Convergence issues

[rejina]

Hi Vesna,
I am learning opensees, just the beginners. I am trying to model the hybrid rocking wall with two unbonded post-tensioned tendons. I couldn't find the perfect material to simulate the tendons other than elasticPPGap material in opensees as I need to include only tension behavior in tendons. But there are some convergence issues if I use this material, while it works well with Steel02 material. Since, I am using displacement control integrator, please suggest me some changes in the analysing part.
Below is the warning while I used the following code as the analysis part.
constraints Transformation;
numberer RCM;
system BandGeneral
test NormDispIncr $Tol 10;
algorithm Newton;
integrator LoadControl 0.1 1 0.1 0.1;
analysis Static
integrator DisplacementControl

WARNING: CTestNormDispIncr::test() - failed to converge
after: 10 iterations current Norm: 5.33672e+008 (max: 1e-008, Norm deltaR: 8170
4.4)
NewtnRaphson::solveCurrentStep() -the ConvergenceTest object failed in test()
StaticAnalysis::analyze() - the Algorithm failed at iteration: 0 with domain at
load factor 10913.6
OpenSees > analyze failed, returned: -3 error flag
Trying Newton with Initial Tangent ..
WARNING: CTestNormDispIncr::test() - failed to converge
after: 200 iterations current Norm: 8.09393e-005 (max: 1e-006, Norm deltaR: 5.1
7172)
NewtnRaphson::solveCurrentStep() -the ConvergenceTest object failed in test()
StaticAnalysis::analyze() - the Algorithm failed at iteration: 0 with domain at
load factor 11368.3
OpenSees > analyze failed, returned: -3 error flag
Trying NewtonWithLineSearch ..
WARNING: CTestNormDispIncr::test() - failed to converge
after: 20 iterations current Norm: 1.33418e+008 (max: 1e-006, Norm deltaR: 6203
5.6)
NewtonLineSearch::solveCurrentStep() -the ConvergenceTest object failed in test(
)
StaticAnalysis::analyze() - the Algorithm failed at iteration: 0 with domain at
load factor 10913.6
OpenSees > analyze failed, returned: -3 error flag
Quasi-static analysis is performed.

[fmk]

i suggest for the initial stiffness iterations you place a 1 at the end of the test command .. this will spit out at each iteration the norm .. you will see it is slowly converging (based on the info you provided) and that if you were to but increase the number of iterations you will probably achieve convergence.

[omaramin]

Hi rejina,
I'm working on a similar model.
Did you eventually figure out the convergence issue and did you end up using ElasticPPGap or Steel 02 for the tendons?
Thanks!

[rejina]

omaramin wrote:
> Hi rejina,
> I'm working on a similar model.
> Did you eventually figure out the convergence issue and did you end up
> using ElasticPPGap or Steel 02 for the tendons?
> Thanks!

Hlo omaramin,

Sorry for the late reply.
I believe u must have already got your answers if not I did use Steel02 for tendons as it can simulate the behavior of the tendons, provided that tension only behavior was simulated by connecting high tensile element in series.