STAAD.Pro Help

Nonlinear Analysis tab

Used to direct STAAD.Pro to perform a nonlinear analysis which can account for nonlinear effects of moderate displacement and small strain. This solution holds for where the element distortion is small and small rotations are assumed.

Note: This feature is available in STAAD.Pro V8i (release 20.07.05) and later; with the Displacement Limit controls requiring STAAD.Pro V8i (SELECTseries 2) release 20.07.07 or later.
Note: The Advanced Analysis Engine package is required to use this feature.

Refer to TR.37.8 Geometric Nonlinear Analysis for additional information.

The first analysis step must be stable, otherwise use ARC control to prevent instability. The procedure does not use follower loads. Loads are evaluated at the joints before the first step; then those loads translate with the joint but do not rotate with the joint. Equilibrium is computed in the displaced position.

Nonlinear entities such as tension/compression members, multilinear springs, gaps, etc. are not supported when using a nonlinear analysis. Additionally, nonlinear analysis does not account for post-buckling stiffness of members.

Note: The older NONLINEAR nn ANALYSIS command will adopt the new procedure unless a SET command is used. If a SET command is entered this will invoke the old procedure for backward compatibility.

The values for the Displacement Limit are used to limit analysis cycle to a specified displacement value and degree of freedom for a monitored node. When two or more Load Steps are specified, the calculated displacement or rotation is compared to the Target Value along or about the DOF for the specified Node each step. If the calculated displacement or rotation meets or exceeds the target value, then the analysis is stopped.

SettingDescription
ARC

Specify a displacement control, which is the value of the absolute displacement limit for the first analysis step. If the maximum displacement is greater than this limit, ARC will calculate a new step size for the first step and a new value for Load Step. Value should be in current length units.

Note: ARC = 0 indicates no displacement control.
Iterations Max. Number of iterations to achieve equilibrium in the deformed position to the tolerance specified.
Tolerance For convergence, two successive iteration results must have all displacements the same within this tolerance. Value entered is in current units.
Load Steps Specify the number of load steps to be used. Load is applied in stages if entered. One means that all of the load is applied in the first step.
Rebuild Steps

Frequency of rebuilds of the tangent K matrix per load step & iteration.

  • 0 = once per load step
  • 1 = every load step & iteration
Use KG Select this option to add the geometric stiffness, KG, to the stiffness matrix, K.
Node Enter a node number or click […]. to enter the selected node to monitor during the geometric nonlinear analysis.
DOF Select the degree of freedom to monitor during the analysis for specified Node.
Target Value Specify a target displacement value along or about the selected DOF for the monitored Node.
Print Option Standard STAAD.Pro analysis print options:
SettingDescription
No Print No analysis results will be printed to the output file.
Load Data Prints all the load data.
Statics Check Provides a summation of the applied loads and support reactions as well as a summation of moments of the loads and reactions taken around the origin.
Statics Load Prints everything that Statics Check does, plus a summation of all internal and external forces at each joint. This option potentially generates a large volume of output.
Note: Since PRINT STATIC LOAD generates voluminous output, the printing of summation of internal and external forces at each joint is done for structures which have less than 1,000 joints. If the structure has 1,000 joints or more, this printing will be skipped.
Mode Shapes Prints mode shape values at the joints for all calculated mode shapes.
Both This option is equivalent to the Load Data plus Statics Check options.
All This option is equivalent to the Load Data plus Statics Check.