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RE: Question on wood Roof Trusses

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Roger,
I have not read all of the posts, however I did read Neil's last comment and
this one from you.
I agree with you on this. The plated truss roof system is isolated as a
separate system in my area. The EOR is only responsible for the lateral
connection of the truss system to the structure and any gravity support of
the girder trusses. A letter is required from the EOR that indicates he or
she has reviewed the calculations ONLY TO VERIFY THAT THE CALCULATED LOADS
ARE WITHIN COMPLIANCE OF THE ACTUAL LOADS USED IN THE STRUCTURAL DESIGN.
If I recall correctly, the latest code or upcoming changes in the next code
require the truss company to provide more information including the
connection of truss to truss or truss to girder truss or truss to hip etc.

There is, in my opinion, a practical reason for this. The EOR does not have
the resources to design the truss connections or even to verify if the
calculations are adequate since the truss analysis is based on proprietary
values protected by the plate manufacturer.

The second issue, in my opinion, would purposely keep the EOR from assuming
any responsibility in the design of the roof system as to place the sole
responsibility for the structural integrity of the roof system upon the
plate manufacturer and the truss fabricator.

While I agree that the information Neil brought up should be considered in
the design of the roof, I am inclined to believe that this is the
responsibility of the truss manufacturer as all information on the loads
applied to the roof are provided by the EOR or Architect of record. To
become involved in a design that you have no control over is taking
unnecessary responsibility.

The EOR, as I stated, IS responsible for the connections at points of
bearing of the roof system to the structure and the appropriate transfer of
shear to the foundation.

You May wish to consult the WTCA (Wood Truss Council of America) on this
issue - (http://www.woodtruss.com).

Dennis
-----Original Message-----
From: Roger Turk [mailto:73527.1356(--nospam--at)compuserve.com]
Sent: Friday, January 12, 2001 9:30 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Question on wood Roof Trusses


Until the plated truss industry will provide me with the forces to be
resisted and locations of the braces while the project is still in the
design
stage, I am going to require that the truss designer be responsible for the
design and detailing of all bracing that is required as a condition of
design
of the truss.

While the plated truss industry is reluctant to admit it, there *are*
self-equilibrating methods of bracing compression members that do not have
to be carried down into the basic structure.

I would be very hesitant to modify anything that the truss designer
provided,
since they could then point to the modifications and say that that was the
cause of a problem.

I have in my files (somewhere) a TPI addendum/letter, ca. late '60's, early
'70's, that says that the building designer is *not* responsible for bracing
that is a condition of the design; that the truss designer is responsible
for
this.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Neil Moore wrote:

>>It appears that you have discovered one of the problems with the truss
industry.  These member are supposed to be braced and this usually appears
on
the truss company's drawings that come to the site.  Apparently these were
not
installed.  What many engineers that specify prefabricated trusses don't
know
is that THEY are responsible for the bracing of the web members.  The truss
company design will indicate what web members are to be braced, but the
ENGINEER (if there is one) has to complete the bracing design.  That is,
possibly being braced off to the gable walls or strutted up or down to roof
diaphragm or to walls below.

>From an older commentary in  the TPI-85 publication:  "The need for and
location of lateral bracing that may be required to reduce the buckling of
individual truss members is determined as part of the wood truss design and
is
the only requirement for bracing that will be shown on the truss design.
Lateral bracing details, including method of connection and transfer of
member
buckling forces to the structure, are to be determined by the building
designer."  ...... there's more.

In your case, you can probably add another 2x4 to the compression webs to
form
a tee section.  The installation should be done with care to prevent
spliting.


Neil Moore, S.E.<<