Concrete Slab Subject to High Temperature Swings

[Beamman]

Hi,

I have to design a slab-on-grade which has compost placed on top of it. While the compost cures, temperatures can go as high as 80 degrees C within the compost. Ambient temperatures can range from +25C to -25C.

Also, compost piles are moved around in order to mix it, so a slab could be almost 80C at the top surface with compost on, then be subject to ambient -25C temperature for a few days until a new pile is placed on top.

My question is: how are the stresses for these conditions calculated and accounted for? To add to it all, glycol piping is within the slab to help recover heat.

Thanks

Beamman

 

[IsaacStructural]

I believe the method is to use strain compatibility between the concrete and steel.

The concrete will want to expand more than the steel, so the steel will resist this deformation. Using the coefficients of expansion, modulus of elasticity and strains, you should be able to compute stresses.

The ACI code provides normal provisions for temperature and shrinkage reinforcing and beyond this, if you provide this steel and provide regular expansion and contraction joints, I believe your slab won't have a problem.

As always, I defer to other posters who have more information or knowledge of the subject to provide additional information and correct me.

 

[rapt]

IsaacStructural,

The code shrinkage and temperature rules are not meant for this situation.

Beamman,
You have 2 problems.
- The overall temperature change will cause expansion and contraction of the slab which is restrained by the subgrade. You will have to calculate restraint forces and put in sufficient reinforcement to counter this.

- You will have a temperature gradient through the slab. This will cause moments in the slab due to attempted curling of the slab. If it is hotter on top, this will cause tension stresses in the bottom of the slab.