Load: Response Spectrum Load Set

Function

Enter the Load Sets, spectrum functions and loading directions for response spectrum analysis.

Call

Model > Load > Response Spectrum Analysis Data > Response Spectrum Load Set

<Response Spectrum Load Set>

Load Set Name

Enter the name of the Response Spectrum Load Set.
 

Description

Enter a brief description of the Load Set.
 

Spectrum Function

Function Name

Select a spectrum function name. If spectral functions have not been defined, click to add new function .
Direction

Select the GCS direction of the response spectrum loads.
Direction Vector

Displays the selected direction in vector.
Scale Factor

Scale factor for the entered response spectrum excitation
Period Modification Factor

A multiplying factor for periods calculated by Eigenvalue analysis. This factor applies to all the natural periods calculated by Eigenvalue analysis for response spectrum analysis. This functionality becomes useful, for example, when the user wants to account for the stiffness contribution of non-structural elements, in which case the user may prefer to reduce the calculated periods.
 

Damping

Damping Ratio

Enter a damping ratio
Correction by Damping Ratio

When a single spectrum is selected, a modifying equation is used to adjust the spectrum applied to each mode having a corresponding damping ratio. Click to prompt the Damping Method dialog box.
 

<Damping Method>

Direct Modal

The user defines the damping ratio for each mode, and the modal response is calculated based on the spectrum function, which is modified by the user-defined damping ratio.
 

<Damping Method - Direct Modal>

Direct Specification of Modal Damping

Directly Specify the damping ratio for each mode.
 

Damping Ratio for All Modes

It applies to every mode except the ones that the user has directly specified. It applies to all the modes other than the damping ratios assigned to the specific modes in the Modal Damping Overrides table below. When the entered damping ratio is different from the user-defined damping ratio in Response Spectrum Functions, the previous spectrum data will be interpolated based on this damping ratio.

Modal Damping Overrides

The user directly defines the damping ratio for each mode.
 

Mode

Mode Number

Damping Ratio

Damping ratio for each mode
 

: to add a new damping ratio
: to modify the existing damping ratio
: to remove the existing damping ratio
 

Mass & Stiffness Proportional

Using the dynamic property and the modal damping ratios of two modes, the damping matrix, which is proportional to Mass and Stiffness, is generated. This damping matrix evaluates the damping ratio for each mode, and the response spectrum analysis is carried out while reflecting the modal damping ratio.
 

<Damping Method - Mass & Stiffness Proportional>

Damping Type

Select if the damping matrix is proportional to Mass or to Stiffness.
 

Direct Specification

The user directly defines the proportional coefficients for the checked Damping Type.

Cal. from Modal Damping

Using the modal damping ratios that are specified by the user , it automatically calculates and inputs the proportional coefficients.
 

Coefficients Calculation

If either Mass or Stiffness Proportional is checked in Damping Type, modal damping ratio of only one mode can be entered. If both are checked, modal damping ratios of two modes can be specified.
 

Frequency [Hz]

Enter the frequency of the corresponding mode to be assigned a damping ratio for calculating proportional coefficients.

Period [Sec]

Enter the period of the corresponding mode to be assigned a damping ratio for calculating proportional coefficients.

Damping Ratio

Enter the damping ratio corresponding to the specified frequency or the period.
 

: It calculates the damping ratio based on the entered proportional coefficient and the frequency or the period. Since damping ratios for only two modes can be specified to reflect the damping effect of mass or stiffness proportional, this tool makes it possible to calculate damping ratios for the other modes.
 

<Damping Ratio>

Interpolation of Spectral Data

Select the method of interpolating the response spectrum load data.

Linear

Linear interpolation method.

Logarithm

Log-scale interpolation method.
 

: Enter new or additional response spectrum analysis load sets
: Modify previously entered response spectrum analysis load sets
: Delete previously entered response spectrum analysis load sets