> 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/examples/moment-curvature.md).

# Moment Curvature

Computes the moment–curvature response of a reinforced-concrete section: a [Patch](/docs/basics/moment-curvature/patch.md) of [Concrete01](/docs/basics/moment-curvature/concrete01.md) for the concrete, a [Layer Fiber](/docs/basics/moment-curvature/layer.md) of [ReinforcingSteel](/docs/basics/moment-curvature/reinforcing-steel.md) for the bars, collected into a [Fiber Section](/docs/basics/moment-curvature/fiber-section.md) and pushed by [Moment Curvature](/docs/basics/moment-curvature/moment-curvature.md).

Use it to see how the materials and the reinforcement layout drive stiffness, yield strength and post-yield behaviour, and as a starting point for section-level studies — M–N interaction, effective cracked stiffness, ductility.

## What to try

* **Sweep the axial force.** Feed a range into **Axial** (negative for compression) and take the peak moment at each level — that is an M–N interaction diagram.
* **Change the bar count.** `NumberOfFibers` on the Layer Fiber, and watch where the curve flattens.
* **Turn `MinMax` on** for both materials, so the curve ends where the section actually fails rather than carrying on past it.
* **Refine the patch mesh.** Each face is one fibre, so the mesh density is the fibre density. Compare a coarse and a fine mesh near the neutral axis.
* **Unpack the fibres.** [Fiber Stress Strain](/docs/basics/moment-curvature/fiber-stress-strain.md) gives the stress and strain history of every fibre, which is how you find out which one failed first and at what curvature.

See [Moment Curvature](/docs/basics/moment-curvature.md) for the reference documentation on each component.

{% hint style="info" %}
Running the definition writes `MomentCurvature.tcl` and a `FiberResults` folder next to the Grasshopper file. They are analysis artefacts and can be deleted between runs.
{% endhint %}

## Download

[moment-curvature](https://raw.githubusercontent.com/Alpaca4d/alpaca4d.github.io/main/doc/examples/moment-curvature/moment-curvature.gh)