Subject: RE: handling joist deflections / alignment when in parallel with bearing wall
From: "Sprague, Harold O." <SpragueHO(--nospam--at)bv.com>
Date: Tue, 6 Jun 2000 11:40:38 -0500
Generally if you have a CMU wall, you are trying to maintain a constant
elevation around the perimeter. In an effort to avoid cutting block, bar
joists will bear at a given elevation that is divisible by 8". When you
turn the corner and you have a deck bearing condition, the bottom of deck
elevation will be 2 1/2" (joist depth) above the joist bearing elevation. I
like to provide a continuous HSS 2 1/2 x 2 1/2 welded to masonry embed
plates, and the deck is then welded to the HSS.
The usual situation is that you have a parapet because your steel deck and
joists slope and you have to attach deck to the side of CMU. The bed joints
of the CMU will be horizontal (no one likes to cut block). I use a WT with
headed anchors welded to the stem. The WT is placed so that the stem is
embedded in every other head joint. This gives me basically a weld plate
that I can weld a continuous angle to for deck bearing.
Now to fix the problem of the cambered joist and flat parallel wall or flat
angles. If my nominal joist spacing is 6'-0", I shorten my last space
(joist to wall to about 2'-6"). This gives me 2 benefits:
1. My deck is stiff enough to handle some out of plane compressive
forces to stabilize the wall.
2. Any difference in elevation can be "adjusted" by a 200 pound
iron worker standing on the deck section that requires "downward adjustment"
prior to welding.
The same problem occurs when you put angle frames on top of joists and when
you have joists with different cambers. I'm drifting back to the days when
I was a 150 pound iron worker and needed to add tools in my belt to "adjust"
Specifically to your issue of a gabled wall and obviously cut block to
slope. I would hold the elevation of the bond beam down to accommodate the
HSS 2 1/2 x 2 1/2 and weld the deck to the HSS. I would place a full height
bond beam as the top course and provide cut block on the next lower course
to get the desired slope. You will have to use a stiffer grout in the top
bond beam than you would otherwise use. I would also hold the first joist
back from the wall about 2'-0" or 2'-6" and find that 200 pound iron worker
for vertical adjustment. A lot of this depends on the specific
architectural detail used at the perimeter.
> -----Original Message-----
> From: Khosrownia, Ghassem SPK [SMTP:GKhosrownia(--nospam--at)spk.usace.army.mil]
> Sent: Tuesday, June 06, 2000 9:42 AM
> To: 'seaint(--nospam--at)seaint.org'; Darrel E. Marchall (E-mail)
> Subject: handling joist deflections / alignment when in parallel with
> bear ing wall
> A nagging problem that needs good solid solution!
> Roof joists run in parallel with CMU bearing wall.
> Roof is gabled, joists will be double gabled (no ridge beam).
> CMU wall follows slope of roof.
> Camber and deflection of joists make it nearly impossible to line up with
> the top of the wall?
> Construction tolerances for the wall and bearing of the joist could
> this effect.
> Specify top of the wall to be slightly lower than the bottom of the
> Use light enough decking so it is a bit more flexible.
> For interior walls running in parallel with the joists discontinue the
> decking to obtain more flexibility. Weld both ends of the decking to the
> steel bearing plate on top of the wall. Use washers or small plates to
> compensate for the inaccuracy.
> These are not meant to be independent solutions, rather a total recipe.
> What do you think. What have you done to remedy this situation?