pour post first then slab?....or all at once....Monolithic including posts

[tinysparky]

After reading through 150 or so posts...i can find anybody who has done this...hence I think this might be a bad idea...

Question: My concrete guy showed up today to give me a price to pour my slab of a 40x72 pole barn. after talking it through with him, he asked me why I am pouring my poles.....then assembly the structure....to then do the slab. he asked why not just pour it as one giant mono slab?

Details - each posts need to be set in a 24" hole, 48" deep. There also needs to be a pad at the bottom that is 5 inches deep, setup prior to the post being installed. In total, it is almost a 13 yards for the posts...( I hate my county...)...

The only concern i really have is...when I go to set the trusses...there always seems to be 1 post an 1/2 inch in or out. do you think pouring it in one slab would hinder that movement?

I would save on only having to rent a pump truch 1 and would save 150 in trip fees for the concrete. but again, i can't find anybody else pouring these at the same time. which is concerning.....

Thoughts?

 

[lakeroadster]

Normally you don't fill the hole for the posts with concrete. You pour a footer for the post to sit on and then compact the native soil back around the post.

You do not want the posts "stuck" to the slab. It's a floating slab, it moves if the ground under it freezes or settles.

The posts are deep in the ground, below frost line... they will not move.

Folks will usually erect the poles and at least install the girts before pouring the slab to ensure everything is in the correct location.

Hope that helps.

 

[tinysparky]

Normally you don't fill the hole for the posts with concrete. You pour a footer for the post to sit on.

You do not want the posts "stuck" to the slab. It's a floating slab, it moves if the ground under it freezes or, settles.

The posts are deep in the ground, below frost line... they will not move.

Engineering requires 6" thick concrete footing. Then a min, 4" concrete floor which is shown going over the post holes. The fill is noted as concrete.

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[lakeroadster]

The fill is noted as concrete.

Really, where is that specified, in the construction note?

Notice the drawing shows all 3 different, not a mono pour.

 

[APEowner]

Engineering requires 6" thick concrete footing. Then a min, 4" concrete floor which is shown going over the post holes. The fill is noted as concrete.

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Are you sure you're reading the note correctly? That would be unusual for the back fill to be concrete.

 

[tinysparky]

Really, where is that specified, in the construction note?

Notice the drawing shows all 3 different, not a mono pour.

In another page. It says it must filled with concrete that is 2500psi after 28 days...

The plan was to through a couple of mixed bags into the holes....inspection....fill rest of the hole with concrete......frame....wrap...the pour the slab.

Though the concrete guy asked why not, after the inspection pour the post and floor at the same time.



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[tinysparky]

Are you sure you're reading the note correctly? That would be unusual for the back fill to be concrete.

Engineering company gave 3 options they felt all met my wind, structural, dead loads, etc....


King county redlined all of them except concrete.

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[tinysparky]

Are you sure you're reading the note correctly? That would be unusual for the back fill to be concrete.

Pretty sure I got their notes right......

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[lakeroadster]

If I were in your shoes, I would direct your question about a monopour to whomever red-lined the drawing.

If you do a monopour, have the PE note that it is acceptable on the drawing, and sign / date it.

I reposted your photo of the notes below, for clarity:

 

[Daniel Dudley]

It is very common to do it that way, particularly in tornado regions.

 

[lakeroadster]

It is very common to do it that way, particularly in tornado regions.

Do what... a mono pour, or concrete backfill?

A mono pour will likely result in cracking of the slab around the post.

 

[Pluribus]

I see where 6" is specified as the pad/footing/cookie for the posts, but are they seriously requiring the ENTIRE hole to be filled around the post with concrete?! Not a construction expert, but I don't recall ever seeing "backfill" on a drawing specifying it as concrete. If that's really the case, you'd still need two truck trips, as the pads at the base of the hole need to be cured/solid before the posts go in, which needs to happen before they can pour around them (if that's really necessary.) Can't imagine why any AHJ would require a concrete pour around a post in the ground, and pouring the slab directly over the top of it would virtually guarantee cracks in the slab radiating out from every single post in the building.

If not, going with the 24" diameter & 6" thickness for the pads, that 13 yards of concrete will be enough for 223 posts.

 

[hoppsxc140]

All of our posts are in concrete. I wouldn’t trust a contractor to do a good enough job compacting with native materials. Think of the utility crossings in a paved road, the bump isn’t from the patch job, it’s from poor compaction underneath and settling over time.

 

[Automobilist]

Oops... You said the dreaded words that change EVERYTHING: King County...

 

[Pluribus]

Oops... You said the dreaded words that change EVERYTHING: King County...

Some clarifying posts were added while I was typing before, but the above negates anything I might have said that assumed reasonable construction requirements. Seems the folks at DPER are sadists who delight in figuring out ways to cost property owners lots of unnecessary, extra money to build on their property. Best construction method in King County is to move out of it.

 

[bullnerd]

Some guy at the county can override the engineer at the pole building company?

Silly. That's a ton of wasted concrete.

Are telephone poles set in concrete in this county?

Move.

 

[tinysparky]

Some clarifying posts were added while I was typing before, but the above negates anything I might have said that assumed reasonable construction requirements. Seems the folks at DPER are sadists who delight in figuring out ways to cost property owners lots of unnecessary, extra money to build on their property. Best construction method in King County is to move out of it.

An old friend of mine gave me some advice....
Put the concrete in the bottom.....inspection....then add a little concrete.....lots of rock after it drys....the top it with concrete for final. I have gone back to my engineering firm and said....HELP

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[Pluribus]

An old friend of mine gave me some advice....
Put the concrete in the bottom.....inspection....then add a little concrete.....lots of rock after it drys....the top it with concrete for final. I have gone back to my engineering firm and said....HELP

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Sgt. Schultz:

 

[Daniel Dudley]

Do what... a mono pour, or concrete backfill?

A mono pour will likely result in cracking of the slab around the post.

Concrete back fill is very common.

I would never do the mono pour, and I would consider some kind of post protection wrap or bolt on base if I were pouring around the pole.

 

[lakeroadster]

I don't see the concrete fill of column holes as a problem, structurally, as long as you make it a separate pour from the slab.

Whoever did the drawings opened the door by providing the option to use concrete in the holes. And the bureaucrat at the AHJ doesn't care about cost.

An interesting link:
http://www.hansenpolebuildings.com/2013/04/pole-barn-post-in-concrete/

 

[ptgarcia]

Whoever did the drawings opened the door by providing the option to use concrete in the holes. And the bureaucrat at the AHJ doesn't care about cost.

Even if concrete wasn't specified as an option the county checker likely would have sent it back to be redesigned for concrete. We do our best to value engineer and specify inexpensive materials and methods but more often than not it doesn't make it through plan check. There's more than one way to skin a cat, and apparently the county in question wants it done with concrete.

 

[77Birdman]

Pour the footing first, set your posts, then form and pour the slab and the backfill around the posts at the same time. Wont hurt a thing.
In my area we put a 12" footing at the bottom of the post below frost (36") then backfill with a material that will drain. Concrete poured around the post is not recommended as the post is prone to rot that way. I would wrap the post with something like an ice shield. I understand why they want it for uplift, but in reality the roof will be ripped off or the post will be sheared before its pulled out of the ground.

 

[Mikeske]

I had a garage built in 2009 and the post were poured first in concrete and later the slab was poured. Specified per the drawings and no options in the drawings. I had no issues with the poles and this has been done this way for a while and I am not in King county but Skagit county.

 

[larry_g]

Down in this country, 159 miles south of the OP, we are also required to backfill with concrete. OP, make sure of how the 48" depth is measured. I didn't and was dinged for to shallow of a hole. I was able to put 'hairpins' in along side the posts and bend over into the floor slab to remedy the problem.

lh
no neat sig line

 

[tinysparky]

I see where 6" is specified as the pad/footing/cookie for the posts, but are they seriously requiring the ENTIRE hole to be filled around the post with concrete?! Not a construction expert, but I don't recall ever seeing "backfill" on a drawing specifying it as concrete. If that's really the case, you'd still need two truck trips, as the pads at the base of the hole need to be cured/solid before the posts go in, which needs to happen before they can pour around them (if that's really necessary.) Can't imagine why any AHJ would require a concrete pour around a post in the ground, and pouring the slab directly over the top of it would virtually guarantee cracks in the slab radiating out from every single post in the building.

If not, going with the 24" diameter & 6" thickness for the pads, that 13 yards of concrete will be enough for 223 posts.

I went to the county. The short version...

Engineer didnt show calc for compacted rock backfill, so county redlined it to concrete. So now I am left with several of the holes being 30" @ 48"....about .7 yards each... ridiculous

Option a) re submit with smaller hole for concrete. County thought I could probably do 18" holes but 24" for sure. Cost is a $500 fee.

Option b) resubmit with the calc, but then I found out I would need to pay for an inspected to be onsite to validate each lift....

Option C) stick build it.....resubmit fee is 1500....but....

Did I mention I dislike my county?

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[earlthegoat2]

You don’t want to go monolithic for the posts and slab. Frost can heave the slab because it’s close to the surface and cause heck with the concrete around the posts that will not want to heave with the floor. Cracks will happen unless you live in the warmest parts of this country like I do.