> For the complete documentation index, see [llms.txt](https://alpaca4d.gitbook.io/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://alpaca4d.gitbook.io/docs/basics/elements.md).

# 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](/docs/basics/elements/force-beam-column.md)           | `ForceBeamColumn`       | A force-based beam–column element from a curve. Switch the unit to [WithHinges](/docs/basics/elements/beam-with-hinges.md) for concentrated plasticity at the ends. |
| [ASD Shell](/docs/basics/elements/shell.md)                             | `ASDQ4/ASDT3`           | Shell elements from the faces of a mesh — `ASDShellQ4` for quads, `ASDShellT3` for triangles.                                                                       |
| [SSP Brick](/docs/basics/elements/brick.md)                             | `SSP Brick`             | A stabilized single-point hexahedral solid from an 8-vertex mesh.                                                                                                   |
| [Four Node Tetrahedron](/docs/basics/elements/four-node-tetrahedron.md) | `Four Node Tetrahedron` | A linear tetrahedral solid from a 4-vertex mesh.                                                                                                                    |
| [Support](/docs/basics/elements/support.md)                             | `Support`               | A nodal restraint, from a point or from a plane for skewed supports.                                                                                                |
| [Hinge Release](/docs/basics/elements/hinge-release.md)                 | `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                                  | **Four Node Tetrahedron**              |

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](/docs/basics/assemble.md) 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.