Pre-Cast Concrete Pad over Existing Slab on Grade

[cehbn]

I've got an existing 6" (150mm) thick Slab on Grade in food manufacturing space. The Intent is to install an automated storage rack with total loaded weight of 65,000lb. The Rack is supported on 8 legs where each leg will carry approx. 8,200lb (3.7 Tons).

After completing the analysis on the existing slab on grade (concrete compressive strength f'c = 25MPa)(3600 psi). the slab will fail due to the tension stress at the bottom. A reinforcement solution will be applied to compensate the new concentrated loads from each of the 8 legs.

since the new vertical storage rack will be installed in manufacturing space, minimal down time, dust and disturbance to operation were requested. So, it was requested to add 8 pre-cast concrete pads ( each under leg) to thicken the existing slab on grade and dowel in to existing slab on grade reinforcement.

Any good reference design guide addressing pre-cast concrete pad over slab on grade? if any Canadian guide or standard would be great.
what is needed to prepare the slab on grade surface under the pre-cast pad?
What might be typical reinforcement use of pre-cast pad?
what might be typical dowel in to existing slab on grade?

thanks

 

[HTURKAK]

IMO, the use of steel base plate having bigger dimensions and thickness will be better than concrete capstone ..
Performing 2D FEM analysis with refined mesh around base plates and distribute the vertical loading to base plate may reduce the tension stress at the bottom.

 

[bones206]

You could install threaded rods into the slab with adhesive. Cast in matching pvc sleeves in the precast pads. Drop the odd over the anchors and secure with large plate washer and nut. Filling the sleeve with grout is an option, but might be smarter to omit that if there’s a chance the equipment will be removed or relocated in the future.