How to assign the gravitational load only to point masses

[giacuni]

Hi,
I'm trying to model a 2D model of a railway track but I have encountered a problem.
Basically, my model is made of:
- the ground: with 9 sublayers
- the ballast
- the sleepers
- the rail pads
- the rail
- and the train
I'm doing a dynamic analysis, in which the only load is the gravitational load and the train, which is a rigid body made of a number of masses:
the mass of the wheels, the mass of the bogie and the mass of the vehicle, is moving at a constant speed.

The problem is that doing in this way all the model will be subjected to the gravitational load and I have two problems:
1. I have unwanted settlements which lead to very high plastic deformation and then the analysis is not converging.
2. I have an unwanted result: I just want the displacements due to the wheel loads (the train load).

Does exist a way to apply the gravitational load only to the train (and then to the masses belonging to the train)?
I've tried to do that, but it does not consider the masses: and then the load is zero.
The masses are linked to reference points. For example below is the part of the wheel:

The fact is that if I assign the gravity load only to the reference points I've got the error: "A gravity region may not contain reference points".

Thank you in advance.

 

[Mustaine3]

I think it is not supported in A/CAE, since gravity has to be applied on elements. The point mass will become a mass element when you write out the .inp. So there you can add the gravity to the mass element only. I've tested it on an simple example and it worked.