Response Spectrum Functions

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 natural periods obtained from the Eigenvalue analysis.

Range of the natural periods obtained from Eigenvalue analysis

From the Main Menu select Load > Response Spectrum Analysis Data > Response Spectrum Functions.

Select Response Spectrum Analysis > Response Spectrum Functions in the Menu tab of the Tree Menu.

Response Spectrum Functions dialog box

Enter new or additional spectral data

Click .

Modify previously entered spectral data

Select the relevant spectral data from the spectral data list of the dialog box and click .

When deleting previously entered spectral data

Select the relevant spectral data from the spectral data list of the dialog box and click .

Click or to display the dialog box below and enter the required data in the relevant entry fields.

Add/Modify/Show Response Spectrum Functions dialog box

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

Note

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.

Scale

Scale Factor: Specify a multiplier for Response Spectrum Data.

 Maximum Value: Maximum value of Response Spectrum Data can be controlled by the user.

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.

Graph Options

Specify whether or not to produce 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/Gen supports the following 4 entry methods:

• 1. 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

Create files containing frequently used response spectrum load cases, then retrieve the files

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

'fn.spd' file format - User-defined

'fn.thd' file format - User-defined ** Comments - Entry allowed anywhere

Access the built-in response spectrum load cases in MIDAS/Gen database

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 :

IBC2012: International Building Code 2012

IBC2009: International Building Code 2009

IBC2000: International Building Code 2000

UBC (1997): UBC 97 standards

UBC 88-94: UBC 91 standards

NBC (1995): NBC 95 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.

IS1893 (2002): Indian Standards

Taiwan (2006): Taiwan Seismic Code

Note

For details of input parameters, refer to Loads > Lateral Loads > Static Seismic Load.

Note

From spectrum Used option, select a Spectrum in order to generate a function. This spectrum Used option cannot be applicable to Static Seismic Loads.

 (a) General Zone

    (b) Near Fault Zone

      (c) Taipei Basin

Generate Design Spectrum dialog box

Taiwan (1999) Horizontal: Taiwan Seismic Code

Taiwan (1999) Vertical: Taiwan Seismic Code

TaiwanBrg (89) Horizontal: Taiwan Seismic Code

TaiwanBrg (89) Vertical: Taiwan Seismic Code

(available upon request)

Japan (Arch, 2000): Japan, Arch. Assoc.- Building structure loading & comm.

Korean (KBC 2005): Korea Building Code-Structural, KBCS

Korea (Arch, 2000): Buildings loading criteria and commentaries

Korea (Arch, 1992): Regulations related to structural criteria for buildings

Korea (Bridge): Specification for Roadway Bridge

China Shanghai (DGJ08-9-2003): Shanghai Code for Seismic Design of Buildings

China (GB50011-2001): Code for seismic design of buildings

Generate Design Spectrum dialog box

Note

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.

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.