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Re: Question on wood Roof Trusses

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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.<<