Failure during pushover analysis

[Elina]

I have a 3D model with fiber sections and displacement-based elements. The static analysis for gravity loads as well as the dynamic analysis using a particular accelogram have no problem at all. But when I try a pushover analysis for my model the message below appears:

UMD2FA: matrix is singular. Only 2775 pivots found.
WARNING UmfpackGenLinSolver::solve(void)- 4 returned in factorization UMD2FA()
DisplacementControl::newStep(void) - failed in solver
StaticAnalysis::analyze() - the Integrator failed at iteration: 0 with domain at
load factor 0
OpenSees > analyze failed, returned: -2 error flag
0.0
UMD2FA: matrix is singular. Only 2775 pivots found.
WARNING UmfpackGenLinSolver::solve(void)- 4 returned in factorization UMD2FA()
DisplacementControl::newStep(void) - failed in solver
StaticAnalysis::analyze() - the Integrator failed at iteration: 0 with domain at
load factor 0
OpenSees > analyze failed, returned: -2 error flag
UMD2FA: matrix is singular. Only 2775 pivots found.
WARNING UmfpackGenLinSolver::solve(void)- 4 returned in factorization UMD2FA()
DisplacementControl::newStep(void) - failed in solver
StaticAnalysis::analyze() - the Integrator failed at iteration: 0 with domain at
load factor 0
OpenSees > analyze failed, returned: -2 error flag
Trying Newton with Initial Tangent ..
UMD2FA: matrix is singular. Only 2775 pivots found.
WARNING UmfpackGenLinSolver::solve(void)- 4 returned in factorization UMD2FA()
DisplacementControl::newStep(void) - failed in solver
StaticAnalysis::analyze() - the Integrator failed at iteration: 0 with domain at
load factor 0

##############################
For the analysis I choose:

constraints Lagrange;

numberer RCM;

system UmfPackvariable TolStatic 1.e-8;

variable maxNumIterStatic 6;
variable printFlagStatic 0;
variable testTypeStatic EnergyIncr ;
test $testTypeStatic $TolStatic $maxNumIterStatic $printFlagStatic;
# for improved-convergence procedure:
variable maxNumIterConvergeStatic 2000;
variable printFlagConvergeStatic 0;

algorithm Newton;

integrator DisplacementControl $IDctrlNode $IDctrlDOF $Dincr;

set analysisTypeStatic Static;
analysis $analysisTypeStatic;

Do you have any idea what goes wrong???

Thanks!!!!

[fmk]

you are doing something different because the matrix is singular .. either there is not enogh boundary conditions or the structure became suddenly unstable due to some 0 stiffness terms.

[meopensees]

Hi everybody.I have the same problem.
I have a 2D model with fiber section and displacement-based element and I want perform a pushover analysis , but I face this error.Do you know what goes wrong?
OpenSees > source Untitled1.tcl
Model Built
WARNING: CTestEnergyIncr::test() - failed to converge
after: 6 iterations
NewtnRaphson::solveCurrentStep() -the ConvergenceTest object failed in test()
StaticAnalysis::analyze() - the Algorithm failed at iteration: 0 with domain at
load factor 9.3315
OpenSees > analyze failed, returned: -3 error flag
WARNING: CTestEnergyIncr::test() - failed to converge
after: 6 iterations
NewtnRaphson::solveCurrentStep() -the ConvergenceTest object failed in test()
StaticAnalysis::analyze() - the Algorithm failed at iteration: 0 with domain at
load factor 9.3315
OpenSees > analyze failed, returned: -3 error flag
Trying Newton with Initial Tangent ..
WARNING - ForceBeamColumn2d::update - failed to get compatible element forces &
deformations for element: 6(dW: << 1.00652e-011)
Domain::update - domain failed in update
DisplacementControl::update - model failed to update for new dU
WARNING NewtonRaphson::solveCurrentStep() -the Integrator failed in update()
StaticAnalysis::analyze() - the Algorithm failed at iteration: 0 with domain at
load factor 781.173
OpenSees > analyze failed, returned: -3 error flag
Trying Broyden ..
WARNING: CTestEnergyIncr::test() - failed to converge
after: 10 iterations
WARNING: CTestEnergyIncr::test() - failed to converge
after: 10 iterations
WARNING: CTestEnergyIncr::test() - failed to converge
after: 10 iterations
WARNING: CTestEnergyIncr::test() - failed to converge
after: 10 iterations
WARNING: CTestEnergyIncr::test() - failed to converge
after: 10 iterations
WARNING: CTestEnergyIncr::test() - failed to converge
after: 10 iterations
WARNING: CTestEnergyIncr::test() - failed to converge
after: 6 iterations
Broyden::solveCurrentStep() -the ConvergenceTest object failed in test()
StaticAnalysis::analyze() - the Algorithm failed at iteration: 0 with domain at
load factor 2.85113
OpenSees > analyze failed, returned: -3 error flag
Trying NewtonWithLineSearch ..
WARNING: CTestEnergyIncr::test() - failed to converge
after: 6 iterations
NewtonLineSearch::solveCurrentStep() -the ConvergenceTest object failed in test(
)
StaticAnalysis::analyze() - the Algorithm failed at iteration: 0 with domain at
load factor 9.3315
OpenSees > analyze failed, returned: -3 error flag
DonePushover

[vesna]

You have convergence problems during the analysis. Try reducing the displacement increment. Check the state of the model at the end of the analysis (pushover curve). Is it in linear or nonlinear range?

[meopensees]

Thanks dear vesna.
The target displacement was too large for a 2-story frame and all models converged up to 27cm.
Now i have another problem.i modeled the frame using BeamwithHinges,nonlinearBeamcolumn and dispBeamColumn . when i plot their pushover there is a slight diffrence between the first and second one, but i faced a very big difference in latter(it overestimates the capacity of the frame).it's so different as if it's another structure!i've studied the difference between force-based and displacement-based elements,but i don't think that difference is reasonable.
could you please help me vesna? is it rational?

[vesna]

If you replace 1 nonlinearBeamColumn element with 1 dispBeamColumn element you will see what you just described in your post. To create a good model that will perform well in nonlinear range of behavior you need several dispBeamColumn elements in place of one nonlinearBeamColumn element. Check out this presentation to learn more about differences between these two element types: http://opensees.berkeley.edu/wiki/index ... ed_Element