Changing period of structure

[e.kian]

Hi
In my modeling when I change "NstepGravity", then period of structure changed. why?
Thanks alot.
updates tangent stiffness at every iteration
set NstepGravity 10; # apply gravity in 10 steps
set DGravity [expr 1./$NstepGravity]; # first load increment;
integrator LoadControl $DGravity; # determine the next time step for an analysis
analysis Static; # define type of analysis static or transient
analyze $NstepGravity; # apply gravity

[fmk]

it could the time series in your load patterns or just due to the fact that it is nonlinear analysis and the step size is too large still and your convergence criteria is too low.

[e.kian]

Thanks for your help
How can I solve this problem?
When I put "Tol 1.0e-8" the model didnt convergence ,when I put "Tol 1.0e2" the model convergence!
I really appreciate if you help me?
I cant put my model on "Message board"
because is very near to final model of my project but I can send for you by mail if you let me.
Tanks a lot

[fmk]

unless you are using a penalty method and a norm of the unbalance you have a problem in your model .. use the 1 flag at the end of the test command to have a look at the disp and unbalance norm .. a 4 will show the individual components of the vectors.