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# How to do a seismic analysis

• A seismic analysis requires the license Seismic Analysis.
• The seismic analysis in Diamonds/ PowerFrame uses multi-modal-analysis. Other types of seismic analysis are not available with the BuildSoft software.

1. Enter the geometry of the structure as you would normally do.
If your model contains multiple independent structures, make one Diamonds-file for each structure.
2. Load group and masses
• Click on . Add a load group and select ‘Seismic’ from the list.
• To calculate the response of the structure due to the seismic load, the modal parameters of the structure (eigen modes and -frequencies) must be calculated by Diamonds. These model parameters depend on the stiffness and mass distribution of the structure.
• The stiffness is known by Diamonds. It is in the geometry of the structure.
• The mass distibution is related to the vertical loads (point loads, line loads, surface loads) (0,981kN -> 100kg).
The correlation coefficient φ multiplied by the combination factor Ψ2 (for Eurocode and Eurocode-like standards) will determine the masses.
For example: a life load of 5kN/m will lead to 5kN/m²  x  Ψ x φ = 5kN/m  x  0,3  x 1 = 1,5kN/m of mass to be taken into account during the model analysis.
3. Define the seismic spectrum: select the load group Seismic from the pull down list and click on . Enter the desired paramters.
Read here how to define a user defined seismic spectrum.
4. Generate the combinations . Don’t forget to check the ULS SC combinations.
5. Run the analysis . In the tab page ‘Dynamic’ choose ULS FC as reference combination.
6. Run the reinforcement calculation , steel or timber design .
Diamonds will take the seismic combinations ULS SC into account.
7. Verify the deformations.