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RE: Use of Collar Ties in Light Frame Wo

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Good idea - I'll do this. Thanks again Charles.
Dennis

> -----Original Message-----
> From: Charles Espenlaub [mailto:Cespenlaub(--nospam--at)martinaia.com]
> Sent: Wednesday, June 06, 2001 6:56 AM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Use of Collar Ties in Light Frame Wo
>
>
> Dennis,
>
> It would seem that it might be difficult to install the HS24, as half the
> nailing must be installed under the new PSL beam.  I would
> suggest two H2.5
> or H5 for each ceiling joist (one each side of the new beam).  These would
> be easier to install, and  give you over 800# capacity per joist.  You may
> want the extra capacity too, as eventhough you assumed no attic storage,
> someone might cut an access in the future and use that nice big space to
> store luggage, X-mas decorations, etc.
>
>
> Charles F. Espenlaub, III, P.E.
> Martin-Espenlaub Engineering
> Tel  215-665-8570
> Fax 215-561-5064
>
>
>
> -----Original Message-----
> From: Structuralist [mailto:dennis.wish(--nospam--at)gte.net]
> Sent: Tuesday, June 05, 2001 8:44 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Use of Collar Ties in Light Frame Wo
>
>
> Charles,
> Yes, the compression side of the beam is designed to be braced at 2'-8"
> maximum along the entire length of the beam. I assumed I could
> brace it back
> up to the roof rafters at alternating sides with "kickers".
> FWIW, the design was done on Trus-Joist's TJBeam program which takes into
> consideration the location of the uniform load (above or below the
> centerline of the beam) and calculates out the maximum distance between
> bracing of the upper (and lower if existing) compression edges.
> With that said, I was still very conservative on the load consideration -
> 10-psf live load and 10-psf dead load (actual dead load is closer
> to 5-psf)
> and attic area is not expected to be used).
> My concern was hanging the rafters as they had been. I have never been
> comfortable with this. The load at each rafter is conservatively 500-lbs
> (24" spacing). The H2.5 currently used is insufficient or my
> loads are much
> too high. I specified the New Simpson HS24 as they are good for about 604
> pounds in tension (normally uplift). The only other choice of wrapping a
> strap below a joist and up the face of the Parallam was not possible here
> without removing the ceiling.
> Any other thoughts. I've shut my phone off because the real estate agent,
> the buyer, the designer and everyone else is yelling for the work as they
> want to complete the work in the next two weeks before escrow closes. How
> can a guy get anything done correctly with all this pressure???????
>
> Dennis
>
> > -----Original Message-----
> > From: Charles Espenlaub [mailto:Cespenlaub(--nospam--at)martinaia.com]
> > Sent: Tuesday, June 05, 2001 5:06 PM
> > To: seaint(--nospam--at)seaint.org
> > Subject: RE: Use of Collar Ties in Light Frame Wo
> >
> >
> > Dennis,
> >
> > Since the ceiling joists are only connected to the bottom of the
> > beam, your
> > 3 1/2" x 14" PSL seems kind of narrow for that span.  Have you
> > checked your
> > beam stability factor, CsubL, or braced the top of the beam at
> one or more
> > locations?  If it is only  braced at the ends, you can loose
> about 30% of
> > the allowable bending stress.
> >
> >
> > Charles F. Espenlaub, III, P.E.
> > Martin-Espenlaub Engineering
> > Tel  215-665-8570
> > Fax 215-561-5064
> >
> >
> >
> > -----Original Message-----
> > From: Structuralist [mailto:dennis.wish(--nospam--at)gte.net]
> > Sent: Tuesday, June 05, 2001 6:37 PM
> > To: seaint(--nospam--at)seaint.org
> > Subject: RE: Use of Collar Ties in Light Frame Wo
> >
> >
> > Roger,
> > Your assessments are correct. Would you believe that this is a
> home in one
> > of the more promanent gated communities and golf courses in the
> > desert? The
> > home, I would guess, is around 2500 square feet and probably
> > sells today for
> > around $400,000.00 with monthly assessments at least another $700.00 a
> > month. Of course this does not include golf course use:o)
> >
> > I don't want to give out the name of the development as it is very well
> > known. It is my experience that the majority of these exclusive
> > developments
> > are simply cheap tract homes constructed by developers who never
> > thought the
> > development would bloom the way it has. There is an exclusive
> area to this
> > place with individual custom home lots and the homes are $1.5
> million and
> > up. I've designed a few beautiful homes in this developement.
> >
> > as to the collar ties. I don't see as I have much choice. I think I can
> > respond better to Samir's comments:
> > " I think collar ties will do the job as they have been installed in
> > conventional framing, meets code, for many years.  I would
> venture to say
> > that if you try to calculate the thrust force in the collar tie
> > using 3- 16d
> > nail you might just get by.  I know that the prescriptive
> nailing schedule
> > in the code, table23-II-B while accepted by code provisions
> hardly calc's
> > out.  The thing that is puzzling in your case is that the ridge
> > board should
> > be a compression member only that supports the rafters and when
> > considering
> > a 2 foot span of the ridge itself, it should not have a bending
> > failure.  It
> > seems to me, may be the owner or prior occupants must
> > have hanged a heavy load, like a car engine, car top or simply a
> > boxing bag
> > to have cuased this failure."
> >
> > Samir actually put his finger on the key issue here. There is a problem
> > (which I think I did mention) with the ceiling joists. Let me explain a
> > little more clearly:
> >
> > The garage is 25-feet deep by 22'-6" wide. The ridge board runs
> > parallel to
> > the 22'-6" and the rafters are supported above the garage
> header and rear
> > stud wall of the garage. 25-foot-long 2x6's are used as rafter ties -
> > certainly not sufficient to support a gypsum ceiling and insulation (and
> > usually some light storage such as decorations for holidays.
> >
> > The original builder spliced together (2)2x8 boards to create a
> > 3x8 beam and
> > ran it below the ridgeline - setting it above the rafter ties. He then
> > connected the rafter ties to the 3x8 using Simpson Hurricane
> Clips. It is
> > most likely that the ceiling and interior finish in the garage
> > was not part
> > of the original design and the only thing being supported on
> the 2x6 ties
> > was the garage door opener.  Now it supports a gypsum ceiling and
> > insulation
> > (as the garage is used as a laundry room as well). Sill, the ceiling is
> > seriously deflected as the 3x8 was not sufficent to support the
> > 2x6 C.J.'s.
> >
> > So now we have a condition where the weight of the ceiling is
> pulling the
> > roof rafters inward at the plate line. In my opinion, this
> still would not
> > have placed the ridgeboard into bending, but would have increased the
> > compression of the rafters against the board. I would expect this to be
> > especially true if the rafters were strapped over the ridge which
> > was fairly
> > common. As the tails come in from the ceiling deflection, the
> rafter will
> > want to rotate around the bottom corner of the rafter at the
> ridge board.
> > This will either force the ridge up or, it the straps are in
> > place, increase
> > the compression against the ridge. BTW, face mounted Joist
> > hangers were used
> > at the 2x ridgeboard.
> >
> > The break must have been due to bending as there is no other reason this
> > could have happened but the only way I can see this happen is if
> > the rafter
> > tails were unrestrained and allowed to move outward. The failure
> > was kicked
> > off by the natural defect in the wood - a change of direction of
> > the grain.
> > Rather than parallel to the face of the ridgeboard, the grain ran at a
> > diagonal from top to bottom over a 48" span of the ridgeboard. Still,
> > something would have had to cause the grain to separate and I
> > have not found
> > a solution to this.
> >
> > This goes back to why I think the collar ties will work. First
> > let me point
> > out that the 2000 IBC Table 2304.9.1 lists "Collar Tie to Rafter" and
> > specifies (3) 10d nails OR (4)3"x0.131" nail (I assume pneumatic)
> > OR (4) 3"
> > x 14 gauge staples face nailed. This is a difference over the 97 UBC
> > Conventional framing that I think you are refering to. The 97 code Table
> > 23-II-B-1 that you refer to does not specify Collar Tie nailing. It does
> > provide for a (3) 16d face nail between ceiling joists and roof
> rafters at
> > the double plate line.
> >
> > With this said, it is common knowledge (and mentioned on this
> > list more than
> > once) that many of the prescriptive methods do not calculate
> > properly which
> > only means to me that there are actions in play that we are not
> > considering
> > or have chosen to ignore. I don't believe that we can adequately justify
> > this type of roof system by calculations - as was said by most,
> > the numbers
> > aren't going to balance. Does it mean that it is wrong or will
> fail. In my
> > opinion, no - it only means that we have not explored what works
> > conventionally in enough depth to find out what we are missing in our
> > analysis.
> >
> > At this point, I am going to use the collar ties for a couple
> of reasons.
> > The failure was not, in my opinion, the result of a bending
> failure but a
> > defect in the ridgeboard. While I am surprised that it appeared
> to drop, I
> > am now not so sure that other areas of the roof did not rise
> > because of the
> > excessive deflection in the ceiling. In other words, we are thinking the
> > failure is downward, but in most liklihood, the rafter tails were
> > pulled in
> > forceing the ridge upward. I don't think this justifies the ridge board
> > failure but suggests a potential solution by relieving the
> > deflection in the
> > ceiling.
> >
> > I designed a ceiling beam to replace the 3x8 spliced beam and an
> > appropriate
> > members works out to be a 3.5" x 14" Parallam PSL 2.0E beam. Once the
> > deflection is relieved, the ridge may drop to the level with the lowest
> > point currently in place.
> >
> > Rogers issue with Creep is equally important as I would not
> > expect the ridge
> > to drop any more since the lowest point represents the maximum
> > creep already
> > occuring in the wood.
> >
> > Therefore, adding the collar ties provides some additional protection -
> > albeit redundant from what the ceiling joists are to provide. Still, the
> > can't harm the system (unless the joist is split in the process
> > of nailing.
> >
> > Inasmuch as I have to have this done tonight, unless I get some critical
> > information to contrary, I am comfortable with progressing based
> > on the 2000
> > IBC's recognition of collar ties as lateral supporting members.
> The final
> > word is with the building offical who may still send it back -
> > I'll see what
> > happens.
> >
> > Thanks to all for your comments and suggestions both public and private.
> >
> > Dennis S. Wish, PE
> >
> >
> >
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