Default Short CommandLSEIS

Seismic loads are taken into account according to the Response Spectrum Analysis method of Eurocode 8 or Turkish seismic code.

Only the response spectrum and some additional parameters have to be defined as Seismic load.

Required spectrums can be defined with the 1583941735786-630.png  Seismic load by using standard spectra (automatic) or by manual definition (unique).


The applied/defined spectra and its properties can be added to documentation as figures and tables by clicking on Add to documentation.

Automatic Design Spectrum Definition (“Standard”)

Clicking on Standard generates the horizontal and vertical spectra based on settings and parameters required by Eurocode 8.

1582804849244-917.pngThe horizontal spectrum is always necessary. The vertical spectrum is necessary when the vertical affect taken into account.

Structure information

Eurocode code:
  • Structure type:
    • Building structure
    • Non-building structure
  • ​ksi: is the viscous damping ratio (generally 5%), which is used in Modal analysis when the summation of the effect of the same direction vibration shapes is carried out by the CQC (Complete Quadratic Combination).
  • qd: behavior factor. The displacements from seismic analysis is increased with this factor.
Turkish seismic code:
  • Structure type:
    • New building

    • Existing building (Limited, Medium or Comprehensive Information level):
    • The Information level affects the cross-sectional resistances in Performance Based Design calculations.
    • Non-building structure.
  • Beta: This coefficient is for checking if the ratio of base shear force calculated with Mode superposition method and Equivalent seismic load is greater than this value.
1582804849244-917.pngStoreys definition is necessary if the user selects the Structure information as building (in Turkish seismic code New or Existing Building)

 For Non-building structures the following result are calculated after Seismic analysis:

  • Equivalent loads
  • Displacements
  • Reactions
  • Connection forces
  • Bar / Shell internal forces

                For building structures additional result are calculated which can be listed after Seismic analysis:

  • Second order effect (P-Delta) coefficients
Horizontal spectra


Figure: Parameters and automatic generation of horizontal spectra

Data of horizontal design spectra (based on Eurocode 8):

  • Type (of spectra: 1 and 2) and Ground type (A, B, C, D and E) specify the values of S, TB, TC and TD;
  • ag is the design ground acceleration;
  • is the soil factor;
  • q is the behavior factor that depends on material and type of the structure;
  • beta is the lower bound factor for the horizontal design spectrum.

Data of horizontal design spectra (based on Turkish seismic code):

  • Seismic zone (1, 2, 3 or 4), Local site class (Z1, Z2, Z3 or Z4), Building importance factor and Probability to exceed in 50 years specify the values of S, TA, TB;
  • Ductility level:
  • Behaviour factor: depends on material and type of the structure;
Vertical spectra


Figure: Parameters and automatic generation of vertical spectra

The vertical design spectrum is derived from the horizontal spectrum using the agv (vertical design ground acceleration)/ ag multiplicator based on Eurocode 8.

1582804849244-917.pngThe vertical spectra is available only in Eurocode and not available in Turkish seismic code.

Custom Design Spectrum Definition (“Unique”)

User can define custom horizontal and vertical spectra in table format or by editing spectra graphically. Switch to Unique mode, and then add T and Sd values to the table cells or place points in the Sd-T(s) curve by clicking in the required points of the figure.


Figure: Custom spectra definition

Unique spectra can be stored in files and exported with Save. Spectra can be imported with Load.

Created by Fredrik Lagerström on 2020/04/02 17:12
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