Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Factory made trusses

[Subject Prev][Subject Next][Thread Prev][Thread Next]
I agree 100% with you, Roger.  My specs specs also *require* that the truss designer design the
web bracing, and the bottom chord bracing if required for uplift.  There's absolutely no way for
the building designer to know what the final roof truss layout,  and bracing locations and loads
will be until the shop drawings are completed, and there's no requirement here in Florida that
the structural EOR, or any design professional for that matter, be involved in the CA phase.
So, if TPI 1-1995 were followed the the bracing wouldn't be designed by anyone.

To close this hole in the TPI spec, all of the local building departments here are now requiring
the truss framing plan, bracing and details be submitted with the application for building
permit, unless a design professional will be reviewing the submittals.  For houses that don't
require a design professional, that means the contractor has to hire the truss plant to design
the trusses *up front* -- and truss plants are charging high fees for this since they know that
some of the buildings won't get a permit and, for whatever reason, won't be built.
Understandably, the contractors are not happy about this.

Lew
=======================

Roger Turk wrote:

> 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
>