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Author Topic: First Outdoor Pavilion Build (Planning)  (Read 2125 times)

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Offline Don P

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Re: First Outdoor Pavilion Build (Planning)
« Reply #20 on: July 11, 2020, 09:27:01 PM »
There was a guy on one forum advocating digging shallow pier footings and then backfilling with sawdust to frost protect them  ::)

When the wind is howling at design load, typically 90mph for most (I'm in a SWR, special wind region), the snow load on the roof at that point is is in the wind. I don't think you need to combine the full design snow live load with the full design lateral wind load. The profile to the wind is the sheathed height of the roof. That lateral push is acting on the top of the posts. They are pinned to the beam and to the ground, free to rotate at their top and bottom. The brace is resisting that force.

There are two other things going on with braces that concern me more than the (relatively short and chunky) brace buckling or compression between post and brace. (A quick aside here, there are allowable design values for compression parallel and perpendicular to the grain. The end of the brace and the side of the post are taking compression at an intermediate angle, not perpendicular to grain, not parallel. The Hankinson formula is how you find the correct intermediate angle compressive strength).

The other concerns are that the post is under a vertical, axial load from the roof, a column usually has a buckling failure mode. The post also has a brace pushing on it from the side, a bending force, while that vertical load that wants to make the post buckle already is at work. You'll find a couple of sections on this in the NDS. And there is possibly a mortise right there where the brace is applying the side bending load to the post, use that net section in thinking about it.

Secondly the brace is acting as a fulcrum wedging against the joint between post and beam. As the brace gets shorter in relation to the length of the post and beam lever arms that force gets on up there. As it gets longer things improve. I've had a few emails with an engineer friend about braces recently. He pointed me to those Simpson brackets, he had specced them recently on a job for the reason that it was easily quantifiable where a timberframed one is no easy thing to quantify. He also pointed out that most bracing you see in typical construction, a few nails, lags or bolts, might stiffen the structure but does not pencil out at design load. There are shear enhancers like split rings or shear plates that can get you there in a fairly simple bolted connection.

That was a ramble, I forget the question :D
The future is a foreign country, they will do things differently there - Simon Winchester

Offline huntandfish88

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Re: First Outdoor Pavilion Build (Planning)
« Reply #21 on: July 16, 2020, 08:52:19 AM »
Sorry guys I've been away on a fishing trip with no cell service! Thanks again for your expertise gents.

It sounds like the direction I will be heading for the beam is 4ply 2x10s. I have just enough pieces left over from a job. 

Question though; seeing as the post is 6x6 (actually 5.5" x 5.5"), am I able to notch the top of the post how i originally intended with just 2 plys sitting on the post, and then cut the other 2 plys so they sit just between the 2 posts? Essentially 2 plys will sit on the post and 2 will stop short, but they will all be nailed and glued as 1 solid 4ply beam. 

I'm assuming this will be okay and similar to a mortise/tenon detail, where the tenon is notched and only the tail of the beam sits in the mortise? 

I'm going to do some more research into concrete pier detail

With regards to the knee brace, I drew up a quick detail in auto cad for what I was planning to do. Let me know your thoughts. heres a link to the timberlok screw website: https://www.fastenmaster.com/product-details/timberlok-heavy-duty-wood-screw.html 






 

Offline Don P

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Re: First Outdoor Pavilion Build (Planning)
« Reply #22 on: July 16, 2020, 09:16:10 PM »
The braces will be much stronger if they are notched into the post so that the small connector is simply holding them in place and the notch is providing the bearing surface. A tapered cut ending at about a 1" table would do it without unduly weakening things.

If all 4 plies of your built up beam bear on the first 1-1/2" of the post top then the outer plies, centered up on the post, run on across the post. Then everything has a bearing, again the connectors simply hold stuff together and the wood is providing bearing.
The future is a foreign country, they will do things differently there - Simon Winchester


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