Slab on Grade Details for Unheated Camper Storage 2

[waytsh]

I would like some opinions on best practices for a slab on grade in a partially open, unheated building. We are in a location where the frost depth is 36". The main interior columns are inboard of the building line and the rafters cantilever 10' to the building line. For the main interior columns I was planning to use mass footings that come to finish floor and extend down to frost. For the endwall frames I intend to use a continuous grade beam.

I was planning to use a floating slab but I have two areas of concern. First, the "free" edge of the slab at the open sidewalls. Second, the interface of the slab at the interior footings and the endwall grade beam.

For the free edge of the slab I was planning to use a thickened edge with no perimeter frost wall. Where the slab meets the grade beam and the interior footings I was planning to butt the slab to them but isolate with pre-molded filler. I threw together a quick rough sketch to help show the conditions (see below).

Thoughts? Anything you guys would do different? Thanks is advance.

 

[dik]

Is the soil frost heave susceptible? Can you do something like:

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[phamENG]

I think I would put normal column footings at frost level (12" or so thick) and float the slab. Provide a means for the column and the slab to move independent of one another. I'd also look at an extra thick sub-base for the slab to reduce the effects of frost heave under the slab.

 

[dik]

If it's not frost heave susceptible, or he can live with slight movement, then you don't need frost cover. We have areas of frost heave susceptible silt but for the most part it's not a real issue if you can live with frost heave (we have 6' of frost depth in this area).

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[waytsh]

Thank you both for taking the time to reply.

I don't know if the soil is frost heave susceptible at this point. This is a small project and there is no Geotech report. My thought was that since this is parking for camper RV's I could tolerate some movement if I isolated the footings from the slab as long as they do not incur damage

dik, In the past I have done something similar to what you are showing on your details, if I am understanding them correctly. You are basically haunching out the slab and doing a continuous pour, correct? Some of the text is hard to read so maybe I am misunderstanding. I was hoping to avoid taking the haunch to frost depth and let the slab float but maybe I am asking for trouble.

phamENG: The reason I was setting up with mass footings rather than thinner spread footings is twofold. The contractor requested them since they would rather pour more concrete than having to form up pedestals. Also, since the building is partially enclosed and a light PEMB, uplift was substantial and I needed the weight. A 12" thick footing was requiring a very large footprint, even considering the weight of the overburden. I know I am showing a lot of reinforcing in my details but I was also hoping to check as plain concrete and maybe only throw in minimal T&S reinforcing to save a little bit on that as well.

Thanks again for the comments.

 

[dik]

yup... but not to frost depth if you can avoid it. If you need to go that deep, then your original comcept of a footing makes a lot of sense. I've used stiffened slabs for heated and unheated structures nearly 1000 miles north of here with no ill effects. It depends on how frost susceptible the soil is. With heated buildings in frost susceptible soil, I rely on DOW high capacity extruded polystyrene...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[waytsh]

It may not have been clear but in my detail above there are no columns bearing on the thickened edge of the slab on either side (the sidewalls). The frames are like T-frames except with two interior columns and the rafters cantilevered on each side.

 

[dik]

Similar details can be used without columns...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik