STAAD.Pro Physical Modeler Help

Create: Response Spectrum Definition dialog

This dialog is used to add code-prescribed parameters for a response spectra analysis to the structure. A response sprectrum is used to model dynamic seismic loading of a structure.

Opens when the Add Response Spectrum tool is selected on the Catalog ribbon tab in the Load Definitions group.

Note: Refer to the Options dialog Dynamic tab for additional settings that apply to all dynamic analysis and response spectrum cases.

In this dialog, there are some instances where a code or parameter selection will result in a control being disabled. In the case where there is not selection to be made or a value to be fixed (as the code only allows for one option), then that selection or value will be displayed but cannot be edited.

Name Type a descriptive name for the response spectrum definition.
Code Select the relevant building code from the list.
Version Select the version of the selected code.
Spectrum Type Select whether whether Acceleration or Displacement spectra will be entered. The relationship between acceleration and displacement values in response spectra data is:
Displacement = Acceleration × ( 1 / ω ) 2
2π/Period (period given in seconds; ω in cycles per second)
Note: Not all codes have provisions for both types of spectra. In that case, the type used is selected but this option cannot be changed.
Interpolation Type Select Linear or Logarithmic interpolation of the input Spectra versus Period curves for determining the spectra value for a mode given its period. Linear is the default. Since Spectra versus Period curves are often linear only on Log-Log scales, the logarithmic interpolation is recommended in such cases; especially if only a few points are entered in the spectra curve.
Note: Not all codes have provisions for different interpolation types. In that case, the type used is selected but this cannot be changed.
Scale Linear scale factor by which the spectra data will be multiplied. Usually used to factor g’s to length/sec2 units. This input is the appropriate value of acceleration due to gravity in the current unit system (thus, 9.81 m/s2 or 32.2 ft/s2).
Note: Not all codes have provisions for scaling the values. In that case, the value of unity is displayed but this cannot be edited.
Save This option results in the creation of a acceleration data file (with the model file name and an .acc file extension) containing the joint accelerations in g’s and radians/sec2. These files are plain text and may be opened and viewed with any text editor (e.g., Notepad).
Use Torsion Check this option to consider the torsional moment (in the horizontal plane) arising due to eccentricity between the center of mass and center of rigidity.
Note: Custom response and Eurocode spectra cannot include torsion.
Dynamic Eccentricity (DEC) For when torsion is included, type the factor to be multiplied with static eccentricity (i.e., eccentricity between center of mass and center of rigidity).
Accidental Eccentricity (ECC) For when torsion is included, type the factor for accidental eccentricity. Positive values indicate clockwise torsion and negative values indicate counterclockwise torsion.
Generate IMR Results Check this option to generate load case results for individual modal response (i.e., each mode).
Note: This option is not available for Russian response spectra.
No. Modes The number of individual modal responses (scaled modes) to be copied into load cases. If greater than the actual number of modes extracted, then this will be limited to the number of modes extracted. Missing Mass modes are not output.
Set Start Load Case Check this option to specify the starting load case number to use for the first individual modal response generated load case. Otherwise, the current highest load case number will just be incremented by 1.
Load Case no Type the load case number to use for the first individual modal response generated load case.
Options (IBC codes only) Select the method to locate the mapped acceleration values from the IBC / ASCE 7 codes:
  • Zip – use the Zip (postal) code
  • Latitude/Longitude – use global coordinates
  • Ss/S1 – type the mapped acceleration values directly
Parameters For parametric response spectra, type the code-related parameter values.
Values For custom or non-parametric response spectra, enter the acceleration or displacement data here.

EN 1998 - 2004 Parameters

Design Ground Acc The "Ground Acceleration On Type A Ground" and defined in Eurocode 8 as ag, as used in equations 3.2 – 3.5. Refer to the Eurocode for further information.
Note: The specified value is the ratio of the ground acceleration (ag) to acceleration due to gravity. That is, this value should be a factor of G, not an actual acceleration (e.g., for a value of ag = 1.5 m/s2, then enter a value = 1.5 m/s2 / 9.81 m/s2 = 0.153).
Behavior factor An approximation of the ratio of the seismic forces that the structure would experience if its response was completely elastic with 5% viscous damping, to the seismic forces that may be used in design, with a conventional elastic analysis model, still ensuring a satisfactory response of the structure.
Subsoil Class This parameter is used to define the subsoil conditions based on which the response spectra will be generated as defined in Table 3.1 Ground Types.  Based on the subsoil conditions the soil types may be of five kinds:
  • Type A: rock or other rock-like geographical formation.
  • Type B: very dense sand, gravel or very stiff clay.
  • Type C: Deep deposits of dense or medium dense sand, gravel or stiff clay.
  • Type D: Deposits of loose-to-medium cohesionless soil or of predominantly soft to firm cohesive soil.
  • Type E: Surface alluvium layer

Please refer section 3.2 of Eurocode 8 for detailed guidelines regarding the choice of soil type.

Load Type The response spectrum loading can be based on either Elastic or Design response spectra. Refer to Eurocode 8.

The capacity of structural systems to resist seismic actions in the nonlinear range generally permits their design for forces smaller than those corresponding to a linear elastic response. To avoid explicit nonlinear structural analysis in design, the energy dissipation capacity of the structure through mainly ductile behavior of its elements and/or other mechanisms, is taken into account by performing a linear analysis based on a response spectrum which is a reduced form of the corresponding elastic response spectrum. This reduction is accomplished by  introducing the behavior factor Q and the reduced response spectrum is termed as "Design Response Spectrum." STAAD.Pro generates the Elastic Response Spectra using the guidelines of section 4.2.4 and Table 4.2 of Eurocode 8.

So, if the structure is supposed to resist seismic actions in the nonlinear range the Design Response Spectra is to be used.

Type Two types of response spectra curve can be generated based on either response spectra type 1 curve or response spectra type 2 curve.

IS 1893 - 2016 Parameters

Subsoil Class Select the subsoil classification or to provide Custom values. Depending upon time period, types of soil and damping, the average response acceleration coefficient, Sa/g is calculated.

If Custom is selected, provide the data pair Values.

SP14.13330 - 2011 Parameters

Zoning Factor The zoning factor based on maximum acceleration factor for the seismic zone. This factor must be modified for Subsoil Class selections other than 2.
Subsoil Class Defines the subsoil conditions on which the response spectrum will be generated.
  1. Non-weathered rock and rocklike geological formation or permafrost subsoil.
  2. Weathered rock or deep deposits of medium dense sand, gravel or medium stiff clays.
  3. Loose cohesion less soil deposits or deposits with soft to medium stiff cohesive soil.

IBC 2015 / ASCE 7 2010

Long Period (TL) Long-Period transition period in seconds. (IBC 2015, ASCE 7-10 Chapter 22)
Fa Optional Short-Period site coefficient at 0.2s. Value must be provided if SCLASS set to F (i.e., 6). (IBC 2006, ASCE 7-05 Section 11.4.3)
Fv Optional Long-Period site coefficient at 1.0s. Value must be provided if SCLASS set to F (i.e., 6). (IBC 2006, ASCE 7-05 Section 11.4.3)
Site Class (SCL) Select A through F for the Site Class as defined in the IBC code. (IBC 2000, Section 1615.1.1 page 350. IBC 2003, Section 1615.1.1 page 322. IBC 2006 ASCE 7-05 Section 20.3)