Geometric Nonlinearity Parameters

Your Ad Here

The Geometric Nonlinearity Parameter options appear on the Nonlinear Parameters form. Access the Nonlinear Parameters form as follows:

Click the Define menu > Analysis Cases command to display the Analysis Cases form.
Click the Add New Case button or highlight a previously defined analysis case and click the Add Copy of Case or the Modify/Show Case button to display the Analysis Case Data form.
Make one of the following selections:

Select Static from the Analysis Case Type drop-down list and select the Nonlinear or Nonlinear Staged Construction option for Analysis Type.
Select Time History from the Analysis Case Type drop-down list and the Nonlinear option for Analysis Type and the Direct Integration option for Time History Type.

Click the Nonlinear Parameters Modify/Show button on the Nonlinear Static, Nonlinear Static Staged Construction or Analysis Case - Nonlinear Direct Integration History form to display the Nonlinear Parameters form.

The geometric nonlinearity options available for nonlinear static and nonlinear direct-integration time-history analysis consist of the following:

None option. All equilibrium equations are considered in the undeformed configuration of the structure.
P-Delta option. The equilibrium equations take into partial account the deformed configuration of the structure. Tensile forces tend to resist the rotation of elements and stiffen the structure, and compressive forces tend to enhance the rotation of elements and destabilize the structure. This may require a moderate amount of iteration
P-Delta plus Large Displacements option. All equilibrium equations are written in the deformed configuration of the structure. This may require a large amount of iteration. Although large displacement and large rotation effects are modeled, all strains are assumed to be small.

Tips: The large displacement option should be used for cable structures undergoing significant deformation, and for buckling analysis, particularly for snap-through buckling and post-buckling behavior. Cables (modeled using frame objects) and other elements that undergo significant relative rotations within the element should be divided into smaller elements to satisfy the requirement that the strains and rotations within an element are small.

For most other structures, the P-delta option is adequate, particularly when material nonlinearity dominates.

If reasonable, it is recommended that the analysis be performed first without geometric nonlinearity, adding P-delta, and possibly large-displacement effects later.

When continuing one analysis case from another, it is recommended that they both have the same geometric-nonlinearity settings.

Note: Geometric nonlinearity is not available for the FNA method.

Return to SAP2000 Index

Your Ad Here