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Mr.S Teacher 08-07-2009 12:38 PM

Pergola Posts a Little Wobbly
Okay... I'm nearly finished with my latest project: a patio, deck, and pergola over both. My latest dilemma is that the pergola posts are slightly wobbly.

I set the 4x4 posts on an U-shaped anchor, attached with nails and lag screws. The anchor is attached to a j-bolt embedded concrete, which goes about two feet down. I'm pretty confident I have a solid footing, yet the posts still wobble. The wobble appears to be stemming from within the anchor, mostly in the direction where the anchor does NOT wrap around the post; the two open sides.

I thought after fastening the beams and rafters, plus a pair of knee/y-braces to each corner, things would stabilize. They did quite a bit, but there's still movement when I push against the posts.

So, I'm looking for some suggestions. I'm considering building a brick/concrete pier that comes up a few feet at the base of the troublesome posts, which I would need to teach myself how to do. Beyond that, I've thought about adding more knee-braces; perhaps angling down to the base, but don't want to create too many obstacles.

Is there something I'm missing? Is there a bracket or anchor that could be a quick fix? Is one option preferred over another? Any tips would be appreciated.

Thank you! - Josh

bob22 08-07-2009 01:52 PM

I'm having a hard time visualizing your problem; in which direction do the posts wobble? What kind of anchor system is being used? Is the anchor to the base above grade? What kind of load is on the posts? How are the pergola beams attached to the post? A picture or two might help.

Mr.S Teacher 08-07-2009 02:05 PM

Thank you for your reply... I'm at work now, but will take some photos tonight; that's a good tip. If you're up for it, I look forward to hearing your reply after I post the photos tonight. Again, thanks.

Mr.S Teacher 08-07-2009 07:17 PM

Wobbly Pergola with Pictures
2 Attachment(s)
Okay, I'm attaching a couple of pics: One is of the post anchor. This is where I feel like the most wobble is occurring. The other is of the entire structure, to give a sense of what I've already done and of the whole load of the project. Again, any suggestions would be greatly appreciated.

Willie T 08-07-2009 09:21 PM

I see your 45 degree braces are bolted to the cross-pieces. That's good. But how are the other ends of them fastened to the posts? That connection could be allowing some flex.

Nice looking work, by the way.

Mr.S Teacher 08-07-2009 10:35 PM

Thanks for your reply and kind words. The braces are fastened at the base by two lag screws.

Willie T 08-08-2009 12:09 PM

1 Attachment(s)
See how much more rigid and resistant to movement the bolted angle brace would be?

vsheetz 08-08-2009 02:20 PM

By wobbly - do you mean the bottom of the post is moving in the bracket, or that the overhead is able to move when you shake a post? If the latter, I think much rigidity will be added by placing addiional top pieces and screw them down securely. Mine was this way until it was all together - in the end it was very solid. And I have no angle braces.

My pictures

Mr.S Teacher 08-10-2009 01:42 PM

Thank you, all of you, for your responses and time. To answer your question, VSHEETZ, the overhead moves when I push against the posts. Each time I secured a level, the structure became more rigid, but it's still a little shaky. I'm a bit reluctant to add more weight to the overhead.

And WILLIE T, I really appreciated your reply. I never would have thought about fashioning the joints like that. Perhaps the next time I tackle something like this, I'll teach myself how to do that; unfortunately, at this stage in the build, it would require a pretty major overhaul.

So, at this point I'm not exactly sure which tack to choose. Again, I'm open to further suggestion if you're up for it. Thank you again... I do appreciate your feedback.

Willie T 08-10-2009 08:49 PM

1 Attachment(s)
It is only my personal opinion, but I'm a firm believer in all post and beam work being built with traditional Timber Framing methods. Look around This Site some, and you'll see what I mean.

Below is a variation on that joint which might be easier for you to cut. Of course, the side flanges wouldn't have to be full height as I've drawn them. (It wastes a lot of wood to do it that way)

Truly well-constructed Timber Joints are a bit more complicated than I've shown here. The heavy duty stuff is replete with inch deep, full-face mortises before the tenon part is even cut... but this kind of work will do for what we're discussing.

bob22 08-11-2009 05:39 PM

Is it more wobbly side to side or front to back?

MEShaner 03-24-2012 06:55 PM

Final Resolution?
I just came across this string of posts (pardon the pun); I was curious about the final outcome? I was curious about the hardware in particular (e.g., the washers and nuts used opposite the bolts)? Did you try bridge washers?

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