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. 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 Type dialog.

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

• Value of a_g - It 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 a_gR and importance factor γ derived from the building class:

  a_g= γ × a_gR.

• Value of the Behavior factor (q). According to point 3.2.2.5, this 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 (design, elastic), as specified in point 3.2.2.
• Direction (horizontal, vertical).
• Parameters describing the response spectrum (defined in 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).

Click Eccentricity Definition to open the Definition of mass eccentricities dialog where you can specify how to account for the eccentricity of a mass in the seismic analysis.

In the lower part of the dialog, the Direction definition,Filters, and Residual mode buttons are located.

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