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thetalkingmule 04-19-2012 11:07 PM

Elevated Deck Swaying
 
Great site!

I'm having some issues with deck swaying that are about half solved. I've added diagonal bracing to my deck at the joints of the posts and the beams which firmed that up nicely, but now I'm having issues with the bases of the posts.

Here's some background info and shots:
(sorry for the longwindedness, but IMO details help)

Quote:

Details:
~11ft tall 6x6 posts on 36in deep concrete piers with raised post bases
Ttriple 2x12s screwed together beams attached to the post with StrongTie BSC2-3/6z
Rubber roofing membrane over the top of the beams
Normal 12in on center framing above in 2x12s with doubles around the outside (16ft joists)

http://i35.photobucket.com/albums/d1...Deck20015b.jpg

http://i35.photobucket.com/albums/d1...Deck20020b.jpg
Quote:

Originally Posted by thetalkingmule (Post 483237)
I intend to through-bolt 2x10 diagonal bracing from the posts to the beams(see high tech artist rendering below). As for sitting the framing on top of the beams, that was the recommendation on most sites and it's a triple 2x12 so not possible to notch the post.

After talking with some folks over the weekend, I think I'll get some 2x10 sections and bolt diagonally from post to beam in both directions. Longer(maybe 5-6ft) sections to run from the post towards the middle and then much smaller ones running from the post to the outside edge of the beam. I had planned to trim the beams flush with the framing above once it was in place, but I'll leave a bit of it now so I can fit this second set of horizontal bracing. I'll find some way to make all this bracing look pretty.

Thanks again for all the input!

http://i35.photobucket.com/albums/d1...5b_bracing.jpg

That is where I started off today before I put all the bracing on. Pretty much all questions above have been solved, but I'll throw today's base bracing question in a separate post. Thanks in advance for the help!!

thetalkingmule 04-19-2012 11:08 PM

The diagonal bracing(just the long pieces pictured in red above) went on today and made a huge amount of difference, but I'm still getting a good bit of lateral sway. We've concluded that though the diagonal bracing at the top post/beam joints has made that connection extremely solid, the posts are still basically rocking on the footings. In order to counteract this, logic dictates that I use the same sort of diagonal bracing that shored up the post/beam joints, however there's no way to do that since I can't very well bolt bracing to my driveway and I can't install top to bottom "X" bracing across my driveway from post to post.

Anyone have a thought on how I can get these posts to stop swaying left to right pivoting on the connection between the base of the posts and the footings? I've read of people putting a second concrete pier to the outside of existing posts, insetting a large eye bolt into the concrete and then running a stainless steel cable from ~5 feet up the post to the eye socket cemented to the ground. This adds tension by pulling the deck both left and right, but that seems a bit extreme to me and I don't really have the room since I'm already close to the lot edge.

Installing the decking should be a big help since it won't let the whole frame go out of square as much, but I just thought I'd run this by you folks for input. The base connection is the Simpson Strong-Tie 6 x 6 Uplift Post Base Z-Max installed with two bolts through the post and one 1/2" threaded J bolt set into the concrete similarly to this.

Here's a pic of my actual attachment. The bracket and the post stay together and the entire thing "rocks" on the concrete footing. The connection was tightened as much as was humanly possible so that's not it. I think it literally needs to have some sort of bracing or it's going to sway. Would simple robust angle brackets bolted into the concrete help? I was thinking of pulling the two bolts out of the base, inserting a custom angle bracket to fit the existing bolts, reinstalling the bolts/nuts and then somehow lagging the bottom side of the angle bracket to the concrete. Might not do anything though.

Any thoughts?

http://i35.photobucket.com/albums/d1...0Deck20023.jpg

joecaption 04-19-2012 11:14 PM

oooooo

thetalkingmule 04-19-2012 11:21 PM

Quote:

Originally Posted by joecaption (Post 902823)
Easy to see why it's swaying.
The two beams that you just set on top of the post where suppost to be installed on a cut out notch on the side of the post. That way the beam could have been double through bolted.

There are no diaganals.

There's just no way that deck would pass any codes in my area.

Thanks for the feedback!

You can't really notch 3 2x12s into a 6x6. This post/beam setup is what's prescribed from what I've read and the diagonal 2x8 bracing from posts to beams that I through-bolted on today has made those joints more than robust enough. It's the base that is the issue now(and perhaps the frame racking since I have no decking in place yet).

joecaption 04-19-2012 11:25 PM

Easy to see why it's swaying.
The two beams that you just set on top of the post could have been installed on a cut out notch on the side of the post. That way the beam could have been double through bolted.

There are no diaganals.

http://images.search.yahoo.com/image...mb=cpCLpHoH11V

robertcdf 04-19-2012 11:28 PM

Easy solution... Install the decking... The decking (especially face screwed) adds a lot of rigidity. Also add roll blocking over the beams.

Gary in WA 04-19-2012 11:54 PM

Remember, this is minimum- Fig. 22: http://www.awc.org/Publications/DCA/DCA6/DCA6-09.pdf
Did you oversize the bolt holes?

Gary

thetalkingmule 04-20-2012 01:28 AM

Quote:

Originally Posted by robertcdf (Post 902838)
Easy solution... Install the decking... The decking (especially face screwed) adds a lot of rigidity. Also add roll blocking over the beams.

Yeah. I knew decking helped stability, but I guess I kept going back to the base being the issue. Then I stepped back and took a look at the whole thing and realized that the framing won't contort once the decking is screwed down and the box can't really go out of square. I do think my super long 16' joists are part of the problem though.

I'm probably just being paranoid this being my first deck and a house I own. I'll lay the decking Saturday and report back. Thanks for the info!

P.S. What's roll blocking? Are you just talking about blocking between the joists over top of the beam?

thetalkingmule 04-20-2012 01:33 AM

Quote:

Originally Posted by GBR in WA (Post 902849)
Remember, this is minimum- Fig. 22: http://www.awc.org/Publications/DCA/DCA6/DCA6-09.pdf
Did you oversize the bolt holes?

Gary

I sandwiched a 2x8 on either side of the beam running diagonally halfway down each post parallel to the ledger. I used 1/2" through bolts in 1/2" bore holes. The connections are snug and the post/beam joints aren't going anywhere ever. I think I overkilled the bracing on these joints a bit, but the swaying worried me. I'll post a picture of where I'm at when the sun comes up. Thanks for the help!

Daniel Holzman 04-20-2012 06:43 AM

The base is not the problem. The base of any deck post is capable of rotation, they are effectively designed as pinned joints. Rotation is prevented by the use of diagonal bracing near the top of all posts, in both directions at all posts. This is particularly important on a free standing deck since you do not get the benefit of a ledger board attached to a house, which normally provides substantial rotation limitation.

I can't tell from your description and your artist's rendering if you intend to provide two way diagonal bracing at each post, but that is necessary. The deck will assist in reducing rotation, but the diagonal bracing does the majority of the work. Do not overtighten the bolts on the base,it will not help and can damage the post.

thetalkingmule 04-20-2012 08:08 AM

Quote:

Originally Posted by Daniel Holzman (Post 902931)
The base is not the problem. The base of any deck post is capable of rotation, they are effectively designed as pinned joints. Rotation is prevented by the use of diagonal bracing near the top of all posts, in both directions at all posts. This is particularly important on a free standing deck since you do not get the benefit of a ledger board attached to a house, which normally provides substantial rotation limitation.

I can't tell from your description and your artist's rendering if you intend to provide two way diagonal bracing at each post, but that is necessary. The deck will assist in reducing rotation, but the diagonal bracing does the majority of the work. Do not overtighten the bolts on the base,it will not help and can damage the post.

Awesome info thanks! I had planned on doing 2x6 diagonal bracing perpendicular to the house as well, I just didn't think it would help the sway issue much. Now that I think about it, you proabbly need all bracing/decking in place to form a proper sway-proof deck. Good to hear that beam terminus is only meant as a "pinned joint" because that's certainly what it is right now. I'll finish all the bracing today and post a fresh pic. Thanks again!

thetalkingmule 04-20-2012 11:33 AM

Where it stands today(i''ll trim and pretty this up later)....

http://i35.photobucket.com/albums/d1...0Deck20029.jpg

thetalkingmule 04-21-2012 08:45 PM

Quick question on diagonal decking....

If I lay my decking in a herringbone fashion like this pic, will I still be getting most of the benefit I hear about from running your decking diagonally or does the decking need to all run in one diagonal direction? Do you need to have one solid piece of decking running corner to corner in order to get the full anti-sway effect of diagonal decking?

Also, anyone familiar with these T straps I keep hearing about? Would I see any benefit from installing one of these from corner to corner since my decking will be herringboned and not one solid diagonal piece?

thetalkingmule 06-02-2012 11:27 PM

I ended up just running the deck horizontally and it turned out great. Absolutely zero swaying that I can feel. You guys were right, once the decking is down it does all the work to keep it from swaying. I also, installed two diagonal T-straps that probably are helping a bit. Thanks again for all the help!

Now on to the railing.....

http://i35.photobucket.com/albums/d1...Deck20042b.jpg

hand drive 06-03-2012 10:15 AM

did you ever install the anti roll blocks above each beam that Robertcdf mentioned. they will help a bunch to keep the joists from wanting to tip with pressure and maintain a vertically aligned cohesiveness. I mainly bring this up because of the length of the joists and the size of them, 2x12. you can add them in easy enough from underneath the deck standing on a ladder. also, if you park under the deck you might want to consider some type of under roofing to help direct water flow that comes down through the deck structure. Good job!


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