> 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/results/beam-forces.md).

# Beam Forces

Internal forces along every beam element — the axial force, two shears, torsion and two bending moments.

## 🔧 Grasshopper component

`Beam Forces (Alpaca4d)` — **Alpaca4d ▸ 08\_NumericalOutput**

### Inputs

| Name        | Nick          | Type    | Default | Description                                                                                               |
| ----------- | ------------- | ------- | ------- | --------------------------------------------------------------------------------------------------------- |
| AlpacaModel | `AlpacaModel` | Model   | —       | The analysed model.                                                                                       |
| History     | `History`     | Boolean | `false` | Read every recorded step instead of one. The outputs become trees `{step; element}`. **Step** is ignored. |
| Step        | `Step`        | Integer | `0`     | Analysis step.                                                                                            |

### Outputs

All six are **data trees, one branch per beam element**. Within a branch, the values are at the element's integration points, ordered from the I end to the J end.

| Name | Nick | Type          | Description                                  |
| ---- | ---- | ------------- | -------------------------------------------- |
| N    | `N`  | Number (tree) | Axial force, in `kN`. Positive is tension.   |
| Vy   | `Vy` | Number (tree) | Shear along the local *y* axis, in `kN`.     |
| Vz   | `Vz` | Number (tree) | Shear along the local *z* axis, in `kN`.     |
| Mx   | `Mx` | Number (tree) | Torsion about the local *x* axis, in `kN·m`. |
| My   | `My` | Number (tree) | Bending about the local *y* axis, in `kN·m`. |
| Mz   | `Mz` | Number (tree) | Bending about the local *z* axis, in `kN·m`. |

## 📈 When to use it

**Use it when**

* You need design forces — the numbers that go into a code check.
* You want the maximum moment in a member: take the branch and find its extreme.
* You are exporting to a spreadsheet or a downstream design tool.

**Do not use it when**

* You want to see the diagram → [Beam Forces View](/docs/basics/visualisation/beam-forces-view.md) draws all six in the viewport.

{% hint style="warning" %}
**The resolution is the element discretisation.** Forces are sampled at the integration points of each element — five per element, Newton–Cotes. A single element spanning a whole beam gives you five points, and the peak moment will be missed unless it happens to fall on one of them.

This is the same reason [Gravity Load](/docs/basics/loads/gravity.md) asks you to split beams. Five or more elements per span is a reasonable default.
{% endhint %}

## 💡 Local axes

`My` and `Mz` are about the element's **local** axes, set by the **ZAxis** input of the [ForceBeamColumn](/docs/basics/elements/force-beam-column.md) component. Turn on **Local Axes** in [Model View](/docs/basics/visualisation/model-view.md) if you are unsure which way round they are on a given member — it is the most common source of a moment that looks like it is about the wrong axis.