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RE: Cold-Formed Joist Lap Splice Question

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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 
> 
>