You can perform a modal analysis instead of a stress analysis. In the modal analysis, resonant frequencies and the associated patterns of structural deformation called mode shapes are determined. For the modal analysis, you can define modal masses to be used instead of static load combinations.

1. On the Analysis & design tab, click A&D models.
2. In the Analysis & Design Models dialog box, do one of the following:

   • To create a new modal analysis model, click New.

   • To modify an existing analysis model, select the analysis model, and then click Properties.

   The Analysis Model Properties dialog box opens.

3. On the Analysis tab, select Yes from the Modal analysis model list.

   This forces Tekla Structures to ignore static load combinations.

4. On the Modal analysis tab, define the modal analysis properties and the load groups to be included as masses in the modal analysis:
   1. Enter the count of modes to calculate.
   2. Enter the maximum frequency to calculate.
   3. Select the appropriate Include self weight check boxes to indicate the directions for which Tekla Structures includes the self-weight of parts in the modal analysis.
   4. If suitable, click Copy seismic masses to include the same load groups in the modal analysis as in the seismic analysis.
   5. To move the appropriate load groups to the Included load groups table, select them and use the arrow buttons.
   6. For each load group in the Included load groups table, enter a load factor and set the mass direction.

      In the Mass direction column, select either:

      • XYZ to include the load in all three directions.

      • Model default to include the load only in the direction of the load.

5. Click OK.