Function
- Enter spectral data for response spectrum analysis.
- Response Spectrum Analysis calculates modal responses using the natural periods obtained by Eigenvalue analysis. Therefore, Response Spectrum Function must be defined, which includes the range of the considered natural periods obtained from the Eigenvalue analysis.
Range of the natural periods obtained from Eigenvalue analysis
Call
From the main menu, selecet [Load] tab > [Type : Dynamic Loads] > [Response Spectrum Data] group > [RS Functions]
Input
Add
Enter new or additional spectral data
Modify/Show
Modify previously entered spectral data. Select the relevant spectral data from the spectral data list of the dialog box and click the Modify/Show button.
Delete
When deleting previously entered spectral data. Select the relevant spectral data from the spectral data list of the dialog box and click the Delete button.
Click the Add button or the Modify/Show button to display the dialog box below and enter the required data in the relevant entry fields.
Add/Modify/Show Response Spectrum Functions dialog box
How to enter spectrum data
Create files containing frequently used response spectrum load cases, then retrieve the files
Import File : Use the method to enter previously created spectral data.The data are saved with a '.sgs' or '.spd' extension and written in the following formats :
'fn.sgs' file format
*SGSw | To define that the file is in "Seismic Data Generator" data format which is a MIDAS/Civil module that auto-extracts seismic data |
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*TITLE, MAINTITLE |
Description for main title Ex. ATC 3-06 Design Spectrum |
*TITLE, SUBTITLE |
Description for subtitle Ex. Soil = 1.0 Aa = 1.00 Av =1.00 RMF = 1.00 |
*X-AXIS, LEGENDX |
Description for horizontal axis Ex. Period Tn (sec) |
*Y-AXIS, LEGENDY |
Description for vertical axis Ex. Absolute Acceleration (g) |
*UNIT&TYPE, UNIT, TYPE |
Description for units in use and data type UNIT: GRAV, MM, CM, M, INCH (IN, IN.), FEET (FT, FT.) allowed. TYPE: ACCEL (Acceleration), VELO (Velocity), DISP (Displacement) allowed |
*FLAGS, SPECTYPE, DAMPINGUSE |
Description for spectrum type and damping ratio in use SPECTYPE: 1 for Tripartite spectrum type, 0 for the other cases DAMPINGUSE: 1 for using Damping Ratio, 0 for not using Damping Ratio |
*DATA |
To define where the data starts |
*DAMPING, DAMPINGRATIO |
Description for damping ratio It is defined when damping ratio is 1 only. |
X-Data, Y-Data |
X: Period, Y: Spectral Data X-Data: Spectral Data for X-axis Y-Data: Spectral Data for Y-axis Ex. 1.00000E-006, 2.50000+000 1.20000E-001, 2.50000E+000 |
*ENDDATA |
To define when the data ends It is used after *DATA is defined. |
Example of a '*.sgs' file
'fn.spd' file format - User-defined
*UNIT |
Description for units in use UNIT: MM, CM, M, INCH, FEET, GRAV allowed |
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*TYPE |
Description for data type TYPE: ACCEL (Acceleration), VELO (Velocity), DISP (Displacement) allowed. |
*DATA | To define when the data starts |
X-Data, Y-Data |
X: Period, Y: Spectral Data Ex. 1.00000E-006, 2.50000+000 4.00000E-002, 2.50000E+000 … (Repeat for each data point) 1.20000E-001, 2.50000E+000 |
Example of a '*.spd' file
'fn.thd' file format - User-defined ** Comments - Entry allowed anywhere
*UNIT, LENGTH, FORCE |
Description for length and force LENGTH: MM, CM, M, INCH(IN, IN.), FEET(FT, FT.) allowed FORCE: KG, KGF, TON, N, KN, LBF, KIP, NULL allowed |
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*TYPE |
Description for data type TYPE: ACCEL (Acceleration), VELO (Velocity), DISP (Displacement) allowed. |
*DATA | To define when the data starts |
X-Data, Y-Data |
X: Period, Y: Spectral Data Ex. 1.00000E-006, 2.50000+000 4.00000E-002, 2.50000E+000 … (Repeat for each data point) 1.20000E-001, 2.50000E+000 |
Example of a '*.thd' file
Access the built-in response spectrum load cases in midas Civil database
Design Spectrum : Use the feature to enter spectrum functions created in accordance with the standards. Select the standard from the spectrum function list and enter the desired parameters.
The built-in design spectrum types are as follows :
IBC2000(ASCE7-98): International Building Code 2000
UBC (1997): UBC 97 standards
UBC 88-94: UBC 91 standards
NBC (1995): National Building Code of Canada 1995
NTC 2018: Italian technical standards
Eurocode-8 (2004): Design provisions for earthquake resistance of structures. General rules. Strengthening and repair of buildings.
Eurocode-8 (1996) Design: Design provisions for earthquake resistance of structures. General rules. Strengthening and repair of buildings.
Eurocode-8 (1996) Elastic: Design provisions for earthquake resistance of structures. General rules. Strengthening and repair of buildings.
Romania (P100-1,2013): Seismic Design Code.
AS 5100.2: 2017: Australian highway bridge design standard
DPWH-BSDS 2013: Philippines highway bridge design standard
IRC SP 114:2018: Seismic Design of Road Bridges
Seismic zone factor, Importance factor and Response Reduction Factor can be specified as user input.
IS1893 (2002): Indian Standards
TaiwanBrg (89) Horizontal: Taiwan Seismic Code
TaiwanBrg (89) Vertical: Taiwan Seismic Code
China (GS50011-2001): For Chinese version
Specific period (Tg) can be modified by the user.
China (JTJ004-89): For Chinese version
Specific period (Tg) and horizontal seismic coefficient (ku) can be modified by the user.
China (GBJ111-87): For Chinese version
Specific period (Tg) and horizontal seismic coefficient (ku) can be modified by the user.
China Shanghai (DGJ08-9-2003): Shanghai Code for Seismic Design of Buildings
Japan (Arch, 2000): For Japanese version
Japan (Bridge2002)
Korea (Bridge): Specification for Roadway Bridge
Korea (Arch, 2000): Buildings loading criteria and commentaries
Korea (Arch, 1992): Regulations related to structural criteria for buildings
Importance factor (I) in the combo box can be defined by selecting the factor in the drop-down menu or by typing the factor directly.
Generate Design Spectrum dialog box
Enter directly the spectral data in the entry fields in the Add/Modify/Show Response Spectrum Functions dialog box
The user directly enters the period and spectrum values in the entry field to the left of the dialog box.
For easy interpretation, the spectrum functions are processed in graphs representing spectrum values vs periods. The spectrum functions corresponding to the natural periods of the structure are linearly interpolated in the response spectrum analysis. Thus, it may be prudent to provide functional values at closed intervals where the curvature suddenly varies. In addition, the range of periods for the spectrum functions must include all the natural periods of the structure.
Function Name
Enter the name of the spectral data. The name is used in "Response Spectrum Load Cases" which is the function used to enter response spectrum load cases.
Spectral Data Type
Assign the spectral data type to be entered.
Normalized Accel. : Spectrum obtained by dividing the acceleration spectrum by the acceleration of gravity
Acceleration : Acceleration spectrum
Velocity : Velocity spectrum
Displacement : Displacement spectrum
If the type of entered response spectral data is changed, the data are not converted according to the unit of the data type. Rather only the application type of the entered data is changed.
Scaling
Scale Factor : Specify a multiplier for Response Spectrum Data. When changing the Spectral Data Type with spectrum data already entered, the data entered will not automatically change according to the new unit. Only the display format will be updated. Therefore, by entering the increment/decrement amount due to the unit conversion as a Scale Factor, you can reduce the inconvenience of having to manually change all the spectrum data.
Maximum Value : Maximum value of Response Spectrum Data can be controlled by the user. For example, if the maximum value of the entered acceleration is 10g, and you enter 2g as the Maximum Value, the maximum value of the spectrum will be scaled down to 2g.
Gravity
Enter the acceleration of gravity.
Damping Ratio
Specify a Damping Ratio applicable to the response spectrum, which will be used in response spectrum analysis.
If the damping ratio applied in the development of the response spectrum differs from the damping ratio of the structure for which the analysis is performed (Apply Damping Method in Response Spectrum Load Cases), the spectrum data is processed and applied according to the damping ratio of the structure. There are several methods for processing spectrum data, including interpolation using multiple spectrum data and correction equations.
Graph Options
Specify whether or not to produce a graph in Log Scale.
Description
Enter a brief description of Response Spectrum Data. When the Design Spectrum has been generated, the basic Spectrum Data such as soil & area coefficients and importance & response factors are displayed.
For convenience, midas Civil supports the following 4 entry methods:
1. Create files containing frequently used response spectrum load cases, which are then retrieved for later uses
2. Access the built-in response spectrum load cases in the database
3. Use Seismic Data Generator to enter the load cases
4.The user directly enters the load cases