Joints in Concrete Equipment Slab?

[Structures33]

I have a 60' x 16' x 8" thick reinforced concrete equipment slab on grade (exterior) that will be supporting electrical equipment. I want to put control joints in the slab because of the length to width differential. I considered saw cutting control joints but I will only be able to provide a joint that is approx 3/4" deep because of the top reinforcing (yes, it needs it). I considered dividing the pad into 3 isolated sections, separated by expansion joints, but this will cause issues with the equipment anchors - there are many pieces of equipment and the anchorage points are freqent.

1. Do you think the pad needs joints?
2. If yes, do you think a 3/4" saw cut will be sufficient depth to be an effective control joint? If not, do you have any suggestions?

Thanks!

 

[hokie66]

If you have enough reinforcement to control the cracks, why would they be a problem? They might not be straight like a sawn crack, but for an equipment pad, they would not affect serviceability. I doubt that a 3/4" deep sawcut would force the crack to occur at that location.

 

[aaronPTeng]

No point putting an expansion joint in if the reinforcement is running through the joint, Only time this would work, for example if you had slab on grade and mesh for crack control cutting every second reinforcement bar segment through the saw joint and then cutting the slab will give you a joint. However you will still need better detailed joints every 3-4 saw joints.

You need to weaken the reinforcement in the location of the saw cut otherwise it wont work. The slab you are doing is very small and i would not see it as an issue, if you are concerned place more reinforcement in the long direction to control shrinkage in this direction.

 

[Ron]

Cracks in reinforced slabs are purely aesthetic and have no functional detriment other than a pathway of water to rebar.
Go ahead and sawcut the joints to the rebar depth. This will help (but not completely) control cracks in the concrete. Sawcuts in reinforced slabs need to be relatively close together (seems intuitively opposite...but not)....keeping in mind you are controlling crack appearance in a highly restrained surface.