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Re: Permit Requirement Question

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Neil,

I too have previously written on this subject on this list.  First, to bring you
up to date, the TPI has published a 1995 version of their specs in which Section
2 defines the responsibilities of the Truss Designer and the Building Designer -
as seen by TPI.  (These responsibilities are more clearly refined in APPENDIX A,
which is clearly marked NON-MANDATORY).

As I've written before, I consider the TPI requirement that the building
designer design web stiffeners for the trusses to be analogous to having a
pre-engineered building designer NOT be responsible for the design of
cross-bracing or for the bottom flange bracing for uplift.  Luckily, I have yet
to have a truss designer ask me to design web stiffeners for him.

My other pet peeve is TPI's requirement that the Building Designer design the
truss anchors.  I've always wondered how I'm to do that without reactions, which
aren't calculated until after I've provided signed and sealed drawings to be
submitted for permits, certifying that the design complies with the code.  Using
the pre-engineered building analogy again, this would be asking me to design the
anchor bolts for the building.  I've yet to have a pre-engineered building
designer not design the anchor bolts.

Fortunately, others here in Florida agree with me.  The Florida Board of
Professional Engineers has adopted a series of Rules, by which "The Board
considers that professional engineers may avoid disciplinary actions by
observing the procedures set forth herein."

I won't quote the entire Rule regarding Prefabricated Wood Components, but here
are the pertinent excerpts:

"Structural engineering documents shall indicate provisions for support,
bearing, cross and lateral bracing, and for all bracing and anchorage required
to resist uplift, gravity and lateral forces."

"Structural delegated engineering documents shall include component details ...
and shall specify member sizes, bracing, anchorage, [and] connections ...."

"The effect of the delegated components ... on other parts of the structure is
the responsibility of the engineer of record ...."

So, in Florida the Building Designer is to indicate *provisions* for support of
the trusses; and, the truss engineer who doesn't design web bracing or anchorage
for his trusses is subject to disciplinary action by the Board - regardless of
the TPI specs.

Best regards,

Lew Midlam, PE
http://www.lcm.com

================
Neil Moore wrote:
> 
> I've posted this item before, but your question provides a place to remind
> our list of paragraph 1.1.5 of the Truss Plate Institute's TPI-85, Design
> Specification for Metal Plate Connected Wood Trusses:
> 
> "1.1.5  This Specification does not cover design for the complete
> structural system of a building.  Provisions shall be made for bearings,
> cross and lateral bracing, bracing to transfer truss member buckling forces
> to the structure, and bracing to resist wind, seismic or other horizontal
> loadings by those responsible for the overall building design."
> 
> So if you specify a prefabricated wood truss system, you do not receive the
> web bracing anchorage.  In fact, the Truss Plate Institute publishes some
> information on how to calculate the forces needed to resist the buckling of
> the web members, but you have to have the loads into the web members in
> compression obtained from the truss manufacturer's engineer's calculations
> before you can do this.
> 
> The point of this is that many engineers, architects and building officials
> don't know about this.  Therefore submitting the truss drawings and
> calculations after the fact leaves out the opportunity of the responsible
> designer to complete the bracing system.
> 
> Neil Moore, S.E.
>