RBE2 versus RBE3 in Nastran
When to use RBE2 (rigid) versus RBE3 (distributing) in Nastran — the difference in stiffness, load transfer and common mistakes.
Engineering Task
Choosing between RBE2 and RBE3 elements when connecting a reference point to a surface or set of nodes in Nastran.
RBE2 versus RBE3
The most common Nastran modelling mistake is using RBE2 where RBE3 is appropriate. An RBE2 on a thin panel makes the panel locally rigid, changing the load path and understimating local stress.
| Aspect | RBE2 | RBE3 |
|---|---|---|
| Stiffness | Rigid — infinite stiffness | Distributing — no stiffness added |
| Load transfer | Independent nodes follow dependent node exactly | Dependent node follows weighted average of independent nodes |
| Effect on model | Over-stiffens the connected region | Does not over-stiffen |
| When to use | Truly rigid connection (e.g. rigid bracket) | Distributing load from RP to surface (e.g. bearing load) |
| When to avoid | Flexible surfaces — local stress wrong | When the connection is actually rigid |
Key Settings
- RBE2: dependent nodes follow the independent node — use for truly rigid connections
- RBE3: independent nodes are weighted — use for distributing loads or constraints
- Check the dependent/independent node assignment — reversing them changes the behaviour completely
- Use UM cards to control which DOF are constrained