Seismic Analysis Parameters (EC 8 - General)

Parameters of a structure seismic analysis depend on a seismic code used during calculations of a structure influenced by seismic impact.

Access
Select seismic code EC 8 - General (requirements adopted for Europe and presented in Eurocode 8) in the New Case Definition dialog or click Parameters in the Analysis Types dialog.

To complete the seismic analysis according to the rules given in a code, define the following parameters.

ag
Specifies the design ground acceleration on type A ground as specified by Local Authorities. The design ground acceleration is defined in terms of the reference peak ground acceleration on type A ground agR and importance factor γ derived from the building class:

ag = γ × agR

q
Specify the value of the Behavior factor according to point 3.2.2.5.
The Behavior factor is a reduction factor of the design response spectrum in relation to the elastic response spectrum. You can edit its value after selecting the Design spectrum option.
Note: The behavior factor q reduces the design spectrum; this way it also decreases seismic loads and the resulting internal forces. However, as specified in point 3.2.2.5, the displacement based on the design response spectrum is multiplied by the behavior factor q. Thus, usually such displacement is not reduced in relation to the elastic response spectrum.
Spectrum
Select a Design or Elastic Spectrum, as specified in point 3.2.2.
Direction
Specify if the direction is Horizontal or Vertical.
Parameters describing the response spectrum
The following parameters are defined in the National Annexes to the code 1998-1-1:2004-General.
  • S - soil factor,
  • B - β lower bound factor for the horizontal design spectrum,
  • Tb, Tc, Td - period parameters (s).

    The response spectrum is calculated based on these parameters according to the formulas for the elastic response spectrum (3.2.2.2 and 3.2.2.3) and design spectrum for elastic analysis (3.2.2.5).

Eccentricity Definition
Opens the Definition of mass eccentricities dialog which allows you to specify how to account for the eccentricity of a mass in the seismic analysis.
Direction definition
Opens the Direction dialog which allows you to define the direction of the spectral or seismic excitation.
Filters
Opens the Filters dialog which allows you to determine the number of modes to be taken into account during dynamic analysis of structures.
Residual Mode
Allows you to calculate pseudostatic forces for a residual mode.

The details concerning this structure analysis method can be found in the mentioned code.

Parent topic: Seismic Analysis Parameters (Dynamics)