Wind Exposure Category "C" or "D"

[Alex M]

Greetings,

I would like to get some opinions on the wind exposure category for the site per the attached images.

Thank you in advance to anyone sharing their thoughts on the subject.

-Alex

 

[Alex M]

more images

 

[Alex M]

and one more

 

[WARose]

I'm not sure where the building you are trying to design is relative to all this.....but for wind loads on a building adjacent to a large body of water (about a mile in width or more) Exposure D should be used. And I think that applies a good distance on-shore (something like 1500 feet the last time i looked).

This appears to be in Florida so you should consult the Florida Building Code and/or ASCE7 (which clearly defines exposure categories).

IIRC, Florida also has a "CCCL line" that has a lot of other requirements for buildings behind that line. (On the sea side.)

 

[Alex M]

Thank you for you response WARose. The building is shown with the yellow pin and the yellow lines are showing distances in couple directions. Building will about 5600 feet away from the main coastline.

Thanks
-Alex

 

[WARose]

There appears to be another large body of water between the point and the ocean......and just eyeballing it, it appears to be really long. For wind coming from certain directions, I'd definitely call this "D".

 

[Alex M]

Thanks again, yes there is large body of water, but even at 45 degree angle it appear to be less than 5000 ft required for exposure "D" per ASCE7 diagram (attached).

 

[WARose]

It could be at any angle. Wind can hit from any direction. But it's your choice.

 

[Ron]

AlexM....Exposure D does not apply under the FBC since your fetch distance is less than 5000 ft. Glad you checked at 45 deg,
because that would be the maximum applicability. Further, if your building is more than 600 feet from the shoreline, Exp D does not apply. Use Exp C.

 

[Alex M]

Ron,

Thank you very much. I kind of lost this battle with building officials, and they would not permit the building unless we change exposure category to "D". In my opinion, they just don't care much about the code and presented information and just defaulting to "D" if it is close to water, and i don't know if I can do anything about it.
I was just trying to to see if there are other, similar to my opinion out where or if most engineers just picking "D" because of the proximity to the coast line.

Thanks
-Alex

 

[elreedyman]

As per ASCE to be near to the shore; but if there are a high rise buildings separate between your builing and shore even it is near to the shore in this case you can relax the wind load by shielding effect or use category C

 

[Ron]

Alex M.....sorry, but the AHJ can do that under Florida law. Unless it results in an inordinate cost increase to the project or if for some reason it might compromise safety, it's not worth fighting with them.