[SML] Unistrut safety factor specs?

[Bill Conner]

> An engineer will always do two calculations for a beam:

Well, almost always at least these two.  I think shear - both
horizontal and vertical - can come into play - and of course with loft
and head block beams bending in the lateral axis.

And the deflection issue for rigging is an interesting.  I believe he
1:360 goes to plaster cracking, and is the code minimum for roofs with
a plaster ceiling, where as a roof with no ceiling - like a stage -
the limit is 1:180. In some occupancies, that is even lower.  I've
wondered if on a 30' loft or head block beam (conveniently 360 inches)
with 2" (1:180) at the center and if even 3 or 4" mattered -
considering this is from no load to full load.  Maybe partly because
provide recommend design loads for a fully loaded arbor (every 6 or 7
or 8 inches - whatever the (standard) spacing is for the project.
Some percentage of that is always there - headblocks and tare weight -
and never all there with every arbor full.  And do you care if it
deflects an inch for  rigging or do you just change the trim?

Or it's just how stated - my 30' span designed for a 2000 pound set
every 8" or 90,000 pounds and supplying 45,000 pounds of weights
initially, while allowing 1:90 deflection isn't much different than
1:180 for as much load a it will ever likely see - and the unlikely
being accounted for in the design factor.

-- 
Bill Conner Fellow of the ASTC