diamond cut in slab around steel column 1

[structuralnerd]

This may seem like a very basic questions, but I have specified the standard detail of the diamond cut around a steel column in the concrete slab at the base for almost every steel project. In the diamond cut, we call out to put 1/2" expansion joint, and then a construction or control joint coming off the corners of the diamond. I've never questioned it before, but now I am wondering why. Why do we do the diamond? Is there a certain clear distance you should keep between the column and the diamond cut? Why? Why not felt instead of the expansion joint material?

Is there a better way to do this detail?

 

[Lion06]

I believe this is to keep the slab from cracking as the coolumn footing settles differently than the S-O-G.

 

[Teguci]

Column does not move but the concrete slab changes volume (thermal, shrinkage, creep) and shifts.

If all of the concrete volume change is away from the column (ie the control joints intersect at the column) you can probably get away with felt.

Otherwise, you have reentrant corners at the column and you need space for the concrete slab to shift around the column.

Sometimes additional reinforcing is desired to minimize the width of cracks that do form at the corners.

 

[JedClampett]

If you don't do it, mother nature will.

 

[ronster]

The control joint around the column is to allow the concrete floor slab to shrink as it cures without interference from the column. This is not cut around the column as you indicated but a form around the column that leaves a void in the slab to be filled in later. A diamond or circular form or blockout may be used. For interior applications, I do not use an expansion joint or felt, as there will be very little movement in the slab once it as cured and the building is enclosed. The bottom of the slab should be kept at least 2" above the top of the footing so that sand or stone slab base can provide a break between the two surface to prevent them from bonding or settling together.