OpenSees for Grasshopper

Structural analysis at the speed of design.

Alpaca4d connects Rhino and Grasshopper to OpenSees, the finite element engine from UC Berkeley (subject to its own license). Model beams, shells and solids, run static, modal, buckling and earthquake analyses, and explore hundreds of design options, without writing a line of code.

Download and try it freeTry it free Read the docsDocs
Rhino 7 & 8 Windows & macOS Free for models up to 50 elements
The Alpaca4d alpaca, a colourful low-poly model
Cited in
Structures Journal of Building Engineering Buildings Shell and Spatial Structures · IWSS 2023 Civil Engineering and Architecture ISPRS Archives E3S Web of Conferences Journal of Design for Resilience in Architecture and Planning Archi BIM Corner
Why Alpaca4d

A research-grade solver, wired like any other component.

Parametric to the core

Your structural model is a Grasshopper definition. Move a slider and the geometry, the mesh, the analysis and the results all follow.

OpenSees under the hood

Alpaca4d writes plain OpenSees input and runs the open-source engine from UC Berkeley: nonlinear materials, fibre sections, dynamics. You never touch Tcl, and the file is always yours.

Made to optimise

Record design studies with Explorer, search them with Non-Linear Optimisation, and let Topology Optimisation carve away what a solid does not need.

10,900+downloads from Rhino's Package Manager
90+Grasshopper components in one tab
14papers, theses and articles that use or cite it
2020the year the first alpaca was meshed
How it works

From a sketch to a structure in four steps.

Scroll to model, support, load and analyse a concrete shell, then explore a whole family of them.

01 · MODEL

Draw it in Rhino.

Turn the curves, surfaces, meshes and solids you already have into beams, shells, bricks and tetrahedra. Assemble Model welds them into one structure.

ForceBeamColumnASD ShellSSP BrickTen Node Tetrahedron
02 · SUPPORT & LOAD

Hold it, then load it.

Fix the corners, tie floors together with rigid diaphragms and links. Apply gravity, point, beam and shell loads, masses and ground motions, grouped in load patterns.

SupportGravity LoadShell LoadLoad Pattern
03 · ANALYSE

Let OpenSees do the maths.

Alpaca4d writes a plain OpenSees file and Run Analysis solves it with the OpenSees on your computer: static, nonlinear, modal, buckling or time history. The results land back on your geometry.

Assemble ModelRun AnalysisModel View
04 · EXPLORE

Then ask: what if?

Every slider is a design variable. Record hundreds of options with Explorer, let Non-Linear Optimisation search for the best, or let Topology Optimisation find where the material belongs.

Explorer RecordNon-Linear OptimisationTopology Optimisation
Feels like home

It reads like any Grasshopper definition.

No scripting and no new interface. Materials flow into sections, sections into elements, elements into a model, and the model into OpenSees, one wire at a time.

NameDBPath
Material
Material Library

01 MATERIALPick a grade from the library, or type in your own values.

HeightWebMaterial
Section
I Section

02 SECTIONStandard profiles, a steel library, or any shape you draw.

LineSectionGeomTransf
Element
ForceBeamColumn

03 ELEMENTBeams, shells, bricks and tetrahedra, straight from Rhino geometry.

ElementsSupportsLoadPatterns
AlpacaModelMass
Assemble Model

04 ASSEMBLEOne model: nodes welded, supports and loads in place.

AlpacaModelSettings
logAlpacaModel
Run Analysis

05 ANALYSEOpenSees solves it, on your own machine.

AlpacaModelStepColors
InfoValues
Model View

06 VIEWContours, diagrams and legends, right in the Rhino viewport.

Everything in the toolbar

The whole workflow, in one tab.

From the first material to the last optimisation run. Every component is documented, with its inputs, outputs and a picture.

Materials

Elastic, uniaxial and nD materials, plus a material library to pick grades from.

Sections

Rectangular, circular, hollow, I, double angle and generic sections, a steel section library and plate fibre sections.

Beams

Force-based beam-columns, beams with hinges, hinge releases and spring links.

Shells

ASDShellQ4 and ASDShellT3 shells, with elastic or plate fibre sections.

Solids

SSP bricks and ten-node tetrahedra for anything with a volume, from a footing to a concrete cow.

Supports & constraints

Supports with any mix of fixities, rigid diaphragms, rigid links and equal DOF.

Loads & masses

Gravity, point, beam and shell loads, mass points, load patterns and time series.

Analysis

Static and nonlinear analysis, with control over integrator, convergence test, steps and damping.

Dynamics & buckling

Natural vibration modes, ground-motion time histories and linear buckling.

Results & views

Displacements, reactions, forces and stresses, as numbers or as contours, diagrams, legends and principal stress lines.

Section design

Moment–curvature, N–My–Mz interaction domains and utilisation checks to EN 1993-1-1.

Optimisation

Explorer design studies, Non-Linear Optimisation and Topology Optimisation.

Need more? Write your own OpenSees commands with Custom Code, open up any object with Deconstruct, or send the model on to FEM-Design.

Examples

Shells, towers, bridges… and a cow.

Every picture here comes from an example in the docs, with its Grasshopper file ready to download, open and take apart.

A concrete shell of four legs, form-found to work in compression, coloured in bands of displacement Compressed ShellKangaroo form-finding, then shells→ A concrete cow in tetrahedra, coloured by vertical stress Spot the Cow5 030 ten-node tetrahedra→ Rows of concrete tanks, each one deformed in another of its first hundred natural modes Natural VibrationA footbridge against the pace of walking→ A cantilever block carved by topology optimisation Topology OptimisationMaterial only where it works→ A lattice high-tension tower coloured by displacement High Tension TowerA lattice of beam elements→ A multi-storey frame coloured by its results Multi Storey BuildingBeams, columns, slabs, diaphragms→ Michelangelo's Rebellious Slave in ten-node tetrahedra, coloured by the vertical stress of its own weight The Rebellious SlaveMichelangelo in 28 000 tetrahedra→ Thirty steel sticks shaken by an earthquake, drawing its response spectrum behind them Response SpectrumThirty sticks, one earthquake→
Browse all the examples
Get started

Up and running in three steps.

1

Install

Find Alpaca4d in Rhino's Package Manager and click Install. Rhino 7 and 8, on Windows and macOS.

Open in Rhino Install guide
2

Set up OpenSees

Download OpenSees from UC Berkeley (subject to its own license) and point Alpaca4d at it once. OpenSees is the engine; Alpaca4d is the cockpit.

Setup guide
3

Learn

Follow the docs, open an example, or spend a day on a workshop with the developer.

Docs Workshop
Without a license

Try it, free

  • Build and analyse models of up to 50 elements, and see them in Model View
  • Read the results with the Results components
  • Topology Optimisation on models of up to 500 elements, and the analysis of its design
  • The section tools, Explorer and the other optimisers need a license
What is included
With a license

Everything, any size

  • Any model size, every component
  • Students 30 €, professionals 490 € a year, + VAT
  • Email support, answered within 48 hours
Marco Pellegrino
Marco Pellegrino
“I wish to be an artist. Meanwhile, I do engineering.”— MARCO
About us

Made by an engineer who would rather be an artist.

Alpaca4d is made by Marco Pellegrino, a structural engineer and researcher who wanted the power of OpenSees without the scripting. He has been building it since 2020, and he answers your emails himself.

Meet Marco
Learn

Learn it your way.

Documentation

Every component explained, with its inputs, outputs and a picture.

Read the docs

Examples

Grasshopper files to open, run and take apart, from beams to dragons.

Open the examples

Workshop

A day online with the developer, from your first model to its results.

See the programme

Explorer

A web app for design studies: filter, compare and pick a design, in your browser.

Open Explorer

Give OpenSees a canvas.

Download Alpaca4d and analyse your first model this afternoon. Free for models of up to 50 elements.

Download Buy a license