TR.37.7.2.4 Consideration of Geometric Nonlinearity Effect
The following command is used to optionally consider geometric nonlinear effects.
You may specify either (or both) the DISPTOL or GEOCYCLE commands to optionally check for convergence.
General Format
GNONL i2
( DISPTOL f4 )
( GEOCYCLE i3 )
Parameter  Description 

i2 
Specifies if geometric nonlinear effects are to be considered

f4 
Convergence displacement tolerance for convergence of Geometric Nonlinearity, in current units of length. The default value is the maximum span of the structure divided by 120. See Note a below. 
i3 
Number of iterations to be performed for convergence of Geometric Nonlinearity. Default value is one. See Note b below. 
Notes

he member end forces are evaluated by performing a convergence check on the joint displacements. In each step, the displacements are compared with those of the previous iteration in order to check whether convergence is attained.
Refer SET DISPLACEMENT command in TR.5 Set Command Specification for additional details. If any displacement on any iteration exceeds the DISPTOL limit, the solution is diverging and is terminated.
 If the number of nonlinear iterations exceeds GEOCYCLE limit the analysis is terminated. Please refer NONLINEAR ANALYSIS in STAAD for more details. However, maximum allowable iteration is 50. If the number of iterations exceeds 50 the analysis is terminated.