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RE: Cold-Formed Joist Lap Splice Question

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This is how it is addressed in the 1996 AISI Cold Formed Steel Design
Manual. If you have a moment at the support of Mneg and the screws are 18"
apart (9" on either side of the support), the the shear force in the screws
would be Mneg/1.5.

The problem I have is that the metal deck I am used to using, the
architectural standing seam type that spans about 5'-0" or so (MBCI Ultra
Deck, et. al) doesn't really laterally brace the purlins to my satisfaction.
Heck, they don't even touch the purlins. They are "connected" to the purlins
via a clip that crimps over the rib and fastens to the purlin. You can see
daylight between the deck and the purlin!

Regards,

Bill Allen, S.E.
ALLEN DESIGNS
Laguna Niguel, CA


> -----Original Message-----
> From: Ritter, Mike [mailto:mritter(--nospam--at)lgt.lg.com]
> Sent: Tuesday, August 17, 1999 12:26 PM
> To: 'seaint(--nospam--at)seaint.org'
> Subject: RE: Cold-Formed Joist Lap Splice Question
>
>
> William, Group,
>
> This is not as simple as designing a standard moment splice in a steel
> beam.  Please re-read the original question and let me know
> if you still
> feel the same way.  I may not be getting the picture across with my
> words.  Two cold-formed joists, 3' lap at the center support.  If you
> simply hooked the two beams together in a single 6" lap directly above
> the support with one cluster of screws, then I would agree with your
> response--this is a moment connection.  However, when you
> have a 3' lap
> splice seperating the two clusters of screws, I think it becomes a
> couple centered about the support.  Am I not seeing this correctly?
>
> Sincerely,   Michael Ritter
>
> > -----Original Message-----
> > From:	William Keil [SMTP:WJK(--nospam--at)brph.com]
> > Sent:	Tuesday, August 17, 1999 1:55 PM
> > To:	'seaint(--nospam--at)seaint.org'
> > Subject:	RE: Cold-Formed Joist Lap Splice Question
> >
> > Mike -
> > IMO, you must design for the negative moment.  Otherwise you will
> > develop a
> > hinge at this point which would not agree with your analysis.  The
> > methodology to develop the moment says that you break the
> moment into
> > a
> > force couple at the flanges or a bending stress diagram
> over the cross
> > section (however detailed you want to be).  Once you have the forces
> > at
> > their respective locations, you can now determine the number of
> > fasteners
> > you need by taking the force divided by the capacity of the fastener
> > (controlled by shear, pullout, etc.)
> >
> > William J. Keil, P.E.
> >
> >
> > -----Original Message-----
> > From: Ritter, Mike [mailto:mritter(--nospam--at)lgt.lg.com]
> > Sent: Tuesday, August 17, 1999 2:33 PM
> > To: 'seaint(--nospam--at)seaint.org'
> > Subject: Cold-Formed Joist Lap Splice Question
> >
> >
> > 	I have a general question for the group regarding approach for
> > lap splice design using light-gage, cold-formed steel
> joists.  I have
> > heard two views on this matter and wish to get the group's concensus
> > if
> > possible.  Here is the situation...
> >
> > 	Suppose we have a two span condition with a 3' long lap splice
> > located over the center support.  At each end of the lap, there is a
> > cluster of self-drilling screws connecting the two members.
>  A couple
> > more screws are used directly over the center support to hold the
> > members together.  Due to the typical gravity loading, there is
> > negative
> > moment over the center support.  The clusters of screws at
> each end of
> > the lap are not at inflection points, so there will still
> be negative
> > moment in the continuous members at those locations.  Now my
> > question...
> >
> > 	Do we design the cluster of screws for :
> >
> > 	a)  the magnitude of negative moment at that exact location; or
> >
> > 	b)  only vertical shear forces due to the resolution of the
> > negative moment into a couple about the center support?  ie, each
> > cluster of bolts would have only shear and no moment.  The moment at
> > these locations would be resisted by the capacity of the single
> > continuous member at that point.
> >
> > 	Thanks in advance for any help or insight,
> >
> > 	Michael Ritter, PE
> >
> >
>
>