The majority of slab designs for warehouses and other heavily loaded areas are either adopted from pavement design or arbitrarily based on the designer's past experience. Westergaard provides a sound basis for slab design, although his original theoretical paper has been modified as a result of experimental studies by Teller and Sutherland and indeed by Westergaard himself.
These pavement designs deal solely with wheel loading, but the problem of designing floors on the ground is one of more complex loading systems. There are three basic types of loading to be considered: wheel loading due to fork-lift trucks, trolleys, etc.; uniform loading due to materials, storage bins and other items placed directly on the floor; and rack loading due to the legs of racking systems used to store materials off the floor.
Existing design methods are proving inadequate for two main reasons. The first is the introduction into warehouses of racking systems which impose a grid of static loads over small areas of the floor. These loads tend to be larger and to be applied over smaller areas than the wheel loads; consequently, they are usually the critical loads on the floor. The second reason is the increase in the magnitude of other loads being imposed upon floors. Any method of designing floors on ground should take into account the characteristics of the subgrade and sub-base, the grade of concrete, the type of loading, the number of repetitions of loading, the area of loading on the floor, the cumulative effect of more than one load or type of load and the efficiency of the load-transfer devices. The floor is assumed to be a plain concrete section in which the mesh reinforcement merely controls any cracking, should it occur, and determines the spacing of the transverse joints.
In the consideration of floor design, the question of economics is of paramount importance. It may be possible to construct a floor relatively cheaply, but it might need a great deal of maintenance and repair at a later date. Consequently, the economic considerations should cover the whole design life of the floor.
It is proposed that the design should be based on the thickness design principle, whereby an adequate thickness of floor is constructed to withstand the induced tensile stresses. For any given set of loading conditions, the necessary thickness of floor will depend upon the grade of concrete used. The optimum design is the most economic combination of floor thickness and grade of concrete.

Modulus of subgrade reaction

Concrete parameters

Combinations of loading

Load safety factors

Position of loading

Load transfer between slabs

Stress due to rack or wheel loading

Stress due to uniform loading

Stress due to adjacent loads

Combinations of loading