Well, I certainly hope you don't build things that I have to use with
your methods. I ran some calcs on standard 12" A36 steel I beams. Using
the published yield strength (the point where it bends and takes a set)
http://www.matweb.com/index.aspx search on A36

of 36,000 psi, I can get deflections in the 1/240 range. This is the
equivalent of NO factor of safety.

These calcs assume multiple beams that are cross braced and do not
include any derating to account for mid space twisting

Oops! Ned you are right. I grabbed the wrong beam condition. BTW I
designed a sail boat trailer for a full keel sail boat using the deflections
as the limiting condition for obvious reasons. Also a spiral staircase, a
hydraulic engine hoist and a building addition, and a helicopter trailer
modification. As well as the deflection calcs for a 30' non standard I beam
with both distributed and concentrated loads. All had some safety factors
added and all have been in use for some time with no failures to perform.
With all that said, the table 4 on page 5-35 does have an easier to use
formula for safe loads. Given that the ends of the I beam are restricted
from rolling or departing from their location, I fail to see that using
deflection, and keeping it small, doesn't yield a safe condition. This
technique was used on the building addition, as well as the 30' non standard
I beam with the concurrance of a P.E.

Stu Fields