Adding FRP laminate to RC sections for moment-curvature

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mohsenrock
Posts: 16
Joined: Tue Mar 07, 2017 4:18 am

Adding FRP laminate to RC sections for moment-curvature

Post by mohsenrock » Sun Mar 19, 2017 8:52 am

I am about to validate my results of Moment-Curvature analysis of a FRP-reinforced RC section with opensees. I have searched the forum questions and I have found out that I have to model the FRP with an Elastic material and also a minmax material. However I cannot obtain reasonable results. My results for the section without FRP match perfectly, but the problem is when I add the FRP laminates. When I define the min value of strain as 0.0 and the max value as the maximum FRP strain the results does not change. But after defining a negative range for the FRP strain the results change, which are not practically acceptable as FRP does not work in compression. I was thinking about the element removal command for doing such task but I do not know how to do it. Here is my code. I will appreciate in advance any suggestions.

# units: Kg , cm

# Remove existing model
wipe

# Create ModelBuilder (with two-dimensions and 3 DOF/node)
model BasicBuilder -ndm 2 -ndf 3

# Define materials for nonlinear columns
# ------------------------------------------
# CONCRETE tag f'c ec0 f'cu ecu
# Core concrete (confined)
uniaxialMaterial Concrete01 1 -124.667 -0.002 -124.667 -0.0035

# STEEL
# Reinforcing steel
set fy 3913.0; # Yield stress
set E 2103800.0; # Young's modulus
set Ef 2500000.0; # FRP modulus of elasticity
set Ff 19000.0;
# tag fy E0 b
uniaxialMaterial Steel01 3 $fy $E 0
uniaxialMaterial Steel01 4 $Ff $Ef 0.0
uniaxialMaterial MinMax 41 4 -min 0.0 -max 0.0076

# ------------------------------------------

# set some paramaters
set colWidth 35.0
set colDepth 35.0
set tf 0.015 # The thickness of FRP laminates
set bf 25.0 # The width of FRP laminates

set cover 3.70
set As 1.539; # area of bar d14
set Ass 1.131; # area of bar d12
set Af 0.3750; # area of FRP layer

# some variables derived from the parameters
set y1 [expr $colDepth/2.0]
set z1 [expr $colWidth/2.0]
# Define cross-section for nonlinear columns

section Fiber 1 {

# Create the concrete core fibers
patch rect 1 10 1 -$y1 -$z1 $y1 $z1

# Create FRP composite
layer straight 4 1 $Af [expr $y1+$tf/2.0] [expr $bf/2.0] [expr $y1+$tf/2] [expr -$bf/2.0]
layer straight 4 1 $Af [expr -$y1-$tf/2.0] [expr $bf/2.0] [expr -$y1-$tf/2.0] [expr -$bf/2.0]

# Create the reinforcing fibers (left, middle, right)
layer straight 3 2 $As [expr $y1-$cover] [expr $z1-$cover] [expr $y1-$cover] [expr $cover-$z1]
layer straight 3 2 $As [expr $cover-$y1] [expr $z1-$cover] [expr $cover-$y1] [expr $cover-$z1]
layer straight 3 2 $Ass [expr $y1-$cover] 4.567 [expr $y1-$cover] -4.567

}

# 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
MomentCurvature2DFRP 1 $P [expr $Ky*$mu] $numIncr

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