Concrete cracking in SOMD

[1437n6]

We placed a 6 1/4" Slab on Metal Deck a couple months ago, and now there are small cracks above every support beam (which are 3'-9" on center). I have attached a drawing showing the resteel layout that was specified. Any insight to why this may be cracking would be greatly appreciated.

 

[par060]

pretty thin slab for 4 diameters of reinforcing and cover....it probably got stepped all over during concrete placement and is laying on the metal deck..

 

[hokie66]

There are a couple of reasons for the consistent cracking I can think of based on your drawing:

1) The primary top bars should have been placed in the 4th layer rather than the 3rd. The distance to the top surface is 5/8" more than it needed to be. Are you sure the correct height chairs were used? That could also have lowered the steel.

2) Deflection of the steel deck during placement means the slab is thinnest over the beams, thus this is the place where shrinkage cracks will logically occur.