Earthquake RSA reloaded

The SSD task task_earthquake_reloaded_small Earthquake RSA reloaded calculates the eigenmodes of the structure, uses the Response Spectra Analysis to define seismic actions and calculates seismic load cases for the modal response superpostion of these actions. A variety of tools, e.g., load-to-mass-convertion, modal damping or shear stiffness reduction account for specific boundary conditions.

The task consists of the following tabs:


Using a new module called FEABENCH for certain calculation steps, this task offers more options to save resources and shows severe performance improvements.


To support established earthquake workflows prior to SOFiSTiK 2022, both the new Earthquake RSA reloaded and the legacy task Earthquake coexist for the time being.

Eigenmodes and Actions

Define settings for the calculation of eigenmodes and seismic actions.

GUI Task Earthquake RSA reloaded - Eigenmodes and Actions Tab

GUI Task Earthquake RSA reloaded - Eigenmodes and Actions Tab (click on image to enlarge)

This tab consists of the following group boxes:


General, Solver Settings

Specifiy the maximum number of eigenmodes and the storage load case number, as well as the computational method used for the calculation.

See also

See the FEABENCH manual for more info.

Damping, Stiffness and Inertial Effects

Adjust modal damping and shear stiffness globally or individually by group. In addition, utilise Inertial Effects to consider or ignore acceleration and mass effects for specific groups.

It is possible to leave cells empty in the secondary groups table, thus leaving the properties unchanged from the settings made in the primary group table.

GUI Task Earthquake RSA reloaded - Eigenmodes and Actions Tab

GUI Task Earthquake RSA reloaded - Eigenmodes and Actions Tab - Group Settings


Primary groups

Each structural element can belong to exactly one primary group. Therefore, the order of the primary groups is unimportant because conflicting settings cannot be made. Individual group settings override the All Groups setting.

Secondary groups

Additionally, structural elements can belong to multiple secondary groups. Therefore, the group settings will be handled from top to bottom, meaning that the bottom-most setting overrides earlier ones, including primary group settings.


New filter options to minimize the number of eigenmodes and hence calculation time, are available. The filter for total mass participation is set to 90% and activated by default. Alternatively, it is possible to filter out all eigenmodes with a mass participation smaller than a specified percentage. In addition, vertical eigenmodes can be eliminated.

Load-to-Mass Conversion

Choose which load cases to consider for the recalculation of the centre of mass.


Direction and Accidential Eccentricity

Choose the direction for excitation and optionally the accidental eccentricity based on the extent of the storey.

GUI Task Earthquake RSA reloaded - Direction and Accidential Eccentricity

GUI Task Earthquake RSA reloaded - Eigenmodes and Actions Tab - Direction and Accidential Eccentricity

Combination of the Effects of the Directional Components of the Seismic Action

Choose the method for the combination of the effects of the directional components to create seismic actions.




EN 1998-1 :2004, (2) and (4)


EN 1998-1 :2004, (3) and (4)

Response Spectra

Make the response sprectra related settings for each direction of excitation.

GUI Task Earthquake RSA reloaded - Response Spectra Tab

GUI Task Earthquake RSA reloaded - Response Spectra Tab (click on image to enlarge)


Define the resulting seismic action load cases which can later on be considered during the superpositioning for your design combinations.

GUI Task Earthquake RSA reloaded - Results Tab

GUI Task Earthquake RSA reloaded - Results Tab (click on image to enlarge)

See also

This interface utilises the following modules. For further information, see the respective documentation:


Use cases



Recalculation of centre of mass, calculation of Eigenmodes


Definition of Response Spectras, Renaming of load cases


Calculation of spectras