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Re: Question on wood Roof Trusses

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While we are discussing roof trusses.  Can someone tell me why the truss
manufacturers use the "Primary frames and systems" Wind Pressure Coefficients (Cq
in the '97 UBC Table 16-H), instead of the "Elements and Components"
coefficients.  I don't see the justification.  For wind uplift, the difference
can be significant, especially for the typical roof truss with less than a 100 sf
tributary area.   I wouldn't design a roof rafter as a primary frame.  What's the
difference with a truss?

If you think the trusses on your project are being designed as elements and
components, you might be surprised if you check the uplift reactions, I was.

Monty Hart
Associated Design Consultants, Inc.
Anchorage, Alaska