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The purpose of this test problem is to demonstrate the difference between body constraint and equal constraints.
Overview
The main difference between body constraint and equal constraint is that the constrained DOFs are coupled in the body constraint (the consequence of this is that the constrained joints move as a [rigid body]), while they are not coupled in the equal constraint. This is illustrated in the attached and the related screenshot below, for which the following comments are made:
- The top and bottom beam are the same, but the top beam is using body constraints to be connected to supports, while the bottom beam is using equal constraints for connection to the supports.
- From the deflected shape for the top beam, you can see the support joint and the adjacent end of beam joint rotate as a rigid body, which makes the beam effectively span between the actual supports.
- From the deflected shape for the bottom beam, you can see end joints of the beam do not deflect downwards, since they have equal UZ constraint with the support joints that are fixed in Z direction. This results in a stiffer system as the beam effectively spans between its end joints, not the support joints.
Screenshots
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Figure 1 - Structural configuration
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Figure 2 - Deflected configuration
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Figure 3 - Shear response
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Figure 4 - Moment response
Attachments
- Body vs equal constraint test problem SAP2000 V11.0.8 model (zipped SDB file)
