Hello everyone.
I am having some logs milled for a 20x24 three bent timber frame clear span no middle posts. Bents 1 and 3 will have 8x8 posts with 8x12x 20'.
I have played around with the span calculators in the toolbox for Simple Beam Uniformly Loaded Eastern White Pine grade 2 (to be safe since I am not having the logs professionally graded). I really don't know how much of a load will be on the beam but when I exceed 4,000 dead and 7,000 live, a 8x12x20 fails. To support the loft along with a ridge beam with minimal deflection, I am wondering if I should increase the size of tie beam for the middle bent. I am wondering if I increase the middle bent posts to 8x10 and the tie beam to 10x14 would be advised. The 10x14x20 does not fail on the calculator. Essentially I have a point load in the middle of tie beam from the king/ collar post along with an even distribution from the loft.
Please share you thoughts.
Can you not truss the middle bent?
Hi Don P. Absolutely that is an option, however for simplicity and saving time I would like to design the frame with minimal complexity. I was thinking of a simple design incorporating a supported ridge beam with rafters. It would also maximize loft space.
Let's check your loads. The ridge support post in the middle bent is supporting halfway to each gable bent on either side of it so 6'+6'=12' and halfway to each eave wall so 5'+5'=10'. The tributary area that post is supporting is 12'x10'=120 square feet.
Assume 15lbs per square foot for dead load, the weight of the materials. NH is all over on snow loads I'm assuming 65 psf but check that.
120 square feet x 80 lbs per square foot (15DL+65LL)=9600 lbspoint load midspan. * A quick and dirty cheat, a point load creates twice the moment of a uniform load, you're going to see me use 20,000 lbs in the simple beam calc in a minute.
Loft floor load is the same 10' of trib length transverse and halfway to the one gable in the other direction 6' so 60SF x (10DL+40LL)=3000lb
Add em up and we'll check 23,000 lbs uniformly distributed.
https://forestryforum.com/members/donp/beamclc06b.htm (https://forestryforum.com/members/donp/beamclc06b.htm)
DL=2400, Span 232"
Hmm, I'm coming in at more like a 12x24 beam
Nothing wrong with that other than its a big tree. I wonder how big of an unsawn log it would take, just curiosity;
https://forestryforum.com/members/donp/logbeamcalc.htm (https://forestryforum.com/members/donp/logbeamcalc.htm)
Looks like 21" small end diameter if you lightly flat top it.
Or explore a truss.
Quote from: Don P on July 09, 2020, 10:15:40 PMHmm, I'm coming in at more like a 12x24 beam
Quote from: Don P on July 09, 2020, 10:15:40 PMLooks like 21" small end diameter if you lightly flat top it.
If I'm reading this right, could I borrow your saw to get a 12"x24" beam out of a 21" log? ;) Did you mean a 31" SE log?
No, I made one of those leaps of logic and forgot to take you along :D
The strength values for unsawn logs is much higher than a sawn timber because you aren't cutting so many of the fibers around the edges, so I was curious what that would translate to size wise. Fb of a #2 EWP heavy timber is 575psi, for the same thing in log form it is 900 psi.