Define Loads Cases

Form:  Load Cases, Load Case Tree

A load case defines how loads are to be applied to the structure, and how the structural response is to be calculated. An unlimited number of named load cases of any type can be defined in ETABS. The load case(s) is selected when the model is analyzed.

Note: Load patterns by themselves do not create any response (deflections, stresses, and so forth). A load case must be defined to apply the load.

Before defining load cases, define any load patterns or functions that will be needed:

• For seismic analysis, the ground-acceleration loads are already built-in and do not need to be defined. For all other loads, use the Define menu > Load Patterns command to define the loads to be applied.

• For response-spectrum analysis, use the Define menu > Functions > Response Spectrum command to create the necessary input acceleration functions.

• For time-history analysis, use the Define menu > Functions > Time History command to input the time functions.

Tip: Every time a new load pattern is defined, the program automatically creates a corresponding linear static load case of the same name that applies the load. For a new model, the program creates a default load pattern called DEAD, which applies the self weight of the structure. The corresponding linear static analysis pattern is also called DEAD.

Use the Define menu > Load Cases command to access the Load Cases form and add, modify, or delete cases.  Use the following buttons on the form to achieve the required action:

• Add New Case button.

• 1. Click the Add New Case button to display the Load Case Data form.

  2. Use the various options on the Load Case Data form to define the new load case.

• Add Copy of Case button. Highlight an existing load case in the Load Case Name/Load Case Type display areas.

• 1. Click the Add Copy of Case button to display the  Load Case Data form and create a new load case based on the settings of the selected case.

  2. Use the various options on the Load Case Data form to change the necessary options to define a new load case.  

• Modify/Show Case button.

• 1. Highlight an existing load case in the Load Case Name/Load Case Type display areas.

  2. Click the Modify/Show Case button to display the  Load Case Data form.

  3. Use the various options on the  Load Case Data form to make the necessary adjustments to the case definition.  

Note: If you change the definition of an load case that has already been run, results for that case and any case that depends upon it will be deleted.

• Delete Case button.

• 1. Highlight an existing load case in the Load Case Name/Load Case Type display areas.

  2. Click the Delete Case button to delete the load case.

• Move Case Up or Down in List  Click on an existing load case to select it, then click the Up Arrow or Down Arrow button next to the case list to move the selected case upward or downward in the list. Rearranging the case list is primarily for viewing convenience. A load case may depend upon other load cases that are above or below it in the list. During analysis, the cases will be run in the order required by their dependencies. For example, a response-spectrum case may be listed before the modal analysis case upon which it depends. When the analysis is run, the program will automatically run the modal analysis case first to generate the modes needed by the response-spectrum case.

• Show Load Case Tree button. Click this button to display the  Load Case Tree form. As the name suggests, the form displays a tree of the load cases defined for the model. Use the Expand All or Collapse All buttons on the form to show all cases or limit the display of cases, respectively. With the load cases displayed, right click on a load case name to display the form needed to edit that load case.      

Note:  The Show Load Case Tree button also is included on the Set Load Cases to Run form.