# Assemblies

Assemblies are way to define an entity that is formed from a collection of elements or members and can be thought of as a super-element. This is not an analysis entity but just a convenience for post-processing such as cut section forces. Typical uses of assemblies include cores, where the core is modelled with 2D finite elements, or trusses where the truss is modelled with top and bottom chords and bracing. In both these cases the assembly is identified by a list of included elements.

Unlike the analysis elements, an assembly does not have a clearly define orientation and location of reference point so these must be defined explicitly.

Assembly results can be in the form of tabulated output, diagrams and contours of displacements, drifts and force/moments, for analysis and combination cases, including envelopes.

The Model > Checking tools > Check assemblies tool checks all assemblies for missing topology items and invalid geometry configurations.


The name is used as a convenient way of referring to assemblies.


Assemblies can be defined in terms of members or elements. Only elements related to the member list or element list are considered. Spring and damper elements are ignored.


This defines the nodes at the ends of the assembly.

Orientation node

The plane formed by the topology items and the orientation node is the xy plane of the assembly. The orientation node cannot be collinear with the topology nodes.

Internal topology

This is a list of nodes that define the curve of the assembly. The order of the nodes is not important as the nodes are ordered along a vector between ends one and two.

Curve fit

For a curved element there is a choice of how the curve is fitted to the points. The default is to use Lagrange interpolation to fit a curve through all the intermediate points. The other option which is only valid if there is just a single internal topology item is for a circular arc from end one passing through the internal node to end two.


The extents of the assembly can be specified directly as end 1 and end 2 or GSA can determine this from the elements that define the assembly.

Point definition

The is how the assembly is defined internally (as use for assembly forces and moments). See Assembly results for more information.