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Old 05-23-2012, 12:07 AM   #1
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Pergola movement


Ok I have started and have finished the framing on a pergola stretching 22 ft by 11 ft. I have set three 4x4 posts every 9 ft o.c. in the front and three on the back running two sandwiched 2x10 beams on the posts stretching 11 ft meeting at the center posts. I have added a 4x4 running from a front post to the back post these posts are also 9 ft o.c. Finally I knee braced everything in every angle using 3 1/2 in lag screws. I forgot to mentioned I used Simpson post bases for the post screwed to existing concrete slab. however, I continue to get some movement when you shake vigorously. I need some help here.

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Old 05-23-2012, 06:28 AM   #2
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Pergola movement


You need to post photos and a sketch of the framing. And you need to carefully define the amount of movement you are getting, for example the southwest post moves 1/2 inch when I push on it, that sort of thing.

Movement of a pergola is probably related to the type of bracing and exactly how you installed the bracing, but the photos will tell the story.

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Old 05-23-2012, 11:02 AM   #3
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Pergola movement


I hope these pictures help you see what i have done so far. The movement occurs at the top
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Pergola movement-photo-1.jpg   Pergola movement-photo-2.jpg  

Last edited by Calalex; 05-23-2012 at 06:39 PM. Reason: picture resolution
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Old 05-23-2012, 11:07 PM   #4
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Pergola movement


I hope these pictures help you see what i have done so far. The movement occurs at the top
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Old 05-24-2012, 05:30 AM   #5
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Pergola movement


You need to add a second bolt near the bottom of the beam through the brace (all of them). The way you have it now just creates a hinge point.

Attaching to the house would stop the the movement in the other direction.
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Old 05-24-2012, 05:42 AM   #6
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Pergola movement


Quote:
Originally Posted by kwikfishron View Post
You need to add a second bolt near the bottom of the beam through the brace (all of them). The way you have it now just creates a hinge point.

Attaching to the house would stop the the movement in the other direction.
Agreed, it also wouldn't hurt to put a second one through the brace into the post aswell (if you have room) to stop movement at the bottom end. It just depends what the movement is.

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Old 05-24-2012, 10:47 AM   #7
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Pergola movement


Thanks kwikfishron for your advice, so you suggest I pull all my 3 in lag screw on my post and beams and put in a carriage bolt with a nut all the way across the post and beam sandwich? My pergola moves from front to back a little meaning from the front 3 posts to the back 3 posts, if that helps identify the problem.
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Old 05-24-2012, 05:09 PM   #8
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Pergola movement


There are a couple of problems with the bracing scheme, although since this is a pergola, not habitable space, there is no reason you need to resist movement. The braces are too short, they should be at least 4 feet long, and as noted they need at least two solid fasteners on each side (minimum four fasteners per brace). Better to have six fasteners per brace in a triangle arrangement.

The front-back movement can be reduced by installing a diagonal horizontal member on the top, although this may affect the aesthetics of the pergola. Attaching to the house, as previously noted, would also stop the movement.
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Old 05-24-2012, 05:39 PM   #9
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Pergola movement


Thanks Daniel for your input and feedback, so is it safe to say I will gain more stability by inserting carriage bolts through my sandwich post and beams? In addition, replacing my knee braces with 4 foot lenght ones with more than one lag screw? This project is making me pull my hair theory and practice are two very different things...

Last edited by Calalex; 05-24-2012 at 06:21 PM. Reason: Rev
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Old 07-08-2012, 05:49 PM   #10
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Pergola movement


The suggestions already posted should solve your issues. Additional bolts on each brace and the diagonal board is where I would start. I know the diagonal board will kill the aesthetics a bit, however, have you considered placing 2x4's across the top for additional shade? Space them about 7 or 8 OC apart. If you did this, you could lay a diagonal board across and it would not be as noticeable. If you cannot achieve the desired amount stability, then you may want to think about attaching it to the house.

Just my .02. I am not an engineer by any means... I am just an IT guy who happened to build a 1200 sq ft deck and pergola lol

You could always check with your local building office and see what they say.
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Old 07-08-2012, 06:14 PM   #11
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Pergola movement


I certainly agree with what the others have said but I do have a question. How much movement are you actually getting? Considering what the structure is a little movement at the top isn't really going to cause any problems. Are you going to do what many people do and have some kind of plantings that will grow across the top? If that's the case their weight as well as their contact with the beams will also helped stabilize the structure.

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