There are two combinations of loading to consider.
(1) Wheel and rack loading. Usually two rows of racks are placed 'back to back'; therefore the two rear legs of each row impose loads on the floor in close proximity to each other. This 'double rack leg' usually controls the design, because it imposes a large load over a small area in comparison with the wheel load. If the racks are placed back to back, the two rear legs should be considered as standing on one base plate equal in area to the two individual base plates.
The radial stress from other loads at the edge (whether rack or wheel) will increase the corner stress and decrease the edge stress when displaced more than 07 from the position of critical stress; the reverse is true for displacements less than 0-7. If the edge position is critical, the tangential stress from any internal loads that are perpendicular to the edge at the critical position will increase the edge stress, providing they are displaced less than 2-5 from the edge.
If the racking system is placed internally on the slab, i.e. at least half a metre from any joint, there are three possible positions of critical stress. These are beneath the wheel at the edge. In the first case, the wheel at the edge, the edge stress is increased by the radial stress from the second wheel at the edge if it is displaced less than 0-7. The edge stress is also increased by the tangential stress from all the internally placed double rack legs which are displaced less than 2-5 from the edge, on a line perpendicular to the edge, at the critical position. In the second case, owing to the wheel at the corner, the critical stress will be increased by the second wheel at the edge when it is displaced more than 0-7 from the position of critical stress. In the third case, beneath the double rack leg, the critical stress will be increased by the tangential stress from the adjacent double rack legs up to a displacement of 2-5 and also by the radial stress from the other legs in a line perpendicular to the double legs through the critical load, and displaced less than 1-0. The 'mezzanine' type of racking system imposes a grid of loads equally spaced on the slab. In this type of racking, the inside legs of the grid impose twice or four times the load of the legs at the perimeter of the grid. The base plates of the legs are usually all the same size; consequently the inside legs control the design and are analysed in the same manner as the double legs in the back-to-back situation.
(2) Wheel and uniform loading. The wheel loading will probably control the design. The corner and edge loading cases should both be checked. The second wheel at the edge will increase the edge stress when displaced less than 0-7 and increase the corner stress when displaced more than 0- 7 from the position of critical stress. In the edge case, if the second wheel is displaced more than 0-7, it should be considered internally; the internal tangential stress will then increase the edge stress. Finally the uniform load should be checked to ensure it does not control the design.