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Re: out of plane anchorage Question

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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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