Media Coverage
Feb 2010
Axle Weight
Everyone in the trucking world knows that the restrictions on axle weight are being more and more tightly enforced and that there are even proposals to reduce maximum axle weights to try and reduce the damage to the country’s roads. But how can a trucker know what the weight is on each axle? Certainly the most direct method is simply to use a weighbridge capable of weighing each axle separately, but in most cases such a facility is not available and even if it is, if the weight is exceeded on an axle the only solution is a time consuming and costly re-packing of the vehicle followed by another iteration on the weighbridge which may or may not be successful.
It is much more desirable to be able to predict the axle mass based on the sum of the vehicle mass and the load mass. Unfortunately this is not so easy to do as it depends on the stiffness of the vehicle bed, the distribution of the loads and the number and position of the axles on the trailer. All of these can and have been put into mathematical models that are quite successful at predicting the axle loads. These models are included in quite expensive software but one very nice, free; internet version is available at www.broshuis.nl (from the home page select the SERVICE menu item, under which is the AXLE LOAD PROGRAM). This interactive web site is supplied by a Dutch trailer building company. It has a variety of trailer configurations and is quite easy to use with a simple to follow help file. The picture below is a screen dump taken from the web site. The only complication with using the system is that, to get a more accurate estimate of the axle and fifth wheel loads, you need to calculate the centre of gravity of the load.
This can be done quite easily using a simple Excel spreadsheet. In the example below I have assumed an 18 pallet trailer where each pallet weighs roughly 1 ton. In this example the pallets are distributed randomly on the truck and we simple want to find the centre of gravity of the load. The first thing we need is the distance (along the main axis of the trailer) from the king pin to the centre of each pallet. I have put these in as starting at 1.5m and increasing by 1m for each pallet. You would have to measure these for each trailer. Then you simply multiply the mass at each distance by the distance and take the sum. The mass midpoint or centre of gravity will be at the weighted distance divided by the total weight as shown in Excel screenshot. You can simple enter these figures into the application at Broshuis to get the axle mass estimates.
Next month, I will continue on this theme to discuss how you can find a pallet configuration that does not exceed and axle weight descriptions given a particular set of pallet weights.If you have any comments or questions, please e-mail me at david.lubinsky@opsi.co.za.
