Response Spectra tab
Used to apply response spectrum loads on the structure.
Common Parameters for all Code options
Setting | Description | ||||||
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Combination Method |
The various methods available in STAAD.Pro for combining the contribution from the individual modes is listed under this heading. The details of these methods are explained in TR.32.10.1 Response Spectrum Analysis. Note: Not all
methods are available for all code options.
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Save | Select this option to generate a file (with .acc. extension) containing the joint accelerations in g’s and radians/sec2 | ||||||
Period vs. Acceleration table | Provide the values of period (seconds) and corresponding acceleration (current length units/sec2) or displacement (current length unit). Spectrum pairs should be provided in ascending value of period. As we provide the curve points, the program displays the curve at the bottom of the dialog box. | ||||||
Spectrum Type | Choose whether the response spectrum curve will be input as Period vs. Acceleration or Period vs. Displacement (Custom and IS 1394 only). | ||||||
Interpolation Type |
From the spectrum data that are provided under the Define Spectrum Pairs tab of the dialog box shown above, STAAD fetches the spectral value for the actual modes of the structure using one of two interpolation methods – Linear and Logarithmic. Linear interpolation is the default method. 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. |
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Damping Type |
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Scale |
Linear scale factor by which the spectra data will be multiplied. Usually to factor g’s to length/sec2 units. This input is the appropriate value of acceleration due to gravity in the current unit system You may choose to provide the spectral acceleration or displacement data as a set of un-normalized values or as a set of normalized values. For normalized values, the normalization factor is specified through the means of the Scale factor. For example, if the curve is input in terms of “g” - the acceleration due to gravity - and the current length unit is feet, the Scale would be 32.2. For un-normalized values, the scale factor is provided as 1.0, which also happens to be the default. The spectra data will be multiplied by the scale factor during the analysis. |
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Missing Mass | Select this option to apply the Missing mass correction. The static effect of the masses not represented in the modes is included. If this option is selected on any spectrum case it will be used for all spectrum cases. | ||||||
ZPA | Zero Period Acceleration: It is used only with the missing mass option. If no value is entered or a zero value is entered, the default considered by the program is 33 Hz. If an acceleration is entered corresponding to the Missing mass mode, then the ZPA value is ignored. If no acceleration value is entered for the missing mass mode, then spectral acceleration corresponding to the ZPA frequency is used. | ||||||
Direction | Specify the global direction(s) in which the spectrum is to be applied. The response spectrum may be applied in one or more directions simultaneously. Directions not provided will default to zero. | ||||||
Use Torsion | (IS 1893, IBC 2012, IBC 2018 and NRC only)
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Signed Response Spectrum Results Options |
Two method are available for added mathematical signs to the spectrum response output:
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Individual Modal Response Load Case Generation |
Select this option to have the program automatically generate primary load cases from the mode shape scaled to the magnitude that the mode has in this spectrum analysis case before it is combined with other modes. A load case is generated for each of first number of modes specified, starting with the specified load case number. Note: The Individual
Modal Response case generation is not available for SNiP II code response
spectra.
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Custom
Setting | Description |
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Generate Spectrum | Opens the Spectrum Parameters dialog, which is used to generate a response spectrum curve per the International Building Code. |
IS-1893 2002
Setting | Description |
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Subsoil Class | Select the soil type for the site (hard , medium, soft, or custom). Depending on the type of soil & time period, average response acceleration coefficient Sa/g is calculated. |
IS-1893 2016
Setting | Description |
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Subsoil Class | Select the soil type for the site (hard , medium, soft, or custom). Depending on the type of soil & time period, average response acceleration coefficient Sa/g is calculated. |
IS-1893(Part 4):2015
Setting | Description |
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RSMIN | Select a factor, given in percent, to multiply by the total seismic weight of the structure to obtain a minimum base shear value. This percentage is taken from Table 2 of IS:1839(Part 4)-2015. The default value is taken for a structure category 1 and zone 2.
If the minimum base shear value exceed the calculated response spectrum base shear, then all analysis results of the response spectrum load case are scaled by the ratio of the minimum base shear to the calculated response spectrum base shear. This multiplying factor will be noted in the output. |
EURO (EC8) -1994
Setting | Description |
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Load Type | Select either a Elastic or Design response spectrum for the loading type. |
Design Ground Acceleration | Specify a design ground acceleration expressed in terms of acceleration due to gravity(g). For most of the application of Eurocode 8, the hazard is described in terms of a single parameter (i.e., the value of effective peak ground acceleration in rock or firm soil). This acceleration is termed as the design ground acceleration. |
Behaviour Factor | Specify the value used to reduce the elastic response spectra to the design response spectra. The behavior factor is 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 minimum seismic forces that may be used in design- with a conventional linear model still ensuring a satisfactory response of the structure. |
Subsoil Class |
Used to define the subsoil conditions based on which the response spectra will be generated. Based on the subsoil conditions the soil types may be of three kinds
Please refer section 3.2 of Eurocode8 for detailed guidelines regarding the choice of soil type. |
EURO (EC8) - 2004
Setting | Description |
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Load Type |
Select either a Elastic or Design response spectrum for the loading type. Two types of response spectra curve can be generated based on either RS1 (for response spectra type 1 curve) or RS2 (for response spectra type 2 curve) f. |
Design Ground Acceleration | Specify a design ground acceleration expressed in terms of acceleration due to gravity(g). For most of the application of Eurocode 8, the hazard is described in terms of a single parameter (i.e., the value of effective peak ground acceleration in rock or firm soil). This acceleration is termed as the design ground acceleration. |
Behaviour Factor | Specify the value used to reduce the elastic response spectra to the design response spectra. The behavior factor is 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 minimum seismic forces that may be used in design- with a conventional linear model still ensuring a satisfactory response of the structure. |
Subsoil Class |
Used to define the subsoil conditions based on which the response spectra will be generated. Based on the subsoil conditions the soil types may be of three kinds
Please refer section 3.2 of Eurocode 8 for detailed guidelines regarding the choice of soil type. |
IBC 2006
Setting | Description |
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Zip | The zip code of the site location to determine the latitude and longitude and consequently the Ss and S1 factors. |
Latitude / Longitude | The geographic coordinates of the site used to determine the Ss and S1 factors. This option may be used if no value is entered for Zip. |
S1 / SS | Mapped MCE for 0.2s spectral response acceleration and spectral acceleration for a 1-second period, respectively. These values may be entered if not geographic coordinate or postal code is provided. |
Long Period (TL) | Long-Period transition period in seconds. |
Fa / Fv | Optional Short-Period site coefficient at 0.2s and Long-Period site coefficient at 1.0s, respectively. Values must be provided if the selected Site Class (SCL) is F. |
Site Class (SCL) | Select A through F for the Site Class as defined in the IBC code. |
IBC 2012
Setting | Description |
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Zip | The zip code of the site location to determine the latitude and longitude and consequently the Ss and S1 factors. |
Latitude / Longitude | The geographic coordinates of the site used to determine the Ss and S1 factors. This option may be used if no value is entered for Zip. |
S1 / SS | Mapped MCE for 0.2s spectral response acceleration and spectral acceleration for a 1-second period, respectively. These values may be entered if not geographic coordinate or postal code is provided. |
Long Period (TL) | Long-Period transition period in seconds. |
Fa / Fv | Optional Short-Period site coefficient at 0.2s and Long-Period site coefficient at 1.0s, respectively. Values must be provided if the selected Site Class (SCL) is F. |
Site Class (SCL) | Select A through F for the Site Class as defined in the IBC code. |
IBC 2015
Setting | Description |
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Zip | The zip code of the site location to determine the latitude and longitude and consequently the Ss and S1 factors. |
Latitude / Longitude | The geographic coordinates of the site used to determine the Ss and S1 factors. This option may be used if no value is entered for Zip. |
S1 / SS | Mapped MCE for 0.2s spectral response acceleration and spectral acceleration for a 1-second period, respectively. These values may be entered if not geographic coordinate or postal code is provided. |
Long Period (TL) | Long-Period transition period in seconds. |
Fa / Fv | Optional Short-Period site coefficient at 0.2s and Long-Period site coefficient at 1.0s, respectively. Values must be provided if the selected Site Class (SCL) is F. |
Site Class (SCL) | Select A through F for the Site Class as defined in the IBC code. |
IBC 2018
Setting | Description |
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Zip | The zip code of the site location to determine the latitude and longitude and consequently the Ss and S1 factors. |
Latitude / Longitude | The geographic coordinates of the site used to determine the Ss and S1 factors. This option may be used if no value is entered for Zip. |
S1 / SS | Mapped MCE for 0.2s spectral response acceleration and spectral acceleration for a 1-second period, respectively. These values may be entered if not geographic coordinate or postal code is provided. |
Long Period (TL) | Long-Period transition period in seconds. |
Fa / Fv | Optional Short-Period site coefficient at 0.2s and Long-Period site coefficient at 1.0s, respectively. Values must be provided if the selected Site Class (SCL) is F. |
Site Class (SCL) | Select A through F for the Site Class as defined in the IBC code. |
SNiP II-7-81
Setting | Description |
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Zoning Factor | Specify the zoning factor per SNiP II-7-81. |
Subsoil Class |
Defines the subsoil conditions on which the response spectrum will be generated.
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Direction | The SNiP code allows an alternate method of specifying directional factors. You may input individual parameters such as KWX, KX1 the product of which is used as the factor along that direction. |
SP 14.13330.2011
Setting | Description |
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Subsoil Class |
Defines the subsoil conditions on which the response spectrum will be generated.
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Direction | The SNiP code allows an alternate method of specifying directional factors. You may input individual parameters such as KWX, KX1 the product of which is used as the factor along that direction. |
NRC 2005
The NRC 2005 response spectrum has no code-specific parameters.
NRC 2010
The NRC 2010 response spectrum has no code-specific parameters.
Chinese GB 50012 - 2010
Setting | Description |
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Fortification Intensity | Fortification Intensity (ref. table 5.1.4-1). Selectable values are 6, 7, 7(0.15g), 8, 8(0.30g), or 9. |
Seismic Frequency | Frequency of seismic action (ref. table 5.1.4-1 and clause 3.10.3), as
specified by:
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Seismic Group | Design Seismic Group (ref. table 5.1.4-2). Selectable values are 1st, 2nd, or 3rd |
Site Class (SCL) | Site class (ref. table 5.1.4-2). Selectable values are I0, I1, II, III, or IV |
Max. Horizontal Influence Factor | Max horizontal seismic influence factor (ref. table 5.1.4-1 and clause 3.10.3). |
Period (Tg) | Characteristic period of the structure (Tg) (ref. table 5.1.4-2). |