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Rigid Members

An Introduction and example use cases of Rigid Members

Rigid members are a powerful and effective member class, that can be used to simulate a fully rigid member. They are often used to transfer forces from one location to another, via some arbitrary, imaginary, infinitely rigid member. See the below video for more information on how they work, how to model them in software, and some use cases:

How to Use Rigid Members

To set a member as rigid, simply specify the member “Type” as “Rigid Link”. Note: you may have to toggle the advanced mode on to see the type attribute:

using rigid members in s3d via ui

You will notice the options collapse (since they are not required for rigid links) but you can still control the end fixities, which essentially controls which loads are transferred. Once you click Apply, you will see that the rigid link is drawn in light grey color with a “R” symbol beside it:

using rigid members in s3d 

Use Cases

Stacked Beams

Rigid Link Members
stacking beam elements results in structural analysis
 
View the full article here on how to model stacked beams.
 

Line Hinges Between Plates

Rigid Links can be useful to define rigid connections between structures or elements. They are often thought of as imaginary stiff links that join members so they can translate and/or rotate together. A rigid link can also be used to manually control for member offsets or connections. Additionally you can change the fixity/releases in the rigid link to control what forces and effects it has on what it connects to. A good example of this is simulating Line Hinges to connect plates by hinges:

Start by adding two plates (that you wish to join by a hinge) and connect them with Rigid members with end fixities FFFFRR. These rigid links are connecting the gap in plates we see below:

 
Solving the structure under these conditions, we can see the results behaving as expected; supporting members have no bending moment force at the hinge, and the plates have a hinge-like deflection.
 
bending moment force of supporting members using rigid links plate deflections joined by line hinge joints
 

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