[solved] Problem with ConfinedConcrete01 and USI

[thomas.ulrich]

Hello,

I'm trying to use ConfinedConcrete01 for the core concrete of my section, but there is a problem when I try to convert the parameters of an example of the wiki to the international units(kg,m, Pa, etc).

Here is my simple code:

Uncomment this 2 line for using the international units:
#set in 2.54e-2
#set Mpa 1e6

With this 2 lines commented, the stressStrain curve looks fine.
With the first line uncommented, it remains the same.
But when both are commented, there are problems.

Thank you for your help,

Thomas.
[code]

model basic -ndm 2 -ndf 3;
node 1 0 0;
node 2 0. 0;

fix 1 1 1 1;
fix 2 0 1 1;

set idmat 1







puts "example of ConfinedConcrete01"
puts "uniaxialMaterial ConfinedConcrete01 1 R -30.0 26081.0 -epscu -0.03 -varUB 500.0 300.0 10.0 100.0 300.0 206000.0 0.0 1000.0 16.0 -stRatio 0.85"



set in 1.0
set Mpa 1e0

#set in 2.54e-2
#set Mpa 1e6

set fc [expr -30.*$Mpa]
set Ec [expr 26081.*$Mpa]
set Fy [expr 300.*$Mpa]
set Es [expr 206000.*$Mpa]
set bs 0.
#length/diameter of square/circular core section measured respect to the hoop center line.
set L1 [expr 500.*$in]
#additional dimensions when multiple hoops are being used.
set L2 [expr 300.*$in]

#hoop diameter. If section arrangement has multiple hoops it refers to the external hoop.
set phis [expr 10.*$in]
#hoop spacing.
set S [expr 100.*$in]
#ductility factor of the hoop steel
set mu 1000.
#diameter of longitudinal bars.
set phiLon [expr 16.*$in]


uniaxialMaterial ConfinedConcrete01 1 R $fc $Ec -epscu -0.03 -varUB $L1 $L2 $phis $S $Fy $Es $bs $mu $phiLon -stRatio 0.85
puts "tested ConfinedConcrete01:"
puts "uniaxialMaterial ConfinedConcrete01 1 R $fc $Ec -epscu -0.03 -varUB $L1 $L2 $phis $S $Fy $Es $bs $mu $phiLon -stRatio 0.85"


uniaxialMaterial Elastic 10 0.1
element zeroLength 2 1 2 -mat 10 -dir 1;

section fiberSec 1 {patch rect $idmat 1 1 -1. -1. 1. 1.}
element zeroLengthSection 1 1 2 1;

set values {
-0.002
0
-0.002
0
-0.004
0
-0.004
0.001
-0.008
0.001
-0.008
0.001
-0.008
0.001
-0.008
}



pattern Plain 1 Linear {
load 2 1.0 0 0
}

recorder Element -file stressStrain.out -ele 1 section fiber 0.0 0.0 stressStrain

constraints Plain; # how it handles boundary conditions
numberer RCM; # renumber dof's to minimize band-width (optimization), if you want to
system BandGeneral; # how to store and solve the system of equations in the analysis

set Tol 1e-4
set test_type NormDispIncr
set Niter 200
set default_algorithm Newton

test $test_type $Tol $Niter
algorithm $default_algorithm

integrator DisplacementControl 2 1 0.01
analysis Static; # define type of analysis: time-dependent

set LastVal 0.
foreach val $values {
integrator DisplacementControl 2 1 [expr 1e-0*($val-$LastVal)/200.]
puts $val
set ok [analyze 200]
if $ok!=0 {exit 0}
set LastVal $val
}
[/code]

[vesna]

In the manual for the material units are not restricted. Check your code again and make sure that you are consistent with your units. I do not know what is the meaning of "in" and "MPa" but inches and MPa do not belong to the same system of units. I also noticed that you did not assign any units to your variable "values".

[thomas.ulrich]

Dear Vesna,

Thank you for your quick reply.
actually you were right: I thought that the units were Mpa and inch, but after your comment, it is probably in Mpa=N/mm and mm.
(Sorry I'm not regular with the barbaric units used by those who drive on the left and their friends )

So I tried converting by using:

set in 1e-3; #in means mm :-s
set Mpa 1e6

But I'm still having the same problem when looking at the stress strain curve.

Finally, I've beeing watching the code and I realized that the code is only made for Mpa/mm:
For instance in the function void ConfinedConcrete01::setupAttardSetunge
[code]
//Initial tangent modulus
if (fpc >= 100) {
alpha = 1.0;
} else if (fpc <= 20) {
alpha = 1.17;
} else {
alpha = 1.17-0.17*(fpc-20)/(100-20);
}
[/code]
-->Clearly, changing the units will have an influence!!
This is something which should be mentioned in the wiki or changed in the code in my opinion.

[vesna]

Thanks for pointing this out!

I modified the wiki page: http://opensees.berkeley.edu/wiki/index ... 1_Material

Is it better?

[thomas.ulrich]

good job