Slab on piers design

[jimtheengineer10]

I have a client who wants to install a 6" slab on top of piers instead of a typical frost wall.

The piers would extend 4' below grade. The house is a double wide and is 26'8" x 44'.

How are apart should the piers be spaced and what diameter should they be?

Should the piers extend above grade? If so, how much?

Should the slab be tied to the piers with rebar?

Thanks in advance.

 

[JAE]

How are apart should the piers be spaced and what diameter should they be?
[red] Depends on the capacity of the piers and the load imparted. You need to calculate this - we can't help you on this site for something like that.
Typically piers need to be spaced at a minimum of 3 x diameter center-to-center)[/red]

Should the piers extend above grade? If so, how much?
[red]To deal with frost heave, the slab needs a void below it and a perimeter means of avoiding soil from eroding into that space below the slab...usually done by a perimeter grade beam on the piers.[/red]

Should the slab be tied to the piers with rebar?
[red]I would think so but this depends on the actual project conditions, location, etc. Hard to develop bars from a pier into a 6" slab, though.[/red]

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[jimtheengineer10]

JAE,
So a 12" diameter pier should be spaced 36" max?

So is their actually just air between the bottom of the slab and the ground (except for where the slab is resting on the beams)?

Do you need to install galvanized decking under the slab like you do on an elevated slab or can the slab span from beam to beam?

Thanks for the help.

 

[JAE]

If you don't want frost heave on your slab - don't let the frost-susceptible soil come in contact with the slab - so air...yes.

Decking - formed slab - up to you.



Check out Eng-Tips Forum's Policies here:
faq731-376

 

[SlideRuleEra]

So a 12" diameter pier should be spaced 36" max?

Reread JAE's post; 36" center-to-center spacing is a typical minimum spacing for 12" diameter piers. Minimum spacing has more to do with the soil supporting the piers than the slab.

Without doing any calcs I can tell you that the maximum spacing will be << 84" for a 6" slab. Span-to-slab depth ratio of 14:1

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[jimtheengineer10]

Great help. Thanks.

If they don't use decking what are the other options?