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Hi, I planning on putting up a 10'x16' area pergola with 6"x6"x16' posts, I don't like using the Simpson metal brackets because they don't account for any lateral forces. Unfortunately I need the height above ground to be about 13', so I was was thinking I could put the posts 3' into the ground with gravel and pour 5" of concrete on top (over the entire area of 10'x16' and then 12" beyond that).

Will this be sufficient or so I need to add another 2' of concrete above ground with form tubes to support the posts. The way I see it, this is better than using the above ground metal brackets cause I have 3' into the ground and 6" of concrete to support it.

I've never built one before so any input would be greatly appreciated.
 

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Concrete just on the surface will be useless and will just crack. As the wood dries out and shrinks there's going to be a big gap.
Post set below grade instead of setting on Sono tubes with post bases at some point will rot off at ground level.
Just build it with diagonal bracing.
Talked to the building inspector yet to see what they require?
 

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personally, i would set the posts in the ground below frost level because you know eventually someone is going to try and swing on it. there are lots of ways to finish the post so it looks nice, or you could use cedar which looks nice from the beginning.

i pulled out 4x4 PT that was 20 years old and it had some rot at ground level, but not too much. yours is 6x6 is pretty beefy and its not really a load bearing structure, so i would expect an in ground install to last a long long time.

don't use the concrete to support your structure. as walking surface sure.
 

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I have built many pole structures and with my method I have not had any problems. You don't state where you live but this method will work anywhere. Dig holes (a minimum 0f 12" in diameter for a 6"X6" post) for post to below frost level or at least 3' deep. Mix up some Sacrete or Quickrete and pour ~6" into the bottom of the hole. Make sure the bottom is clean. Let it set up overnight and place you posts into the hole.

Begin placing soil you removed when digging out the hole in ~6" lifts and compact. Use a 2"X4" to pound the soil till it won't compact any further. Keep doing this until the hole is filled with soil.
 

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yes i agree with landfill. when i said don't use concrete to support, i meant in the way OP described.
 
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