Load Case Data - Nonlinear Static Form

Use the Load Case Data - Nonlinear Static form to view and change the definition of a nonlinear direct-integration time-history load case. A direct-integration time-history analysis solves equations for the entire structure at each time step, as compared with a modal time-history analysis, which uses the method of mode superposition. Nonlinear static analysis can be used for many purposes:

Perform an initial P-delta or large-displacement analysis to get the stiffness used for subsequent superposable linear analyses.
Analyze structures with tension-only bracing.
Analyze cable structures.
Perform static pushover analysis.
Perform snap-through buckling analyses.
Establish the initial conditions for nonlinear direct-integration time-history analyses.
Perform any other static analysis that considers the effect of material or geometric nonlinear behavior.

Use the following areas on the form to define the nonlinear direct-integration time-history load case.

Load Case Name edit box. Use the name shown or type a new name in this edit box. It should be unique among all load cases of all types. Click the Set Def Name button to use a default name for the load case.
Notes Modify/Show button. Click this button to access the Load Case Notes form. Use the form to add notes to the model file specific to this load case.
Design button. Click this button to access the Design Load Type form. Choose Program Determined, or User Specified and then a design type from the drop-down list. Design load types are used in creating automatic design load combinations.
Initial Conditions.
Geometric Nonlinearity Parameters options

Modal Load Case and All Modal Loads Applied Use Modes from Case drop-down list. To apply any modal loads (inertia loads that are proportional to mode shapes), choose the modal load case whose modes are to be used. The modal load at a joint degree of freedom is calculated as the product of the modal displacement times the mode's circular frequency squared (w2) times the mass tributary to the joint along that degree of freedom.

Tip: Although not required, it makes the most physical sense for the selected modal load case to be based on the stiffness matrix from the same nonlinear load case (or zero) that is used for the initial conditions of the current nonlinear static load case.

Loads Applied options. Apply the loads from one or more load patterns, built-in acceleration loads, or even inertial loads proportional to mode-shapes (the latter is used for static pushover analysis). All loads specified will be scaled, added, and applied in combination.
- Load Type drop-down list. Choose whether the load to be applied is a load pattern, a built-in acceleration load, or an inertial load proportional to a mode shape.
- Load Name drop-down list. Choose the load case pattern, the global direction of ground acceleration, or the mode number, depending on the type of load.

Note: For modal loads, if a mode number is chosen that was not calculated in the specified Modal Load Case (see bullet item above), a warning will be issued and the applied load will be zero.

- Scale Factor edit box. Enter a scale factor that multiplies the load before adding it to other loads applied. For acceleration loads, the scale factor has units of acceleration, and should be consistent with the length units currently in use. For load cases and modal loads, the scale factor is unitless.
- - Add button. After the Load Type, Load Name and Scale Factor have been specified, click the Add button to add the load.
  - Modify button.
  - 1. Highlight a load in the set of applied loads
    2. Make any changes to the load type, load name, and scale factor at the top of the table.
    3. Click the Modify button.
  - Delete button.
  - 1. Highlight a load in the set of applied loads.
    2. Click the Delete button.
Other Parameters
- Load Application display box. The display box shows the load to be applied during the analysis. Click the Modify/Show button to access the Load Application Control for Nonlinear Static Analysis form and specify the load application, control displacement and monitored displacement for the analysis.
- Results Saved display box. The display box shows the results that will be saved from the analysis. Click the Modify/Show button to access the Results Saved for Nonlinear Static Load Cases form and specify the results to be saved for the analysis.
- Nonlinear Parameters display box. The display box identifies the parameters as Default or User Defined. Click the Modify/Show button to access the Nonlinear Parameters form and specify user defined Nonlinear Parameters for the analysis.