New Chicago Building Code - Wind Load

[RFreund]

I wanted to confirm my understanding of the new Chicago building code.
Section 14B-16-1609 LINK
Sub Section: 1609.6 Alternative wind loads for enclosed structure with mean roof height of 60 feet or less.
There appears to be a fairly substantial reduction for low rise buildings. Previously it was always 20psf, now we are looking at 0.6*25psf = 15psf.
I'm assuming since the requirements are much more restrictive, you can use the lower wind pressure. This is probably more inline with what you would get using ASCE7 (or maybe even higher).
Just want to make sure I have this correct.
Thanks

EIT

http://www.HowToEngineer.com

 

[DaveAtkins]

I agree with how you are reading the code.

It is interesting that Chicago is finally aligning with ASCE 7. As I recall, they used ANSI A58.1-1982 until very recently.


DaveAtkins

 

[RFreund]

Yeah, I think that's right.
There are finally earthquakes in Chicago now too.

EIT

http://www.HowToEngineer.com

 

[MrHershey]

I'd guess they did their conversion based on Exposure C instead of B. Perhaps doesn't make sense in a heavily urban area like Chicago, but is in line with the maps in ASCE 7 (which are all based on Exposure C).

Pressure for Exposure C is 32 psf. With 0.6 factor that becomes 19 psf. Slight reduction, but in the ballpark of the previous 20 psf number.

It is interesting that Chicago is finally aligning with ASCE 7. As I recall, they used ANSI A58.1-1982 until very recently.

Technically still are for the time being. New code isn't even optional for another month and a half. Mandatory compliance not until August 1 next year.