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Stiffness Doubling Issue in Non-Linear Damping Material Modelling in SAP2000

aasish27

Civil/Environmental
Mar 10, 2025
1
Dear all,
I am modelling a suspended ceiling system in SAP2000, where damping materials are applied at the periphery to provide energy dissipation under lateral movement. These damping materials exhibit a non-linear force-deformation behaviour, which I have defined using a multi-linear elastic material. The force-deformation curve accurately represents the compression behaviour, while the tension behaviour is extended with negligible stiffness to indicate that the material does not resist tension.

When I compare the modal period obtained from SAP2000 with my manual calculation, they only match when I double the compression stiffness in my calculation. This clearly indicates that SAP2000 is considering the compressive stiffness from both ends simultaneously, effectively doubling the overall stiffness of the damping material.
Using a GAP element with a single stiffness value is not suitable for my case, as the damping material follows a non-linear force-deformation relationship.

How can I achieve this scenario in SAP2000 so that the damping material:

  • Only contributes stiffness when compressed (i.e., when the ceiling moves towards one side and compresses the material).
  • Remains inactive when subjected to tension.
  • Accurately represents the non-linear force-deformation curve of the damping material.

Any suggestions or guidance on how to resolve this issue would be greatly appreciated.


kind regards,
Aasish
 
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I suspect the modal analysis may not be compatible with nonlinear elements.
 

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