SkyCiv Documentation

Your guide to SkyCiv software - tutorials, how-to guides and technical articles

SkyCiv Structural 3D

  1. Home
  2. SkyCiv Structural 3D
  3. Modelling
  4. Supports


Supports need to be added in order to restrain the structure. If no supports were present then the stucture would not be static and be unsolveable. It is important to remember that a structure must be restrained in every direction at some point by any of the supports. i.e. every degree of freedom must be accounted for by at least one ‘F’ in the structure.

Similar to the connections between members, the supports are given a 6-digit code to specify which of the node’s degrees of freedom are restrained. Each of the degree of freedom’s must be defined as either Fixed (‘F’), Released (‘R’) or Spring(‘S’). The degrees of freedom are in the following order:

  • X Translation
  • Y Translation
  • Z Translation
  • X Rotation
  • Y Rotation
  • Z Rotation

There are 3 types of letters (or dof releases) you can use:

  1. “F” – Fixed – This means the degree of freedom is fully fixed and the member will transfer this force to the node
  2. “R” – Released – The force is not being transferred for this degree of freedom
  3. “S” – Spring – The force is being transferred with some stiffness factor. This will require an additional input.

A pin support (which only allows rotation about the z axis) would be denoted by the code ‘FFFFFR’ whereas a roller (which allows rotation about the z axis and movement in the x direction) would be given the code ‘RFFFFR’.

Supports can be selected from the pre-configured support buttons. Along with their fixity codes, these include:

  • Fixed Support – ‘FFFFFF’ – Fixed in all translations (x,y,z) and rotations (Mx, My, Mz).
  • Pinned (Hinge) Support – ‘FFFFFR’ – Fixed in all translations (x,y,z) and but free to rotate about the z-axis (in this 2D case).
  • Roller Support (in x) – ‘RFFFFR’ – Free to ‘roll’ along the x axis and rotate about the z-axis.
  • Roller Support (in y) – ‘FRFFFR’ – Free to ‘roll’ along the y axis and rotate about the z-axis.
  • Spring Support (in y) – ‘FSFFFR’ – There is a spring support allowing some force to be transferred in the y translation.

For more information on these fixity codes, please visit our blog piece on Fixity codes.


Settlements are movements of the supports of a structure. It can occur if the supports/foundations are not fully compacted, and soil settles around it. To model settlements, click into the “Supports” menu, and then click the “Settlements” button on the top right. Settlements can only be applied to nodes that have a support specified at that node. The amount of translation or rotation of the settlement can be specified in the form.
Was this article helpful to you?
Yes No

How can we help?

Try SkyCiv Today

Structural Analysis Software free signup widget. SkyCiv Structural Design Software.

Powerful, web-based Structural Analysis and Design software