Pile supported slab on ground

[Crikkky]

Hello everyone,

I am working on a project where we have this large pile supported slab (200' x 300') with a design load of 400psf (heavy racking).

The slab will be 14" deep with 4" drop panels around the pile caps.

Does anyone has any advice on what to do to prevent cracking on this slab?

We plan to use a square pattern for the pouring of the slab with keyed construction joints. Would you stop the reinforcement at these joints? How long would you wait between the pourings?

Apart from those joints, there will be no other joint.

Any advice?

Thanks a lot



Chris Laroche, P. Eng

 

[Zambo]

What is the pile spacing - about 3m I guess. The piles would be expected to provide restraint that would make the provision of expansion joints ineffective.

I would prepare the construction joints well and use expanded metal formwork to give additional bond. I think it is best to make the reinforcing steel continuous through the joints.

 

[dik]

You might want to consider using a thinner slab (maybe 8") and thicker drop panels (maybe 8") if your spacing is 3 m... I tend to use drop panel depths approaching the slab thickness and run it as an elastic strip... The slab interface with the drop panel approaches a fixed end condition... relative stiffness being in the order of 8:1.

There's economy to be gained by designing reinforcing cut-off points and staggering the bars... Say 3000 span then the bot bars would be approx 3000*.8*2, centred over the support lines.

Dik

 

[Crikkky]

Thanks to you both.

The pile spacing is somewhere between 5,5m and 6m.

We chose that large spacing because the piles have to be very long (12 - 15m).

Does it change your opinion?


Chris

 

[dik]

Depending on the design loads, you might want to use a 9" or 10" slab and 8"/10" drops (7-1/4"/9-1/4" [2x8 or 2x10] + 3/4" ply forming). I've often used 8" slab with drops for 27'-28'. Thicker drops have a bigger influence on short and long term deflections... Comments about reinforcing remain...

Dik