ASCE 7-05 - wind corner zones

[a2mfk]

I have been told by another SE (peer review) that INSIDE corners are exempt from zone 3 and 5. I don't disagree, I just cannot find this in ASCE. Its for my C and C diagram for the CDs, not for calcs... Can anyone point me to the note or section that says this?

 

[Ron]

a2...I agree, but ASCE does not properly address this. My opinion is that the inside corner does not represent a positive-negative change...the outside corner does.

 

[msquared48]

I don't know that I can totally agree in this case...

It seems to me like the wind could get "trapped" as it were at an inside corner, locally increasing the lateral pressure to the wall, especially if the wind was at an angle to the inside corner.

Then again, there could be a local eddie effect in the inside corner. Seems like you might have to do a wind tunnel test with a smoke stream to see what really happens, or just be conservative and apply the extra pressure if in doubt.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Ron]

Mike...I think you might be right, but no one has shown us the wind tunnel data to reflect such. I worked on a 26 story project a couple of years ago that went with wind tunnel data rather than the analytical method. There was no increase for inside corners.

 

[a2mfk]

UPDATE:
The peer reviewer said he is not aware of anything official from ASCE, this is his assumption based on his understanding of fluid mechanics. I tend to agree, though this is really just academic since the only people that may even use our C and C roof diagram is the roof membrane installer. I checked my deck fastening for worse case corner zone anyway...

 

[WillisV]

SEAW/ATC 60 discusses this on page 108 (Section 9.2.2). Basically a "corner" is defined as an outside corner whose included angle is less than 170 degrees. Inside corners do not cause airflow seperation. However, be careful as small re-entrant corners are actually the worse case for pressure buildup.

 

[a2mfk]

Thanks WillisV.

This one is not in my library, but before I go ordering it I guess I should wait until they update it for ASCE 7-10, but I suppose that could take a couple of years or more... Great system where the spec/code is so complicated and under-explained you have to buy software or another guideline to understand it!