Force Beam Column

A force beam column is a frame element with a force-based (flexibility) formulation. The section response is integrated along the member, so the element captures the real distribution of curvature along the span rather than assuming a shape function for it.

🔧 Grasshopper component

ForceBeamColumnAlpaca4d ▸ 02_Element

Inputs

LineCurveCentreline of the element, in m.

SectionSectionCross-section, from any of the Sections components.

Carries the material, and with it the mass density.

GeomTransfGeometricTransformationGenericLinearGeometric transformation.

If left empty a Linear transformation is built from the line and ZAxis.

ZAxisVectorhorizontalLocal z axis of the element.

If left empty it is horizontal, so local y — the depth of an I-section, the height of a rectangle — points as near straight up as the beam allows, and gravity bends a floor beam about its strong axis (Vy, Mz). A vertical member gets local y along global X.

ColourColourAlpaca4d beam colourDisplay colour in the Rhino viewport.

ElementIdText(empty)Optional name for the element, used to pull its results out later.

Free text, and yours to repeat: one name over twenty curves labels all twenty, and asking for it returns all twenty. Give a list to name them apart.

LineCurveOne bar per line, in m. Its two ends become nodes.

It must be straight: anything but a line is an error.

SectionSectionThe bar's area and material: any beam section, a tube from Section Library included.

Its shape only draws the bar.

WorksInTextBothBoth, Tension or Compression: which way the bar carries load.

A tension-only bar goes slack when pushed, a compression-only one lets go when pulled. Connect a Value List to pick from them.

PrestressNumber0The axial force the bar starts with, in kN, tension positive.

A cable needs it: straight and slack, it has no stiffness across its length. A tension-only bar takes zero or more, a compression-only one zero or less.

ZAxisVectorhorizontalLocal z axis, squared off the bar.

It only turns the section, for drawing and for the steel check; left empty it is horizontal, as on a beam.

ColourColourAlpaca4d beam colourDisplay colour in the Rhino viewport.

ElementIdText(empty)Optional name for the element, used to pull its results out later.

Free text, and yours to repeat: one name over twenty curves labels all twenty, and asking for it returns all twenty. Give a list to name them apart.

A truss is always corotational, so it holds for large displacements too. A line load on it goes to its two end nodes, half each. A tension-only or compression-only bar needs a non-linear analysis to let go: the Newton algorithm, in several steps.

Outputs

ElementElementBeam element, to be connected to Assemble.

A switcher component. The Element Type menu selects the unit:

• ForceBeamColumn — a plain force-based beam, described here.
• WithHinges — the same element with plastic hinge zones at the ends, described in Beam With Hinges.
• Truss — a bar that carries axial force only: in tension and compression, or in one of the two. Its inputs are below.

📈 When to use it

Use it when

• You are modelling any line-like member: beams, columns, braces, truss bars.
• You want the spread of yielding along the member length to be captured.
• You need realistic curvature and rotation demands for pushover or seismic work.

Do not use it when

• Inelasticity is confined to the member ends and you would rather control the hinge length explicitly → switch the unit to WithHinges.
• The member is really a surface or a solid → use Shell or Brick.

🔗 Relation to OpenSees

The component writes a geomTransf and a forceBeamColumn:

geomTransf Linear $transfTag $zx $zy $zz
element forceBeamColumn $eleTag $iNode $jNode $transfTag NewtonCotes $secTag 5 -mass $massDens

• The integration is Newton–Cotes with 5 points, created automatically.
• $secTag comes from the Section input.
• $massDens is mass per unit length, from the section area times the material density.
• Transformation and integration tags are numbered automatically per element.