🎢 Elements
Elements are the pieces the model is actually made of. Alpaca4d turns Rhino geometry — curves, meshes — into OpenSees finite elements, and adds the boundary conditions that hold them up.
Components in this tab
| Component | Nickname | Builds |
|---|---|---|
| ForceBeamColumn | ForceBeamColumn | A force-based beam–column element from a curve. Switch the unit to WithHinges for concentrated plasticity at the ends. |
| ASD Shell | ASDQ4/ASDT3 | Shell elements from the faces of a mesh — ASDShellQ4 for quads, ASDShellT3 for triangles. |
| SSP Brick | SSP Brick | A stabilized single-point hexahedral solid from an 8-vertex mesh. |
| Ten Node Tetrahedron | Ten Node Tetrahedron | A quadratic tetrahedral solid from a 4-vertex mesh, with a node added at the middle of each edge. Needs an OpenSees newer than 3.8.0. |
| Spring Link | Spring Link | A spring between two nodes that are apart, with its own stiffness in each local direction. |
| Support | Support | A nodal restraint, from a point or from a plane for skewed supports: Rigid, or through springs, Elastic or Compression Only. |
| Hinge Release | Hinge Release | A release condition consumed by the WithHinges beam unit. |
Choosing an element
| Geometry | Use |
|---|---|
| One dimension much longer than the other two — frames, columns, braces, trusses | ForceBeamColumn |
| Yielding expected only at member ends | ForceBeamColumn, unit WithHinges |
| One dimension much smaller than the other two — slabs, walls, plates, roofs, tanks | ASD Shell |
| Fully volumetric, and meshable as hexahedra | SSP Brick |
| Fully volumetric, and only meshable as tetrahedra | Ten Node Tetrahedron |
| A connection with its own stiffness between two parts — a bearing, a bolt, an interlayer | Spring Link |
Most models combine several: beams for the frame, shells for slabs and walls, solids for the local 3D regions that need them.
Node matching
Elements are not wired to each other explicitly. Assemble collects every element endpoint, shell vertex and solid corner, and merges the ones that fall within its Tolerance into a single node. Two members share a node when their geometry meets within that distance — so if a connection does not transfer force, check the tolerance before anything else.