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Struggling with ASCE 7-02 Wind Loading

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I'm struggling with the wind loading found in the ASCE 7-02. As I read the
process to design a regular wood structure by the Method 1 procedure, I get
confused about the negative pressures in the horizontal zones B & D. I'm
looking at the 85 mph Basic wind speed and a 10° Roof Slope. So, When
I read the numbers in Fig. 6-2 and Note 7 of that same figure, I get the impression
that I should be neglecting the negative or outward forces in zones B & D
so that the loading isn't less than if those zones were zero. This is counter-
intuitive to me. I'm used to designing for wind loading as prescribed in the
UBC's (94 & 97). With the UBC wind loading, I get an increase in pressure
as I ascend the building. The ASCE 7-02 seems to take the upper or roof
area as having no loading or a negative loading, which would reduce the net
loading on the projected area. This seems backwards.

When I go back to a fundamental idea of impact of the wind mass on the projected
area of the building, I get an increasing load as I ascend the building, due to the
increased velocity of the wind at that height. This makes sense to me from a
physics point of view. When we subtract out the uplift due to the Bernoulli effect
of the wind over the roof, it still seems that the uplift would be on the lee side
of the roof ridge and that the windward side of the roof would have a downward
pressure. Because of this, it seems that the projected area would have a positive
pressure and not a negative pressure.

I'm wondering if the ASCE Publication: Guide to the Use of the Wind
Load Provisions of ASCE 7-02 is any help in sorting out the application
of these loadings? Does the book have example problems? Is it worth the

Any help on this subject is appreciated.

Lloyd Pack
Thank you, Lloyd Pack, P.E. Project Engineering Consultants, LTD. (208)466-7190 (208)466-7168 Fax (208)250-2992 Cell

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