Parameters for FEMA 440 Equivalent Linearization Form

Additional forms:  FEMA 440 Coefficients for Beff, FEMA 440 Coefficients for Teff

Use the Parameters for FEMA 440 Equivalent Linearization form to specify the parameters for displaying pushover curves in accordance with FEMA 440 Equivalent Linearization guidance.

• Name edit box. The program will suggest a default name. Use this name or type a new one in this edit box.

• Units drop-down list. Use the units displayed or select another from the list; the units displayed will be used on the plot of the pushover curve.

• Plot Axes area. Choose the plot axes as Sa-Sd (spectral acceleration vs spectral displacement), Sa-T (spectral acceleration vs period) or Sd-T (spectral displacement vs period).

• Set Axis Data button. Click this button to access the Overrride Axis Labels and Range form. Use the options on that form to change the minimum and maximum horizontal and vertical ranges and the axis labels for the curve.

• Demand Spectrum Definition. Choose to define the demand spectrum based on a function or user specified coefficients.

• • Function option, drop-down list, and SF (Scale Factor) edit box. When this option is selected, choose a previously defined spectrum function from the drop-down list and use the default scale factor or use the edit box to specify the SF.

  • Use Coeff and Ca and Cv (Seismic Coefficient) edit boxes. The shape of the demand spectrum with 5% damping is controlled by the values input in the Ca and Cv (Seismic Coefficient) edit boxes. Refer to ATC-40, Chapter 4, for an explanation of, and appropriate values for, Ca and Cv. The default value for both Ca and Cv is 0.4. Demand spectra for other damping levels are created from the 5% damped spectrum using the spectral reduction factors described in Section 8.2.2.1.1 of ATC-40.

  • Include Soil-Structure Interaction Effects check box.  Checking this box will add soil-structure interaction effects to the plot and will also enable the Modify/Show SSI button. Click that button to display the FEMA 440 Soil-Structure Interaction form. Use the options on that form to specify the Kinematic effects and foundation damping parameters for the SSI interaction effects.

• Damping and Period Parameters Definition.

• • Inherent + Additional Damping edit box. In the Damping Parameters area, type a value in the Inherent/Additional Damping edit box. The value input into this box must be between 0 and 1, inclusively. The default value is 0.05. Referring to ATC-40 equation 8-8, the b0 term is automatically included by the SAP2000 analysis method, and the 5% inherent viscous damping term can be specified in the Inherent/Additional Damping edit box as 0.05. If additional viscous damping is provided in the structure, perhaps by viscous dampers that are not specifically included in the model, this damping should also be included in the Inherent + Additional Damping edit box. Thus if the damping inherent in the structure is assumed to be 5% of critical damping, and dampers that provide an additional 7% of critical damping are assumed to be added to the structure (although they are not actually in the model), the value input in the Inherent + Additional Damping edit box should be 0.12, since 0.05 + 0.07 = 0.12.

  • User Defined Effective Damping, Beff. Checking this check box and clicking the Modify/Show button will display the FEMA 440 Coefficients for Beff form. Use that form to specify the effective damping coefficients.

  • User Defined Effective Period, Teff. Checking this check box and clicking the Modify/Show button will display the FEMA 440 Coefficients for Teff form. Use that form to specify the effective period coefficients.

• Items Visible On Plot area. Choose the items to be displayed on the plot.

• • Show Capacity Curve check box. Checking this check box will show the capacity curve on the plot.

  • • Color. The default color for the capacity curve is green. Click the color box to display the Color form and change the color of the capacity curve.

  • Show Family of Demand Spectra (MADRS) check box. Checking this check box overlays a family of demand spectra on the capacity curve in the ADRS format.

  • • Color. The default color for the family of demand spectra curves is red. Click the color box to display the Color form and change the color of the demand spectra.

    • Ductility Ratios. The family of curves can include up to four demand spectrum curves, each with a different ductility. By default the program plots curves with ductilities of 1, 1.5, 2 and 2.5. The ductility ratios for any of the four curves can be changed by editing the values in one of the Ductility Ratio edit boxes.

  • Show Single Demand Spectrum (MADRS) (Variable Damping). Check the Show Single Demand Spectrum (Variable Damping) check box to display the demand spectrum as a single curve.

  • • Color. The default color for the single modified demand spectrum curve is yellow. Click the color box to display the Color form and change the color of the demand spectrum.

The family of demand spectra and the single demand spectrum (variable damping) can be displayed at the same time, or they can be displayed separately.

• Show Constant Period Lines At check box. Check the Show Constant Period Lines At check box to display lines of constant period. These lines appear as radial lines on the capacity spectrum plot. By default the program plots lines for T = .5, 1, 1.5 and 2 seconds. The periods for any of the four curves can be changed by editing the value in one of the four associated edit boxes. A value of 0, or a blank edit box, means to omit that period line.

• • Color. The default color for the period lines is gray. Click the color box adjacent to display the Color form and change the color of the period lines.

• Reset Default Colors button. Click the Reset Default Colors button to reset all of the colors to the defaults.