FEMA 440 Soil-Structure Interaction Form

Use the FEMA 440 Soil-Structure Interaction form to specify kinematic effects and foundation damping to be applied to the demand spectrum in accordance with FEMA 440.

Include Kinematic Effects check box. Check this check box to include Kinematic effects for the soil-structure interaction. With the check box checked, use the default values or specify other values for the Effective Foundation Size, the Foundation Embendment, the Shear Wave Velocity, and the Shear Wave Velocity Reduction Factor in the associated edit box. These items are specified in FEMA 440 Section 8.2.
Include Foundation Damping check box. Check this check box to include foundation damping. With the check box checked, use the default value or specify another value for the Modified Damping Ratio of the System in the associated edit box. The damping ratio specified here is the flexible-base damping ratio calculated in accordance with FEMA Equation 8-10.
Show Spectra Comparison for SSI Effects button. Click this button to display the Spectra Comparison for Soil-Structure Interaction Effects form, which will display the spectral displacement vs spectral acceleration, period vs spectral acceleration, or period vs spectral displacement plot, depending on the option selected.
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 soil-structure interaction effects curve.
Reset Defaults button. Clicking this button will return all options on the form to program defaults.

Access the FEMA 440 Soil-Structure Interaction form as follows:

Define a nonlinear static analysis case whose Load Application type is Displacement Control and whose Results Saved type is Multiple States, and run an analysis.
Choose Method a, b, or c to specify the display for a pushover curve, define parameters for it, or save the options as a Named Set, respectively:
1. Click the Display menu > Show Pushover Curve command to display the Pushover Curve form. Select FEMA 440 Displacement Modification or FEMA 440 Linearization for the Plot Type, and click the Add New Parameters button, or select an existing curve definition and click the Add Copy of Parameters or Modify/Show Parameters button, to display the Parameters for FEMA 440 Displacement Modification form or the Parameters for FEMA 440 Equivalent Linearization form.
2. Click the Define menu > Pushover Parameter Sets > FEMA 440 Displacement Modification command or the Define menu > Pushover Parameter Sets > FEMA 440 Equivalent Linearization command to display the Define Pushover Parameters for FEMA 440 Displ Mod or the Define Pushover Parameters for FEMA 400 Eq Linear form; then click the Add New Parameters button, or select an existing parameter set definition and click the Add Copy of Parameters or Modify/Show Parameters button, to display the Parameters for FEMA 440 Displacement Modification form or the Parameters for FEMA 440 Equivalent Linearization form, respectively.
3. Click the Define menu > Named Sets > Pushover Named Sets command to display the Define Pushover Named Sets form. Then click the Add New Named Set button, or highlight a previously defined Named Set and click the Add Copy of Named Set or Modify/Show Named Set button, to display the Pushover Named Set Data form. On that form select FEMA 440 Displacement Modification or FEMA 440 Linearization for the Plot Type, and click the Add New Parameters button, or select an existing named set and click the Add Copy of Parameters or Modify/Show Parameters button, to display the Parameters for FEMA 440 Displacement Modification form or the Parameters for FEMA 440 Equivalent Linearization form.
Check the Include Soil-Structure Interaction Effects check box and then click the Modify/Show SSI button.