I've been watching this thread with great interest. It is no small wonder
that OSHA has found the need to promulgate "idiot" rules for those with no
real experience in the art of ironworking.
I am under the impression that the longitudal beams frame into the web of
the traverse bents and that the web connection area is cluttered with
stiffner plates interfering with the option of "scissoring" either the 2nd
or 3rd tier beams in place. Since the 2nd tier beams are already in place
(as I understand the problem), the prudent solution is to loosely 2bolt one
end of the top beam and rig a vertical come-a-long from the other end of the
top beam to the 2nd tier beam. The 2nd tier beam can now be unbolted, being
supported by the come-a-long and in turn the crane hoist line. The two
beams are now properly vertically spaced by manipulating the come-a-long,
entered into the cluttered web area and bolted. Hell, even an engineer
should have figured this out.
Of course, a good ironworker foreman would have "grapevined" ( hoisted the
beams one hung under the other) the tiered beams on the first lift, negating
the need for all this time consuming rigging.