- Apr 26, 2016
- Reaction score
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.From an aesthetic point of view I like the look of a free standing pergola better than attached with ledger but thats my tastes is all.
When you dont attach it to the structure you do loose stability of the building.
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.