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# RE: Cold-Formed Joist Lap Splice Question...One more time

• To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
• Subject: RE: Cold-Formed Joist Lap Splice Question...One more time
• From: "Ritter, Mike" <mritter(--nospam--at)lgt.lg.com>
• Date: Tue, 17 Aug 1999 15:29:43 -0500

```Let's change my question slightly.  Suppose we have a two span
condition, using (2) 2" x 12" timber members, each 12' long.  They will
each span 10', and there will be a 4' overlap at the middle, right over
the center support.  Now, the contractor uses a single bolt, right at
mid-depth at each end of the overlap (2 bolts total).  These single
bolts will not develop moment in the connection (the moment is in the
members) but the entire assembly is still stable.  Right?  I would
simply design the two bolts for a shear force (again, no moment in a
single bolt).

I see this all the time in pre-engineered buildings, where the purlins
are lapped over the rigid frames.  The purlins carry moment, but the
structural bolts connecting them together simply take shear.  Does this
principle not apply to light-gage material also?

Thanks again,  Michael Ritter

> -----Original Message-----
> From:	William Keil [SMTP:WJK(--nospam--at)brph.com]
> Sent:	Tuesday, August 17, 1999 3:19 PM
> To:	'seaint(--nospam--at)seaint.org'
> Subject:	RE: Cold-Formed Joist Lap Splice Question
>
> 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
> >
> >
>
>

```