Problem with Fiber stressStrain Recorder in Cyclic M-phi

[Rand]

I have a cyclic-moment curvature analysis which matches experimental data well, but I cannot get the rebar fiber stressStrain recorders working properly to compare strain data. My intention is simply to impose the recorded curvature history on the fiber section and compare the resulting moments and strains to those obtained in the test.

The analysis itself works fine, but the recorders cannot locate rebar fibers in the locations where I thought they would be. The section is circular with 16 rebar placed evenly over 360 degrees at the distance $rc from the center of the section.

These are the four lines that are causing the problem:
recorder Element -xml bar0.out -time -ele 1 section $ColSecTag fiber $rc 0. $IDreinf stressStrain
recorder Element -xml bar90.out -time -ele 1 section $ColSecTag fiber 0. $rc $IDreinf stressStrain
recorder Element -xml bar180.out -time -ele 1 section $ColSecTag fiber -$rc 0. $IDreinf stressStrain
recorder Element -xml bar270.out -time -ele 1 section $ColSecTag fiber 0. -$rc $IDreinf stressStrain

The entire code appears below if it would be any help for addressing the problem.

model BasicBuilder -ndm 2 -ndf 3

set IDconcCore 1;
set IDconcCover 2;
set IDreinf 3;

# MATERIALS
# ---------
# CONCRETE $mattag $f'c $epsc0 $f'cu $epsU $lambda $ft $Ets
# Core cocnrete (confined)
uniaxialMaterial Concrete02 $IDconcCore -9.006 -0.0052 -6.814 -0.0262 0.1 0.0 0.0
# Cover concrete (unconfined)
uniaxialMaterial Concrete02 $IDconcCover -6.814 -0.002 0.0 -0.0064 0.1 0.0 0.0


#uniaxialMaterial ReinforcingSteel $matTag $fy $fu $Es $Esh $esh $eult < -GABuck $lsr $beta $r $gama > < -DMBuck $lsr < $alpha >> < -CMFatigue $Cf $alpha $Cd > < -IsoHard <$a1 <$limit> > >
uniaxialMaterial ReinforcingSteel $IDreinf 68.086 94.79 29000.0 830.0 0.01458 0.1331

# SECTION GEOMETRY
# ----------------
set pi 3.1415;
set DSec 24; # Column Diameter
set Across [expr ($pi/4)*pow($DSec,2)];
set coverSec 0.875; # Column cover to reinforcing steel NA.
set numBarsSec 16; # Number of longitudinal-reinforcement bars in column
set ColSecTag 1; # set tag for symmetric section
set dbar 0.75; # Long. bar area
set barAreaSec [expr ($pi/4)*pow($dbar,2)];

# Generate a circular reinforced concrete section
# with one layer of steel evenly distributed around the perimeter and a confined core.
# confined core.
#
#
# Notes
# The center of the reinforcing bars are placed at the inner radius
# The core concrete ends at the inner radius (same as reinforcing bars)
# The reinforcing bars are all the same size
# The center of the section is at (0,0) in the local axis system
# Zero degrees is along section y-axis
#
set ri 0.0; # inner radius of the section, only for hollow sections
set ro [expr $DSec/2]; # overall (outer) radius of the section
set nfCoreR 8; # number of radial divisions in the core (number of "rings")
set nfCoreT 24; # number of theta divisions in the core (number of "wedges")
set nfCoverR 2; # number of radial divisions in the cover
set nfCoverT 24; # number of theta divisions in the cover

# Define the fiber section
section fiberSec $ColSecTag {
# Core radius
set rc [expr $ro-$coverSec]
# Define the core patch
patch circ $IDconcCore $nfCoreT $nfCoreR 0 0 $ri $rc 0 360
# Define the cover patch
patch circ $IDconcCover $nfCoverT $nfCoverR 0 0 $rc $ro 0 360
if {$numBarsSec <= 0} {
return
}
# Determine angle increment between bars
set theta [expr 360.0/$numBarsSec]
# Define the reinforcing layer
layer circ $IDreinf $numBarsSec $barAreaSec 0 0 $rc $theta 360
}

# Set axial load
set P -170

# Define two nodes at (0,0)
node 1 0.0 0.0
node 2 0.0 0.0

# Fix all degrees of freedom except axial and bending
fix 1 1 1 1
fix 2 0 1 0

# Define element
# tag ndI ndJ secTag
element zeroLengthSection 1 1 2 $ColSecTag

# Create recorder
recorder Node -file section$ColSecTag.out -time -node 2 -dof 3 disp

recorder Element -xml bar0.out -time -ele 1 section $ColSecTag fiber $rc 0. $IDreinf stressStrain
recorder Element -xml bar90.out -time -ele 1 section $ColSecTag fiber 0. $rc $IDreinf stressStrain
recorder Element -xml bar180.out -time -ele 1 section $ColSecTag fiber -$rc 0. $IDreinf stressStrain
recorder Element -xml bar270.out -time -ele 1 section $ColSecTag fiber 0. -$rc $IDreinf stressStrain


# Define constant axial load
pattern Plain 1 "Constant" {
load 2 $P 0.0 0.0
}

# Define analysis parameters
integrator LoadControl 0.0
system SparseGeneral -piv;
test NormUnbalance 1.0e-9 10
numberer Plain
constraints Plain
algorithm Newton
analysis Static

# Do one analysis for constant axial load
analyze 1

#Cyclic Load
#------------------------------------
pattern Plain 2 Linear {
load 2 0.0 0.0 1.0
}

# Set up analysis parameters
constraints Transformation ;
numberer RCM ;
system BandGeneral ;
test EnergyIncr 1.e-6 25 0 ;
algorithm Newton ;

set controlnode 2
set loaddirection 3
set currentDisp 0.0

foreach Dincr {1.15281E-08 -2.78857E-08 4.70203E-08 -4.98285E-08 1.12686E-07 -1.04865E-07 1.85453E-07 -1.52032E-07 2.86759E-07 -1.60783E-07 2.80375E-07 -1.6609E-07 2.80767E-07 -1.59281E-07 4.4191E-07 -3.52734E-07 5.43003E-07 -3.79395E-07 5.42824E-07 -3.96946E-07 9.76309E-07 -6.48097E-07 9.11999E-07 -6.27167E-07 9.03656E-07 -6.30824E-07 1.33468E-06 -1.07703E-06 1.24101E-06 -1.07316E-06 1.22591E-06 -1.06579E-06 1.67068E-06 -1.45724E-06 1.66875E-06 -1.43886E-06 1.64788E-06 -1.41722E-06 2.48416E-06 -2.18756E-06 2.32142E-06 -2.03076E-06 2.26014E-06 -1.94699E-06 3.05928E-06
} {
integrator DisplacementControl $controlnode $loaddirection $Dincr
analysis Static
set nSteps 1000
if { $Dincr > 0 } {
set Dmax [expr $Dincr*$nSteps]
set ok 0
while {$ok == 0 && $currentDisp < $Dmax} {
set ok [analyze 2]
if {$ok != 0} {
puts "Trying Newton with Initial Tangent .."
test NormDispIncr 1.0e-6 2000 0
algorithm Newton -initial
set ok [analyze 2]
test NormDispIncr 1.0e-6 6 2
algorithm Newton
}
if {$ok != 0} {
puts "Trying Broyden .."
algorithm Broyden 8
set ok [analyze 2]
algorithm Newton
}
if {$ok != 0} {
puts "Trying NewtonWithLineSearch .."
algorithm NewtonLineSearch 0.8
set ok [analyze 2]
algorithm Newton
}
set currentDisp [nodeDisp $controlnode $loaddirection]
}
} elseif { $Dincr < 0 } {
set Dmax [expr $Dincr*$nSteps]
set ok 0
while {$ok == 0 && $currentDisp > $Dmax} {
set ok [analyze 2]
if {$ok != 0} {
puts "Trying Newton with Initial Tangent .."
test NormDispIncr 1.0e-6 2000 0
algorithm Newton -initial
set ok [analyze 2]
test NormDispIncr 1.0e-6 6 2
algorithm Newton
}
if {$ok != 0} {
puts "Trying Broyden .."
algorithm Broyden 8
set ok [analyze 2]
algorithm Newton
}
if {$ok != 0} {
puts "Trying NewtonWithLineSearch .."
algorithm NewtonLineSearch 0.8
set ok [analyze 2]
algorithm Newton
}
set currentDisp [nodeDisp $controlnode $loaddirection]
}
}
}

[linguan118]

The same problem to me!

[Rand]

I solved the problem. I used the following recorder to get the strain history at the center (0,0) of the section.

recorder Element -file 1.out -time -ele 1 section 1 fiber 1 stressStrain

Using the output strain hystory for (0,0) and the output curvature history, the strain profile is known at every data point. The results for the extreme fiber reinforcement strains agree well with those obtained in the test so I have confidence in this method.

Thanks, hopefully this helps somebody else out.

[linguan118]

Rand wrote:
> I solved the problem. I used the following recorder to get the strain
> history at the center (0,0) of the section.
>
> recorder Element -file 1.out -time -ele 1 section 1 fiber 1 stressStrain
>
> Using the output strain hystory for (0,0) and the output curvature history,
> the strain profile is known at every data point. The results for the
> extreme fiber reinforcement strains agree well with those obtained in the
> test so I have confidence in this method.
>
> Thanks, hopefully this helps somebody else out.
But how if I want to get the stress-strain curve of that particular fiber??

[Rand]

I use the following code to translate a strian history into a stress history with a given fiber.

In the code the entire strain history is entered with individual lines of the following code, with one line for each strain data point to be converted to a stress data point.

strainUniaxialTest $strain ; set stress [stressUniaxialTest] ; set tangent [tangUniaxialTest] ; puts $outFile "$strain $stress $tangent" ; set strain STRAIN1 ;

The above is for a single strian value, and the code sets the next strain value to STRAIN1. The next line of code would calculate the stress at STRAIN1. Then the current strain would be set to STRAIN2. Keep adding as many lines and as many strain values as you need to complete the strain history to convert to a stress history.


__________________________________________________________________________________

# modelbuilder to test uniaxial material
model test 1

# open file for output
set outFile [open stress.out w]

# material properties
#uniaxialMaterial ReinforcingSteel $matTag $fy $fu $Es $Esh $esh $eult < -GABuck $lsr $beta $r $gama > < -DMBuck $lsr < $alpha >> < -CMFatigue $Cf $alpha $Cd > < -IsoHard <$a1 <$limit> > >
uniaxialMaterial ReinforcingSteel 1 68.086 94.79 29000.0 1000.0 0.012 0.1331

# test material 1
uniaxialTest 1

set strain 0.0 ;

strainUniaxialTest $strain ; set stress [stressUniaxialTest] ; set tangent [tangUniaxialTest] ; puts $outFile "$strain $stress $tangent" ; set strain STRAIN1 ;

close $outFile

[linguan118]

That's very smart! That helps! Thanks!
For me I will just input the strain history to the Truss element made of that material, so that the stress history can be extracted.
I do know the scripts in your code: uniaxialTest/strainUniaxialTest
These are your own functions or built-in functions in OPENSEES?

[Rand]

I found the uniaxialTest script in another forum post talking about calibrating material models to test data. This is what I use the code for.

[linguan118]

Oh, I see.
Could you please share it with us?
For calibrating material, I'm using just truss element similar to those in the Maxwell_Material in the document.
http://opensees.berkeley.edu/wiki/index ... l_Material

[Rand]

I forgot to mention that these must be built in because I did not add any additional code.

[linguan118]

Yes, maybe the code is tcl script. Could you share it please?

[linguan118]

We still don't know why stress-strain responses can not be extracted in zerolength section element, since the administrators are not replying. If we can, it will facilitate us a lot.
Sometimes for dispBeamColumn element, the same problem occurs! While for forceBeamColumn, it works fine!
I don't know why, maybe some bugs exist here!

[fmk]

remove the sectionTag from the element recorder.

[linguan118]

fmk wrote:
> remove the sectionTag from the element recorder.
Dear fmk,
Thank you for your reply, but it still doesn't work for me!

[wuhaoshrek]

linguan118 wrote:
> fmk wrote:
> > remove the sectionTag from the element recorder.
> Dear fmk,
> Thank you for your reply, but it still doesn't work for me!

recorder Element -file $dataDir/C22_stressStrain_Ele100_3450_RSD7_N.out -time -ele 100 section fiber -34.500 0. $IDBondSteelD7 stressStrain;


like this it's working. btw I used zero length fiber section element.