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RE: Cold-Formed Joist Lap Splice Question

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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