Frame

Frame elements are used to model slender structural members like beams and columns. All frame elements are constructed with the form

Model.element(name, tag, nodes, *, section, transform)

Add a frame element to the model.

Available frame elements include

Name	Description
ElasticFrame	Prismatic linear-elastic frame
ForceFrame	Force formulation
HermiteFrame	Cubic displacement formulation without shear. Added in 0.1.33
LagrangeFrame	Lagrange displacement formulation with shear. Added in 0.1.33
CosseratFrame	Geometrically exact displacement formulation

Defining a frame element involves the following steps:

1. Define nodes with appropriate coordinates

2. Create a coordinate transformation with the element orientation

3. Define section behavior for the element

4. Optionally define an integration rule, if supported by the element type

5. Create the frame element, connecting it to nodes, sections, and a transformation

6. Optionally apply element loads

The available frame elements are summarized in the table below:

Name	Shear	Geometry	Integration	Interpolation
ElasticFrame	Elastic	Basic	None	None
ForceFrame	Optional	Basic	User	Fixed
HermiteFrame	No	Basic	User	Fixed
LagrangeFrame	Yes	Basic	Fixed	Nodes
CosseratFrame	Yes	Exact	Fixed	Nodes

In view of these capabilities:

• ElasticFrame is ideal for elastic members of any shape that are expected to undergo small to moderate displacements.

• ForceFrame is an ideal general-purpose frame element for inelastic members undergoing small to moderate displacements. In this setting the element can achieve exceptional accuracy with minimal mesh subdivisions. Unlike displacement formulations, shear effects can be conveniently toggled in this element using the shear option. However, this element involves local iteration that may fail to converge on occation.

• CosseratFrame is typically ideal for members undergoing large displacements and rotations.

• HermiteFrame is a suitable fallback when ForceFrame fails to converge in a problem without significant shear effects. However, in order to achieve comparable accuracy with ForceFrame, a finer mesh is typically required.

• LagrangeFrame is a suitable fallback when ForceFrame fails to converge in a problem with shear effects. However, in order to achieve comparable accuracy with ForceFrame, a finer mesh is typically required.