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windowguy 09-05-2012 12:08 PM

PT beams warp or twist off posts?
i can post pics tomorrow:

ten year old deck. 4X4 PT posts, double 2X12 PT beams on posts, PT joists on beams. decking and rails are Trex.

the beams span about 20 feet on 3 posts. (3 sets of beams) several of the beams over the years are "twisting" off their posts. I say twist because the top of the beams that are toe nailed into the joists sitting on top of them have not moved, its like the bottom of the double beam wants to "slide" off the post. they've "twisted/curled" about 3/4 of inch off the posts. The posts are still vertical its just bending the aluminum "clip" off the top of the post.

Is it normal for a 20 foot span of double 2X12 (NOTE: its not one 20 foot piece of 2X12, they were 12 footers nailed together, staggered to make 20 feet long) to warp twist?

So either 1) the wood is twisting/warping naturally. or 2) there is frost heave is lifting the deck in some parts and "pulling/shifting" the beams off the posts. (yes i know proper footings should not allow frost heave, but i'm troubleshooting anything that would make beams curl off their posts)

Sorry i do not have a picture now..

allthumbsdiy 09-05-2012 12:33 PM

are your beams attached to posts via post caps or just toe nailed in?

JonM 09-05-2012 01:05 PM

Get a couple 2.5 foot 2 x 4's and place one one each side of the 4 x 4's and up the 2 x 12's...bolt with 4 galvanized bolts washers and nuts....the bolts should be about 8 inches long

windowguy 09-05-2012 01:48 PM

NOT toe nailed in. its just that flimsy cap. looks like a simpson cap but even flimsier.. its just bending that cap right off.

is it that simple? could this have been avoided if the beam was nailed to the post? i think the builder just figured gravity was good enough.

i think i can jack the deck up to take the weight off, wedge a 2X4 against the bottom of the beam (using the adjacent concrete pillar) and smush it back under, then nail off.

I can do that, but i wanted to figure out the source of the problem first.

allthumbsdiy 09-05-2012 06:12 PM

No, I was not advocating the toe nailing method at all (I've always used Simpson BCS post caps and H1 hurricane connectors for the beam-to-joist connections in my decks).

As far as assembled beams twisting, I guess anything is possible, though I've seen more bowing beams (curving in one direction) in my old decks.

What type of soil is under your deck? Is it pitched to direct water away below? I read that if you have a clay-like soil on the surface, it can possibly cause frequent lateral ice heaving.

GBrackins 09-06-2012 07:24 AM

I may have a solution, but want to wait until I see the photos ....

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