Load Application Control for Nonlinear Static Analysis Form

Use the Load Application Control for Nonlinear Static Analysis form to select a load-controlled (i.e., Full Load) or displacement-controlled nonlinear static analysis. For both options, the pattern of loads acting on the structure is determined by the combination of loads specified in the applied loads table on the Analysis Case Data form. If you don't know what to do, select Full Load control. It is the most common, physical situation.

• Load Application Control. Select the appropriate option:

• Full Load. Select full load when the magnitude of load that will be applied is known and the structure is expected to be able to support that load. An example would be when applying gravity load because it is governed by nature. Select a displacement component to monitor in the Monitored Displacement area of the form.

• Displacement Control. Select displacement control when the distance the structure is to be moved is known, but the amount of load is unknown. This is most useful for structures that become unstable and may lose load-carrying capacity during the course of the analysis. Typical applications include static pushover analysis and snap-through buckling analysis.

• Control Displacement. Choose the appropriate option.

• Use Conjugate Displacement option. Choose the Use Conjugate Displacement option and then select a displacement component to be monitored in the Monitored Displacement area of the form. Be sure to choose a displacement component that monotonically increases during loading. Use the Use Conjugate Displacement option if the analysis is having trouble converging. The conjugate displacement is a weighted average of all displacements in the structure where each displacement degree of freedom is weighted by the load acting on that degree of freedom. In other words, it is a measure of the work done by the applied load.

• Use Monitored Displacement option. Choose the Use Monitored Displacement option and select a displacement component to be monitored in the Monitored Displacement area of the form.

•  Load to a Monitored Displacement Magnitude of edit box. Use this edit box to specify the magnitude of the displacement that is the target for the analysis. The program will attempt to apply the load to reach the specified displacement.

• Monitored Displacement. Use this area of the form to specify the displacement component to be monitored. This may be a single degree of freedom at a joint, or a previously defined generalized displacement (select the displacement from the drop-down list).

Important: Using displacement control is NOT the same as applying displacement loading (see Joint Loads - Displacements) on the structure! Displacement control is simply used to MEASURE the displacement that results from the applied loads, and to adjust the magnitude of the loading in an attempt to reach a certain measured displacement value.