Hypothetical question guys.
A standard length (16.5m) artic on 6 axles. Assume the load is 26 pallets all evenly distributed. Doesn’t matter if fridge flatbed curtains etc. Fully loaded to 44 tonnes. What sort weights (approximately) would be imposed on each axle?
Now take away the unit. What weight would be on the landing legs? And would there be more weight on the trailer bogie without the unit or less?
When you say “trailer bogie” you`re meaning the 3 trailer axles?
Seems to me that the weight imposed on the landing legs would be exactly that which would be imposed on the unit. And that the weight on the trailer axles would stay the same, independent of whether the rest of the weight went through the legs or through the rubbing plate.
Hold on 2nd thoughts…
OK, I was wrong.
I’d say the weight on the legs would be more than on the unit as the legs are further back than the 5th wheel.
Imagine the legs as a trestle exactly where the rubbing plate/pin is: that will give the same weight through the legs, so also the same weight through the wheels.
Now imagine the legs as near the wheels as possible without a nose dive: (sort of half way point of the chassis) The weight through the legs will now be almost the total weight of the trailer. (Take a moment about the legs, clockwise and anti-clockwise moments must be equal in a system at rest, the weight in front of the legs must equal the weight behind the legs). Proof ? Imagine moving the legs even nearer the wheels. . now the wheels become airborne as the trailer nose dives, and ALL the weight is on the legs.
So with normal landing legs there will be less weight on the wheels with the unit taken away.
Edit, as DJC says more weight on legs than on the unit.
There is a moderate amount of maths needed to determine the loads at various points on the trailer. A trailer is essentially a beam, like a bridge or a joist in your house. Bridges and joists are usually supported at the two ends, but a trailer is supported at points further in.
If the load is uniformly distributed, it can be considered to act at a point in the middle of the trailer - the loads at the supports (legs and wheels) would be the same whether the pallets were spread out, or piled up in the middle (assuming it didn’t break the trailer). A 20,000kg load would impose a pressure at either end of 10,000kg and this would be the same, if both supports were moved closer together but remaining equally spaced. The problems start when one support is nearer the centre than the other.
If one support (the rear axles) stays fixed, and the other is moved closer to the centre, more of the load will be imposed on the nearer support and less on the one further away. Taken to the extreme, if it was moved right under the centre, it would take 100% of the load. Since the load is always the same, it follows that if one support takes more, the other must take less, so the nearer the legs are to the centre of the load (plus the trailer itself) the more weight they carry and the less is imposed on the rear wheels. Because the legs have to be closer to the centre of the load than the kingpin, it follows (as said above) that they will carry a greater percentage of it.
There is another important factor: The load on the front legs is concentrated over a few square centimetres, while the load at the back is spread over six large wheels. This explains why it is fairly common for the legs to sink into the ground.