Construction of Laminated posts for Pole Barn

[buckeye]

As I get closer to building a pole building, I have been reviewing the posts presented in the forum relating to such. The information contained in this forum is simply amazing.

After looking at these threads, the use of laminated or built-up posts really interests me. Compared to a standard 6x6 post, they seem to have some advantages. I don't mind the time it would take to make these laminated posts, but I was wondering about some basic construction techniques for such:

1.) I know we want to stagger the board joints, but is there a good rule of thumb for the length of stagger between the boards joints? 1-2ft or somewhere in between?

2.) What is the best way to combine the boards to make a good composite structure? Should a construction adhesive be used between the boards combined with mechanical fastening like deck screws or carriage bolts? What is a minimum distance between the use of mechanical fasteners?

3.) Is there a good standard length of board to get (8', 10') etc? I know I can get a really long board and cut it to length, but is there a good or preferred length for the board used in the pole? I would assume a minimum of joints would be preferable, but you never know.

Thanks for any information you may have!

 

[Anonymous Poster]

<font color="blue"> Compared to a standard 6x6 post, they seem to have some advantages. </font>

Hi,

What would those advantages be?

Like to give some suggestions...but I am having trouble seeing the advantage of using a laminated post over a pressure treated 6x6 for a pole building...

 

[mikim]

<font color="blue"> What would those advantages be?</font>
Not having any idea myself - but would the cost be less?
6x6x12 pt vs. 2.5 - 2x6x8 yp & 2- 2x6x8 pt

 

[knucklehead]

I'll take a crack at it, and maybe generate some replies in correction to my statements. /forums/images/graemlins/grin.gif

I also like the idea of using them, especially using pressure treated in short lengths in the ground and splicing standard framing lumber into that, saving money and weight in handling the PT stuff. However, if I had a choice, I'd want to use laminated posts without spliced joints at all. After thinking about it, I thought I might pour concrete posts in the ground and build on them with standard framing lumber.

I have made a couple sets of pump jack posts from 2x4's - 20' and 24' lengths in the last 10 years. Standing near the top of my little 2x4 posts while pumping up the staging before bracing below (can't jack by the braces), I've developed a good "feel" for the problems encountered with biaxial loading. /forums/images/graemlins/blush.gif I only used two pieces to fit inside the jacks; a third piece would've significantly stiffened the posts by having every joint backed up or overlapped by two solid layers.

I did a little quick search and the only spec I could find was a maufacturer's recommendation that 6x6 posts be three continuous pieces of 2x6 glued, clamped, and nailed on 12" centers on both sides. Every comment I read gave the impression that gluing was crucial. The problem with unglued laminations is that you are kind of depending on the strength of the fasteners in one direction and on the weak axis of the lumber in the other (not totally but basically correct).

Personally, for the small structures I would build (under 30'x40'), I think only nailing and then locking everything into the building structure as construction progresses would keep loads pretty vertical. I'd say 24" overlap would be minimum - 48" would be better, and keep the joints as far away from each other as possible. As far as lengths of lumber goes, I always try to go 2-2-2 when making up a beam length that can't be done with standard lumber full length. For example, if you wanted 24', I'd go 16 & 8, then 12 & 12, the 8 & 16. It get's harder the longer you go, and you need to go 2-3-2 after a while to avoid close joints. It's easy to sit down with a 12" ruler and divvy up the length and see graphically how far apart the joints come, and try not to have two joints fall on each other on opposite sides of the post.

This is all seat-of-the-pants comment - I'd welcome some more intelligent comment, and I am getting closer to putting together some beams myself.

 

[MarkV]

Buckeye,

Good set of questions. There are sources that would tell you in engineering terms very explicit answers to most of those questions. Now I'll tell you how I would do it.

1. Joint Stagger; Use as long of pieces as you can. If you need 16' post, use 3 2x6x16's. If you need 20' posts, 2 - 10 ft. for the middle, 2 -16ft. for sides and 1 8' to make up the difference.
2. Fastening, Bolts are strong but unneeded in a laminated pole. I am a big fan of glue but it is questionable on pressure treated wood. Screws are great but again unneeded on a laminated pole. Keep in mind that with a pole there are no shear loads or side loads. All the weight is being carried straight down. A laminated beam requires more attention to fasteners because of shear loads. For a pole, 2-16p galvanized nails every foot will be fine. (from both sides of course)
3. Board Length, Just depends on what you want to end up with. The longer the better for the most part.

Jim, let me offer an alternative idea. I have never used this system but will on my next pole building. The idea came from here on the forum and I believe the discussion was about Morton pole barns. Build a laminated pole from pressure treated lumber to a length that will reach your frost line plus 3'. Make the centerboard of this pressure treated pole 2' shorter than the sides forming a mortise or pocket. When these much easier to handle posts are set in the ground the pocket will be 1' above grade. Depending on the desired wall height of the building you can now insert a yellow pine 2x6 into the pocket. Bolt this joint together with 6 carriage bolts and add the side pieces to complete the upper pole.

What I like about this system is that one man can do it with out having to muscle around 16' pressure treated 6x6's You don't have to use pressure treated above grade so there is less twisting and shrinking and 12' are about as big as you will have to move.

Wow, sorry, I got carried away. /forums/images/graemlins/blush.gif There are a number of good ways to do your poles. Just make sure you are pressure treated below grade and down below frost line with good soil at the base. Any of the fasteners you mentioned will work fine.

MarkV

 

[Anonymous Poster]

<font color="blue"> What I like about this system is that one man can do it with out having to muscle around 16' pressure treated 6x6's You don't have to use pressure treated above grade so there is less twisting and shrinking and 12' are about as big as you will have to move. </font>

MarkV,

I guess you hit the nail on the head as far as a possible advantage of a laminated post...the only thing I could think of was maybe needing extra height...

A post can experience side loads though...high winds would be an example...personally I kind of like solid posts...or posts that are laminated and glued together with a glue that won't fail.

16 foot 6x6 pressure treated posts are not all that hard to handle alone. Even easier if the tractor helps a little! /forums/images/graemlins/smile.gif

 

[DVerbarg]

In additition to the price advantage and weight/handling issues I would assume that laminate posts would have the advantage that laminate beams do, lack of twisting and warping.

 

[Anonymous Poster]

Hmm. If you use the combination of PT posts below grade and non-PT above grade, as MarkV suggests, then the problem of glueing PT could be solved by using 2-part Marine expoxy glue - comes in 2-2qt cans, mixes 50/50, and looks like yellow butter. Because those below grade posts are relatively short, the epoxy is not too expensive. Then, use regular contruction adhesive on the upper, non-PT laminates because there are no chemical issues. I would also stagger the nails left and right as you go along the post.

I would think the reasons for laminated beams have all been mentioned in various posts - less twisting and warping, easier to get whatever length you need, easier to handle, and definitely less expensive - 2x6's in shorter lengths will always be less expensive than the premium length and width stuff, which always has to come from one tree. Also, the whole thing may be stronger, because, while not cross-grained like plywood, you are interrupting the grain structure that goes all the way through a 6x6 and could lead to cracking or splitting all the way through. I'll bet it would be a little harder to break one the way Spencer accidentally did.

 

[Anonymous Poster]

Adv: It's a lot cheaper, easier to work with, and stronger. Have you checked the quality of 6x6 of late? You don't get a knot all the way through, or a crippled up twisted mess.... And a lot of farmers are needing 18' or more sidewalls, hard to get 24' beams & pay for all that pressure treating...

The way to do it is the short pressure treated stumps like the one fellow said, then go up with regular wood. However, I've never seen the exact joint he describes. You never want 2 joints at the same spot. All that is left is a single 2x6 holding things down. you want all three pressure treated parts different lengths - one above ground level, one 2' higher, and the third 4' higher.

--->Paul

 

[Slamfire]

But three 2x6s don't make a 6x6, the finished dimension would be 4.5x5.5. A bit short on one side. /forums/images/graemlins/shocked.gif

 

[buckeye]

Thanks for all the great input! I knew I would not be disappointed from your all's comments and advice.

I guess I am looking into the laminated posts instead of 6x6 due to what I have seen around lumber yards here. Basically to get a 16' or 18' 6x6 that is straight or true is difficult, and they are usually still wet at the yard. When they dry, I expect them to warp and twist causing problems.

Secondly, while at the Ohio Farm Science Review last year I noticed that several of the large building manufacturers were making laminated posts. I just casually noticed this at the time and did not look very closely at the construction. I'll definetely look at them this September at the Farm Science Review, but I hope to be underway with my project by then.

I like the idea of pressure treated posts for the first set and then using regular lumber for the upper sections. Talking to one of my buddies last night, he said this is what Morton is doing (or at least he has seen them do it).

Thanks for the comments and if you have any more, keep them coming!

 

[buckeye]

</font><font color="blue" class="small">( I did a little quick search and the only spec I could find was a maufacturer's recommendation that 6x6 posts be three continuous pieces of 2x6 glued, clamped, and nailed on 12" centers on both sides. Every comment I read gave the impression that gluing was crucial. )</font>

Knucklehead:

Where did you search to find this information. I did a quick Google search, but did not really find anything like what you are talking about.

Thanks for your comments. I found them very interesting and helpful.

 

[MarkV]

I sure don't have all of the answers but do have a couple of thoughts as this post progresses. I don't believe I would go with a laminated post just to save money. I agree that the non-pt wood is cheaper but I bet after you look at the cost of the bolts, nails and glue, if used, that pricing will not be much different. You also need to consider that it will take some time to build the post and factor that into the pricing equation.

I believe a little research would find that a laminated post is stronger than a solid 6x6 with or without glue in this application. It also doesn't make much difference because both are adequate for what we are talking. If your snow loads or dead loads are going to be greater than normal you need closer spacing of your posts, not stronger posts. The important factor is the distribution of the load to the ground or footing to minimize the point loads.

In my opinion side loads, wind load, glue and to some extent even the splice are a moot point in this situation. When you think about the skeleton of the normal pole building the posts transfer the weight of the structure to the ground. On top of the posts sets a beam on which the trusses will sit. The beam transfers the roof weight to the posts. The posts are not carrying side load and there fore the glue and heavy fasteners are of less importance in this application. Multiple 2x4's nailed together carry huge headers in a house. Wind load or shear does need to be considered but that is a function of the sheathing or diagonal bracing in a pole building. Your sheathing and or bracing turns the building into a ridged diaphragm that distributes the side loading over the whole structure not the individual post. It is like a stud wall before it is sheathed. There is very little lateral strength and you can shake the whole wall easily. Add some sheathing and you have created a diaphragm that distributes the load over the whole wall and it is very ridged. There is very little force being applied that would cause a post to delaminate.

The important thing to remember when we talk laminated posts is that we are not talking beams. A beam is for carrying side load and the engineering of size and fastening becomes much more important. It is a totally different application than we are discussing in this post.

Now I am not a structural engineer, just a guy that has been swinging a hammer for a lot of years to pay the bills. Hopefully one of our engineer members will chime in and verify or correct my thinking about laminated posts.

MarkV

 

[cowboydoc]

Adv: It's a lot cheaper, easier to work with, and stronger. Have you checked the quality of 6x6 of late? You don't get a knot all the way through, or a crippled up twisted mess.... And a lot of farmers are needing 18' or more sidewalls, hard to get 24' beams & pay for all that pressure treating...


Rambler you are exactly right!!! The last barn I built we needed 30' posts. Try and find a 30' treated 6x6 that long! They are also ALOT cheaper and the strength is greater than a 6x6.

 

[cowboydoc]

You also need to consider that it will take some time to build the post and factor that into the pricing equation

These posts are available everywhere at lumbar yards. Really no need to make them. They also come with a 50 year guaranty. Anything happens not only will they replace the post but they'll pay to have the new ones put in. At least this was the warranty on the last ones I got.

 

[Inspector507]

I saw a post on here recently that contained the name of a Pole Barn "erector/builder". I can't find that post now, but on the builders website, it gave the test results of 6x6PT vs laminated posts. The laminated post had less sway and more resistance to side loads.

 

[RobS]

A friend has a Morton building with laminated posts. Very well built. The laminating provides several benefits: Using PT for the lower sections has already been mentioned but it also makes attaching the header beams a lot easier. You can let the center lamination run to full height and cut the outers shorter by the width of your header. Now you've got a tenon to accept a 2X header on each side. A couple of bolts in each and you're all set for trusses.

Some pictures at Morton /forums/images/graemlins/smile.gif

 

[s1120]

One thing I don't see anyone saying is that a 2x6 can be PTed a lot better then a 6x6 post. The inside of a 6x6 will have very little treating, wile a made up post, will be treated better. The treating will soak into the center of a 2x6 more.

 

[SteveBenson]

>Keep in mind that with a pole there are no shear loads or side loads. All the weight is being carried straight down.

This statement is very untrue. Extremely large bending loads are placed on the poles due to wind loading. Some states require 120 mph wind loading, like FL. Depending on the orientation of the lamination, shear loads may be present in the lamination boundary due to the bending load.

 

[SteveBenson]

>These posts are available everywhere at lumbar yards. Really no need to make them.

Yes, I've seen Glu-lam posts advertised in Lancaster Farming. I will definitely use these on my next building. the ones I saw advertised came in any length, the base PT to .80 CCA (that's marine grade PT), and used finger joints to join the board ends. I know morton makes there own, but I would buy them. Those guys are pros at lamination and you get the warrentee.

All these points have been brought up, but I would agree with the following statements:

1) GL Posts are much stronger.
2) They are much more dimensionally stable.
3) Better PT at base (for the manufactured ones).
4) Cheaper for long lengths.
5) High quality (straight) long posts are possible.