Override Diaphragm Eccentricities Form

Access the Override Diaphragm Eccentricities form as follows:

Method 1

Click the Define menu > Load Cases command to display the Define Loads form.
Select a Quake Load Type.
Specify an Auto Lateral Load other than None and click the Add New Load button.
Highlight the newly defined load case and click the Modify Lateral Load button to display the {Code} Seismic Loading form.
Click the Override button to display the Override Diaphragm Eccentricities form.

Method 2

Click the Define menu > Analysis Cases command to access the Analysis Cases form.
Click the Add New Case button, or highlight a previously defined case and click the Add Copy of Case or Modify/Show Case button, to display the Analysis Cases Data form.
Select Response Spectrum from the Analysis Case Type drop-down list to display the Analysis Case Data - Response Spectrum form.
Click the Overrides button in the Diaphragm Eccentricity area of the form to display the Override Diaphragm Eccentricities form.

When defining automatic seismic lateral loads as part of a load case definition (Method 1 above), an option exists to specify that the load is eccentric to the center of mass of the diaphragms. An eccentricity ratio may be specified that applies to all diaphragms. In addition, the eccentricity may be overwritten individually for one or more diaphragms.

Eccentric loading is applied to diaphragm constraints only; it is applied as a torsional moment. The non-eccentric portion of the load is applied to the whole model based on mass, and does not require diaphragm constraints.

Diaphragm constraints must be assigned to joint objects in the model for the auto lateral load to apply eccentric loads.

Note: Eccentricity overrides apply to diaphragm constraints whose associated coordinate system is Global, and whose associated axis is Z. Thus, this type of diaphragm must be included in the model for this feature to be available.

Use the following buttons on the Override Diaphragm Eccentricities form to override the eccentricity ratio for one or more diaphragms.

Add button

From the Diaphragm drop-down list, select the diaphragm name for which eccentricity values are to be specified.
Enter a value in the Eccentricity, X-Dir (Eccen Y) or Y-Dir (Eccen X) edit box
Click the Add button.

Note: Eccentricities are specified as lengths, not ratios. If you are defining a load in the X direction, the eccentricity is measured in the Y direction, and vice-versa.

Modify button

In the Diaphragm/Eccentricities display areas, select the diaphragm name for which eccentricity values are to be modified.
Enter a revised value in the Eccentricity, X-Dir (Eccen Y) or Y-Dir (Eccen X) edit box.
Click the Modify button.

Delete button

In the Diaphragm/Eccentricities display areas, select the definition to be deleted.
Click the Delete button.

Return to SAP2000 Index

Your Ad Here