Axle Weight Distribution 2

[VPbris]

Hi

I'd like to ask you for some inputs on this problem I'm having.

I've done some axle weight load distribution calculation before for some trucks with two axles. However this time I've been asked to perform it for a tanker trailer truck, which is a tractor unit (1 steer axle at front and two driving axles in tandem at the rear) and the semi trailer which has a triple axle in tandem at the rear.

I have all the weights and the location of all centres of gravity of the semi trailer unit and the supplier information of the tractor unit loads on both front and rear axles. However, differently from the past calculations I've made this one is an hyperstactic problem as I have three reaction forces. The method for solving for the hyperstactic situation is rather complicated due to geometry issues and my guess is that there is some rule of thumb or simplification to solve this.

Does anyone have experience with this?

Kind Regards

 

[BrianPetersen]

Look at the way the multi-axle suspension is designed.

Frequently the two axles will be connected with a lever that works like a "teeter-totter" and whose purpose is to equalize the loading between the two axles. (Common on leaf-spring and rubber-spring designs)

Frequently the two (or more) axles will use air-bag suspension with the pressure equalized between the two (or more) axles in some way.

 

[VPbris]

Hi BrianPetersen,

Thank you for your reply! Just took a look on what you said. However I think I may have not expressed myself clearly. My problem is that the group (tractor unit + semi trailer) has 3 suspensions, two on the tractor unit (front and rear) and one on the semi trailer, Hence a Hyperstatic problem.

I'm inclined to neglect the effects on the front suspension of the tractor unit and consider only the suspension under the fifth wheel and the semi-trailer for calculations. What do you think?

 

[NormPeterson]

You should be able to consider the "fifth wheel" where the front of the trailer is connected to the tractor as a pin connection, as the 5th wheel should not be capable of resisting moments about the axis of its own pivot. That will allow you to separate the problem somewhat, into the trailer on a pin support up front and the tandem axle set, with a point load from the trailer acting on the 5th wheel's pivot divided between the steer axle and the tandem drive axle set.

You will most likely have to consider the effects of fluid sloshing on the load distribution.


Norm

 

[truckandbus]

SAF Holland has some good technical literature on trailer load distribution through the 5th wheel location

 

[VPbris]

Hi,

Thank you for your inputs, I gues that separating the problem is the best way to go, as you proposed Norm.
I made a simple sketch on my understanding of what you said, can you give it a look to confirm?

truckandbus
Thanks for the tip! I took a look on google but found nothing, is this material available for free somewhere? If so, could you point me towards it?

Regards

 

[truckandbus]

google "weight distribution trailer saf Holland" and you should see a result for 'about fifth wheels - SAF Benelux' that links to a PDF of 5th wheel facts four or five results in