The following assumed loads (transport, handling and storage loads) presuppose the normal loads encountered during transport, handling and storage and form the basis for designing and constructing normal fit-for-purpose transport packaging.

If unusual loads are to be expected, these must be explicitly identified and taken into account when dimensioning the packaging measures.

Thus, for instance, a distinction must be made as to whether a box is to be stowed as normal general cargo in the hold of an ocean-going vessel with other cargo stacked on top of it, or whether the box is to be transported in a container/flatrack or even at a position in the hold where it is subject to no loads at all. In the first of these cases, considerable stacking forces can be expected, whereas these are negligible in the other two cases, provided that it can be guaranteed that no other cargo will be stacked on top of the package during the course of downstream logistics processes, such as subsequent storage. Irrespective of these considerations, a box must always be constructed in such a way that the forces generated by load-securing measures can be absorbed without difficulty.

Three fundamentally different types of loads are distinguished:

• Mechanical loads
  
  Mechanical loads are subdivided into:
  - Static loads
  - Dynamic loads
  
  
• Climatic loads
  
  
• Biotic loads (biotic - deriving from living organisms)

1.2  Static mechanical loads

Static mechanical loads encountered during shipping are always storage loads or loads that occur on the loading areas of motionless means of transport. The most typical type of static load is pressure (stacking crush pressure) resulting, for instance, from packages being stacked in a warehouse, a container, a truck or in the hold of a general cargo vessel. Pressure loads such as these act on the surfaces of the lids of the packages subjected to the loads and must be dissipated to the loading surface through the sides and bottoms of the packages.

To achieve the best possible load-bearing capacity with wooden packaging and to prevent the stacked packages from tipping, they must always be placed on a flat, horizontal surface and the load must be evenly distributed across the surfaces of the lids of the packages.

In the case of stacked boxes, an evenly distributed vertical, static load of

F_pressure = 10 kN/m²    [1 t/m²]

is assumed to be acting on the surfaces of the lids.

1.3  Dynamic mechanical loads

Dynamic mechanical loads result from the movements of the means of transport and during handling. Dynamic loads are always given as a multiple of the acceleration of gravity. The acceleration of gravity is constant at 9.81 (∼10) m/s² = 1 g.

Dynamic loads cause packages to slip on loading areas, change the pressure loads on the lids, cause packaged goods to break free within the packages and distort the packages.

Static stacking loads are overlaid by dynamic components during transport and handling, which can result in the pressure load being increased or decreased. Vertical acceleration forces that occur during transport and handling are responsible for this. See Table 1.

If, for instance, a static load on the lid of 1 t/m² is overlaid by a dynamic vertical component of ± 0.8 g (see the Guidelines for Packing of Cargo Transport Units), this means that the load on the lid varies between 0.2 and 1.8 t/m².

For this reason, a load on the lid of 1.8 t/m² is always assumed when calculating the strength of boxes that will have packages stacked on them.

When loads are applied to the lids of boxes, care must be taken to ensure that such loads are distributed evenly. Suitable measures such as the use of wooden dunnage must be adopted to convert point loads and line loads to area loads.

If higher or lower stacking crush pressures are to be expected, the static stacking load is to be calculated using the following formula, where the weight of the load stacked above the package must be known:

where:

Sample calculation: Assumptions  Height of package = 3 m  Height of hold = 8 m  Mass per unit volume of the load stacked above the package = 0.2 t/m³

In maritime transport, different hold heights result in higher stacking loads. This is less likely with land transport and when transporting containers.

The dynamic loads for the various means of transport are listed in various directives and standards:

VDI 2700	For land transport by truck
VDI 2700 / 7	For intermodal transport
Guidelines for Packing of Cargo Transport Units	For intermodal road-rail-sea transport operations
RID