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TPI - Plated roof truss discussion started by Tom Harris

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-----Original Message-----
From:	Roger Turk [SMTP:73527.1356(--nospam--at)compuserve.com]
Sent:	Monday, November 10, 1997 11:05 AM
To:	seaoc(--nospam--at)seaoc.org
Subject:	Re: Permit Requirement Q

Tom Harris wrote:

. > I believe too many truss calcs are being done by truss 
company
. > technicians ( high school grad or ? ) and being sent to be 
rubber stamped.

According to an engineer who worked for one of the *big* truss 
plate
companies, this (being rubber stamped) is exactly what happens. 
 Several
years ago, at a meeting of the Tucson Chapter, SEAOA, he stated 
that the
fabricators input the design information on a remote terminal, a 
computer
does the analysis and design, and a licensed structural engineer 
stamps them
as soon as they come out of the computer --- that he doesn't 
have time to
look at them and faxes them to the fabricator.  Paraphrasing, 
"the computer
program is so good that he doesn't need to look at them."

At one time, TPI essentially required the EOR to be responsible  
 for the truss
design.  Then, it was changed so that all requirements that are 
a, "condition
of the design" were the responsibility of the truss 
fabricator/truss plate
manufacturer.  Now it appears that TPI is trying to put the onus 
back on the
EOR.  We can't let this happen!  A simple addition to the 
general notes to
the effect that all bracing that is a condition of the design is 
to be
detailed by the engineer responsible for the truss (or other 
proprietary
element) design should address the problem.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Roger & Tom,
I started a new thread on this topic because I felt that it 
raised a separate problem that was not covered under Tom's 
original post.
I found that plated roof trusses are also "rubber-stamped" out 
here in the Coachella Valley (Palm Springs California area). In 
the course of reviewing truss calculations, I rarely found a set 
of calcs that represented what the final truss would look like. 
In most cases, undo pressure was placed upon me as the EOR to 
accept what was provided and to have the contractor tweak out 
the design in the field with the truss company.
I refused to do this and when noting irregularities in the truss 
package, provided a letter to the building official documenting 
the issues that were not in compliance with my design as part of 
the plan check submittal. Out here, the building official in 
over half the local cities will not accept a plan check 
submittal without a set of truss calculations.  This has led to 
truss companies submitting "dummy calc's" because they were not 
guaranteed the truss business and did not want to waste their 
time producing calculations.
Another problem I found was that the Truss company would design 
the trusses but wanted the EOR to design the connections of 
truss to truss (at truss hips, valleys or girder trusses). My 
opinion is that once I design the connection, I become liable 
for the entire truss design rather than the engineer hired by 
the truss manufacturer.
I understand that the 97 code will require the Truss 
manufacturer to provide connection details as indicated above, 
but as of this time it is like pulling teeth to get them to do 
this.
I have also run into a problem where the Truss manufacture 
refuses to provide the information that I require and I want to 
use an different manufacture. The architect or contractor who 
have built a relationship with this company will refuse to abide 
by my wishes and generally expects me to compromise. The only 
thing I have been able to do is to require a pre-construction 
meeting with the Truss Company included and to address my 
concerns in front of the architect, GC and Truss company so that 
these issues are stated for the record. By doing this, I try to 
force a resolution prior to placing the order for the trusses.

There is a definite discontinuity between the roof and structure 
when working with a roof truss manufacturer. I have been 
successful in resolving the problems related to roof to wall 
connections and shear transfers, but have not had sufficient 
luck with truss to truss connections. My fear is that if I 
specify a connection that places a reaction from on truss on 
another that had not been intended to be designed that way, I 
could be affecting the stability of the main truss. Truss 
packages are notorious for omitting instructions for connections 
or for showing how the loads transfer in the chords from one 
truss to another.

Dennis Wish PE