Uniaxial

A uniaxial material describes a 1D stress–strain relationship. It is what a beam cross-section, a fibre or a hinge is made of — anywhere only one stress component matters.

🔧 Grasshopper component

UniaxialAlpaca4d ▸ 00_Material

Inputs

MatNameMaterial NameText(empty)Label for the material. Name it after a steel grade — S355, S355JR — and Utilisation checks its beams as that grade; any other name is only a label.

ENumber210000000Young's modulus in tension, in kN/m².

EnegNumber210000000Young's modulus in compression, in kN/m².

Equal to E unless you need a different one.

EtaNumber0.0Viscous damping parameter.

0.0 for purely elastic behaviour.

GNumber90760000Shear modulus, in kN/m².

νNumber0.3Poisson's ratio.

RhoNumber7850Density, in kg/m³.

ColourColour(empty)The colour the material is drawn in when Model View colours the elements by material.

Left empty, Model View gives each material a colour of its own. Display only: the analysis never reads it.

Outputs

MaterialMaterialUniaxial material, for any section or fibre.

Note

Only E, Eta and Eneg reach the OpenSees material. G, ν and Rho are used by Alpaca4d itself — G for the section's torsional and shear terms, Rho for the element mass density. That is why they live on the material rather than on the section.

A switcher component: pick the unit in the drop-down under it, or right-click it ▸ Units:

• UniaxialElastic — linear elastic, described below.
• ElasticPerfectlyPlastic — not yet implemented. It shows its inputs — Material Name, E, epsyP, epsyN, eps0 and Rho — and a warning, and outputs no material.

📈 When to use it

Use it when

• You are defining a beam cross-section of any kind.
• You need a fibre material for a Fiber Section and elastic behaviour is enough.
• You want a material that is not in the standard grades.

Do not use it when

• The element is a shell, brick or tetrahedron → use an nD material.
• You want a standard grade → the Material Database is faster and keeps E, G and ρ consistent.
• You need real non-linearity in a fibre section → use Concrete01, Steel01 or ReinforcingSteel from Moment Curvature.

🔗 Relation to OpenSees

uniaxialMaterial Elastic $matTag $E $eta $Eneg