Weight distribution of heavy loads in containers

By Christian Bohlken, Master Mariner and Marine Surveyor, Battermann & Tillery Global Marine GmbH, IUMI Professional Partner,

Standard container cargo does not usually require special provisions with regard to load distribution. However, detailed calculations of the expected transport strains and effects on the container structure are necessary for, among others, heavy units such as steel coils or granite blocks.

The container payload is a first indicator of whether load distribution is necessary or not. Generally, load distribution is required if the maximum permissible line load (container floor’s maximum load per metre) is exceeded. This is achieved by homogenous load distribution across the full width of the container (area load) in reference to the International Convention for Safe Containers (CSC) Code (Annex II). The assessment of the expected line load is generally based on the following parameters:

  • Payload
  • Loadable length
  • Cargo weight
  • Length of cargo contact surface

In case the permissible line load is exceeded, reasonable measures must be taken. The major goal of any action is to distribute the weight to as many container cross members as necessary in order to avoid excessive bending moments. Thus, the first layer of any bedding (squared timber sections or HEB steel beams) should be distributed in a longitudinal direction. Transverse beams might have to be placed on top in order to distribute the load to the outermost longitudinal beams. In any case, the maximum permissible free length (additional length of beams able to carry a load, e.g. 20 cm x 20 cm timber has a free length of 100 cm) must not be exceeded.

In cases where the properties of the cargo do not allow for the installation of bedding across the full width of the container, bending moments will increase for the container’s cross members. Thus, the strains are to be distributed over a larger number of cross members and, consequently, the bedding is to be extended longitudinally.

In many cases, the construction of appropriately dimensioned skids has proven useful. The benefits are clear: handling is possible even without special equipment (push and pull) and skids can be reused up to three or four times. Furthermore, those skids may already provide cargo securing by means of bolted or welded beams, fitted directly against the cargo.