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

RE: Question on wood Roof Trusses

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Stu,
Thank you for the response (please don't be shy about making it public). I
also received a response from Brad Cameron of Keymark to let me know that
they do not produce your software - my error.

I do not think I stated that the trusses are proprietary, I was pretty clear
that it is the plates which are proprietary but will make sure that this is
made clear on the Lists.

When I first learned of plated trusses some 8-years ago, I learned quickly
that engineers could not design trusses in-house. It was not the limitations
of the software, as any program like Risa2D or 3D will design the chords and
struts axial loads and stresses. The plate information was protected as was
any proprietary information necessary in the manufacturing process (press
plate pressure et.al.).

At first this was disturbing as it was expected that the EOR would be
responsible for the entire design but was limited as to what he could verify
by calculations so as to develop a confidence level in plated truss design.

Simpson listed a plate at the time, but it was a nailed plate. When I called
Simpson, they were clear that the plate capacity was predicated on the shear
capacity of the nails with a metal side plate. Press plates were dependent
on many more issues - pin length and embedment, tested capacities etc.

WTCA has done a great deal to help create standards in the Truss Industry
and this is important because, in my opinion (least I stick my foot in my
mouth again), plated wood trusses are the most viable way to design because
they use the least materials to provide the greatest strength and are most
economical to erect. The development of standards has helped reduce quality
problems in the industry and probably create greater competition between
fabricators.

With that said, I still think that the majority of engineers designing homes
are uncomfortable to a degree with plated trusses simply because we don't
have the same design control - the ability to evaluate and develop an
intuition for the materials as we do by our understanding of the strength
and materials. We have to rely upon what is obtained by another engineer -
usually not of our choosing and more often by price competition - and we
must take responsibility for designing everything up to the roof system
working on the expectation that all of the information will be clearly
disclosed as to what is needed, be it bracing, girder truss supports etc.

Finally, just last year, one fabricator provided the calculations for each
truss in a complicated roof but did not provide me with information as to
how smaller trusses are connected to girders or girder trusses. When asked,
the truss company engineer indicated that he was not responsible for the
connections, only the trusses. This was disturbing as the connections are as
important in the performance of the trusses as are the trusses themselves
and in this case, you can not easily differentiate the Engineer of Record
from the engineer designing the roof trusses. This has changed and as I
recall, the Truss designer must provide more information as to how the
system ties together. The makes the separation of responsibility easier to
differentiate as the EOR can now be responsible for the transference of load
to the structure while the Truss manufacturer stays responsible for the
truss system.

One final word - respectfully, these are responses to posts on the list that
confirm that the truss industry (and other industries being discussed) are
listening to the threads. I don't understand why the responses have to be
private. It is in the interest of everyone in the professional community to
know where I have been wrong or misinformed. It is also in the professional
communities best interest to have a representative from the industry
(preferably more than one) who is willing to discuss these issues openly. We
simply can not be well informed and can only speculate on what we learn or
know from experience without the knowledge of those in the industry to
provide us with the facts.

I implore all industry representatives to participate in the discussion as
we can not do our job properly until you make it clear what the facts are in
the issue.

Respectfully,
Dennis S. Wish, PE

-----Original Message-----
From: Stuart Lewis [mailto:SLewis(--nospam--at)www2.alpeng.com]
Sent: Monday, January 15, 2001 8:46 AM
To: Structuralist
Subject: RE: Question on wood Roof Trusses




As mentioned by others, design values for proprietary truss plates are
usually available through the model code evaluation reports.  They are also
typically available from the plate company or whoever did the truss design
if someone other than the plate company.  I am responding specifically
because you referred to <Alpine Truss>.  Alpine Engineered Products, Inc.
(my employer) will provide a copy of our model code evaluation report to an
EOR upon request.  Perhaps you are referring to a specific truss
fabricator, which I cannot speak for.  I would guess that if they refuse to
provide you plate properties, then that fabricator may not have them on
hand.

In addition, the trusses are usually not proprietary, as only the truss
plates are proprietary (there are exceptions as certain fabricators may use
proprietary lumber or proprietary practices).  Considering the trusses
proprietary is akin to considering a roof structure designed with
conventional-construction practices proprietary because it uses a
proprietary 2x6 hanger instead of just toe-nails.  The engineered truss
design is, of course, proprietary just as any of your engineered designs
would be, and the plates are typically proprietary, but the truss itself is
usually not.

In another e-mail, you state Alpine's software is produced by Keymark,
which is not true.  Alpine provides its own software.  Keymark or other
companies may produce software that can design trusses using Alpine plates,
but this software is not distributed by Alpine.  To my knowledge, the
Keymark software which specifies Alpine plates uses the same plate design
properties for those plates that are available to any other engineer in the
model code evaluation reports.

Best Regards,

Stu

---------------------------------
Stuart L. Lewis, P.E.
Research & Development Manager
Alpine Engineered Products, Inc.
1950 Marley Drive
Haines City, FL 33844
ph# 863-422-8685
fax#863-422-6573
e-mail: slewis(--nospam--at)www2.alpeng.com



---original messages posted 1/13/00 to seaint-----
--------------------------------------------------------------------------
9                                Message:0009                            9
--------------------------------------------------------------------------
From: "Structuralist" <dennis.wish(--nospam--at)gte.net>
To: <seaint(--nospam--at)seaint.org>
Subject: RE: Question on wood Roof Trusses

George,
One issue with your explanation that I happen to agree with. It is not
possible for an engineer to design the connections of a plated truss
without
the design information on the specific truss plate used. This information
is
protected as proprietary information by the different Plate company's and
is
not available to the EOR. If you ask Alpine Truss for their plate data so
you can design the truss in your office with the intention of producing a
job-built truss or to take to other lumber yards to manufacture, you will
not get it. They work with specific software developers like Keymark
Industries who create the truss program and then license it to lumber yards
who produce trusses using the proprietary press plates.
Truss fabrication is a highly competitive industry - especially here in the
desert. When I left Los Angeles eight years ago, I had a custom home which
I
wanted to design with trusses. I was only able to find one company in
Ventura county at the time who would provide the trusses, including the
design. When I arrived in the desert, I felt like an apprentice again when
I
discovered that virtually every home was constructed with trusses. In fact,
in the last eight years, I am working on my first home that was constructed
using stacked lumber and I simply can not see how the designer justified
the
cost. I have, admittedly, gained a tremendous respect for plated trusses.
There is no question that engineers or inspectors (especially on
conventionally framed homes) need to have a keen eye to identify the
defects, but to protect the trusses from unauthorized and dangerous
modifications by contractors in the field.
I remember a number of homes where the contractor nailed braces for soffits
to the bottom chord of the truss at plate locations effectively splitting
the lower chord. I've seen trusses stored on top of homes laid upright at
an
angle supported to stud walls with 2x4 braces until the trusses could be
distributed and set permanently in place (a technique that will warp and
possibly damage the trusses). I've seen struts cut to allow for mechanical
ducts to pass and the inspectors had not caught the problem. There are a
number of possible field abuses.
Most of my point is that the truss is proprietary and it is next to
impossible for an engineer to design a plated trusses without the
proprietary information that the manufacturer protects. Until this changes,
there is little we can do other than act as the EOR of the project and
distance ourselves as much as possible from possible problems with the
system that we can not anticipate without the proprietary information.

I don't add for truss review to my contract, but then again, I don't reduce
my fee because a client wishes to use trusses over having me design the
roof. I figure, that the time I save in the design I pick up in the
coordination and responsibility as the EOR. So far no client has complained
about this.

Dennis S. Wish, PE


--------------------------------------------------------------------------
17                               Message:0017                           17
--------------------------------------------------------------------------
From: "Structuralist" <dennis.wish(--nospam--at)gte.net>
To: <seaint(--nospam--at)seaint.org>
Subject: RE: Question on wood Roof Trusses

Stan, you can get the icbo reports on the plate data but there is specific
plate capacity information and physical properties that are not indicated
in
the ICBO report that are used for plate stress calculations which are
protected by the plate manufacturer.

Plate manufactures don't necessarily design their software as one other
person suggested. Keymark industries is the manufacturer of Truss software
for many plate manufacturers, including Alpine. The specifications,
tolerances and capacities (stress and load ratings) are protected by the
plate manufacturer. The truss software is licensed by the plate
manufacturer, but the software is often produced by one company - Keymark,
although there are a couple of different software's available to truss
companies.

Dennis