Compression Only Supports and Springs

[Anonymous]

What is the best way to define compression only supports, with infinite rigidity?  Basically, I want a support (constraint) that I can apply to a part that acts like a pin in compression but free in tension.  For instance, a steel plate bearing on concrete with a bending moment applied to the plate.  I want the plate to not be able to push into the concrete, but still be able to pull away from it.  And i don't want to model the concrete at all.

Similarly, how can you define a compression only (or tension only) spring?  We use these in normal structural analysis quite often, say to simulate soil stiffness, but can't see how i can do it in Nastran in-cad.

Thanks.

[John_Holtz]

Hi @Anonymous

The best way to define a rigid, compression only support in In-CAD is to use the method that you do not want to use: model the other part and define separation contact. For the case of a flat object against a flat object, like your plate/column on concrete example, you can model the concrete using 1 shell element, so the size of the model is not affected very much.

For spring supports that act in compression-only (or tension-only), your options are limited by what you can do in the CAD model (since everything in In-CAD is driven by the CAD model). In a nonlinear analysis, you can define bar and beam elements using a stress-strain curve, so the stiffness in tension and compression can be different. It may not be possible or realistic to connect every node on the model's face to a bar/beam element, but you could create a rectangular array of elements would connect to some of the nodes on the face. To create the bar/beam elements, you need to create sketch lines and use them to define the bar/beam elements. (To connect the bar/beam to the solid, you can add a mesh control point to the end of each sketch line. This will force a node on the solid that is shared with the bar/beam elements.)

Note that for the tension-only case, you could use a "Connector > Cable" if you had a limited number of points to support. With Connectors, you need to attach them to a vertex on the CAD model. That is, they are defined by the endpoints of edges on the CAD geometry or sketch points.