ASCE 7-98 Wind Loads for Wood Decks

[bridger71]

Here's my situtation. I am designing a wooden patio deck for my back yard and I am trying to use ASCE 7-98 for wind loading. The problem is I am not sure what structure type to consider for my deck? Is it an "Open Building" or an "Open Structure"? If an open structure is more accurate, then is Table 6-12 or Table 6-13 more appropriate for determining the force coefficient, Cf.

Thanks in advance.

 

[fritzee]

From what you explained you can consider your deck as an open lattice structure table 6-13. However, you should probably look at the tables to use a more conservative loading. I think that you will find that the design will be more governed by the vertical loading. Good luck

 

[bridger71]

Here is a little more detail on the deck itself. It is a 40'x15' frame with 8' long 2x8 joists @ 2.25' framing into 15' long 4x8(two 2x8) girders. The girders are continuous beams with 3-5'spans supported on 1'dia x 1' deep concrete footers. The entire structure will sit at ground elevation so the vertical profile will only be approximately 8-10" tall.

My uncertainty is in calculating my uplift force and sizing my footers acoordingly to resist the net uplift force.

I am in Palm Beach, Florida, so wind loads are not taken lightly by the building departments down here. This is almost to a fault now-a-days.

 

[boo1]

Consider the Moist condition strength reduction. We often use the 40 to 60 psf live load, 10 psf dead load, 360 deflection for designs.

 

[bridger71]

I used those exact criteria boo1.

Thanks!

 

[Lutfi]

Hey Bridger,

Where are you going to get uplift on your deck from? The only uplift that I can see is from overturning moment. I couple of hours north of you on the east coast. Unless you have a roof over the deck, I would work on the overturning moment.

Am I missing something?

 

[Ron]

Bridger71...also a few miles north of you...I would expect the DL+LL case to be more critical than net wind load, evn if you considered the influence zones (perimeter, corners) as for a building. For your case, I would probably treat the deck as a "low roof". Since it's less than 15 feet high, doesn't make any difference anyway, whether roof or deck. Overturning perp. to long direction might be a consideration, though I doubt it. Still have to check it though.

When I'm feeling conservative, I usually just set Cf=1.0 for open structures and plug away.

 

[bridger71]

I think I wasn't clear enough. When I refer to net uplift I am basically talking about the overturning moment. And you are correct, from a flexural & shear standpoint the DL+LL does govern. However, the city I live in requires me to "Sign & Seal" a form stating the structure has been designed to the latest wind load code..i.e ASCE 7-98. Just trying to cover all my basis (typical structural engineer .


On a side note, I did not realize this forum existed. I will definitely be coming back for more input and to provide my own "2 cents worth" when possible.

Thanks for all the input, its very much appreciated!

 

[boo1]

Welcome, hope to see your posts soon.

 

[Ron]

bridger71...welcome, also

These forums are the greatest. The more input, the more accurate the final "answer" will be for the person asking the question to mold together from the input. The concept is as simple as a paper clip and easily as useful!

Kind of chilly in South Florida this week, huh?

 

[PvB]

I guesse the other thing you might consider would be a possitive pressure from under the deck (GCpi table 6-7). I suppose this deck is against a house - that would be one side enclosed, and if an adjacent side is also blocked, maybe a garage or something, you could get a condition of "partially enclosed" where a + pressure could occure under the deck causing additional uplift. Not real likely, just a thought