The ISO 1161, ISO 1496 standards define the container design specifications. The shipping container is in fact a device for the intermodal transport of goods without having to be unload and reloaded. To ensure the possibility of transshipment from a road vehicle carrying container to a railway wagon, or to be stacked on a cargo ship, the container must comply with specific dimensional and interface requirements.
Containers are equipped with twistlocks, which allow the container to be quickly and safely connected to the vehicle. The ISO 1161 standard, “Series 1 freight containers – Corner and intermediate fittings – Specifications”, establishes the basic dimensions and the functionality and strength requirements for container twist locks conforming to ISO 1496.
Twistlocks can be of various types, retractable or non-retractable, manually or automatically operated. The requirements regarding the material and the mechanical resistance characteristics are then established.
The ISO 1496 standard, “General cargo containers for general purpose”, establishes the construction and performance requirements of containers. For containers intended for general use, called “general purpose freight containers”, the standard establishes the following structural strength for the walls:
Front wall and door: they shall be capable of withstand 40% of the permitted payload “P”, if the load is uniformly distributed on the wall
Side walls: they shall be capable of withstand 60% of the permitted payload “P”, if the load is uniformly distributed on the wall
with P = (gross mass – tare) x 9.81
For example, a container with a payload of 30.480 kg guarantees the following resistance values:
Front wall and door: Resistance = 30.480 x 9.81 x 0,4 = 119.603 N = 11.960 daN
Side walls: Resistance = 30.480 x 9.81 x 0,6 = 179.405 N = 17.940 daN
If the cargo is secured by general blocking using the container walls, it must be checked that the resistance values obtained above are higher than the required blocking capacity calculated according to the EN 12195-1 standard. Otherwise, auxiliary securing devices shall be used, for example by resorting to the use of web lashings to secure the load by lashing.