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