Okay bosarge66, not having to deal with the roof loads is good. We can
use 10 psf dead load and 40 psf live load for the two floors. So, we
have a total of 100 psf on the beams.
The beam formulas for this loading are:
M (maximum bending moment) = wl^2/8
D (deflection @ center of span) = 5wl^4/384 EI
w = (34'/5 spaces) x 100 psf = 6.8' x 100 psf = 680 lb per ft
l = 9.75'
D = l/360 = (9.75 x 12) / 360 = .325"
Where E is a constant for steel = 30,000,000 psi
And I is the moment of inertia
Solving for M:
M = 680 x 9.75^2 / 8 = 8,080 ft lb = 96,960 in lb
The allowable bending stress for structural steel (s) = 0.55 x 36,000 psi
= 19,800 psi
The section modulus of the required beam (S) = M/s = 96,960/19,800
= 4.89 in^3
Now we must calculate the required I (moment of inertia):
Solving for I in the above formula for deflection we get:
I = 5wl^4/384 ED = (5 x 680 x 9.75^4 / 384 x 30,000,000 x 0.325) x 1728
NOTE: 1728 is a conversion factor to get the proper units for I
I = 14.2 in^4
Now we can look for a beam with these minimum properties.
A good choice would be a 6 inch deep Wide Flange beam weighing 8.5 #
per ft (W6x8.5)
S = 5.08 in^3
I = 14.8 in^4
If you have some other beam you would like to use, or there is
anything that you don't understand, please ask for a clarification and
I will try and help.
Good luck with your project, Redhoss |