Minimum design wind load

[h-badawy]

Greetings,
As per ASCE7-10 section28.4.4 , the minimum design wind load shall be 0.77 kN/m2 for wall and 0.38 KN/m2 for slab , my question, is the value of P=q *( GCpf - GCpi) shall calculate for each each wind exposed element ( leeward, windward , end zones , side pressure,…….etc) and then compare with the min. Values above and take the max.
For sure there are many values will be lesser than the above min. Values , because of this i feel there is another condition to use the above min. values, please see snap below and advise.

Thank you

 

[phamENG]

I'm not entirely sure what your question is. You are correct that these are the minimum values, as stated in ASCE 7-10. These apply to the wind load you use in the load combinations. In other words, if you run through all of your calculations and determine that the applied wind load would be 13.8psf on the wall, you use 16psf. If you determine it should be 24psf, you use 24psf. So if you're doing ASD, 0.6W=9.6psf for the minimum (which is approximately 10psf as required by earlier editions of the code) or for LRFD 1.0W=16psf for the minimum (which is equal to the 1.6*10psf as required by earlier editions of the code).

What other condition do you feel it's appropriate to use this? It sets a floor for the applied wind loading to ensure buildings aren't under-designed, since the formulas we use can under-predict loading at the low end.

 

[h-badawy]

I mean, these minimum values shall be applied to all elements , for example if the windward and leeward are both lesser than the minimum i have to increase both of them to be 16psf. I feel the total pressure on the building will be too much especially for steel building.

Thank you

 

[phamENG]

Why would the wind care what the building is made of? If it hits a flat surface, it'll exert a pressure. Sure, a loose sail will likely experience a different loading than a 1" steel plate, but for all practical purposes in structural design the cladding is going to be stiff enough that it doesn't really matter.

The minimum load provisions in chapter 28 are the same as those in 27. The application is explained in the commentary of chapter 27. They even give you a picture.