Building a model
Geometric transformations
Linear, PDelta and Corotational transforms and the vecxz vector.
A geometric transformation tells a beam how its local axes relate to global axes and whether geometric nonlinearity is included. Beams reference a transformation by ID. They live in the Transforms group.
| Type | Meaning | Carapace |
|---|---|---|
| Linear | Small displacements | Supported |
| PDelta | Includes P-Δ effects | Supported |
| Corotational | Large displacements | Supported in 2D; in 3D it runs as Linear with a warning |
vecxz in 3D
In a 3D model every transformation needs vecxz, a vector in the beam's local x–z plane. The local axes follow the OpenSees rule: y = vecxz × x, then z = x × y. Beam loads, deformed shapes and force diagrams use these axes. See Concepts.