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Factory made trusses

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"I agree that compression web bracing usually gets no respect, unless from you."
Chuck Greenlaw

The design of the compression web bracing and companion diagonals required
to stabilize the lateral web braces is the responsibility of the building
designer, usually an engineer or architect in commercial construction.  The
"truss designer" is responsible for specifying the points on each truss that
require lateral support.  A reference on this matter would be ANSI/TPI
1-1995  National Design Standard for Metal Plate Connected Wood Truss
Construction which has been adopted by the three model codes.  See
specifically paragraph 5.3 Permanent Bracing.

There's more to permanent bracing than web bracing.  Chords under valley
sets, the  flat compression chord of a piggyback system, etc. require
permanent bracing design by the building designer.  Basically, wherever you
have a compression member that is not sheathing, the truss drawing will note
a requirement of lateral support at some interval.
I am doing research on permanent bracing design now.  This subject will also
be covered in our November short

A well known rule for designing lateral support for wood trusses is the 2%
rule--the restraining force equals 2% of the compression.   This rule can be
found in TPI HIB-91, a temporary bracing pocket book, published by the Truss
Plate Institute (608-833-5900).  In about a year, we will have some
practical design information for the more complicated truss bracing cases.

Frank Woeste, P. E.
Professor of Wood Construction & Engineering
Virginia Tech 
Blacksburg, VA 24061