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- To: <seaint(--nospam--at)seaint.org>
- Subject: Detailing Question
- From: "Dickey, David" <David.Dickey(--nospam--at)mhgrp.com>
- Date: Thu, 2 Jan 2003 12:48:53 -0500
A question was posted by another engineer on
this forum back in May that I was interested in, however, it received no
responses that I know of. Maybe someone could share their experience with
this problem if I restate it.
Say you have a sloping roof beam, running
parallel to steel joists, with a moment connection with bolted flange
plates. The top flange plate may be an inch thick and the bolt heads and
washers add another 3/4" or so. How do you detail the metal roof deck at
Here are some thoughts and problems
associated with each:
1: The roof deck could be bent over
the flange plate and bolts producing a ~1 3/4" bump. The bump in the deck
could possibly be compensated by cutting the rigid insulation above. This
could be difficult and depend too much upon the worker's skill.
2: The metal roof deck could be cut
around the flange plate and the deck would be supported on the top flange of the
beam. But, is it wise to detail the flange plate to have 3 or
4 inches less width than the beam's top flange? What could support
the roofing where the deck is cut?
3: The direction of the joists could
be changed such that the beam with the moment connection would support joists
rather the metal deck. This would provide at least 2 1/2" between the top
of steel and the roof deck to allow room for the moment connection. But,
this can cause problems because now the beam becomes a "girder" with a larger
moment of inertia required. When designing a moment connection based on
the capacity of the beam (FEMA 350), a larger beam results in a bigger moment
connection. I would also like to keep the span of the joists parallel to
the slope of the roof.
4: The beam's elevation could be
lowered, and a "spacer" (such as a 4"x4" tube) could be intermittantly welded to
the beam's top flange and run the length of the beam. The spacer would
support the roof deck. At the flange plate, the "toe" of a steel angle
could be welded between the two rows of bolts, and the outstanding leg would
support the roof deck. Can you weld anything to the flange plate of a
moment connection without affecting the prequalification of the
Maybe I've missed the simplest solution of
all. Moment connections for sloping roof beams seem fairly common...surely
someone has solved this problem before. Any thoughts or comments would be