Thoughts on construction of laminated post

[frazman]

What are your thoughts or experience on laminated post. I'm looking at making some posts for my mill shed. I will mill the wood out of white spruce. I'm thinking of 6" x 6" or 6" x 8". What's a better choice to accomplish the 6" thick dimension , 3 pcs at 2" thick or 4 pcs at 1-1/2" think. I will be glueing/nailing/screwing the lumber to make the post.

These post will be set in the ground at approx 6 feet with 10' to 12' above ground. I was also thinking of using engine oil / diesel  ( 50/50) to coat the bottom part that's set in the ground to preserve the posts.

Any thoughts ?

[Cosmo52]

The guys using laminated posts around here use pressure treated sections on the bottom and splice non treated lumber for the top. For instance you would laminate a 6' and an 8' and a 10' piece to start and finish the post length with untreated lumber.  The splices are staggered and the treated end of the post is buried, untreated post is mostly above ground and no special fasteners are required

[Don P]

This is an article from one of the builder mags about nail laminated columns;
https://www.constructionmagnet.com/frame-building-news/what-every-post-frame-builder-should-know-about-laminated-columns

And the EP (engineering practice) related to nail lam;
https://www.midwestpermacolumn.com/nail-laminated-column-design-ansi-asae-ep559
Pay attention to nailing patterns and spacings, it takes serious nailing to get it to act as a unit. Basically don't use screws unless they are structural screws, the typical screw is not good in shear which is what you are dealing with.

You can google David Bohnhoff and nail laminated columns and read a lifetime of research on it, he's been busting them for years.

[Brad_bb]

I would not put the wood in the ground even if treated.  That was done alot in the 60's-90's, but even kreosote treated will only last 18-20 years and will still rot off at ground level.  Concete piers may be an additional cost, but are well worth it.  After the piers are poured and cured, install brackets for laminated posts.  You will drill the piers for and epoxy in the anchor bolts for the brackets.
Sturdi Wall Brackets
I just had a building put up using these brackets, but I had a footer and stem wall to make sure to keep rodents out.  After the brackets, you will use a laser to measure any height difference between piers, then you can adjust your final post lengths accordingly.

Another cheaper option, provided that the building will be closed and posts protected from rain....  Is to use plastic post protectors.  It's a plastic sleeve that slips over a laminated post bottom and can be installed in the ground.  any moisture can evaporate out the top of the sleeve, but It cannot be exposed to rain that could get in the top of the sleeve.  Also, you cannot seal the top of the sleeve or you'll get rot.
Post Protector sleeve

[Don P]

There is no free lunch, understand the difference in building performance when swapping out elements.

Something not often thought about when going to this type of connection, especially when someone sticks in on a smallish pier;

Bending moment capacity of all Sturdi-Wall brackets assumed to be zero

In other words view the connection as a hinge. The paper I referenced and what we were talking about views the post as having moment capacity, a rigid post. This relates to how you brace the building for wind or seismic and whether the pier can overturn under lateral load.

Also read the comment on wet set vs bolted connector.

[Brad_bb]

My focus, Don, is to avoid having wood in the ground.  Yes the building would be stiffer with the post in the ground, but it opens it up to deterioration, which would then eliminate that benefit of rigidity.  

Most of the pole buildings I have experience with, many of which are Morton buildings with wood in the ground, generally have a 25 year guarantee (because of the posts mainly).  In actual experience though, many of them have posts rotted through at 25 years.  The rot starts much earlier than that.  I've seen compromised posts at 18-20 years.  They may not be rotted all the way through, but are probably 50 percent compromised.  I've observed this in multiple types of post treatments from full creosote  to the green copper stuff (before they changed the formulation in recent years). 

As we've discussed many times on this form, they posts always rot just at ground level where both air and moisture are always present/alternating.  Below ground where the post is wet and there's insufficient oxygen, the wood is still solid.  Above ground where there's no moisture, still solid.  

The OP's post is for a mill shed, which means at least one side will be open.  This means that he can't use post protectors there.  This is why I suggest something else- like piers or a foundation. 

I always recommend that the building be "engineered", even in an area where it is not required by the governing body.  You need to know it's going to stand up to the wind and snow loads it will be exposed to.  So, yes the building needs to be sufficiently rigid, and not rely on the brackets for bending resistance.  They are anchors. Your engineered trusses and bracing along with any sheathing will make the building rigid.

[wbrent]

I have done this a couple times in the last few years and if you can afford it I highly recommend Screwposts. Comes with Brackets to hold a 6" square post and you can keep them just above ground. I see you're Canadian as am I, and can tell you they come in around $275 a post Canadian. Not cheap. But super slick. 

[D L Bahler]

If we're concerned about bending moment and also not having the posts driven into the ground, something like perma-collumn seems like a reasonable enough compromise. A lot of guys around here use those. They claim if you do the connections right they have significant strength against bending, and so you can engineer the structure more or less as an earth-shorn post structure. 

I don't know if I believe it, but that's the idea anyway. Not endorsing it, not denying it, just pointing it out.

[frazman]

Lots of good ideas posted but I want to keep the cost down. I have to keep it real as I'm no spring chicken. The mill shed is for a hobby mill and maybe in five years I'll have the mill sold who knows but cost has to be low. Yes if this was a large pole building the construction would be different but I want to keep it simple with material I have or can mill.

The size of the shed will be 14' x 30' and I'm using engineered floor joist placed at 24" c/c for a sloped roof something like a lean to with a 20 foot opening for loading logs with no poles. The roof will be 12' (+or-) high on one side and maybe 10 feet high at the opposite side. The height is still in the works. The floor joist were given to me so no expense with those.

I very much appreciate the info passed on the laminated columns from Don P. 
Thanks for all the help.

[Brad_bb]

In that case, with only 5-10 years in mind, it almost makes you wish it could be move-able, so you could sell it down the road.  Lots of guys wanting a mill shed.  I understand you're trying to work with free materials you can mill, but what about one of those canvas/steel framed clear span buildings?  The good ones the canvas is good for 20 years before you replace it, and the frame is totally move-able?  Probably more money than you want to spend up front, but you would get money back out of it when you sell it.  Just a thought. I  wonder what it would cost?  I know a farmer that I've helped that has one of those for a horse arena and two hay sheds.  They are nice, and fast to go up.

[frazman]

Any type of good canvas steel frame around here can be expensive. The less expensive one don't last long around here with our snow and strong winds. I have purchased a number of these garage in a box and within a couple of years the cover start to come apart.

I'm going to stick with my original plan and looking forward to starting it this year. I may follow up with pictures and post them once the job is done, we'll see.

[Don P]

This is an article that explains a good bit of what I've been talking about here, I would encourage those who have posted with suggestions to try to read and understand at least the first few pages;
https://s22327.pcdn.co/wp-content/uploads/FN-0117-RT.pdf

In this situation I would think hard about what Cosmo proposed. One advantage of treated laminated posts is the treated plies are thinner and the treatment is more uniform than in a solid post.

It sounds like the next elephant in the room is that 20' beam supporting about 140 square feet of snow and roof weight.

[fishfighter]

OP, when I built my mill shack, I installed treated 6"x6" 3' in the ground that were sticking up 2'. Then jointed oak post to that. I did treat the areas with motor oil and used some 5/8" bolts.

I'm sure the treated post will last around 20 years, but I 62, so no problem there. ;D

[D L Bahler]

Don, the literature published by the manufacturers of perma-culmuns does specifically note not to model the connection as a pin, but as a rigid connection

Again, not endorsing it just restating what I've read. In the end I'm not concerned because I don't build pole buildings, and don't have any plans to have one built. They're not as good us the designs shown at the end of your linked document though. So perhaps my skepticism is merited? 

[Don P]

Well, we're all advising someone who is building one :D

It's a good bit more complex than plug and play substitution, here is that paper;
https://www.permacolumn.com/downloads/open/243/perma_column_design_and_use_guide.pdf

Scroll down to pg 14 where it goes into the semi-rigid behavior of that joint and the equations there. This is not the same as a solid post. To give a real seat of the pants number, the published connection load is capable of about 2500 ft-lbs, if the post is 10 feet tall above that connection and unbraced it is good for about 250 lbs shoving on it up top... a 6x6 or laminated post is a good bit stronger in bending.

Notice a couple of caveats, fully sheathed building providing uniform bracing, no kneebraces, laminated columns loaded in the face width plane only. That is not what we are talking about here.

That is one observation I was kind of hoping someone would point out in all this. A laminated post is good in bending across that wide face plane, not so good in the across the edges plane because of slip between plies. Notes call out sheathed bracing girts.

Glue would probably help there but cannot be relied on, most field available glues and applications also slip or fail, but it doesn't hurt. The NDS is silent on all this but it is something to consider, the EP posted above is more detailed.

[frazman]

Fishfighter, looks like we have couple things in common, age & make of mill ;D

As for the open 20 foot span and snow load, this will be accomplished with the joist as previously mentioned, as long as I do my part with enough laminated poles. The joist are designed for 3 level condos.

Lots more excellent info to digest, Don P

Thanks to everyone for the feed back. Much appreciated. This should make for an interesting build. 8)

[D L Bahler]

If you're ever in Switzerland and make it to the Ballenberg museum (which you absolutely should if you're ever in the country) There is an old mill shed built in the 1800's some time, with a massive clear span accomplished with a very very deep beam.
Except this is no simple beam, it's built up of many layers of timber, joined together into what is called in German "Verzahnte Balken" -which you can google if you want to see what it looks like. Basically, the beam is mechanically laminated by cutting an interlocking tooth pattern into the "laminates" and then bolting the assembly together. It's an old fashioned approach to the idea of laminated timbers for large spans. 

I'm sure this is beyond the scope of anything you want to do, but the discussion reminded me of this, and I thought I'd share.