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Re: Use of Collar Ties in Light Frame Wood Construction

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A very good idea to hang the ceiling.  If you cut the ceiling joists and
flush frame the beam, you have just severed what has been serving as a
tension tie.

Good luck

Conrad
----- Original Message -----
From: "Structuralist" <dennis.wish(--nospam--at)gte.net>
To: <seaint(--nospam--at)seaint.org>
Sent: Tuesday, June 05, 2001 2:25 PM
Subject: RE: Use of Collar Ties in Light Frame Wood Construction


> Thanks Conrad,
> I had considered the option and was hoping to find some reference to the
use
> of collar ties in conventional construction first. We are in the low
desert
> which means that we never have to deal with snow and rain is generally not
> an issue (especially since the roof is a 3:12 pitch).
>
> The only feasible solution here is the collar ties as I have also had to
> correct an undersized built-up wood beam (2-2x8's spliced together
spanning
> 22'-6" to support a 12'-6" tributary ceiling). The original design was
> obviously conventionally done as the double 2x8 would never have worked
and
> the deflected ceiling is evidence of this. I designed in a 3.5 X 14"
> Parallam PSL 2.0E beam which the ceiling will need to be hung from (as it
is
> now). This does not leave me a lot of room for the collar ties, however,
> they will work if placed slightly below the top third (2/3H) of the peak
of
> the roof).
>
> Thanks for your suggestion, I may resort to this, but want to check out
any
> known references first.
>
> Dennis
>
> > -----Original Message-----
> > From: Conrad Guymon, P.E. [mailto:conrad(--nospam--at)karren.com]
> > Sent: Tuesday, June 05, 2001 11:38 AM
> > To: seaint(--nospam--at)seaint.org
> > Subject: Re: Use of Collar Ties in Light Frame Wood Construction
> >
> >
> > From the modeling we have done here, collar ties just don't work,
> > particularly the connections to the rafters.  (We usually have 30 psf
snow
> > load and up.)  If the collar ties do work, the rafter tails usually end
up
> > overstressed in bending.  If you can use the ceiling joists to
> > form a bottom
> > truss chord, this takes some of the curses out of it.  I would try a
RISA
> > model of a single rafter/ceiling joist/collar tie (I think you mentioned
> > that you use RISA) with the appropriate members, and see if the
> > members even
> > pass a wood code check.  I would neglect the ridge, since it has
> > failed.  If
> > they work, you will then have the forces you need to design ALL the
> > connections.  Ends up being a site built truss.
> >
> > HTH
> >
> > Conrad Guymon, P.E.
> >
> > ----- Original Message -----
> > From: "Structuralist" <dennis.wish(--nospam--at)gte.net>
> > To: "SEAINT Listservice" <seaint(--nospam--at)seaint.org>;
> > <aec-residential(--nospam--at)polhemus.cc>
> > Sent: Tuesday, June 05, 2001 1:27 PM
> > Subject: Use of Collar Ties in Light Frame Wood Construction
> >
> >
> > > I have a client with a home in escrow. There is a cracked ridge board
in
> > the
> > > garage and it appears that the ridge has dropped a few inches.
> > The framing
> > > is rafter tied by the 2x6 ceiling joists to the 2x8 roof rafters, the
> > ridge
> > > board is a 2x12 DF. The crack in the ridge board is parallel to grain
> > which
> > > runs diagonally through this section of the board - an obvious defect
in
> > > material not found during original construction.
> > >
> > > I intended to jack up the roof and install 1x6 collar ties at 1/3 the
> > > distance down from the peak of the roof. The attic is accessible to
> > install
> > > the collar ties and all other existing framing looks pretty good.
> > >
> > > The 2000 IBC lists the use of 3-10d nails to secure the 1x to
> > the rafters.
> > > However, this 2000 IBC is not used in California and collar tie
> > nailing is
> > > not indicated on the 97 UBC Nailing Table. The only reference to
collar
> > ties
> > > I could find was in Appendix Chapter 23 - Prescriptive Masonry
> > Construction
> > > in High-Wind Areas where Section 2112.10.2 states: "Gabled and
> > sloped roof
> > > members not supported by the ridge shall be tied by ceiling joists or
> > > equivalent lateral ties located as close to where the roof
> > member bears on
> > > the wall as is practically possible, at not more than 48 inches
> > on center.
> > > Collar ties shall not be used for these lateral ties."
> > >
> > > Now I am at a loss. In my opinion (as this was a common form of
> > construction
> > > for many years) collar ties are ideal to resolve this situation but
this
> > > condition requires them to act as lateral support. The existing
ceiling
> > ties
> > > obviously help, but are not restraining all of the outward thrust of
the
> > > rafter tails since the ridge board cracked. Installing a Ridge
> > beam seems
> > an
> > > inappropriate solution here as it would redistribute the roof load and
> > > require the possible addition of two foundations at each end -
requiring
> > > that we cut through one slab and underpin the exposed slab edge.
> > >
> > > Any suggestions or information that would help me justify the use of
> > collar
> > > ties?
> > >
> > > If I still use collar ties (assuming the building department accepts
the
> > fix
> > > as I suspect they will) I intended to install a 1x6 on each
> > side and face
> > > nail each end to the rafters with (3) 10d nails - spacing the
> > collar ties
> > > every other bay or 48" on center.
> > >
> > > Regards,
> > > Dennis S. Wish, PE
> > > Structural Engineering Consultant
> > > mailto:structures(--nospam--at)engineer.com
> > > (208) 361-5447 E-Fax
> > >
> > >
> > >
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