Sonotube Caisson Questions 5

[anominal]

My uncle and I are planning on using sonotube "caissons" for a steel barn. We'll likely be using post hole diggers and want them to be as small as possible.

See attached .PDF of what I've laid out so far.

Is 1.5" of concrete cover enough for the anchor rods/reinforcement? (It isn't cast against earth)

Is there a minimum distance between the square steel column baseplate and the edge of the concrete caisson?

 

[BAretired]

If these are friction piles, you can't use cylindrical forms below grade or you won't get any friction between concrete and soil. If they are end bearing piles, you won't carry much load with a 12" diameter pile.

What is the maximum load on a pile? What type of soil do you have at the site?

BA

 

[TXStructural]

Based on the use of post-hole diggers, I suspect that these are not engineered piers, and so my comments here are based on that:

Use the tube only near the surface. If the soil is loose, and you need the tube to prevent collapse deeper in the holes, remove the tube once the concrete is in the hole; this can be done little by little as concrete is placed. The concrete in piers needs to be cast against undisturbed soil. Piers placed against disturbed soil may move laterally, and they not provide resistance to axial forces in the region formed and backfilled.

Minimum cover requirements are for two purposes: 1) confinement of reinforcement for development, and 2) protection of reinforcement from corrosion. !-1/2" cover is adequate, so long as the cover is within tolerance - cast against soil has a high variability. If the reinforcement is needed, be sure there is adequate, well-consolidated cover. If you do not need reinforcement, and are not willing to maintain cover distance, avoid steel reinforcement.

Anchor bolts should be confined in the pier reinforcement. ACI 318-08 section 10.14 describes the requirements for bearing, such as with baseplates.

 

[cvg]

I'm not a structural engineer but... If these footings are to resist uplift caused by wind, then 12" seems a bit small to me.

 

[anominal]

Piles, piers, footings. What are these anyway? I'm anal when it comes to terminology.

Also I haven't estimated any loads yet. I don't experience with non-highway engineering and I thought this would be more of a detailing exercise. Maybe that should be my first step.

 

[anominal]

Why isn't there an edit button...

 

[Zambo]

Ah ha.. there isn't an edit button so that you get a chance to reflect on your post.

In fact this is an international forum so the terminology isn't common to all. For example even between the US and the UK there are significant differences.

As a first step you need some bore holes and a soils investigation report. This will enable you to design the piles (AKA caissons in some countries)

You also need a basic design for your steel barn so that you have some loads.

For your purpose I suggest driven precast concrete piles (but after the SI you might find you don't need piles at all but instead can use pad foundations).

http://www.roger-bullivant.co.uk/products/piling.html

 

[anominal]

Thanks Zambo.

We have a basic design and I was going to draft a quick plan set for him so that he could show it to the proper town authorities. I suppose I'm getting caught up in minutia at this point.

I also did not know that borings and a soils report were necessary for residential construction. Would this add significant cost? Are conservative soil strength estimation guidelines not available in IBC?

 

[Zambo]

StationChump,

I usually work on international construction projects, so I don't have experience on "residential construction". In my experience a simple soil investigation wouldn't be that expensive and could provide savings in construction costs. But as I mentioned I'm not sure on this type of project.

 

[vandede427]

it's a barn people!

caissons and steel columns are probably plenty adequate.

 

[BAretired]

How would you know that?

BA

 

[Zambo]

Vandede427

"probably plenty adequate"

I would have thought that a steel framed building would be ideal. This will have to be designed so that not only are the steel memebers adequate for the job, but also that they are not over sized and therefore excesively expensive for the job in hand.

Likewise foundations need to be designed, this requires some knowledge of the underlying soils.

 

[Splitrings]

Here is a reference we use for post type foundations. If your posts carry only vertical and lateral loads it will be fairly straight forward. If your posts transfer moment to the foundation it is a little more difficult and likely a 12" diameter won't be sufficient. Design snow loads can be significant here in Vermont on structures of this type.

 

[vandede427]

I'm just saying. This guy and his uncle are building a barn and you all are going "geotech report" on him.

how do I know that it's probably adequate? because every other barn I see drivng down the road is 100 years old made of rotten wood and they're still standing.

 

[anominal]

Splitrings, thank you. I'll look at it when I get a chance.

Zambo, it is a steel framed building. We're using members that my uncle has acquired legally from working in the boilermaker trade... shipping steel for large power plant components. Although I haven't run a single number the steel he has appears to be overkill for this barn application.

 

[BAretired]

You need to know the type of soil on the site. You do not necessarily need a geotech report, but at the very least, the OP should dig a test hole and determine whether he is in soft clay, medium stiff clay, stiff clay, glacial till, silt, sand, shale or other soil type.

BA

 

[anominal]

BA: I can do THAT

 

[Zambo]

Vandede427,

you have a point in that if you are driving down a road and there are multiple barns with a specific foundation type then it is likely that your nearby barn can just follow a similar design.

In this case the poster is considering a steel framed barn which may be a bigger structure than your timber barns. We are also not informed of similar use of "sonotube caissons" on nearby structures.

 

[cvg]

unless you are really in the boonies, you will probably need a building permit for this barn. Go ask for help at the building department.