The GEO5 FEM - Earthquake module allows the user to generate an artificial accelerogram corresponding to the desired response spectrum defined in the Eurocode 8 standard.
The "Generate accelerogram" option in "Earthquake" frame prompts the "Generate accelerogram" dialogue window to specify parameters of the generated acceleration record.
The generated accelerogram follows a typical shape of the acceleration record: stage of gradual increase, stage of strong motion and stage of gradual dying away. Providing the "Stationary" option is checked, neither the initial nor the final stage is taken into account and the amplitudes of acceleration are more or less constant in time.
Duration of earthquake ts determines the overall span of the generated record.
Proportional damping ratio ξ specifies proportional damping. This value is used in the determination of the elastic response spectrum of the generated accelerogram.
Damping correction factor appears in the parametric description of response spectrum provided by the EN 1998-1 standard. Its value equals 1 for damping ratio ξ = 0.05.
For different values of ξ it holds:
When adopting generated accelerograms, EN 1998-1 requires application of at least three different records. Changing the parameter "Alternative" allows us to receive a different record with a similar (standard) response spectrum.
In addition, it is necessary to specify the parameters pertinent to either horizontal or vertical elastic response spectrum.
Once specifying all parameters and then choosing "Generate" the program generates the acceleration record. Upon accepting by choosing "OK" the acceleration record is displayed in the "Earthquake" frame.
EN 1998-1: Design of structures for earthquake resistance - Part 1: General rules, seismic actions and rules for buildings, (2006).