TRANSPORTING ROUNDWOOD: HOW DO YOU SECURE LOGS?
Bron: DOLL Fahrzeugbau GmbH
Roundwood is a type of cargo that you rarely come across in the Netherlands and transporting it requires special skills. Roundwood is usually transported using a body that is lightweight yet robust enough to take the load capacity. While shortwood (shorter than 2.5 metres) can be transported crosswise or in the direction of travel of the vehicle, longer timber should only be transported lengthwise. But how do you secure roundwood safely? And what must you always consider? Our load securing specialist Niels Bouwmeester provides answers to these questions in his new blog.
HOW DO YOU SECURE ROUNDWOOD?
Roundwood demands a unique method of load securing: there are various methods that can be used depending on the way in which the logs or other roundwood are loaded.
FRICTION BETWEEN LOGS
Let’s start with the friction between logs. This is extremely variable and dependent on the type of wood, weather conditions and the formation of the logs. In addition, trees are not generally ‘clean’ but rather smeared with dirt such as earth, leaves and sawdust.
The friction between logs is also different depending on whether they are with or without bark. You might think that the coefficient of friction would be higher between logs with the bark still on, however test centres have not established any regularities between logs and the corresponding friction coefficients.
TRANSPORTING ROUNDWOOD IN CONTAINERS
Under 7.2.9. of the CTU code, it is stated that standard containers are not suitable for long, heavy and irregular loads such as roundwood. The side walls of containers are not designed to withstand the acceleration forces of this type of cargo which is long, heavy and irregular and can cause damage in the form of bulging.
In Germany, there is a lack of clarity regarding this and for that reason, various test organisations have carried out dynamic road tests based on DIN EN 12642. Loading advice providing guidance on how to load longwood in a container safely is due to be published soon. That advice has been drawn up as a result of collaboration between all stakeholder organisations including the police, the Federal Office of Public Health, shippers, forwarders, associations and ministers. The CTU will not be adapted in line with this for the time being.
The best way to load shortwood logs is transversely but because transverse loading can lead to heavy load movements on bends or sideways movements among the logs, you should always use a trailer with side panels. To do this, use stanchions to create sections of 2.5 metres across the width of the vehicle (see the figure below). Secure the logs with at least 2 lashings per section so that the logs are held down properly. You can also use certified nets for this purpose although using nets with logs can be difficult. Securing the load then takes a little more effort.
Tests have shown that cross-lashing from front to rear is not a suitable load securing method to use when securing short roundwood. Another option for shortwood is to load it in the direction of travel but only if you also take account of the form-fitting conditions as described above.
TRANSPORTING LONGWOOD SAFELY
When transporting longwood, it is the length of the logs that presents the greatest challenge. That length problem can be solved by using normal trailers with a longer overhang. You can also load logs on two rotating bodies fitted with stanchions.
This is normally done using a dolly which is connected to the towing vehicle via the load. Dollies have a steering axle which is mechanically or hydraulically controlled by the angle between the load and the dolly. The dolly has its own brake system.
Constructions of this type are constructed by specialist coachbuilders. You also have many different variations to choose from. There are even vehicles with strips on the loading floor for reducing movement. With these, the first layer of logs ‘eat’ into the strips as it were.
HOW DO YOU SECURE LONG LOGS?
Long logs are always loaded from the outside in, securing the outside against at least two stanchions. Wood that is shorter than the distance between two stanchions should always be placed in the middle of the load. Because logs taper in terms of thickness, I advise you to stack them top to tail which will give you an evenly distributed load.
If you secure your load of timber by means of form-fitting, you will need at least one lashing device per stack of wood. If there is no form-fitting in the direction of travel (in the case of vehicles without a bulkhead, for example), you will need at least two ties per stack in order to increase friction. However, you always calculate the exact number of lashing straps based on load mass, load type, friction and preload forces.
USE CERTIFIED STANCHIONS
Manufacturers often have stanchions tested and certified by reputable institutions based on the principles of physics. However unfortunately, there are still plenty of manufacturers who do not test their stanchions at all. Not only that, I haven’t found one single stanchion manufacturer and/or total concept constructor in Europe who has certified his stanchions based on Eumos 40511.
If stanchions and stanchion tubes comply with the Eumos 40511 standard, a ‘number’ will be punched into the stanchions and the vehicle will be given a sticker bearing the same ‘number’ as the stanchions. In addition, the owner will be given a certificate and VIN code so that during an inspection, he can prove that the stanchions are certified and comply with the Eumos 40511 standard.
REFERENCE BLOCKING CAPACITY OF STANCHIONS
The RBC (Reference Blocking Capacity) of stanchions varies from 250 to 10000 daN. The RBC is very difficult to estimate as it depends on the strength of the material, the dimensions of the cross-section and the strength of the mounting. Therefore the vehicle manufacturer must always certify the RBC and the stanchions may only be used on the vehicles for which they were designed and tested.
The RBC of certified stanchions for transporting logs (not a Eumos 40511 certificate) varies between 5000 and 9000 daN depending on the type of material chosen. So if you are purchasing stanchions, make sure that they come with a certificate.
Stanchions for transporting logs are available in aluminium or steel but solid stanchions can also be manufactured on request. Stanchions are available in a conical or telescopic design. In the case of telescopic stanchions, the basic height when retracted is approximately 2.2 metres which can be steplessly adjusted up to a height of approximately 3 metres. The angle of a stanchion can also be set inwards by a number of degrees.
Make sure that the stanchions protrude at least 20 centimetres above the centre point of the highest log against the stanchion so that the logs cannot topple over the stanchion. See the figure below.
LOADING AND LASHING DOWN WHEN TRANSPORTING ROUNDWOOD
There are a number of special characteristics to be taken into account when transporting roundwood because a load of logs will not act as one. Because each log is unique, numerous spaces can often be created between the logs during loading.
When loading logs, make sure that the load is convex so that the lashing strap or cable comes into contact with each log as much as possible (see the figure below). This will have a beneficial effect on the downward pressure created. Make sure that the highest point is no more than half the diameter of a log above the stanchion. If the top of the load is flatter, the downward pressure created will be significantly lower.
In order to ensure that the preload forces are distributed as evenly as possible throughout the load of timber, apply the tensioning elements such as ratchets by alternating between the left-hand side and the right-hand side. Flexible lashing strap guards ensure that the lashing strap is not twisted and prevent it from being damaged. Only use ergonomic ratchets with a higher preload force, not standard ratchets. The only way to measure the preload force that is actually left is by using a preload gauge.
HOLLOW SPACE WHEN LOADING LOGS
Because of the different thicknesses of logs, hollow spaces are created not only in the top layer but also between the logs stacked in the middle. That means that a thinner log in the middle may not produce sufficient downward pressure or that a tunnel or bridge effect might be created in the load. Try to prevent this as much as possible. The only indicators of individual log movements which occur are the effect mentioned above and as shown below.
The statement that the logs in the middle are held down by the downward pressure created, by means of a tensioning device or by the weight of the logs on top of them is therefore definitely an assumption. In particular, the lengthwise gaps in the load can have huge consequences in the event of an emergency stop. Hollow spaces can occur anywhere between the logs, even when they are loaded against the stanchions.
TOOLS FOR SECURING ROUNDWOOD
A tension pulley is a handy tool for securing roundwood which is mounted on the vehicle and mechanically or pneumatically operated. The benefit of pneumatic tension pulleys is that they adjust the tension of the lashing strap automatically while you are driving along. The preload force of a tension pulley will vary from one manufacturer to the next. However it is handy to use a self-tensioning element, even though such systems are more expensive to buy.
The vehicle must always be equipped with suitable lashing eyes or frame constructions. Always check the load and the lashing devices before leaving a forest road and joining the public highway.
Source: Loadinfo actuele informatie over ladingzekering
The vehicle must always be loaded in accordance with a load distribution plan. As described above, the correct loading method will depend on the size and weight of the log and where it can be placed.
Take extra measures when transporting wood in wintry conditions. A load covered with snow or ice means even greater risks because then there is no longer any contact between the bark on the logs.
Placing a loading crane on top of the load is not a way of securing it either.