Wind Uplift on Multi-Level Residential Beach House Deck 1

[waytsh]

Need a quick sanity check from you guys. I have been asked to design a steel beam, post, and footings for a two-level deck on a residential home near the shore. There is a large clear width requirement under the outside edge of the deck which is driving the requirement for the steel framing. I am debating with myself on how to account for wind uplift on the deck floors. I ran some numbers treating both floors of the deck as overhangs and I am getting some pretty large uplift values. The beam and post design is controlled by DL+LL so no real problem there. The concern comes with the footings for the two support posts. They will need to be quite large, in the range of 6'x6'x24".

Am I being overly conservative to treat the decks as overhangs? Is there better method to account for the wind uplift?

 

[phamENG]

I usually look at free roof uplift with obstructed wind flow. Overhangs would be easy too conservative.

 

[hokie66]

Adjacent to the wall, the deck would be subject to the same pressure as the wall, then decreasing toward the edge. But that would largely cancel out where the deck is exposed both above and below.

 

[phamENG]

Depending on the size, you can look at asce 7-16 guidance for canopies. Probably good for balconies less than 8ft.

For multilevel decks, I agree with hokie that pressure buildup between levels will start to neutralize the effects.

 

[waytsh]

That is a good point about using the guidance for canopies. The deck only extends 8' from the exterior wall of the home and I am working under ASCE 7-16. I assume you are referring to section 30.11? I will run the numbers and see how it compares. Thanks!

 

[waytsh]

Yes, much better values. Do you know where I can find the actual equations used for Figures 30.11-1A-B?

 

[phamENG]

You mean for pressure coefficient? I haven't found them published anywhere. Which is quite annoying given the lack of useful graduation on the scale.

 

[waytsh]

Yeah, I agree. If they are only going to give us the chart it would be nice if they could at least give us the flat line values. Then at least we could interpolate on the sloped portion.