September 18, 2023

Principles of loading and weight distribution in a container

All this damage could have been avoided if the packers/loaders had known the basic rules of weight distribution in a container.

What are the risks and consequences of improper loading?

In many cases, packers minimize container loading principles.

In the course of our many claims appraisals, we have observed frequent tipping of containers during road transport, following the uncoupling of a semi-trailer or during handling.

Examples of appraisals carried out:

  • Container tipping after uncoupling at a logistics company. The reel loading plan is directly to blame.
  • Container containing dangerous goods tips over when trailer is uncoupled. 87% of the cargo’s mass was loaded over 50% of the container’s length.
  • Tipping the container onto the road in a straight line at low speed! Fortunately, there were no injuries, but the goods and container suffered considerable damage.

All this damage could have been avoided if the packers/loaders had known the basic rules of weight distribution in a container.

When loaders don’t have the basic knowledge, the heaviest and/or highest loads are often placed first from the front wall, finishing with the lightest loads. When loads are not complete, there is often a gap in the doors.

The “staircase” loading method is also used (especially for loads that are not palletized). While this method (placing the heaviest loads from the front) may make sense from the point of view of maximum acceleration in road transport (emergency braking), it is absolutely unsatisfactory from the point of view of proper weight distribution.

In addition, the front wall should be positioned in the direction of travel, but a container can be loaded in both directions.

What are the loading regulations for containers?

IMDG Code (stuffing certificate)

According to chapter 5.4.2.1, the packer must undertake to load the goods appropriately. Thus, by signing the stuffing certificate, he certifies that the mass of the cargo has been properly distributed in the container.

For further details, the IMDG Code refers readers to the CTU Code (cargo subjection requirements “as set out in the CTU Code”).

– Non-active carbon blacks of mineral origin

– A shipment of coal which has passed the spontaneous heating test in accordance with the Manual of Tests and Criteria (see 33.4.3.3), and which is accompanied by the relevant certificate issued by a laboratory recognized by the competent authority, attesting that trained personnel from the laboratory in question have correctly taken the sample from the product to be loaded and that the test has been properly and successfully passed.

– Steam-activated coals.

Load distribution according to CTU code (3).

Chapter 3 covers general requirements. It includes a paragraph on planning (3.2):

“Develop a loading plan if deemed necessary.

Do not exceed the permissible payload of the machine (…)”.

Loading rules are also covered (3.3):

“Distribute heavy cargo appropriately over the floor surface”.

Load the cargo, ensuring that its center of gravity is correctly positioned in the transport vehicle”.

The loader is responsible for ensuring that the cargo is correctly distributed in the transport vehicle and adequately supported if necessary.

Loading responsibilities in the CTU Code - 4.2.3

In his chapter on the chain of responsibility and information, we find the following sentences:

“The packer is responsible for ensuring that the cargo is correctly distributed in the transport vehicle and suitably supported if necessary.

In view of the above, we note the responsibility of the empoteur. The planning stage of the loading plan prior to execution is therefore essential, and should never be neglected. However, it has to be said that this preliminary study is rarely addressed.

What are the principles of container loading?

Appendix 7 of the CTU code (loading and subjection in transport equipment) provides essential guidelines for determining the correct weight distribution in a container:

“Containers, platform containers and platforms are designed in accordance with ISO standards, in particular in such a way that the permissible payload P, if evenly distributed over the entire loading surface, can be safely transferred to the four corner posts under all transport conditions. If the payload is not evenly distributed over the loading surface, the limitations applicable to concentrated loads should be taken into account.

If containers, including platform containers and flatbeds, are to be lifted and handled horizontally during transport, the cargo should be arranged and secured in the container in such a way that its center of gravity is near the middle of the container’s length and middle of its width. In general, the cargo’s center of gravity should not be off-center by more than ± 5%. The following empirical value can be used: 60% of the total cargo mass over 50% of the container length. An eccentric position of up to ± 10% may be accepted in certain circumstances, as modern container handling spreaders are capable of adjusting to such an eccentric position.”

To sum up, it is necessary to place the load’s center of gravity in the middle of the container (at the center of the loading surface), with the small tolerance shown above.

In the case of the above-mentioned tilts, the center of gravity of the entire load far exceeded this tolerance, yet we continue to observe these incorrect placements on a regular basis during our numerous visits to the emptier sites.

What are the steps and methods involved in loading a container correctly?

To ensure proper weight distribution. We recommend several methods.

First of all, check the maximum payload of the transport vehicle/container, so as not to overload the equipment. The total weight of the merchandise must never exceed this value.

The PAYLOAD is visible on the CSC plate and on the right-hand door of the container. This is the total gross weight minus the tare weight of the equipment.

1) First method (simple)

To load a container correctly, we recommend the following steps:

  • Identify the weight of each handling unit (refer to packing list, load/pallet labelling, etc.).
  • Check the number of handling units / pallets (if applicable) on the floor
  • If possible, unload any loads/pallets that can be unloaded to take up as much floor space as possible (this reduces loading voids and simplifies load securing).
  • Identify the heaviest loads in the batch to be loaded (if there are significant gaps between loads, make sure they are placed in the center of the container, or find an acceptable configuration).
  • Adapt and center the side loading surface (right/left).
  • Finally, we recommend the use of a loading plan (in paper or computerized format) to group handling units by zone according to the chosen configuration. The loader places the loads in such a way as not to exceed the empirical value given in the CTU code: 60% of the cargo weight over 50% of the length.

2) Second method

The second method is more technical, requiring the exact positioning of each handling unit in the loading enclosure to be recorded.

Appendix 4 of the CTU code provides a simple calculation method for determining the longitudinal location of the cargo’s center of gravity. The formula below allows us to determine the distance d from the front part. The distance and mass of each load must be known.

In general, this method is not practical / fast enough to be used on site, but it should be implemented for mass distribution planning when deemed necessary. If method 1 does not allow you to accurately determine the right distribution due to the complexity of the load, you will need to use the advanced calculation.

As part of preliminary studies or post-loss appraisals, experts assess the conformity of the loading plan with a calculation of this type.

Conclusions

We’ve covered some of the basic loading rules. The case of concentrated loads has not been addressed (specific methods need to be applied).

Our work in the field has highlighted a constant lack of knowledge about the correct distribution of weight in a transport vehicle, and more particularly inside a container. The consequences can be disastrous for the entire transport chain.

The impossibility of checking the inside of a sealed container no longer makes it possible to correct a problem attributable to stuffing. These problems are usually discovered too late, during transport or handling.

We strongly recommend that loading sites implement a strict three-stage control system (planning / execution / supervision), and that all those involved renew or acquire the necessary knowledge.

Take a look at our “CTU Code” training course to find out more.