hello all
i have a small horse shelter i'm building
3 bents
32' long
16' wide
one my tie beams is looking a little on the small side
i designed each tie is 16'
half dovetailed into the top plates on either side
with a lag bolt counter sunk from the top into the plate
3' 4x6 braces going into 8x8 posts
all wood is dfir except for one spruce post
see attached drawings
i guess i can't attach drawings
the span is 8'8" between the braces
there is an 8x9 ridge plate coming down onto 3 king-posts

question:
steve chappell says in his book (the older one)
R=1.5PL / bd(squared)
(supported at ends with a concentrated load at the center (king post))

R is the modulus of rupture (breaking point?) lb. per sq. inch
he gives two numbers depending on specific gravity
i don't know if i'm interior fir north, south, or west
i will go with the weakest number for safety
6,800 or 11,900

these are big differences
how can i understand these two numbers better?

i will use the weaker number until i better understand these

6800=1.5xP(maximum load, pounds)x L(distance between supports in inches) / b(width of beam) x d(depth of beam)(squared)

how do i determine P? dead loads are the timbers of the roof?
live loads are the wind and snow? i need help here

L is 132.5"(11'1/2")
b is 7"
d is 8"

6800=1.5xPx132.5/7x8(squared)
6800 x 448 / 198.75 = P
P = 15327

he says for the beam to be acceptable, the results must be from 6 to 8 times less than those given in the table

how am i to read this?
kind thanks for any ones help and valuable time
michael hollihn

Hi Michael,

I would need to see your drawings, there was none attached from what I could tell. Steve's stuff can be hard to glean things from sometimes and I always recommend that you contact a PE. if not sure of your numbers. Engineering advice is tricky at best considering the variability of wood and it's nature. You may also try posting on the Forestry Forum, there just is more traffic there and folks to ask questions. It is an easier forum to use format wise as well. Go to their timber framing section.

Regards, jay

If you don't object to European standards, the Eurocodes (Eurocode 5 specifically and associated standards) define various "standard" values for different timbers and give appropriate scalars to ensure that your building doesn't fall down on you. I don't know how the standards compare to those in the US, but having run through some of the maths, my feeling is that they're stricter. I could (one day) talk you through the maths with the obvious caveats that you should have everything checked by an engineer. Calculating snow loads would be a "local" problem though. My tables for snow loads are for France and not applicable to Canada.