Function
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Group Damping is used to assign different damping ratios, which results from time history analysis, to element and boundary groups.
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When the materials, vibration control devices or vibration isolators in a structure have different damping ratios, elements with different damping ratios can be assigned to different Element Groups.
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It is common to assign structural members such as beams and columns to a Structural Group and assign boundary conditions (including structures assigned with vibration isolators or vibration control devices) to a Boundary Group in order to define different damping ratios.
Call
From the main menu, Select [Properties] tab > [Damping] group > [Group Damping] > [Strain Energy Proportional]
Input
Group Damping : Strain Energy Proportional dialog
Default Values for Unspecified Elements and Boundaries
Apply the default damping ratio to the elements and boundaries to which damping ratios are not assigned by groups or materials
Damping Ratio : Enter the Damping Ratio.
Damping Ratio for Specified Elements and Boundaries
Enter the damping ratio by materials or groups.
Material : Enter the damping ratio by materials. The damping ratio will be applied to the elements assigned with the Material Data.
Structure : Enter the damping ratio by element groups.
Boundary : Enter the damping ratio by boundary groups. This option is applicable to Elastic Link, General Link and Point Spring boundary conditions.
Name of Material / Group
1. Material : Select the name of the Material Data.
2. Select a group name, which was defined in Treff Menu>Group>Structural Group or Boundary Group.
Define the global damping ratio by selecting ’r;All Material Data’.
- Select ”All Material Data” (Default).
- Click ”Define” : Define the global damping ratio using the damping ratio entered in the ”Material Data”.
Use Material Data : Use the damping ratio defined in the Material Data.
Direct Define : Directly define the damping ratio (It will be disabled when Type>Material>All Material Data is selected).
Time history analysis is performed using damping ratio defined in Default Values for Unspecified Elements and Boundaries for members or boundary conditions not specified as a group, and damping ratio defined in Damping Ratio for Specified Elements and Boundaries for members or boundary conditions specified as a group.
Calculate Only When Used
When performing analysis using mode attenuation, Alpha and Beta values can be automatically obtained using the frequency of the main mode in Result > Modal Damping Ratio based on Group Damping. However, this feature is only enabled when Check Off.
Damping Ratio Select Option dialog
Damping Ratio Select Option
When multi damping ratios from Material Data and Structure Group are assigned to one element, select the option to apply.
Priority between Material Data and Structure Group
Selects the priority when the attenuation of Material Data and Structure Group is set to overlap for one element.
Material Data : Apply the damping ratio defined in the Material Data to the analysis.
Structure Group : Apply the damping ratio defined by Structure Group to the analysis.
Priority between Structure Groups
Selects the priority when attenuation of two or more Structure Groups is set to duplicate for one element.
Smallest Damping Ratio : Apply the small damping ratio.
Largest Damping Ratio : Apply the large damping ratio.
For the elements and boundaries unspecified by groups, ’Damping Value for Unspecified Elements and Boundaries’ will be applied for the time history analysis. For the elements and boundaries specified by groups, ’Damping Ratio for Specified Elements and Boundaries’ will be applied for the time history analysis.