STAAD.Pro Help

A. To specify a nonlinear analysis

To instruct the program to perform a static, geometric nonlinear analysis of the structure, use the following procedure.

Note: This requires a STAAD.Pro Advanced license.

The following limitations should be noted regarding static, geometrically nonlinear analyses:

Large rotations in one step should be avoided by using more steps.
Very large displacements, unstable structures, and/or post-buckling should be avoided.
Geometrically nonlinear only. No tension/compression or contact is considered. No yield, plastic moment hinges or bilinear behavior is considered.
Solids cannot be used for this analysis method.
Temperature loads are not supported for geometric nonlinear analysis.

Either:

select the Analysis page

or
on the Analysis and Design ribbon tab, select the Analysis Commands tool in the Analysis Data group

The Analysis/Print Commands dialog opens.
Select the Nonlinear Analysis tab.
(Optional) Specify the nonlinear analysis parameters as necessary:
1. Type a absolute displacement limit for the first analysis step in the ARC field.
2. Type the maximum number of Iterations to use to achieve equilibrium in the deform position within the specified tolerance value.
3. Type the Tolerance to use for achieving convergence between two sequential iterations.
4. Type the number of Load Steps to use for applying load in stages.
5. Type frequency of Rebuild Steps of the tangent K matrix.
Check the KG option to add the geometric stiffness to the stiffness matrix.
(Optional) Check the Set Displacement Limit option to specify a target displacement:
1. Either:
  
  type a Node number
  
  or
  click […] to select a node in the view window
2. Select a DOF (degree of freedom from the drop-down list).
3. Type a Target Value distance for the displacement limit.
Select the Print Option you want to use.
Click Add. The perform nonlinear analysis command is added to the input file.

The maximum displacement should be reviewed for nonlinear analyses because this analysis type may result in buckling or large displacements.