Wind loads on rooftop equipment 2

[JAE]

A small debate in our office. We have two 12' x 24' long (in plan view) condensers sitting above a roof of a large building. The condensers are 16 feet tall. They will be set parallel to one another such that the 24 ft lengths will align.

The two 12 ft. widths will be separated by a 4 foot gap.

The units will sit on a steel framework of beams supported by columns extending through the roof of the building.

We are using ASCE 7-05 for the wind load on roof-top equipment. In ASCE 7 it has a section titled "shielding" that states that for buildings and other structures you cannot use one element to shield another.

The debate is whether, in this case with two large condensers sitting only 4 feet apart, does the "projected area of the units" mean we have to put the wind load on both of these or does the small width of the gap (4 feet) mean that in essence we have "one" unit and receive wind on one face only?

See the attached sketch.

 

[hetgen]

@Dik,

interesting... do you have the other 26 charts or can you quote a source?

;-) haha "other 26 charts"..


I though i did quote the source "BS". slickdeals got it right it's from British standard.

You will also find a simplify version of the reduction factor on EC-1-4 (Euro code) see attached.

 

[SteveGregory]

In my first post, I used the word "anchorage". But the ASCE language for 6.5.15 and 6.5.15.1 does not imply that it only applies to the unit design or the anchorage. It only gives an equation to determine the wind force on the "Other Structures" or "Rooftop Structures and Equipment for Buildings
with h ? 60 ft".

This wind force then must have an adequate load path through the MWFRS. There is a provision for reducing the 1.9 factor down to 1.0 depending on the size of the AHU.