Maximum strain at section analysis

[nibas]

I try to perform a section analysis, of reinforced concrete.
I would like to ask how may I set a criterion,
in order to stop the strains of concrete at 0.0035
and the steel's strains at 0.01

Thank you

[silvia]

i am curious as to whether you can do it in the analysis, too!
i just have been doing it in the post-processing!

[fmk]

you could use a a MinMax material .. after min or max reached it returns 0 for stress and tangent; otherwise it returns the stress and tangent of the other material.

uniaxialMaterial MinMax matTag? otherMatTag? -min minStrain? -max maxStrain?

otherwise you could go into the source code & modify to suit your needs!

[nibas]

Thank you silvia and fmk for your replies

I 'd like to ask fmk what is the "otherMatTag?",

and where may I get information about this material,

because the 1.6 edition of the manual does not write anything bout

Best Regards,

[fmk]

the otherMatTag? is the material whose strain you are imposing the limits on .. you pass the MinMax to the section or element and your steel or concrete is passed to the MinMax.

[nibas]

fmk,

thanks a lot!!!

i carried out the analysis,

with the uniaxialMaterial MinMax 4 1 -min -0.0035 -max 10

and it works.

it was very usefull to me!!!

[silvia]

congratulations!!!
don't forget to attach one to the steel!

[nibas]

[silvia]

Nibas,
can I ask you to please post the part of your script where you do this? I'll add it to some examples.

[nibas]

Ok Silvia,

just give me a couple of days

[nibas]

# Define model builder
# --------------------
model basic -ndm 2 -ndf 3

# Define materials for nonlinear columns
# Units: kN-m
# ------------------------------------------
# CONCRETE tag f'c ec0 f'cu ecu
# Core concrete (confined)
uniaxialMaterial Concrete01 1 -16000 -0.0035 -12000 -0.014

# Cover concrete (unconfined)
uniaxialMaterial Concrete01 2 -16000 -0.0020 0 -0.006

# STEEL
# Reinforcing steel
set fy 500000; # Yield stress
set E 200000000.0; # Young's modulus
# tag fy E0 b
uniaxialMaterial Steel01 3 $fy $E 0.01

# Define cross-section for nonlinear columns
# ------------------------------------------



uniaxialMaterial MinMax 4 1 -min -0.0035 -max 10
uniaxialMaterial MinMax 5 2 -min -0.0035 -max 10
uniaxialMaterial MinMax 6 3 -min -10 -max 0.01


# set some paramaters
set colWidth 0.4
set colDepth 0.4

set cover 0.04
set As 0.000314; # Φ20

# some variables derived from the parameters
set y1 [expr $colDepth/2.0]
set z1 [expr $colWidth/2.0]

section Fiber 1 {


# Create the concrete core fibers
patch rect 4 10 1 [expr $cover-$y1] [expr $cover-$z1] [expr $y1-$cover] [expr $z1-$cover]

# Create the concrete cover fibers (top, bottom, left, right)
patch rect 5 10 1 [expr -$y1] [expr $z1-$cover] $y1 $z1
patch rect 5 10 1 [expr -$y1] [expr -$z1] $y1 [expr $cover-$z1]
patch rect 5 2 1 [expr -$y1] [expr $cover-$z1] [expr $cover-$y1] [expr $z1-$cover]
patch rect 5 2 1 [expr $y1-$cover] [expr $cover-$z1] $y1 [expr $z1-$cover]

# Create the reinforcing fibers (left, middle, right)
layer straight 6 3 $As [expr $y1-$cover] [expr $z1-$cover] [expr $y1-$cover] [expr $cover-$z1]
layer straight 6 2 $As 0.0 [expr $z1-$cover] 0.0 [expr $cover-$z1]
layer straight 6 3 $As [expr $cover-$y1] [expr $z1-$cover] [expr $cover-$y1] [expr $cover-$z1]

}



# Estimate yield curvature
# (Assuming no axial load and only top and bottom steel)
set d [expr $colDepth-$cover] ;# d -- from cover to rebar
set epsy [expr $fy/$E] ;# steel yield strain
set Ky [expr $epsy/(0.7*$d)]

# Print estimate to standard output
puts "Estimated yield curvature: $Ky"

# Set axial load
set P 0

set mu 15; # Target ductility for analysis
set numIncr 100; # Number of analysis increments

# Call the section analysis procedure
source MomentCurvature.tcl
MomentCurvature 1 $P [expr $Ky*$mu] $numIncr $y1 $z1

[silvia]

okey,
i did pretty much what you have. however, my analysis of a circular section keeps going, as only one fiber has reached such strain. i get a little kink in the mom-curv, but nothing more.
how can I improve my analysis?

[motalaat]

I have to say first that I am thankful for this discussion. It has been very useful to learn about the MinMax material. I will need to use is shortly and I had been resorting to an ungraceful manipulation of hysteretic-trilinear instead.

As for the section analysis continuing after the farthermost fiber reaching the maximum strain spaecified, I am afraid the only way about that - besides post-processing, will be to create a MinMax section However, why the need to do? A section where fibers are elimintaed as individul fibers reach their maximum strains will display a more realistic gradual softening behavior as damage progresses inwards. This unless you are modeling brittle failure - such as sections confined by rupture-prone FRP wraps, and then you will have to wait for a month or so for me to provide you with a cross section that is sensitive to lateral confinement. Hopefully by the OS workshop

Again, thanks for that MinMax material. It will be great in modeling multi-linear behavior of brittle wrapping material. One question to Frank, though. If a MinMax material exceeds the maximum positive strain once and then goes back to a lower strain, does he MinMax material (a) still return zero stress and strain still, or (b) does it return that of the "other material"? What happens in the other "negative" direction, are they completely uncoupled?

M.Talaat
PhD. Candidate, UCB

[Zephyre]

Hi Mohamed,

I have read your paper "A computational model for RC members confined with fiber reinforced polymer lamina" published on 2006 and as it says you have succeed to introduce a fiber-section model for nonlinear analysis confined RC members into OpenSees. Are those sections and materials available to use with OpenSees? That would be very useful for researchers working of this.
Thank you in advance