Cracks in supported concrete slabs are usually the result of normal and expected behavior of a reinforced concrete structure due to shrinkage and deflection.
Certain patterns and wider cracks may indicate a structural overload. This overload may be caused by loads for which the slab was not originally designed, by inadequate design, or by construction deficiency.
Although the applied loads may be larger than originally anticipated, or the slab and its reinforcement may not have been built as designed, retrofit still may not be required.
If analysis determines that there is a deficiency that needs to be corrected, there are several approaches: to increase the thickness of the slab, installing additional reinforcing bars, or installing concrete shear collars or steel brackets on the underside of the column-slab junction.