I had some time to run some deflection #'s.
The formula for steel I-beam deflection is
d=(F x S^3)/(48EI)
Where:
d=deflection in inches
F=Force applied in pounds
S=span in inches
48=constant
E= modulus of elasticity (for steel, this is 30,000,000psi)
I=Moment of inertia (I^4). Can be found online and is different for every beam.
Deflection limits for i-beams sould use L/360. So a span of 120"/360 would give you an allowable deflection of .333"
So reverse figuring to solve for I we get the following(assuming 4300lb point load becasue that is how strong you 8x8 woudl be):
(4800 x 120^3)/(48 x 30,000,000 x I)=0.333
5.76/I=0.333
result, I>17.28 (I must be greater than or equal to 17.28 to have the same strength of the 8x8 hemlock).
So now we can look at some beam charts to do some shopping:thumbsup:
I like this website for that
Structural Steel W Flange Section Properties Moment of Inertia, Steel Beam Size,Cross Section Area - Engineers Edge
So it looks like a W8x10 beam is the lightest beam that would meet the criteria with an I4 in the xx axis of 30.8 That is a 8" beam that weighs 10lb per foot. So only 200lbs of steel:thumbsup: Probabally will only cost you $150 at the most. And with the I4@30.8, would actually hold a point load in the middle of over 8500lbs. So a good bit of saftery factor as well.