Designing racks taking into account the dynamics of forklifts
The basis for the structural design of a pallet rack is the total static load of the pallets, multiplied by a safety factor of 1.5 (50% overload).
This applies in most European countries, with the exception of France, where a factor of 1.3 has been accepted (see Table 1). Pallet racks are operated by pallet trucks and forklifts (e.g., reach trucks, turret trucks). In high-bay and automated warehouses, stacker cranes and column cranes are used for this purpose. Depending on the country, taking into account the dynamic interaction between the truck and the rack, a horizontal force ranging from 0 kN to a maximum of 0.5 kN is assumed for calculations. Of course, the value of the calculated horizontal force does not correspond to the forces occurring during a collision of a truck (e.g., weighing 4000 kg and moving at a speed of 5-15 km/h) with the rack. Therefore, it is necessary to ensure working conditions for trucks between pallet racks that would maximally eliminate the possibility of a collision (Fig. 1).
Key structural elements
Due to the need for easy disassembly and the possibility of changing the position of the load-bearing beams, the uprights are made with continuous perforation. The beam is connected to the upright using a hook connector (Fig. 2). An example rack is shown in Fig. 3.
Load-bearing beam
The following types of load-bearing beams are most commonly used in pallet racks:
■ hot-rolled I-beams
■ cold-formed beams consisting of two joined C-channels (Fig. 4)
■ cold-formed Sigma-type beams (Fig. 5).
■ cold-formed beams consisting of two joined C-channels (Fig. 4)
■ cold-formed Sigma-type beams (Fig. 5).
Relatively high resistance to bending and torsion has a positive effect on the load-bearing capacity of the beams shown in Figs. 4 and 5. This concerns:
■ flexural-torsional stability of profiles made of I-beams or a composite pair of C-channels
■ first and second-order torsion for Sigma-type profiles.
■ flexural-torsional stability of profiles made of I-beams or a composite pair of C-channels
■ first and second-order torsion for Sigma-type profiles.
Manufacturers often determine the load-bearing capacity of a beam empirically (Fig. 6). Attention should be paid here to slots intended for storing three or more pallets. In such a situation, it is worth considering additional reinforcement in the horizontal plane, because in the event of incorrect pallet handling, significant horizontal forces may appear in the middle or near the middle of the beam.
Upright
The pallet rack upright is almost always produced as a cold-formed open profile with one axis of symmetry (Fig. 7). These profiles are variants of the basic “C” shape.
The complex stress distribution in the upright material, resulting from its perforation, as well as the possibility of buckling and susceptibility to deformation, mean that the upright profile must always be determined empirically (Fig. 8).
The article comes from the magazine “Logistyka 2001/1.