the beams for this structure.  This will take care of about 6 of the 200 wind blown trees that I have to cut and haul to the mill. Between the wind blown trees and the 70 year old Aspen groves that need to come down, I have more Aspen that I will use in my lifetime.

The structure will be made from 8 x 8 beams.  When I look at the beam dimensions and size of the structure, it is clear to me that from an engineering standpoint "She will be alright!"

However, for the heck of it, I ran this through Don P's calculators.  I got stuck at the end figuring loads,  I would like any input on if my logic is on target.

For this case, I am setting aside dead load.

Snow load in Minnesota is 42 psf

The structure is 10' x 12' = 120 sf

To determine total load,  multiple the footprint area by snow load.  The foot print is used, I don't use the actual square footage of the roof.

120 sf x 42 psf = 5040 p

To determine the load on the plate, I divide the total load by 2 as only 1/2 the load is shared between the ridge and plate.   

5040 p / 2 = 2520 p

Then, since this load is shared between the ridge and the plate I divide the load again by 2 to get the load on the plate

2520 p / 2 = 1260 p

This gives me a loading on the plate of 1260 p

Here is where I am confused....

Is 1260 p the uniform loading on the plate? Or do I have to divide by 2 because I have 2 posts  that share the load to get the uniform load on the beam?

One other item.  If anyone has source for the following data on Aspen (Big Tooth or Quaking) for beams, please point me in the right direction.   

Max Fiberstress       Modulus of Elasticity   Max Shear

psi                         million psi                      psi

[Jim_Rogers]

The plate would be considered a uniformly loaded beam as it has many rafters pressing down on it.
So don't divide again.

As for values, I'll have to see what I can find.

Or if someone else has these values maybe they will post them.

Jim Rogers

[jander3]

Thanks Jim.  I feel better now. 

[PrestonT]

 Jander,

As my 1st post to this awesome form, I hope this helps!



 

[Jim_Rogers]

Those values are for 2" to 4" pieces of lumber.
You can't use them for timbers larger than 5" x 5".

Jim Rogers

[jander3]

PrestonT,

Thanks I appreciate the attempt.  As Jim indicates values for beams are a little different.  I have yet to find specific values for Aspen so I end up checking things using a species that is close.

[Jim_Rogers]

I'll email an engineer right now and see if he has something we can use.

Jim Rogers

[Jim_Rogers]

From one of my engineer's by email:

I do not have the values run at this point.  Since there aren't any grading rules for timber sizes nor have I used it for structural applications as timbers before, to get official values I'd have to go through the ASTM process, which is fairly arduous.  Looking at the numbers, and, doing a "soft" conversion, normally you can use the "Lumber" values for most hardwood species, and just discount the Fv by 10-15psi and the E by 100,000-200,000psi, depending on the magnitude.

For Aspen, I'd reduce Fv/E by 10/100,000psi, and use lumber values.  This should yield numbers close enough for most timber framing purposes.  Hope this is enough for you?


That's the best I can do at this time.

Jim Rogers

[Jay C. White Cloud]

http://www.woodworkweb.com/woodwork-topics/wood/146-wood-strengths.html

This link shows "Aspens" Modulus of Elasticity, Grain- Max Crushing Strength, Compression Perpendicular to Grain, Fiber Stress at Prop. Limit, and Shear Parallel to Grain-Max Shear Strength.  With these you can do a lot, including comparing to "like species" specs, for your calculations.

Does that help?

[beenthere]

Those values come from the Wood Handbook "Wood as and Engineering Material" and are for clear wood specimens.
The wood design specs published are from testing graded material, and because not published (apparently) there must be a reason.

However, I think Jander3's original suspicion that he will be just fine with his design is a sound decision.

Myself, if using wind-blown beams I would set up some individual testing to pre-load each beam. Check the deflection with two different loads (say like 100 lb and 200 lb) to sort out any beams that have abnormal deflection which may be from internal decay or wood failure due to being stressed if trees were blown over. A couple sawhorses, and weights using the tractor loader, and a tight string will give one some very valuable info for sorting out some potentially bad actors.
To me, this would be better than visually trying to grade the beams, or trying to extrapolate un-graded beam values from clear wood values.

[Jay C. White Cloud]

A PE referenced the sight for my "rough in" calculations, so there must be some merit to them.

[beenthere]

A PE referenced the sight for my "rough in" calculations, so there must be some merit to them.

No comment, 'cept PE's (like so many others) love to have a paper trail, and they don't really give a DanG what type of paper it is. ;)   And am sure you know that as well as the rest of us.  ;D

[jander3]

Man, as Beenthere indciated right back to "She will be alright!"  Or in other words..."It will be fine." 

What I actually did, was use a table similar to the one Jay posted.  From that you can see on these tables, Aspen is roughly the same as White Pine.  I ran Don Ps calcs using my dimensions and selected white pine as the species, I had plenty of margin.

Since I have a butt-ton of Aspen, that is what I will build with. 

The engineering only has to satisfy me as I am so far back in the woods, there is no such thing as a building inspector.

[VictorH]

Welcome PrestonT to the forum and my favorite section of it!!

[Jay C. White Cloud]

Hey Jander3,

Went back through some old notes, just to make sure that my lead to that site was from a PE, (it wasn't-it was an architect not a PE---but the info is still good) and the advice in detail was exactly what you did.  Look at the chart, find a comparable to Aspen like...guess what they said?...White Pine.  They have almost the same properties.  Now that I have worked with a few Aspen frames, it has really grown on me...I like the wood, it's lite cream color, and the general work ability.  All in all, it's really a great timber framing wood. 

Let us know what you think after a few joints cut...

Regards,

jay

[PrestonT]

Jim, thank you, didn't notice that it said 2-4" thick at the top of the page. Looking through the section that says Timbers 5x5 and larger there is no aspen listed in the table...

Thank you Victor