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RE: factory-made roof trusses

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John Jones brought up a couple of items that I didn't touch upon.

. > there is usually a little box labeled something like allowed stress 
. > increase and in my area (Central Alabama) the box is usually labeled 
. > 1.15. The code does allow a repetitive stress increase of 15% for bending 
. > members provided you meet a few requirements. This is not clearly spelled 
. > out the way the little box is described on the output.

This could also be a load duration factor (2 months cumulative maximum 
loading over the life of the structure), however, you're right, it's not 
spelled out clearly, like many things on their shop drawings.  Another thing 
with respect to the load duration factor is the recent code authorized value 
of 1.6 for wind and earthquake.  I am still hesitant to accept a value that 
high, so I specify that the maximum load duration factor to be used is 1.33 
for wind and earthquake.

. > On our drawings and specs we always require that the shop drawings and
. > calcs be stamped by a licensed (registered ->whichever it is this week)
. > engineer in the state that the project is taking place in.

At a Tucson Chapter SEAOA meeting a couple of years ago, a person who worked 
or had worked for a fabricator in Arizona stated that the way the 
engineering was done was the fabricator (who may have no engineering 
knowledge or experience) input the load information and truss information via 
a local terminal and a computer in California spit out the results.  There 
was an engineer in California who was a registered Civil in Arizona that 
stamped and signed the output, but he was so busy, that he never had time to 
review the output; besides, the computer program was *so* good, he didn't 
need to.  The output was then faxed to the fabricator who then submitted it 
to whoever for review and approval.

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