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To All with Interested In Manufactured Truss Construction

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The first question that I have is; Who are you talking with to get the
answers to these questions? The engineer that sealed the drawing? It really
needs to be the engineer that seals the drawings. He/she is the final
authority on the design, and should have a good working knowledge of how the
truss design model is working.

The design models developed by our industry take into account the testing
that has been completed on trusses, which typically has been done on a
proprietary basis. Factors are employed to take into account rotational
stiffness of the truss plates. There is fairly significant rotational
stiffness present. Forest Products Laboratory has data on this truss plate
attribute.

We are currently working on this area within our industry. It all begins
with the truss design standard, ANSI/TPI and will move into other facets of
design and modeling as we continue to develop the all the technical
attributes of our industry. We would enjoy the perspectives of everyone on
this list.

I would suspect that unbalanced loads are taken into account given that this
analysis is required by the code. All the load conditions considered by the
program and the engineer should be able to be easily printed out and can be
provided to you.
If you have trouble getting any information that you need, please bring all
the specifics to our attention, and we?ll bring it up at the next
TPI-Technical Advisory Committee or WTCA Engineering Review Committee
meeting to discuss. Our industry has been built on sound engineering and the
reputations of all our engineers are at stake. We need to be proactive in
dealing with any concerns anyone has and we will.

Part of the reason that this component engineering process is delegated is
to save all of you time. As Dennis rightly says this also transfers your
risk and exposure. The truss design engineer must ensure that the component
will transfer all loads to bearing points with the appropriate magnitude of
each on a worst case scenario basis, given code required load checks.
You can obtain computer programs that should allow you to do quick checks
and ensure that magnitudes are what you expect. Purdue Plane Structures
Analyzer (PPSA) is one program that works quite well. I also know that
Keymark has a truss design program that they sell to design professionals.

My company Qualtim, besides managing WTCA, also does forensic engineering.
The best way for the truss manufacturer and the truss design engineer to
lose a case is to have a design error. Juries don?t give companies that look
like they have deep pockets off the hook too easily. It is also impossible
to defend the Truss Company as a defense expert if the design is done
poorly. I have yet to be in trouble in this particular area in any case we
have been involved with.

Please keep us plugged into your problems as we enjoy working through these
issues. They can only make our industry better.

Kirk Grundahl, P.E.
WTCA Executive Director
www.woodtruss.com