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RE: Bracing for Nail-Plate Wood Trusses

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I have been meaning to respond to this thread for a while now.  What I have
been doing recently is what many of you have already stated, i.e. "permanent
bracing of the trusses is the responsibility of the truss manufacturer", and
this is in our general notes.

Most truss manufacturers will specifiy that bracing can be accomplished by
one of two methods -

1) T-brace the compression member which is subject to buckling under the
design loads.  This member is usually a 2x4 with the length, grade and
attachment noted on the truss design drawing.
2) Provide 1x4 minimum continuous lateral bracing (CLB)at locations as
specified on the truss drawing for specific web members.  We then as the SER
need to to provide x-bracing at the end of the CLB line to take the load
into the roof and ceiling diaphragms.

The problems I have with method 2 are:

a) I am bothered by the fact that a manufacturer is providing me with a
pre-engineered component that fails under the design loads unless CLB is
installed.  To me this is analogous to specifiying a K series joist and then
receiving shop drawings advising me that I need to provide reinforcement or
bracing of certain web members or they will potentially buckle under the
design loads.

b) Most of the wood frame structures I deal with have roofs with a level of
complexity such that it is usually unlikely that more than 4 or 5 adjacent
trusses have the same web configuration, making the use of CLB extremely
impractical.

c) CLB is rarely installed and when it is, it is usually poorly installed
and bracing lines often terminate perpendicular to a plane of non-structural
atmosphere.

d) Truss manufacturers rarely provide the forces in these members for which
the SER is expected to provide bracing.

The document that indicates that design of permanent truss bracing is the
responsibility of the SER is WTCA-1, "Standard Practice for Metal Plate
Connected Wood Truss Design Responsibilities".  Many know that this document
was produced by the Wood Truss Council of America.  Someone has already
stated that it is going through or has gone through committees to become an
ANSI standard.  I had an article about this but don't know where it is right
now.  I have been in active communication with the president of my company
to discuss this issue at the meetings of the various code committees he is
involved with.

I hope that we change the current direction that this document is taking /
has taken, and will let you know of any progress I become aware of.  I will
continue to specify on our contract documents that the design of permanent
truss bracing is the responsibility of the truss manufacturer.

Albert J. Meyer, Jr., P.E.
Senior Project Engineer
Cagley, Harman and Associates
Structural Engineers / Parking Consultants
1015 West Ninth Avenue
King of Prussia PA 19406-1222
ameyer(--nospam--at)cagleyharman.com
(610) 337-3360
(610) 337-3359 Fax
www.cagleyharman.com


-----Original Message-----
From: Kris Hamilton [mailto:kph(--nospam--at)geigerengineers.com]
Sent: Wednesday, April 02, 2003 5:26 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Bracing for Nail-Plate Wood Trusses


Chris Banbury, Pat Clark, et al:

Interestingly enough, the "Metal Plate Connected Wood Truss Handbook," 2nd
Edition, Wood Truss Council of America, 1997, does *not* consistently place
the responsibility in the same way that the TPI does.  Some quotes from
Chapter 15 of the Handbook, 2nd edition,

"Section 15.4 Contractor Recommendations:
"2. Prior to erection and installation, determine necessary truss bracing,
locations of bracing, and methods of installation.  The services of a
structural engineer may be required.  ...
"4. Have a structural engineer review installation and erection procedures
using DSB-89."

Elsewhere, they toe the same line as the TPI, except that they do several
places say that the bracing should be "... installed and fastened per the
building designer's specifications."  Implying, I guess, that we can specify
the performance of the bracing, and hand it back to the fabricator.

Also, document HIB-91 that is often referred to includes phrases such as
"Permanent continuous lateral bracing as specified by the truss
engineering," in a note pointing to a diagram of web bracing.  Again, not
consistent.

So, it seems we all agree that for reasons of construction sequencing, total
roof system economics, and a reasonable placement of responsibility and
liability, it makes no sense whatsoever for the EOR to come back into the
project after shop drawings are done and design the bracing.  We all know
*how* to do it, if need be, but it is really neither standard practice or
sensible practice.

Now, does anyone know or have any ideas how we go about changing the
situation?  Get all of our SEA's to set policies and write letters to ANSI,
TPI, WTCA, ICBO, ICC, Florida State Board, and so on?

We also should insist that the building departments enforce the same rules
for all buildings with truss roofs, including the "building designer"
projects that we never see, and not just the ones that are designed by
engineers.  About the tenth time that the contractor has to go out to hire
an engineer just to design the bracing, he/she will start leaning on the
truss fabricators for a change.

--
Kris P. Hamilton, P.E.
Geiger Engineers
114 West Magnolia Street
Suite 505
Bellingham, WA  98225
Ph: 360 734 7194
Fx: 360 734 7399


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