could not invert flexibility

[songwang]

Dear all:

I'm new to OS and try to build a simple model to test material stress-strain curve. I want to use forceBeamColumn element with fiber section to test the behavior of ConfinedConcrete01 material under cyclic compression (half cyclic). However, I always get error information as “ ForceBeamColumn2d :: update () - - could not invert flexibility" . Does anyone know why this happens? Also, I tried to change to dispBeamColumn, even though the model cannot converge after certain interations, but the final results make better sense than using forceBeamColumn element. Below is the script:

wipe

# unit: N, mm, MPa

model BasicBuilder -ndm 2 -ndf 3


puts "Model Geometry"
# nodal coordinates:
node 1 1 0
node 2 0 0


puts "Boundary Conditions"
# boundary conditions
fix 1 1 1 1
fix 2 0 1 1


puts "Materials"
# UniaxialMaterial
uniaxialMaterial ConfinedConcrete01 1 C -95.0 45809.933 -epscu -0.026 \
-varub 150.0 0.1 100.0 1.0 1.0 0.0 1000.0 1.0 \
-wrap 0.6 0.6 0.55 2663 125.7e3 -stRatio 0.85

geomTransf Linear 1
section Fiber 1 {
patch circ 1 18 6 0.0 0.0 0 0.5642 0.0 360.0
}
element forceBeamColumn 1 1 2 1 Lobatto 1 5
#element dispBeamColumn 1 1 2 5 1 1

puts "Define Element Recorder"
# element recorder
file mkdir data
recorder Node -file Data/DFree.out -time -node 2 -dof 1 disp
recorder Node -file Data/RBase.out -time -node 1 -dof 1 reaction

puts "Display Recorder"
# display recorder
recorder display "Model" 10 10 400 100 -wipe
prp 0.5 0 1
vup 0 1 0
viewWindow -2 3 -1 1
display 1 5 1


puts "Time Series"
# time series
timeSeries Linear 1


puts "Load Pattern"
# load pattern
pattern Plain 1 1 {
load 2 1 0 0
}


puts "Analysis Command"
constraints Transformation
numberer RCM
system BandGeneral
test EnergyIncr 1e-11 10 0
algorithm Newton



foreach disp {0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020

0.022 0.024 0.026} {
integrator DisplacementControl 2 1 1e-3
analysis Static
analyze [expr int($disp/1e-3)]
integrator DisplacementControl 2 1 -1e-3
analysis Static
analyze [expr int($disp/1e-3)]
}


I appreciate any help and advises. Thanks a lot.

Song

[songwang]

Does anyone know how to solve this problem? Need help!

[fmk]

keep it simple and use a truss or zerolength element to do your analysis (axial load only). You may also need some initial stiffness iterations when tangent goes to 0.

[songwang]

fmk wrote:
> keep it simple and use a truss or zerolength element to do your analysis
> (axial load only). You may also need some initial stiffness iterations when
> tangent goes to 0.

Hi fmk:

The reason why I use forcebeamcolumn or dispbeamcolumn is because I plan to use the same element, same material to model a column under later cyclic pushover analysis, therefore I want to test the cyclic compressive behaivor of the same material with the same element for axial force only.

Also, could you please give me further advise about "initial stiffness iterations"? What does that mean and how can I achieve that goal? Thanks.

Song

[HassanF]

Hello Song,

Did you solve this problem? If so, would you please post here? I have the same problem.

thanks,
Hassan