fixing sway in the roof on my dock

[reynoldsautree]

So I have added some images but will give a short and sweet version of my problem. We have built three docks. 2 are walkways one is a big hang out area they are supported by 6x6 post and 2"x12 s underneath. They are not square but are sturdy. Since the posts were not put where they needed to be we had to saw them off flush with the decking instead of using them to support the roof.

We then built a roof structure over 2 of the boat slips using 4x4 posts and 2"x12 s. The post are attached to deck with metal brackets that bolt into end of post and to the decking. We then cut some diagonal pieces of 4x4 to go around ends of post to help sturdy the post.

The entire structure still sways in both directions pretty easily the entire roof is constructed out of 2"x12 s other than the 2x4 diagonal pieces we added for extra support.

Please look at photo and give some ways to correct the sway

Thanks

 

[RonnyRaygun]

 

[AronSearle]

/not an engineer.

But those diagonals look far to weedy to stop sway if the posts are not rigidly fixed at the base (which those metal brackets won't achieve).

The vertical timbers look a little undersized as well

 

[RonnyRaygun]

/not an engineer.

But those diagonals look far to weedy to stop sway if the posts are not rigidly fixed at the base (which those metal brackets won't achieve).

The vertical timbers look a little undersized as well

Didn't have time to post a reply when I linked photos, but I agree.
The sway is likely occurring because the posts themselves are bending under wind load and other horizontal forces. If the posts aren't stiff enough, they will deflect.
The connections between the posts and the bracing do not look particularly substantial either and any movement at the connections will transfer to sway within the frame.

There are two ways to create a "rigid" structure.
The first one is to use structural members that are stiff enough not to bend under horizontal forces, along with connections that can transfer the forces from the vertical members onto the horizontal ones.
The second way is to use bracing, which can allow for smaller vertical members and simpler connections between the horizontal and vertical members. The connections between the bracing and the vertical / horizontal members are critical in this situation.

As to how to resolve your problem, it's possible that steel cross bracing to a bay on each face would prevent the sway, but as said above, the posts themselves do look a bit spindly and ideally could do with being beefed up a bit.

You might also want to think about uplift forces for a canopy such as that.

Get a structural engineer involved.

 

[^woody^]

If the posts are firm in the ground and not rocking from there, they can be stiffened with angle iron which will be unobtrusive.

If they are loose in the ground then they will need diagonal bracing top to bottom.

And horizontal diagonal bracing in the roof too.

 

[noseall]

And horizontal diagonal bracing in the roof too.

I was thinking a layer of screwed ply, prior to fitting the corrugated sheets may have helped.

 

[RonnyRaygun]

And horizontal diagonal bracing in the roof too.

I was thinking a layer of screwed ply, prior to fitting the corrugated sheets may have helped.

Looks to me like there is already some roof bracing in the form of diagonal timber members underneath the main joists.

However, roof bracing is not going to stop the structure swaying. It would help to transfer horizontal load from the central posts to the outer ones so the posts in the middle would not need bracing (or stiffening by some other means).

 

[^woody^]

It all depends on how it is swaying

 

[RonnyRaygun]

It all depends on how it is swaying

 

[theprinceofdarkness]

I think your triangulation piece at the junction of the posts and the roof are put in in the wrong axis. It you consider a short bit of roof and a post as a "T", then the way its going to move , is the top from left to right. Bracing it with a bit of 3 X 1 screwed on in your axis means there is very little bearing surface. They should be slapped on the face on the post and the roof timbers on all post and around the corners as well. To make them neat,screw them to the face of the post, but cut them so they bear on the underside of the roof plank, then glue and screw a butt strap across the joint on the back.
Frank

 

[reynoldsautree]

It all depends on how it is swaying

It sways in all directions if you rock any of the posts back and forth.
I think the sway is originating from where the posts connect to the decking. How might i get a more solid connection from post to deck.

 

[reynoldsautree]

If the posts are firm in the ground and not rocking from there, they can be stiffened with angle iron which will be unobtrusive.

If they are loose in the ground then they will need diagonal bracing top to bottom.

And horizontal diagonal bracing in the roof too.

the posts are not in the ground. they are bolted to the floor with a metal bracket that goes over the end of the post and then bolts to the floor of the deck. We added some 4x4 supports around the bases of the poles thinking they might help stiffen things up, but i think the structure still sways from the floor connection.

How might i better connect the posts to the dock?

or should i attempt to replace with bigger posts; 6x6's ?

will putting my triangular bracing on the face of the posts and the rafters make a differnce like theprinceofdarkness suggested?

 

[RonnyRaygun]

It all depends on how it is swaying

It sways in all directions if you rock any of the posts back and forth.
I think the sway is originating from where the posts connect to the decking. How might i get a more solid connection from post to deck.

How about cutting some triangular pieces of 3/8" ply and screwing that to your upper bracing. You will need it in both the X and Y planes, but that will stiffen things up nicely.
I think the problem you have at the moment is that none of your connections are stiff enough to brace the structure. If your top connections are stiff enough in both the X and Y directions, then the lack of rigidity at the base should not be an issue, as long as the posts are held in position.

You might still get a bit of sway as the posts look undersized, but it should be bearable.

As I said above, ensure you have some good strapping from roof to supports as I suspect you might get some high winds in Alabama that could cause the canopy to take off!

 

[^woody^]

If the pivot is at the bottom of the posts at the connection with the deck, then that needs to be dealt with, rather than strengthening the posts.

It looks like you might be able to fix a timber to the side of the posts (pack out if need be) and run this down the side of that jetty and fix into the side of that.

Or get a custom bracket made that comes up the side of the jetty, along the deck a bit, and then up the post.

That's the principle anyway, strengthening the connection at the deck. Look at that.

 

[RonnyRaygun]

If the pivot is at the bottom of the posts at the connection with the deck, then that needs to be dealt with, rather than strengthening the posts.

It looks like you might be able to fix a timber to the side of the posts (pack out if need be) and run this down the side of that jetty and fix into the side of that.

Or get a custom bracket made that comes up the side of the jetty, along the deck a bit, and then up the post.

That's the principle anyway, strengthening the connection at the deck. Look at that.

Well...that was my first thought...then I changed my mind

Belt and braces would be to also stiffen the connections at the base by maybe doing as said above and fixing into the side of the jetty, if possible.
It would certainly reduce the deflection in the posts, as long as a stiff enough connection into the jetty can be created.