In the Selection of Shapes tab, you can specify which mode shapes are relevant for the response spectrum analysis of the selected load case. Because the analysis is based on a multimodal response spectrum method, you can select as many shapes as are required for the design.
If there are no results of the modal analysis, the table is empty. You can then use the
button to determine the shapes without leaving the dialog tab.
Mode Activation
In the table 'form activation' are the eigenperiods T with the corresponding accelerations Sa of the response spectrum and # extbookmark manual|effectiveModalmassFactor|Listed effective modal mass factors # fme that exist in the X, Y, and Z directions. The response spectrum of the selected table row is shown in the section below as a diagram. The information in the table and in the diagram are preset in relation to the natural period (button
in the diagram).
In the table, select the mode shapes to be used for the response spectrum analysis. All shapes are preset
. You can define your selection manually by activating or deactivating the check box of a mode shape.
The buttons below the table facilitate the selection of the mode shapes. The buttons have the following functions:
| Button | Function |
|---|---|
|
Selects all eigenmodes |
|
Deactivates all mode shapes |
|
Deactivates all mode shapes with an effective modal mass factor less than the value you can specify in the field on the right |
In the chapter # extbookmark manual|effectiveModalmasses|Natural Frequencies # see more information on how to determine the effective modal mass factors.
Graph
The lower section shows the response spectrum as a diagram. If you select a table row, the associated values are displayed on the graph. In this way, you can quickly check in which area of the response spectrum the eigenmode lies.
To switch between the diagrams of the directions of excitation in X, Y and Z, use # extbookmark manual as in the chapter|diagramResponseSpectra|Response spectrum # describes the buttons to the right of the graphic.
With the button
you can switch the diagram to the representation of the natural frequencies f (see chapter # extbookmark manual|frequency|Response spectrum #). This also affects the table.
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The values Sa in the table and in the diagram are marked with the # extbookmark manual|diagramScaleFactor|Scaling factor # afflicted, which is entered in the register 'response spectrum' for each excitation direction. If the response spectrum is rotated by an angle α, the directions X and Y given in the table 'Shape activation' denote the corresponding rotated local directions.
Attenuation with CQC combination rule
For the CQC rule, Lehr's damping values Di are required, which can be defined identically (constant) or differently for each eigenmode of the model. If you have specified in the Spectral Analysis Settings that the attenuation values 'are different for each shape ', then these must be specified separately in the' Attenuation ' column.
