|Photo of the month – January 2012
Aluminum rods leaning to the right
We all know of tendencies to the right or the left in the political arena, but it is perfectly possible to encounter such tendencies on the roads as well.
Joking aside, what we see here is 20 tonnes of aluminum rods loaded into stacks in such a way that they were almost certainly liable to tip.
Figure 1 [Olli Fegert]
It’s quite bad enough that the estimated value of this load comes to around €100,000. What is worse is that the load represents a hazard for other road users.
It is a fundamental principle of load securing that it is not the value of the load that commands respect, but rather firstly its weight, secondly whether it has sharp edges, and thirdly its shape, e.g. sharp ends. If it moves, it can destroy the vehicle or even slip from the loading area.
It is not only the value of the load that should act as an encouragement to the shipper and the recipient, and the carrier as well, to take extreme care. Every load must be transported safely.
But let us return to the case in hand:
The packages of aluminum rods were loaded with a gap of approximately 3 m to the end wall. This means that the center of gravity of the load is probably almost exactly at the ideal position for the trailer to handle such a heavy load, so there can be no complaints about the positioning. On the other hand, that’s the last positive thing we can say about the way in which this cargo is loaded.
Let’s start with the packaging, which, as we know, is the starting point for loading cargo safely. Four aluminum rods are resting on four pieces of squared lumber and strapped together with steel bands to form a unit. We cannot see whether the squared lumber has a groove along the bottom to accommodate the steel strapping, thus preventing it from being damaged when it is moved using forklift trucks. If the resulting load units are stacked, as is the case here, the load will be liable to tip, which means that the effort involved in securing the load will be significantly greater. This does not contribute to safe and economical loading. We shall look at a possible solution later.
There are gaps in the load both to the front and rear, and the load was secured using only tie-down lashings. In this case, the number of lashings, the friction and the pre-tensioning force would need to be so high that this type of securing would be able to handle securing to the front and rear as well through friction alone. Otherwise, the load is not secured to the front or back except by a small amount of friction.
How much securing force can be expected from the seven tie-down lashings?
Before we deal with the actual securing method, however, let us see what securing force is needed for a load such as this. The weight to be secured is approximately 20,000 kg, and the coefficient of friction µ between rough-sawn lumber and the loading area and the aluminum rods is 0.3 – and this is a generous assumption. This means that 50 % of the weight force of the load has to be used as the securing force. For a weight force of 20,000 daN for the load, this means that 10,000 daN of securing force is required.
What is the securing effect of the measures taken in this case? If we make the generous assumption that each belt was pre-tensioned to 250 daN, and if we ignore any K value, all the belts together give a pre-tensioning force of 3500 daN (7 x 250 daN x 2). The lashing angles are so small that they can be ignored. Because lashing belts achieve their effect through friction alone, this 3500 daN must be multiplied by 0.3. The resulting securing forces therefore 1050 daN. This means that 8950 daN remained to be secured. If we assume that the load is liable to tip, 6950 daN of securing force to the side is quite simply missing.
Let us use our imagination:
Let us assume that each belt was pre-tensions to 1000 daN using an extra-long lever on the tensioners, and that this 1000 daN was also able to be transmitted to the other side without loss. Then, a massive 14,000 daN of pre-tensioning force would be available. When, however, we multiply this by 0.3, we get 4200 daN, which still leaves a shortfall of 5800 daN. By now at the latest, any champion of tie-down lashings must realize that the person responsible for loading this load should either have systematically and significantly increased friction – between each individual load package -or should have chosen a different method of securing from the start.
Before we continue, another word about tie-down lashings: Even with a coefficient of friction of 0.6, they would still have been a shortfall of 4000 daN securing force. This could easily have been secured if 6667 daN of pre-tensioning force had been available.
But now, we shall turn to a solution that is much more attractive to an experienced load-securing columnist, namely direct securing. Four loop lashings, two to each side, are required. This works excellently for this type of load, which is rounded and has no sharp edges. Direct securing becomes problematic longitudinally, i.e. to the front and rear. Because the load is made up of individual packages, artificial end walls must be created using pallets and suitably strong wooden beams to allow this load to be secured longitudinally using two direct lashings in each direction. If the lashing angles are ignored, a maximum of 8000 daN can be secured in this way.
Anyone following closely will now be shouting: „There is still a shortfall to the front, at least!“ And they would be right! Even if you are enamored by the idea of direct securing, you still appreciate the advantages of good friction and make use of it as a matter of course with a load like this. We shall therefore place friction-enhancing mats between each of the individual packages in order to secure the load superbly. The minimum securing force, which we have argued for in this column for many years is guaranteed by the direct lashings, which have been well pre-tensioned. This is because these direct lashings have vertical components which ensure that the oscillations and vibrations are attenuated and the good friction of the anti-slip mats is upheld for the entire journey.
Finally, a solution to deal with the risk of tipping (see also the Photo of the Month for October 2011):):
If you load these bundles of aluminum rods in such a way that four wooden beams that are as long as the load is wide are placed laterally between every second layer, this will eliminate the risk of tipping and transform the load into a stable and solid load. This may use up some lumber, but it reduces the effort involved in securing the load and makes an immense contribution to safe loading. These beams must, of course, be integrated in the friction chain.
May we wish all those who are interested in load securing safe journeys and well secured loads throughout 2012.
Your Load Securing Team
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