# 1D members

This entry explains a couple key components of a 1D member definition and how they're used in GSA.

## Topology​

The topology of a 1D member is represented by its end nodes and any intermediate nodes, if it is an arc member.

The local x axis of a member goes from node 1 - node 2. All elements associated with that member will also have the same local axes as the member.

Our references entry on topology provides more information on how to define member topology in GSA.

## Type​

1D generic, beam or column are all member types that represent a piece of physical geometry. There is no fundamental difference between these members except that beam and column types can be used with GsRevit when coordinating the model with BIM.

A 1D member can also be defined as a void cutter. It takes the section property and cuts a hole in 2D members if it intersects with a 1D void cutter. It cannot be used to create a void in a 1D member.

## Analysis type​

You can also define the analysis type to specify which kind of elements you want to create.

The options are:

• Bar
• Beam
• Cable
• Damper
• Rod
• Spacer
• Spring
• Strut
• Tie

## Orientation​

The orientation angle and node modifies the local axes of the member from the default. See our entry on Axes for a diagram describing the default local axes.

## Offset​

Axial offsets are used to model a member at the face of the supporting member, instead of at the centreline. An axial offset result creates an FEA element that is shorter than the centreline to centreline geometry and connects it rigidly to the supporting node. In GSA, you can define:

• x1 offset: axial offset at end 1
• x2 offset: axial offset at end 2

When Automatic offsets are checked off, GSA uses the section properties of surrounding members to automatically assign an axial offset to the member, so that the member end aligns with the face of the supporting member.

Transverse offsets are used to model a member away from the centreline of the member. In GSA, you can define:

• y offset: offset in local y axis
• z offset: offset in local z axis

## Design options for effective length​

To carry out steel design, one of the three effective length options must be selected so that GSA can use the appropriate effective length in member capacity calculations.

Choose between:

• Automatically calculated – effective lengths are calculated in each direction using the member's end restraints and any intermediate bracing points in accordance with the design specification.
• User-specified internal restraints – the effective lengths are calculated in each direction using the member's end restraints and manually specified internal restraints. The location of internal bracing points are determined by the framing geometry.
• User-specified effective length - the effective lengths are manually defined, assuming one bending segment per member.

## Design variable overrides​

Design variable overrides can be assigned to override the automatically calculated values for certain variables (e.g., equivalent uniform moment factor and moment amplification factors) during steel design.