Author Topic: Post and Girder Bracing  (Read 294 times)

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Offline retiredmarine

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Post and Girder Bracing
« on: June 12, 2019, 11:45:29 AM »
Only the tax code is harder to read than the building code for me!!  My built up girders 3 - 2X10 are supported by 6X6 post on a full concrete footing. Each post is 36 - 38 inches tall. Does the code require diagonal bracing or plywood gussets? and where does it say that (so I can learn to read it for myself).


Offline ChugiakTinkerer

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Re: Post and Girder Bracing
« Reply #1 on: June 12, 2019, 01:08:08 PM »
Someone with a little more expertise will correct me if I'm wrong, but I believe you only need to worry about vertical loads.  The continuous perimeter concrete foundation provides the lateral support, further strengthened by the floor sheathing.

Make sure you've got an adequate termite barrier.
My cabin build thread: Alaskan remote 16x28 1.5 story

Offline MountainDon

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Re: Post and Girder Bracing
« Reply #2 on: June 12, 2019, 01:52:53 PM »
Each post is 36 - 38 inches tall. Does the code require diagonal bracing or plywood gussets? and where does it say that (so I can learn to read it for myself).

How much post length in the ground and how much length above the ground?

The part of the IRC that covers bracing is pretty much expressed with the words.... "designed in accordance with accepted engineering practice" ... that is a phrase that recurs here and there in the IRC.

Our cabin which was originally built on 6x6 piers (13-15" above grade, 44 to 48" below grade) ended up with 3/4" PT plywood shear walls being retrofitted on the advice of two engineers I met after the construction. That was a lot of uncomfortable work
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline retiredmarine

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Re: Post and Girder Bracing
« Reply #3 on: June 12, 2019, 05:10:47 PM »
Thanks ChugiakTinkerer!

Don, You convinced me long ago not to go with a pure post footing structure!  I had a full crawlspace poured. The posts are sitting on concrete anchors on the center footing which runs the length of the house (40ft). There are 5 of them spaced 8 feet apart (give or take an inch).  They are about 37 inches tall to the girder.   There's another girder but that one only runs 17 feet of the house but it's built the same way and supported by a full footing as well. Did that make sense?

Offline MountainDon

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Re: Post and Girder Bracing
« Reply #4 on: June 12, 2019, 05:27:38 PM »
Did that make sense?

I think so. (I did not search back to see what pictures there might be and don't recall....)  If the full crawlspace means there is a perimeter footing and foundation wall, and the cabin side walls are supported on them, and if I am correct in now thinking these piers are just central supports then these piers probably do not need any bracing as any possible lateral movement would be resisted by the perimeter foundation. As ChugiakTinkerer stated, these piers would simply be supporting vertical load.
Just because something has been done and has not failed, doesn’t mean it is good design.

Online Don_P

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Re: Post and Girder Bracing
« Reply #5 on: June 12, 2019, 06:18:18 PM »
Correct, your bracing walls (the exterior walls on a small structure) are over braced continuous foundation walls so all external lateral force is resisted by them.
Code cites R404.1.9.2 and .3, R407.3- read the exception

The code is the minimum. When I order an engineered girder the engineer defaults to accepted engineering practice so somewhere in that paperwork it usually calls for lateral restraint over every support. Simpson makes a strap that ties to a joist, travels at a 45 degree angle through air and wraps under the girder then back up and makes a 45 to a joist on the opposite side. I've also just nailed a vertical 2x4 to the faces of the girder and cut a plywood gusset that nails to the joist and the 2x4 on each side of the girder as close to the post as possible. I do attach the post to the girder and footing. The lateral I'm concerned with their is not from wind or seismic but from vertical load. If the girder tries to deflect down but there is a post there it wants to roll out one way or the other, that is the reason for the lateral brace over or very close to the post. So there is the minimum requirement and generally accepted engineering. The minimum typically works but the lateral girder bracing is certainly better. As a girder becomes more square it becomes more stable, as it becomes taller and thinner that bracing becomes a better idea.

Online Don_P

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Re: Post and Girder Bracing
« Reply #6 on: June 13, 2019, 08:12:40 AM »
This is a pic of the bracing on one side of a girder, it has the same thing on the other side, at each post location

Offline ChugiakTinkerer

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Re: Post and Girder Bracing
« Reply #7 on: June 13, 2019, 08:27:28 AM »
Don, that picture says it better than 1,000 words!  Thanks for sharing it and where do I sign up for the CE credits?  [cool]
My cabin build thread: Alaskan remote 16x28 1.5 story

Offline retiredmarine

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Re: Post and Girder Bracing
« Reply #8 on: June 13, 2019, 02:44:59 PM »
I should have posted a picture, goodness knows it's better than my description! This change anyone's mind?



MountianDon If I never said thank you for convincing me to go with a full foundation over piers then here you go .. THANK YOU!!  Such a better idea!!

Online Don_P

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Re: Post and Girder Bracing
« Reply #9 on: June 13, 2019, 03:03:49 PM »
It doesn't worry me in the least. If you are at all concerned a 2x4 up the post and girder nailed to both will also stiffen that connection.

Offline MountainDon

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Re: Post and Girder Bracing
« Reply #10 on: June 13, 2019, 03:35:54 PM »
.. THANK YOU!!  Such a better idea!!

You're most welcome!  Thank you!

That (in the picture) looks great.
Just because something has been done and has not failed, doesn’t mean it is good design.

 

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