Strength of finger joints in wood posts

[BSPE90]

I designed for my boss a wood pole barn building (16 ft eave height) for an outside architect. We specified the (4) 2x8 wood posts to be treated for the whole length. These posts are embedded 6 ft down in concrete so we assumed a fixed base in the design, which is why we say to treat the whole length.

The architect came back and "highly recommended" the posts be laminated 2x8 columns, treated 1 ft above finished floor down and then finger jointed with untreated the rest of the way up. They also sent drawings from multiple projects with the finger joint notes on the S drawings backing up their claim. My boss doesn't like the finger joint note but he says if I can find a resource that states the finger joint bond strength is sufficient, we can go with that note.

I tried to do my own research but I did not find anything (a lot of stuff online for wood working for furniture). Does anyone here have any experience with this?

 

[dik]

He may want it for aesthetics... being an architect (him, not me)... I think it can be done... I'd be reluctant to bury in concrete without real protection... here we have PWF which offers better protection... but I'd be reluctant to embed that in concrete, too. Most tar modified epoxies are carcinogenic... don't have a real solution for you... do you need the moment resistance... compacted granular OK?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[BSPE90]

She said it was to save on cost since treating the full height would be too expensive. The architect has been very specific/strict on what we can do since they have a lot of past pole barn projects they can point to that are still standing. This is our first time designing this type of building (and working with this architect) and it has been a challenge so far.

 

[dik]

I would have thought that pressure treating would be cost less than fingerjointing... to properly treat wood requires the material be incised... which looks really ugly... use granular bedding if you can and you might be able to pressure treat the ends without fingerjointing... need to be a foot above grade, though... I'm not into pressure treating, there are others on eng-tips that are... but, have done a lot of reports on brown rot (aka dry-rot) damage. Also use PT process about 50 years back called Boledin (sp?) treatment for a school and some teacherages up north... and, last I heard, they're still standing... I had clad the school with cedar... so it would weather into a beautiful silver... when I went up there for the addition, they had painted the cedar a 'boxcar orange'... just heartbreaking...

I've done a few timberframed buildings, and I'm not really into residential stuff... it's my favourite construction. I've taken photos of several dozen timberframed barns in Ontario... with interest in the joinery... The Frank barn had floor beams @ 12' centres... 75' long and 16"x14" without a joint. I've encountered siding with 32" widths...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Brad805]

There is a large supplier of pole buildings in my area that uses nail laminated columns for this application. Below grade is treated, above grade is not. They have a well oiled team of erectors on site, and it works very well. Would I seal it, not sure, but they have an engineer that does. Finger jointing on site is pointless unless the contractor is equipped to make finger joints efficiently. Scarf joints, maybe, but those are typically done with a slope that is not practical to do on site. Unless you get a good fit they add nothing but cost. Done properly they are wonderful.

In the current economy I am not sure you will realize much of a savings, but availability might be better for the un-treated lumber. I suggest the architect stick to details inside her wheelhouse. If the owner is fine with treated all the way up, that is the solution.

 

[dik]

Nail laminated posts are ugly, IMHO... there has to be another way...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dauwerda]

Yes, finger jointed glulam columns are quite common in the post frame industry (as are nail laminated columns). Each ply of the built up column will have its splice staggered from the neighboring ply. Here is one of the manufacturers I am used to seeing:

https://www.timber-technologies.com/titan-timbers/

They also have put together a video demonstrating the strength of a glulam vs nail-lam cloumn, here:

https://www.youtube.com/watch?v=91nUG_n4Hwk

With a 16ft eave height and 6ft embedment your post is at least 22ft long. Around these parts any dimensional lumber over 20ft is pretty hard to come by, so I would expect you would need to have some sort of splices in your plies anyway. A finger joint with structural glue to ASTM 2559 is going to be pretty hard to beat.

 

[dhengr]

BSPE90:
There are/were a number of GlueLam suppliers who sold these type pole barn col. sections just like they sell GlueLam beams. When was the last time you questioned a finger jointed end to end splice in a GlueLam beam ply? Some outfits are using/selling finger jointed individual 2x studs which are better than (straighter, stronger, etc.) than normal lumberyard stud material. Tests of well made (fitted and glued) finger joints never (almost never) break at the joint, they always (almost always) break in the virgin mat’l. And, in the single studs they are not protected by adjacent plies. The suppliers should be able to provide some literature on their finger joint testing. Two suppliers I can think of are: Gruen-Wald Engineered Laminates, Inc., Tea, SD,

http://www.gruen-wald.com,

605-498-8004; Rigidply Rafters, Inc.,

http://www.rigidply.com,

they are out east PA and MD I think. Their std. detail is a 6’ or 7’ treated butt end, with the remaining length untreated. Finger joints are staggered of course. Ask the smart Arch. where they got their col./post sections locally on their last few jobs.

 

[SWComposites]

Why would an architect be needed for a pole barn??

 

[dik]

He wants it to look pretty? Never herd (sic) of contented cows?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik