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RE: Factory made trusses

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Absolutely Roger!  The EOR need only provide the truss designer with
appropriate loads both gravity and lateral so that the truss can be
effectively designed. The design of any member, connection, bracing, plates,
bridging, hangers etc, are (or should be) the express responsibility of the
truss designer.

I believe the 1997 UBC makes this a requirement although I have not searched
out the section. I received this information from another engineer. Until
it's adopted, truss manufactures try to get around any extra design time
that may be required. This is due, in part, to them earning their profit on
the number of trusses manufactured and shipped, not on the truss design
itself. More time paid to their engineer in design and detailing is taken
away from their profits or pushes them outside the competitive range.

Once the '97 UBC is adopted, they will have to be clearer in the
specifications booklet about truss to truss connections, bracing etc. Until
then, I generally make it clear from the start that this is what I expect or
my client will seek another yard.

Dennis

-----Original Message-----
From:	Roger Turk [mailto:73527.1356(--nospam--at)compuserve.com]
Sent:	Sunday, August 02, 1998 1:01 PM
To:	seaint(--nospam--at)seaint.org
Subject:	Factory made trusses

Frank Woeste wrote:

. > 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.

Hogwash!

Only the truss designer knows where compression members need to be braced
and
the bracing force.  The building designer has no knowledge of this until the
shop drawings are received.

Regardless of what TPI 1-1995 says, my specifications will *require* that
*all* bracing that is a condition of design of the trusses is to be
specified
and detailed by the truss designer.

The Truss Plate Institute went thru this once before (early 1970's) and at
that time put in their specs that all bracing which is a condition of design
is the responsibility of the truss designer.

. > 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 ...

Right, but who determines where the chords under valley sets are located?
Who decides where compression web members go and how long they are?  Who
determines where piggyback systems are divided?  Not the building designer!

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