Generic Section

A section defined by its stiffness properties directly, with no geometry behind them. Use it when the properties come from somewhere else: a homogenised deck, a section computed in another tool, a value taken from a catalogue table.

🔧 Grasshopper component

Generic SectionAlpaca4d ▸ 01_Section

Inputs

SecNameSectionNameText(empty)Label for the section.

AAreaNumberCross-sectional area, in m².

IzzNumberSecond moment of area about the local z axis, in m⁴.

IyyNumberSecond moment of area about the local y axis, in m⁴.

JNumberTorsion constant, in m⁴.

AlphaYNumber5/6Shear area factor along the local y axis: the fraction of the area that carries shear. 5/6 for a rectangle. 0 makes the section rigid in shear, which ignores shear deformation.

AlphaZNumber5/6Shear area factor along the local z axis, as AlphaY.

MaterialMaterialA Uniaxial material, supplying E, G and the density used for element mass.

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

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

Outputs

SectionSectionBeam section, for a ForceBeamColumn.

📈 When to use it

Use it when

• The properties were computed elsewhere and you want them used verbatim.
• You are homogenising something — a ribbed deck, a built-up member, a stiffened panel reduced to an equivalent beam.
• You want to run a sensitivity study on Izz alone, without re-deriving a geometry.

Do not use it when

• A parametric section describes the member → use it, and the extruded preview in Model View will show you the real shape.

Warning

The area you give also sets the element mass, as A × ρ. If you enter a reduced or effective area, the mass goes with it — which matters for Natural Vibration and any dynamic run.

🔗 Relation to OpenSees

section Elastic $secTag $E $A $Izz $Iyy $G $J $alphaY $alphaZ

Every input maps straight through.