Homemade, prefab, concrete and pine post

[two_bit_score]

This thread is not about slabs.

He was being helpful and answering a question. Why is that a problem for you?

 

[lpakiz]

Altho not everyone has access to these, I used used grader blades as an anchor. Even the curved ones work fine. The wood posts were bolted thru the grader blade holes and into the 4X4. I used 5/8” bolts and nuts, not lags, and I can tighten them a bit every several years. If there is a lot of weight to be carried, perhaps a short angle iron ledge should be bolted or welded to the iron, for the post to set on.
Dig the holes to below frost dept, which is over 4’ here.
Stretch string over the post holes for the true location of the blade where it interfaces with the wood.
Drive the grader blade into the bottom of the hole, enough to hold it in position and vertical, maybe 8” more or less. Insert a piece of 1/2” rebar or an old, long bolt, or some kind of metal pin CROSSWISE thru the hole nearest the bottom of the post hole. This bolt sould be at least 6” long, or as long as the hole width allows. You might need a coat hanger or some device to help fish the bolt thru the blade. Or you could pre-install it and weld it or wedge it in place just until you get the blade installed.
Brace or anchor the blade temporarily to hold it in position.
Mix up some quick Crete and pour a layer into the hole, at least a couple inches above the bolt. The whole layer should be 6” thick, at least.
When it is cured, backfill a bit, but leave an opportunity to adjust the blade a fraction of an inch after you attach your post.
I arranged it so the blade was to the backside of the deck, unseen from the outside, and the wood was just above the final grade.
In this system, the wood doesn’t soak up water, frost or wind can’t pull the concrete slug up, nor can gravity push it deeper.
A D6 Caterpillar couldn’t lift them out of the hole when I came to move my woodshed.

 

[LouNY]

Yeah, like you we also have snow loads, and a standard pole-barn is just a non-starter. We need roughly one square foot of footing for every 40 square feet of roof, a wooden post just isn't going to provide that. Once you have to pour footings a lot of the allure of a pole barn goes away.

There are many pole barns built in my area which get more snow load then Rhode Island with no large footers.
The standard practice around here is a bored 24" hole or bachhoe dug hole with the bottom of the hole below the frost line,
then a concrete slab is poured in the hole and the post is set on top of that concrete.

 

[Sawyer Rob]

I built them in Alaska, I set a home made cement post pad below frost line and then the PT pole on top of that. Never had one problem at all, even with HEAVY snow years...

SR

 

[rbstern]

I'm a civil/structural engineer, and I cringed a little when I read your post-to-footing solution. That one stick of 1/2 rebar will provide absolutely ZERO resistance to uplift, and next to absolutely ZERO resistance to lateral forces. I fear you'll be sorry (and sooner, not later) if you proceed that way. Use either the wet-set Simpson brackets in Sonotubes, or the PermaColumns, and you'll be good-to-go ! Also, I love the laminated, untreated post idea, as long as you keep the base of the wood at least 4'' above the finished floor elevation, which is easy to do with PermaColumns (I'm a big fan of these and used them on my own Shop Building). "Dipping" the bottom of the posts isn't a bad idea, especially if you're closer to the FF like you would be with the Simpson brackets... or you can start your laminated posts with treated 2x6's at the bottom. Happy building!!

Thanks for offering your insight. I understand the uplift point, but how can a 1/2" mild steel bar not have any lateral/sheer resistance? The material itself has something like 60Kpsi of yield strength. Is the rest of the joint the problem? Assuming the concrete is 4000psi, that's certainly going to resist lateral forces. Don't know what psi an average pine SYP 6x6 can stand up to in lateral loading, but there's a lot of SYP joists and rafters holding up against a lot of sheer forces in pretty much every part of the modern world, and in many cases, fastened with less than 1/2" of round steel.

Also, and setting aside for a moment that my described concept is a bad way to do the joint, does your opinion about the uplift change if a high strength construction adhesive is used in the bored hole? My own experience with construction adhesives in wood-to-cement joinery, is that the materials fail before the adhesive, even in tensile applications. If enough force is applied to the joint, the fastener and adhesive stay put, but the wood and/or concrete fail.

 

[Doughknob]

Yeah, don't do your idea. The rebar inserted in the wood is the problem. With the grain into the end of a post like that, it is the weakest way to attach wood to anything. Expansion/contractio, wood splitting on the end is a recipe for disaster.

Think about firewood - you split it from the ends, not from the sides where it is MUCH stronger. The permacolumn type things work because they sandwich the post from the sides and the fastening bolts or screws go across the grain.

 

[s219]

This is what I have been doing to marry my rough-sawn posts to a treated base -- marry up a 4' section of treated lumber on the bottom with a lap joint, construction adhesive, and 1/2" bolts. I hate to even spend the money to buy the short sections of treated lumber, but it lets me create 16' posts for *way* less than what it would cost to buy them nowadays.

 

[rbstern]

This is what I have been doing to marry my rough-sawn posts to a treated base -- marry up a 4' section of treated lumber on the bottom with a lap joint, construction adhesive, and 1/2" bolts. I hate to even spend the money to buy the short sections of treated lumber, but it lets me create 16' posts for *way* less than what it would cost to buy them nowadays.

View attachment 702655 View attachment 702656

Yep. Love that. Nice work.

You put anything through the post bases (rebar or fasteners) to prevent pull out from the concrete, or do you feel comfortable with the concrete's grip on the post?

And what tool(s) are you using to make that joint cut?

 

[Diggin It]

You put anything through the post bases (rebar or fasteners) to prevent pull out from the concrete, or do you feel comfortable with the concrete's grip on the post?

I had something sketched out the other day but scraped it because I couldn't get it to show what I was thinking. It was basically your original idea (and mine), but added a bolt through from the side of the post to tighten against the rebar like a set screw type of thing. One from each oppositre side would apply equal pressure against the rebar.


Then the enginmuneers got into the thread and I figured they'd rag on the idea of removing more wood by drilling the holes.

 

[bigtiller]

This is the way Morton did the bottom of my posts.