Return to index: [Subject] [Thread] [Date] [Author]

RE: handling joist deflections / alignment when in parallel with bearing wall

[Subject Prev][Subject Next][Thread Prev][Thread Next]
What I have done in a similar situation is to specify the first joist
closest to wall as "no camber" (or 50% camber).  This informs the joist
supplier that you need a larger section for the joist chords to limit the
deflection and thus help not overstress the deck.

JD
-----Original Message-----
From: Sprague, Harold O. [mailto:SpragueHO(--nospam--at)bv.com]
Sent: Tuesday, June 06, 2000 1:56 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: handling joist deflections / alignment when in parallel
with bearing wall


Bob,

The reason that I reduce the spacing for the last joist is to cut down on
the unbraced length of the deck to resist out of plane forces on the wall.
If the first joist is 5'-0" or 6'-0" from the wall the compressive strength
of the deck takes a nose dive.  

If you put the last joist too close to the wall, you have the problems that
you stated.

Regards,
Harold Sprague


> -----Original Message-----
> From:	Bob Shaw [SMTP:rshaw(--nospam--at)steelstructures.com]
> Sent:	Tuesday, June 06, 2000 3:32 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	RE: handling joist deflections / alignment when in parallel
> with bearing wall
> 
> I think Harold has the right solution (as he always does). Place the joist
> away from the wall (I'd use a standard joist spacing, not the 2'-6"), and
> attach the deck to an embed plate or angle.
> 
> It is important to keep the joist away from the wall when running
> parallel.
> When loading is applied to the roof, the joist will deflect, but the wall
> is
> fixed, and you put plenty of flexure into the roofing material over a very
> short distance. Good place for a roof leak to develop over time,
> particularly when roofing materials get brittle.
> 
> Bob Shaw
> Steel Structures Tech Center
> www.steelstructures.com
> 
> -----Original Message-----
> From: Khosrownia, Ghassem SPK [mailto:GKhosrownia(--nospam--at)spk.usace.army.mil]
> Sent: Tuesday, June 06, 2000 7:42 AM
> To: 'seaint(--nospam--at)seaint.org'; Darrel E. Marchall (E-mail)
> Subject: handling joist deflections / alignment when in parallel with
> bearing wall
> 
> 
> A nagging problem that needs good solid solution!
> 
> Situation:
> 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.
> 
> Problem:
> 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
> compound
> this effect.
> 
> Solution:
> Specify top of the wall to be slightly lower than the bottom of the
> decking.
> 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?
> 
> Ghassem.
> 
> 
> 
> 
>