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Old 05-21-2010, 11:03 PM   #1
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Pergola design help


I'm having a 14' x 11' pergola built in the back yard. The posts and beams are 6x6. The rafters are 2x6. I think it's a pretty simple design but I am concerned about the 14' span on the 6x6 beams. I fear that without a post in the middle of that 14' span there will be dipping and warping. Can you recommend a method to engineer the beams so they don't dip without putting a post in between?

Please see the link below for design specs:

http://pergola15.shutterfly.com/pictures
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Old 05-22-2010, 03:21 AM   #2
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Pergola design help


For some heavy reading you could look at:

http://www.awc.org/pdf/wsdd/c2b.pdf

and

http://www.awc.org/pdf/wsdd/c2a.pdf

Suffice to say, weight will be on the beam relatively uniformly, the table at the end of the first link only goes up to 13' spans. Depending on the Fb value of your wood choice (basically PSI it can support before bending) it should support anywhere from 1279 at the low end to 2844 at the high end, which sounds like plenty unless this is really heavy wood.

I'd be a little bit more concerned about how you plan on attaching the beams to the post as the diagrams don't show it.

oops, weight's in above post are in pounds

Sorry, I'm finding the above articles very interesting. Just so you know you can get more support strength from a 2X12 beam that a 6X6 and it might be cheaper too, course it may not look as nice.

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Old 05-22-2010, 12:06 PM   #3
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Pergola design help


Quote:
Originally Posted by Troglodyte View Post
For some heavy reading you could look at:

http://www.awc.org/pdf/wsdd/c2b.pdf

and

http://www.awc.org/pdf/wsdd/c2a.pdf

Suffice to say, weight will be on the beam relatively uniformly, the table at the end of the first link only goes up to 13' spans. Depending on the Fb value of your wood choice (basically PSI it can support before bending) it should support anywhere from 1279 at the low end to 2844 at the high end, which sounds like plenty unless this is really heavy wood.

I'd be a little bit more concerned about how you plan on attaching the beams to the post as the diagrams don't show it.
Thanks Trolodyte. I'm afraid this is all Greek to me. Actually the span on the beams is only 13' because they will be attached on the face of the posts rather than across the top (follow the link in my original post for all the specs). What are your concerns about this method?
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Old 05-22-2010, 01:23 PM   #4
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Pergola design help


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Originally Posted by lalaland View Post
Thanks Trolodyte. I'm afraid this is all Greek to me. Actually the span on the beams is only 13' because they will be attached on the face of the posts rather than across the top (follow the link in my original post for all the specs). What are your concerns about this method?
BTW, it would still be a 13' span, even if the beams were sitting on top.
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