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ASCE 7-95

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The wind sign convention used by ASCE 7 (and its predecessor, ANSI 
A58.1-1982) can be very confusing.  Pressures acting *toward* the surface are 
POSITIVE; pressures acting *away* from the surface are NEGATIVE.

Therefore, an INTERNAL pressure, pushing the surface off the building, is 
POSITIVE; while an EXTERNAL suction, pulling the surface off the building, is 
NEGATIVE, even though both are trying to do the same thing, i.e., remove the 
the surface from the building.


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

Chris Daniels wrote:

. > I'm looking for some advice on the component and cladding loadings from
. > figure 6-5B in ASCE 7-95.  How are the component and cladding values for a
. > gable roof applied?  I have a heavy timber truss system (11:12 trusses @ 
. > 14' O/C), purlins and common rafters.  My question is, how are the values
. > applied to the truss?  Is it the same as MWFRS, wind perp to ridge under
. > positive internal pressure, wind perp to ridge with negative internal
. > pressure, wind parallel to ridge windward edge and leeward edge with
. > positive and negative internal pressures.  Or is the maximum positive and
. > negative pressures applied without considering windward and leeward 
. > effects?