How to constrain some nodes immovable in one direction(only negative)?

[alin09]

I analyze a structure which consist a beam on the ground. I would like to constrain the beam in that way that it can be movable in positive Z direction but immovable in negative Z direction. (Z is vertical to the ground) How do I do that?

From Patran displacment constraint, I can only make it zero.

Thanks for any input!

 

[alin09]

Thanks a lot, everyone!

I solved a simple beam problem, which has some part on the ground. From Utilities->Applications->Linear Gaps, I used Gap to Ground option. The result shows reasonable. The beam elements contacting the ground can deform above the ground but not into the ground.

 

[Onda]

Ok. Now if you look for a stiffness in the ground direction you can connect the linear gap to a grid point connected to a CELAS or a CBUSH. the other grid point of the elastic element should be connected to ground.
In this way in compressive direction you have the elasticity of the Celas (Cbush). If the load is inverted the Linear gap open.

Onda

 

[alin09]

Thanks, onda.