Sawcuts in a mat foundation

[theclipper]

I have a 10" mat foundation with #5 bars 16" c/c top and bottom - anybody know of any reference documents on how to detail the contraction joints for a mat foundation? thanks in advance.

 

[hokie66]

Contraction joints are not used in mat foundations. Sawcuts are for ground supported slabs, but a mat foundation is a structural slab. You may have construction joints, but these should be detailed so the slab is continuous. The quantity of reinforcement should be sufficient to control the width of cracks. For mat foundation slabs (which are invariably heavily restrained), I would never use less than .006Ag, and you only have about .0039Ag.

 

[archeng59]

If the mat foundation is not exposed to view, why worry about how it cracks? No one will see the cracks anyway.

 

[Ron]

First of all, a 10" slab hardly qualifies as a "mat foundation"...just a reinforced slab. Secondly, hokie66 is exactly right...don't worry about it.

 

[rowingengineer]

I don't know about the rest but I would still want a joint in the slab after about 60m.

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

 

[theclipper]

thanks for the input. I currently have construction joints detailed for roughly 60'x60' squares with greased dowels through the construction joint.

Hokie66 - do you know of a reference for the .006 or is it what you've become comfortable with through experience?

thanks again

 

[hokie66]

.006 Ag has been a number used in the Australian concrete code AS3600 for a long time, applying to shrinkage control where a high degree of crack control is required. I think the latest code has more complicated provisions, but I still like this one. You will find similar quantities required in various codes for water resisting concrete structures.

 

[theclipper]

Thanks hokie66,

Ron - I agree that it's not a typical mat foundation - but its' supporting a low rise lightly framed cold formed metal frame building with bearing wall loads of less than 5 kips/ft and no column point loads. The building is a very long/narrow structure with transverse bearing walls 12' c/c and the contractor has been building a lot of these. Typically, I've been laying these bearing walls out on 2' wide strip footings below a 4" slab on grade on 4,000 psf soil. The building is 600' long, and to save on the time to do formwork for the strip footings, and then pour a 4" slab on grade on top of that - the contractor asked if there was any way to do it all in one pour. I utilized RAM Concept to model a mat foundation on springs and this is the output that I am currently evaluating. Due to such small loading and good soil, I am getting very few strength requirements governing in the slab and am finding there are more detailing issues....

Thanks for any additional thoughts.