Building Pergola : questions about wood

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mbrittb00

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From an aesthetic point of view I like the look of a free standing pergola better than attached with ledger but that’s my tastes is all.

When you don’t attach it to the structure you do loose stability of the building.
After giving this some thought, I planning to do it as a free standing using 6"x6" posts. Since it isn't attached to a structure, then stability is something I'm going to have to sure up. My thought was to put angle braces in the each of the corners (both directions for a total of 8) from about the 2' mark on both the vertical and horizontal. The only problem is with my design (partially for aesthetic reasons) is that both the end beams and the outer main beams will be sandwiched around the posts (not on top of it), so there is not direct angle from the post to the beams. I have a couple of thoughts on how to resolve this, and am interested in any feedback or other ideas.

Idea 1: Make a compound miter cut (45deg and ??) in 2"x4"s? so that the braces would angle out slightly from the posts and come directly under the beams. This would have the advantage of the braces attaching to the bottom of the beams giving them direct support. This would also be helpful on the 13' span.

Idea 2: Make simple 45deg miter cuts on the 2"x4", and attach them to the beam with a bolt. This is the simpler solution, but also won't provide as much support under the 13' span.

Also, I decided to add up the wight (using PT as a worst case) of the rafters (528 lbs) and the center beams (97 lbs) to see how much weight is actually going to be on the center of the 13' end beam span. The one place I wasn't sure is weight distribution. For instance, each rafter sits on top of 6 main beams. Do each of those main beams get 1/6th of the weight or do the center beams get significantly more. I'm going on the theory that it is evenly distributed. With that assumption the two center main beams together would be supporting ~210 lbs. Again assuming even distribution, the end beams and beams near the house would each (pair) be supporting 105 lbs, and thus each of individual beams would have to support ~52 lbs at the center.

I'll be honest that doesn't sound like a lot, but then again, I'm not sure how to make the deflection calculations in order to determine if that is acceptable.

Thanks again for all your feedback so far.
 

bud16415

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After giving this some thought, I planning to do it as a free standing using 6"x6" posts. Since it isn't attached to a structure, then stability is something I'm going to have to sure up. My thought was to put angle braces in the each of the corners (both directions for a total of 8) from about the 2' mark on both the vertical and horizontal. The only problem is with my design (partially for aesthetic reasons) is that both the end beams and the outer main beams will be sandwiched around the posts (not on top of it), so there is not direct angle from the post to the beams. I have a couple of thoughts on how to resolve this, and am interested in any feedback or other ideas.

Idea 1: Make a compound miter cut (45deg and ??) in 2"x4"s? so that the braces would angle out slightly from the posts and come directly under the beams. This would have the advantage of the braces attaching to the bottom of the beams giving them direct support. This would also be helpful on the 13' span.

Idea 2: Make simple 45deg miter cuts on the 2"x4", and attach them to the beam with a bolt. This is the simpler solution, but also won't provide as much support under the 13' span.

Also, I decided to add up the wight (using PT as a worst case) of the rafters (528 lbs) and the center beams (97 lbs) to see how much weight is actually going to be on the center of the 13' end beam span. The one place I wasn't sure is weight distribution. For instance, each rafter sits on top of 6 main beams. Do each of those main beams get 1/6th of the weight or do the center beams get significantly more. I'm going on the theory that it is evenly distributed. With that assumption the two center main beams together would be supporting ~210 lbs. Again assuming even distribution, the end beams and beams near the house would each (pair) be supporting 105 lbs, and thus each of individual beams would have to support ~52 lbs at the center.

I'll be honest that doesn't sound like a lot, but then again, I'm not sure how to make the deflection calculations in order to determine if that is acceptable.

Thanks again for all your feedback so far.
I think I would sink the 6x6 posts in the ground for footing and added stability. I placed a 6x6 PT post 4’ deep and mounted a large farm bell on it well over 20 years ago and it still looks like the day I put it in. I didn’t add concrete into the hole but doing that makes for a very good anchor. On the top I would notch and make a ledge for the beam to sit on and then any angle braces I used would be inline with the post and the beam. They would add support but I would also cut them to be a design element.

As to the span and the weight, without a deck or roof on top I wouldn’t even be slightly concerned with the weight of the rafters beams. If you really want to calculate the weight distribution or look at some charts, search on rafter span tables and you will find many tables and calculators to help you figure that out. If you need help finding one you like just ask and we will help.

The design possibilities are endless from quite simple to quite ornate. I would just start with a photo search and find a look you like and then plan from there. :)

https://www.google.com/search?q=pergola+designs&rlz=1C1TSNF_enUS500US657&espv=2&biw=1361&bih=710&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjrgKeZ6rjMAhUEGD4KHRU2Cn8Q_AUIBigB&dpr=0.9
 

Snoonyb

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Beside which, it then becomes an individual, freestanding, architectural element.

Adding corbels, ordered from a lumber yard, are milled to your specifications, fitting your choice of aesthetics.
 

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