Definition of a Pinching4 Material

[danielcastro88]

Dear,

I need to model a pinching4 material for my work, however I have got a problem.
Both OpenSees tutorial as OpenSees Wiki are not clear to explain the "unloading stiffness degradation", "reloading stiffness degradation" and "strength degradation". Well there is an explanation about what it is, but there is none how the parameters are defined.

$gK1 $gK2 ...
$gD1 $gD2 ...
$gF1 $gF2 ...

There is an example on the tutorial of these parameters, but in fact I can't find the idea how they are obtained.

If anyone knows it, I would be thankful for the explanation. Actually, if there is any design of it where I can visualize, it would be better.

[vesna]

Check the reference given on the material page:
http://opensees.berkeley.edu/wiki/index ... 4_Material

I hope you find information you are looking for.

[danielcastro88]

Dear Vesna,

I'm trying to develop a pinching material, however I always get an error. Immediately it stops in the first increment.
Could you please check the code and give me some advices about it?

Best regards.

..................................................
puts "Begin Pinching_Definition"
puts "Begin ModelBuilder"
# creat the ModelBuilder object

model BasicBuilder -ndm 2 ndf 3

# add nodes - command: node node ID xCrd yCrd
node 1 0.0 0.0
node 2 0.0 0.0

# set boundary conditions - command: fix node ID xResrnt yResrnt mzResrnt
fix 1 1 1 1
fix 2 0 0 0

puts "DONE_ModelBuilder"
puts "Begin Cyclic_Analysis"
# procedure for reverse cyclic displacement control analysis given the peak pts. #
# analysis type used : STATIC #

#############################################################################################
proc Cyclic_Analysis { incre nodeTag dofTag peakpts} {
set x [lindex $peakpts 0]
set fir [expr $x/$incre]

integrator DisplacementControl $nodeTag $dofTag 0.0 1 $fir $fir

# create the analysis object
analysis Static

# perform the analysis
analyze $incre

integrator DisplacementControl $nodeTag $dofTag 0.0 1 [expr -$fir] [expr -$fir]
analyze [expr 2*$incre]

integrator DisplacementControl $nodeTag $dofTag 0.0 1 $fir $fir
analyze $incre

for {set j 1} {$j < [llength $peakpts]} {incr j 1} {
set tx [lindex $peakpts $j]
set tinc [expr $tx/$fir]
set rt [expr int($tinc)]

integrator DisplacementControl $nodeTag $dofTag 0.0 1 $fir $fir
analyze $rt

integrator DisplacementControl $nodeTag $dofTag 0.0 1 [expr -$fir] [expr -$fir]
analyze [expr 2*$rt]

integrator DisplacementControl $nodeTag $dofTag 0.0 1 $fir $fir
analyze $rt
}
################################ end procRCycDAns.tcl #######################################
}
puts "DONE Cyclic_Analysis"

puts "Define_MATERIAL"
uniaxialMaterial Pinching4 1 45.58519 0.00512919 71.10000 0.0122 77.50791 0.02671772 41.20000 0.0832 -66.00000 -0.00665 -86.55090 -0.01843756 -84.50000 -0.0439 -4.14823 -0.08029056 0.5 0.25 0.05 0.5 0.25 0.05 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 10 "energy"
puts "Material_Defined"

puts "Done Pinching_Definition"

puts "Begin SPRING_ELEMENT"
###----------RotSpring2D----------------###
# SETS A MULTIPOINT CONSTRAINT ON THE TRANSLATIONAL DEGREES OF FREEDOM,
# SO DO NOT USE THIS PROCEDURE IF THERE ARE TRANSLATIONAL ZEROLENGTH
# ELEMENTS ALSO BEING USED BETWEEN THESE TWO NODES

# eleID - unique element ID for this zero length rotational spring

# nodeR - node ID which will be retained by the multi-point constraint

# nodeC - node ID which will be constrained by the multi-point constraint

# matID - material ID which represents the moment-rotation relationship

proc rotSpring2D {eleID nodeR nodeC matID} {
# Create the zero length element
element zeroLength 1 1 2 -mat 1 -dir 3

# Constrain the translational DOF with a multi-point constraint
# retained constrained DOF_1 DOF_2 ... DOF_n
equalDOF 1 2
}
puts "Spring_Done"

puts "RECORDER"
recorder Node -file displacement.out -time -node 2 -dof 3 disp
puts "Done_recorder"

puts "Begin PARAMETERS_ANALYSIS"
# build the components for the analysis object

system ProfileSPD

constraints Plain

test NormDispIncr 1.0e-8 20

algorithm Newton

numberer RCM

## analysis type used in the procedure is Static
puts "Begin_PARAMETERS"
set peakpts [list 2.33000 3.21751 4.13264 5.08900 10.13713 10.40406 16.15209 15.49375 22.90578 23.35951 30.04103 30.20917 36.64938 37.41836 44.08802 44.38898 51.18235 51.53760 59.41386 59.28576 65.88622 68.15400 75.70108 75.88379 83.54687 84.51398]

set incre 10

set nodeTag 2

set dofTag 3
puts "Done_Parameters"

## start procedure for feeding in
## Reverse Cyclic loading to the model by Disp. control
Cyclic_Analysis $incre $nodeTag $dofTag $peakpts
puts "done proc"

# print the results at nodes
print node
puts "DONE"
.........................................................

[danielcastro88]

Dear Vesna,

Is there any chance you check up the commands I developed?

Best regards.

[danielcastro88]

Dear Vesna,

I kindly ask you for a check up on the previous command. I can't progress on my thesis work and the deadline is getting closer.

Graciously,
Daniel Castro

[aodonne1]

I am also looking for a better definition for the input parameters of the Pinching4 Material. I have visited the material webpage on the OpenSEES wiki and read the attached PEER report but have not been able to find a thorough definition for what each of the parameters actually does with regards to degrading stiffness and strength.

I have also examined this equation on the OpenSEES wiki page but it appears as though the value specified for gK4 isn't even used.
http://opensees.berkeley.edu/wiki/image ... 82cbcb.png

Can someone please tell me if there is a typo in the equation and how to use these degradation parameters?

Thanks,
Andrew