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RE: out of plane anchorage Question

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Remember that is a LRFD value, in ASD its 300 plf min. I will be trying
to figure this one out too Tarek... I have a project I'm starting next
week with Insulated Concrete Forms (i.e. Styrofoam forms with concrete
at the voids ... similar in construction to mortarless masonry) where to
me the critical thing is wall anchorage. Like your situation, it will be
anchored to a gang nail roof trusses. Perharps in a week or so we could
email each other privately and come up with something we can both use.

This case is a little different than what the code writers intended. The
sub-diaphragm in a tilt-up is generally heavily nailed from above
(through the sheathing)... the danger is having a plywood edge (panel
edge) on your anchor strut (a 2x, 3x, or 4x) at the wall that is heavily
nailed (say 10d @ 2" o.c.) and then you are adding two rows of staggered
nails for a strap or side bolting an HD for the positive connection to
the wall. That's a lot of penetrations in a small area and your roofer
turned carpenter with a nail gun will probably barely hit the wood when
shooting nails while standing on top of the ply. Splitting is likely....

I think using a 2x where you can side attach the wall anchor at a point
below the nail penetration from above would be okay. This means
something deeper than a 2x6.. otherwise, I think the 3x minimum is
appropriate. Also, you will want to have closely spaced anchors to avoid
the need for a blocked diaphragm (or maybe you can't avoid it) when
doing the sub-diaphragm check. Now if your truss goes from wall to wall
(like it sounds) you might not be dealing with sub-diaphragm behavior if
you anchor both ends of the truss. The anchorage force never leaves the
truss and does not enter the diaphragm. In a tilt-up, the tie back
usually goes in about 3-4 bays (24-32 feet) and stops, creating a chord
at the last purlin, and creating s diaphragm to transfer the forces to
the glulams or OWSJ's which are then spliced at columns and in turned
anchored at the pilasters.

In a tilt up, typically the anchors are every 6-8ft o.c. using an HD on
ea. Side of a 4x6. But the forces are rarely based on the minimum value
for Zone 4 buildings.

-gm

-----Original Message-----
From: Tarek Mokhtar [mailto:tarooky(--nospam--at)earthlink.net] 
Sent: Wednesday, November 12, 2003 8:50 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: out of plane anchorage Question

Paul,
I did consider doubling up the trusses at some spacing, however
the min. code requirement of 420 plf would almost dictate a double
truss @ 24"o.c which is a bit over the top for an 8' tall wall IMHO

Tarek Mokhtar, SE
Laguna Beach, CA







>Pat,
>
>I do not think they intentionally wanted to remove plated truss
construction
>from masonry or concrete wall structures, and I do not think these
>provisions prohibit their use, but in essence the provisions have made
this
>traditional construction approach more difficult.
>
>The primary wall anchorage failure experienced was for tilt-up and
masonry
>warehouse structures with tall walls and large diaphragms.  These are
>typically panelized systems with parapets utilizing sub-diaphragm
design to
>develop wall anchorage.  According to the SEAOC blue book, the
limitation on
>the net thickness of the wood member for bolted connections, where wood
>member thickness should be a minimum of 4.5 times the bolt diameter for
>ductile behavior in the connection.  When translated into code language
this
>became "The wood element shall have a minimum net thickness of 2.5
inches",
>without differentiation regarding bolted or nailed construction.
>
>In my personal opinion, most of the thought at the time was of limited
>focus, similar to the rho issues with wood construction.  The subject
of
>study was failures of one type and the consideration of the impact on
all
>the other types of construction was not 100% realized until the
applications
>were applied in practice.  However, with all that being said I
personally
>don't think this is such a bad idea.  It is possible to design
accordingly.
>The wall anchorage is the weak link in any bearing wall system.
>
>I am reasonably confident that a double truss adequately joined to act
as a
>single element, similar to a girder truss, would comply with the
provisions
>of the code.  I am also reasonably confident that this could be
adequately
>explained to most plan checkers.
>
>I also think there is definite room for improvement in these
"traditional"
>systems anyway.  Top bolts set in the grout cells acting perpendicular
to
>the wall perform poorly.  The table values in the UBC do not adequately
>address this, but if you read the actual equations the calculated
allowable
>value is pretty limited.  The top plate perpendicular to grain bearing
is
>not the most efficient and reliable way to resolve dynamic out of plane
wall
>forces.
>
>It is not too difficult to detail a more appropriate direct connection
>system and still use a plated truss system.
>
>
>Paul Feather PE, SE
>pfeather(--nospam--at)SE-Solutions.net
>www.SE-Solutions.net
>----- Original Message -----
>From: "Pat Clark" <bcinc(--nospam--at)nanosecond.com>
>To: <seaint(--nospam--at)seaint.org>
>Sent: Tuesday, November 11, 2003 4:23 PM
>Subject: RE: out of plane anchorage Question
>
>
>> I thought that the requirement was for the sill plates or ledgers.
Did
>> they intentionally want to remove all plated truss construction from
>> masonry and concrete wall structures?
>>
>> Patrick Clark, P.E.
>> Building Concepts, Inc.
>> 1228 Pep Circle
>> Gardnerville, NV 89410
>> (775) 782-8886 x22
>> (775) 782-8833 fax
>>
>>
>> -----Original Message-----
>> From: Paul Feather [mailto:pfeather(--nospam--at)SE-Solutions.net]
>> Sent: Tuesday, November 11, 2003 3:59 PM
>> To: seaint(--nospam--at)seaint.org
>> Subject: Re: out of plane anchorage Question
>>
>>
>> Correct, you would have 3x minimum chords for anchorage attachment if
>> you are using the truss for anchorage.  This makes this "traditional"
>> construction system a bit harder to implement.
>>
>> Paul Feather PE, SE
>> pfeather(--nospam--at)SE-Solutions.net
>> www.SE-Solutions.net
>> ----- Original Message -----
>> From: "Tarek Mokhtar" <tarooky(--nospam--at)earthlink.net>
>> To: <seaint(--nospam--at)seaint.org>
>> Sent: Tuesday, November 11, 2003 3:25 PM
>> Subject: out of plane anchorage Question
>>
>>
>> >
>> > consider a 35' x 18' one story masonry building with a wood truss
roof
>>
>> > The masonry walls have a 4x nailer on top, where the trusses are
>> > attached for bearing and out of plane forces.
>> >
>> > Section 1633.2.8.1 states that wood elements of the anchorage
system
>> > shall be 2 1/2" minimum, does this mean that the trusses have to be
3x
>>
>> > thick?
>> >
>> > Tarek Mokhtar, SE
>> >
>> > Laguna Beach, CA
>> >
>> >
>> >
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