> 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/assemble.md).

# Assemble

**Assemble** is the hinge of the whole workflow. It takes the loose pieces — elements, supports, load patterns, constraints — works out which of them share nodes, numbers everything, and produces the single `AlpacaModel` object that every downstream component reads.

Nothing before Assemble knows about anything else. A beam does not know which other beam it meets; a point load does not know which node it lands on. All of that is resolved here, and resolved **geometrically**.

## 🔧 Grasshopper component

`AssembleModel (Alpaca4d)` — **Alpaca4d ▸ 06\_Assemble**

### Inputs

| Name         | Nick           | Type                      | Default   | Description                                                                                                                                                                        |
| ------------ | -------------- | ------------------------- | --------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Elements     | `Elements`     | Element (list)            | —         | Every element in the model: beams, shells, bricks, tetrahedra.                                                                                                                     |
| Supports     | `Supports`     | Support (list)            | —         | Every [Support](/docs/basics/elements/support.md).                                                                                                                                 |
| LoadPatterns | `LoadPatterns` | LoadPattern / Load (list) | *(empty)* | [Load patterns](/docs/basics/loads/load-pattern.md) **and** [mass points](/docs/basics/loads/mass-point.md); the two may be mixed freely on this input. Anything else is an error. |
| Constraints  | `Constraints`  | Constraint (list)         | *(empty)* | [Rigid diaphragms](/docs/basics/constraints/diaphragm.md) and [rigid links](/docs/basics/constraints/equal-dof.md).                                                                |
| Recorders    | `Recorders`    | Recorder (list)           | *(empty)* | Extra OpenSees recorders. No component currently produces one; the standard result recorders are added automatically by [Run Analysis](/docs/basics/analysis/run-analysis.md).     |
| Tolerance    | `Tolerance`    | Number                    | `0.01`    | Distance below which two positions are treated as **the same node**, in `m`.                                                                                                       |

### Outputs

| Name        | Nick          | Type   | Description                                                                                                                                                                                                        |
| ----------- | ------------- | ------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| AlpacaModel | `AlpacaModel` | Model  | The assembled model — feed it to [Model View](/docs/basics/visualisation/model-view.md), [Run Analysis](/docs/basics/analysis/run-analysis.md) or [Natural Vibration](/docs/basics/analysis/natural-vibration.md). |
| Mass        | `Mass`        | Number | Total mass of the structure, in `kg`. Element mass is `area × ρ × length` and so on; a [Mass Point](/docs/basics/loads/mass-point.md) contributes only the **Z** component of its `TransMass`.                     |

## 📈 When to use it

**Use it when** you have finished building elements, supports and loads. Every model passes through Assemble exactly once; there is no other route to an `AlpacaModel`.

**Do not use it when** the model already exists as an OpenSees deck → [Deserialise](/docs/basics/utility/deserialise.md) assembles one directly from a `.tcl` file.

## 💡 Tolerance is the setting that matters

Every element endpoint, shell vertex and solid corner is collected, and any two within **Tolerance** of each other become one node. Two members are connected when, and only when, their geometry meets within that distance.

The same search attaches [point loads](/docs/basics/loads/point-load.md), [mass points](/docs/basics/loads/mass-point.md), [supports](/docs/basics/elements/support.md) and the nodes named by a [constraint](/docs/basics/constraints.md).

| Symptom                                                          | Likely cause                                                                                  |
| ---------------------------------------------------------------- | --------------------------------------------------------------------------------------------- |
| A member carries no load, or the structure is a mechanism        | Tolerance too **small** — the members never met, and the model has more nodes than you think. |
| Assembly throws *"… is not part of the model"*                   | A load or support has no node within tolerance.                                               |
| Distinct nodes have silently merged; a short member has vanished | Tolerance too **large**.                                                                      |

Check the node count in [Model View](/docs/basics/visualisation/model-view.md) with **Node IDs** turned on before trusting any result.

## 💡 Degrees of freedom

A node gets **6 DOF** if any beam or shell touches it, and **3 DOF** if only solids do. This is why:

* A brick sharing a node with a beam transfers force but no moment.
* Moments on a [point load](/docs/basics/loads/point-load.md) and the rotational terms of a [mass point](/docs/basics/loads/mass-point.md) are dropped at a 3 DOF node.

## 💡 What happens next

```
Assemble ──► Model View            (check it)
         ├──► Run Analysis          (static or transient)
         ├──► Natural Vibration     (modes and periods)
         └──► Serialize             (write the .tcl and read it yourself)
```

The model that comes back out of an analysis component is the *same* model with results attached — which is why the [Results](/docs/basics/results.md) components take an `AlpacaModel` rather than a separate result object.