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Rigid links

In a structural analysis model, elements (beams, columns, walls, slabs, … ) are schematically represented by the lines and surfacs to which constructive features are assigned. To assure the force transfer between these elements, they are interconnected.
In most cases, the force transfer is done through the common nodes between the elements. However, if these elements have a large eccentricity relative to each other, they don’t have common nodes. You’ll have to connect the elements using rigid links.

In a steel hall, the frames (blue) are connected to each other by continuous beams (gray). There is a significant distance between the axes of the continuous beams and the axes of the frame. Therefore, the axes are connected to each other by rigid links. The rigid links are selected in this image, which is why they are shown in yellow. In a volumetric representation, the rigid links are drawn as cilinders.

What is a rigid link?

A rigid link is:

  • An infinitely stiff element that transfers all internal forces.
  • It displaces (moves) as a rigid body. It cannot deform.
  • A rigid link has no cross-section or material.
  • Rigid links are represented by a dashed pink line.
Two floors are at different levels and are connected by a high beam. To model this, the floors and beam were connected by rigid links. The rigid links are not selected in this image, which is why they are shown in pink.
  • It’s not possible to show the results in a rigid link, although they contain forces!
To illustrate the presence of rigid links, the beam and column of a frame are set eccentric. When looking at the bending moment, it seems as if the beam-column connection is not in equilibrium. That’s because Diamonds doens’t show the internal forces in rigid links. The end of this article mentiones an alternative way to model rigid links that allows you see the internal forces.
  • Some cases of eccentricities can be modeled using this button . Here, Diamonds will automatically add the rigid links to the model.

How to make a rigid link?

  • Select the bars you want to define as a rigid link.
  • Click on . The rigid link is created.
  • Any necessary boundary conditions at the bar ends of the rigid link, can be defined using the button .

How to remove a rigid link?

  • Select the relevant rigid links and hit DEL or .

How to transform a rigid link back to a regular bar?

  • Assign a random cross-section & material to the rigid links. Choose for example a steel cross-section from the library .

Alternative way to model rigid link-behaviour

The downside to rigid links is that it’s not possible to consult the internal forces in them. As a work-around, you could model the rigid link as a regular bar:

  • Open the material library and create a new material with a very high Young’s modulus (E-modulus) and neglectable self-weight.
    Make sure the Young’s modulus is a least 10x as high as the concrete/steel/timber used in the model.
  • Draw a line.
  • Assign a large cross-section (you can exaggerate) and the new material to it.
  • Any necessary boundary conditions at the bar ends of the rigid link, can be defined using the button .
  • Assign the rigid links to a new Design type to make it easier to turn their results on/off.
  • Also define a minimum element size for bars to avoid unnecessary mesh nodes and long calculation times.

On this page

  • What is a rigid link?
  • How to make a rigid link?
  • How to remove a rigid link?
  • How to transform a rigid link back to a regular bar?
  • Alternative way to model rigid link-behaviour