A floor when constructed is divided into a number of smaller slabs. For wheel and rack loading, there are three basic positions of loading on a slab to be considered: the internal loading position, when the centre of the load is at least half a metre from the perimeter of the slab; and the edge loading position and the corner loading positions, which are self-explanatory. The area of loading on the floor is considered as circular at the corner and internal loading positions and semi-circular at the edge. Internal and edge loading produce a maximum tensile stress at the bottom of the slab, directly beneath the load. Corner loading produces a maximum tensile stress at the top of the slab, at a distance from the corner. This position of maximum corner stress was suggested by Westergaard1" and confirmed experimentally by Teller and Sutherland.
Research by Childs and Kapernick suggests that, for flat slabs, the free edge loading is critical. However, it is unlikely that the slab will remain flat, as drying out from the exposed surface tends to make the slab curl upwards at the perimeter. This curling does not have a significant effect upon the tensile stress in the cases of internal or edge loading, but it does considerably increase the tensile stress in the corner loading case. The corner loading is usually critical for a curled, isolated slab.