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RE: Cold-Formed Joist Lap Splice Question

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If the analysis requires a continuous member then all of the forces must be
resolved.  If the all of the forces are not resolved then the actual
behavior of the system will not coincide with the analysis of a continuous
beam.  If the connections were made at inflection points then the only force
present is shear and you have choice (b).  If the connections are made any
place else then both, shear and moment, must be transferred to the other
member, choice (a).  If your analysis supports the condition of a balanced
cantilever (i.e. see below) with two hinges then yes you can design for
condition (b), otherwise it must be condition (a).

      hinge       hinge
-------o----------o----------
^            ^              ^
Support    Support         Support

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 
> 
>