Interpretation of effective wind area in ASCE7-05

[mfstructural]

I have a question regarding interpretation of the effective wind area used to compute wind pressure on a building. I am looking at a wall that is approximately 150' wide by 250' tall. The effective wind area for the 10% edges is going to be smaller than that for the "field" center portion of the wall. The wall consists of siding panels 12" wide with a continuous span (they span over sub-girts spaced at 4' o.c.). Regarding interpretation of the effective wind area to use on the field; do you use the total area of the field = 120'x250' = 30,000 or the tributary or effective area of each siding panel of 4'x 1' wide = 4 sq. ft? This yields a huge difference, especially at zone 5. I have attached Figure 6-17 from ASCE7-05 showing the pressure coefficient table. I also attached and excerpt from ASCE7-02 wind design guide. Questions 19 and 20 basically imply to use the smaller effective wind areas? If this is the case (especially for a masonry wall, see question 20), when would you ever have an effective wind area greater than 1000 sq ft?

 

[JAE]

The wind area depends upon the element that you are designing.

For a single screw attaching the panel to the girt, the wind area is fairly small (area trib to the single screw).

For the 12" wide panel, I'd use the 12" x 48" as the panel effective area.

For the girt, I'd use the girt span x 48".

Etc.