Combination floating concrete slab and slab on wall.

[woodman1967]

Hello all again

I am working on a project where an addition is being built to an existing industrial shop. This is a small industrial shop (60'x30') that is on a floating, thicken slab. The addition will double the size of the shop and will be on a similar floating slab, except for one end. At this wall they want a loading dock built so that the floor of the truck will be level to the floor of the slab. In order to do this the existing grade will have to be lowered and the slab will need a wall under it with a retaining wall on either side of the loading dock or maybe (depending on the grade, it does slope slighty down in this area) a retaining wall on one side of the dock and then the wall extending to the corner and around the corner until it is not necessary because of the level of grade (does that make sense).

All that detail may not be necessary, just the question have any of you had experience of a combo slab part floating, part on a frost wall. Is this something you would be comfortable with?

Thank you for any advise.

 

[Hemifun]

I have run into similar situations quite often. I have always been worried that the backfill behind your wall will settle leaving your floor slab suspended. Typically, I call for crushed stone backfill to minimize settlement and I don't set the floor slab on the perimeter wall. I raise the wall so the top of the wall is at floor level and run the slab up to the wall. In situations where I can't do this, I have designed the slab to act as a suspended slab.

 

[hokie66]

I would take the slab over the wall but thicken it and design that part as a suspended slab. "Semi-suspended" is a term some use.

 

[rowingengineer]

I agree with Hokie, I would normally suspend the slab past the 45 degree line, by a comfortable margin.

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it

 

[Ron]

Agree with hokie and RE...run the slab over the wall....otherwise even slight settlement will cause serviceability issues.

 

[graybeach]

This is like a bridge approach slab. Sometimes we run them over the back wall and make them continuous with the superstructure slab. When continuous, we make a saw cut in the slab along the centerline of the back wall and seal it for crack control. In either case, the approach slab is reinforced for bending due to settlement of the fill.

 

[woodman1967]

Thank you for all your responses,

We are looking at the suspended slab suggestion. The concern raised by a local inspector is with part of the slab as a thickened slab and part on a wall how will the differential settling be addresses. The inspector is concerned with how this differential settling will effect the building itself. We are insulating the slab.

Thanks again

 

[rowingengineer]

woodman1967,
When you say "we are insulating the slab", what do you mean by this statement? What are the propertie of the soil, are we talking a highly reactive site or poor soil strength?

An expert is a man who has made all the mistakes which can be made in a very narrow field

 

[woodman1967]

rowingengineer

We are placing 2" rigid insulation on grade before the concrete is placed and also the same insulation will extend 4' from the footing to prevent frost from getting under the slab.