Experimental study of FRP reinforced concrete panels Lafayette College Dept. of Mechanical Engineering Univ. of Kentucky Center for Applied Energy Research January 14, 2009 Jeffrey Helm Stephen Kurtz Evan O’Brien Abdul-Rahman Salkini An experimental testing system for fiber reinforced polymer (FRP) strengthened concrete panels under uniform pressure loads
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Exp
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rein
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co
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En
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Univ. of Kentucky Center for Applied Energy Research
January 14, 2009
Jeffrey Helm
Stephen Kurtz
Evan O’Brien
Abdul-Rahman Salkini
An experimental testing system for fiber reinforced polymer (FRP)
strengthened concrete panels under uniform pressure loads
Exp
eri
men
tal
stu
dy o
f F
RP
rein
forc
ed
co
ncre
te p
an
els
Lafa
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e C
oll
eg
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ep
t. o
f M
ech
an
ical
En
gin
eeri
ng
Univ. of Kentucky Center for Applied Energy Research
Jeffrey Helm
Stephen Kurtz
Evan O’Brien
Abdul-Rahman Salkini
An experimental testing system for fiber reinforced polymer (FRP)
strengthened concrete panels under uniform pressure loads
January 14, 2009
Exp
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Overview of the presentation
•Motivation for the research
•Concrete panel and FRP configurations
•Loading system
•Digital image correlation basics
•Testing results
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Motivation
Reinforced Concrete
Bridge
Carbon Fiber
Sheet Bonded
With Epoxy
•Determine the design parameters that govern use of fiber reinforced
polymer (FRP) strips for external reinforcement of existing concrete
structures
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Concrete panel specimens
2.1-m
2.1
-m
64-mm
2.1-m x 2.1-m x 64-mm panels
Cylinder strength: 30MPa
9.5-mm coarse rock aggregate
Phase 1
3.42-mm diameter – 75-mm spacing
Yield: 710 MPa
Ultimate: 731 MPa
Elongation: 0.5%
Phase 2
6.35-mm diameter – 150-mm spacing
Yield: 314 MPa
Ultimate: 459 MPa
Elongation: 27.5%
Coated with epoxy bonded sand
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FRP patterns
Phase 1
* *
Phase 2
* Glass fiber strips
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Uniform pressure loading
FRP (tension)
Concrete (compression)
Steel (tension)
Pressure
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Loading system
concrete
panel
pressure bladder
rocker
assembly
stiffening plate
top plate
outer frame
tube
bolt
sleeve
strong floor containment
basin
Maximum pressure = 62 kPa
Distributed load = 278 kN
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Loading system
concrete
panel
pressure bladder
rocker
assembly
stiffening plate
top plate
outer frame
tube
bolt
sleeve
strong floor containment
basin
Maximum pressure = 62 kPa
Distributed load = 278 kN
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DIC in two dimensions
PC with digitizer
Specimen
CCD camera
White light sources
90°
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Measurement basis
Two-dimensional image correlation is based on the ability to accurately
match portions from one image to corresponding locations in a second
image.
Correspondence can be determined to within 0.02 pixels
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Measurement basis
Because the method is computer based we can perform the matching on
a large number of points in the image.
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Displacement example
X img (pixel)
Yim
g(p
ixe
l)
400 600 800
0
200
400
600
800
V (pixel)
120
110
100
90
80
70
60
50
40
Vertical displacements
2.0 pixels/contour
X img (pixel)
Yim
g(p
ixe
l)
400 600 800
0
200
400
600
800
U (pixel)
7.5
5
2.5
0
-2.5
-5
-7.5
-10
-12.5
Horizontal displacements
0.5 pixels/contour
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DIC fundamentals
The image correlation method can be broken into four segments that
answer the following questions:
1. How do you differentiate a positions on the image?
2. How do I get from here to there?
3. How do you work on a scale smaller than a pixel?
4. How do you determine the optimal mapping parameters?
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Patterns and grayscales
From an image, how do you know where you are on the surface?
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Patterns and grayscales
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Mapping from one image to another
C
Q
q
c
uc
vc
Image N
Image 0
Constant displacement mapping:
qx = Qx+uc
qy = Qy+vc
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Mapping from one image to another
C
Q uc
vc
Image N
Image 0
Constant strain mapping:
q
c
qx = Qx + uc + (Qx-Cx)duc/dx + (Qy-Cy)duc/dy
qx = Qx + vc + (Qx-Cx)dvc/dx + (Qy-Cy)dvc/dy
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Mapping from one image to another
C
Q uc
vc
Image N
Image 0
Constant strain mapping:
q
c
qx = Qx + uc + (Qx-Cx)duc/dx + (Qy-Cy)duc/dy
qx = Qx + vc + (Qx-Cx)dvc/dx + (Qy-Cy)dvc/dy
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Working at sub-pixel scales
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Working at sub-pixel scales
0
100
200
0
2
4
6
8
10
0
2
4
6
8
10
0
100
200
0
2
4
6
8
10
0
2
4
6
8
10
Gra
y le
ve
l
Gra
y level
0
100
200
0
2
4
6
8
10
0
2
4
6
8
10
0
100
200
0
2
4
6
8
10
0
2
4
6
8
10
Gra
y level
Gra
y level
Raw image data Bi-linear interpolation
Bi-cubic interpolation Cubic spline interpolation
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Optimizing the mapping parameters
How do we determine the optimal mapping parameters?
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Error functions
common error functions:
(a) i|I’(qi) – I(Qi)| (magnitude of the
intensity differences)
(b) i(I’(qi) – I(Qi))2 (sum of the squares
of intensity differences)
(c) 1 - i(I’(qi) I(Qi))/((i(I’(qi)2)½ (i(I(Qi)
2)½) (normalized cross-
correlation)
error is minimized using a Newton-Raphson based optimization technique
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Extension into 3D Space
PC with digitizer Camera 1
Camera 2
Specimen/grid
location
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Camera parameters
Intrinsic Parameters:
PhD - Pinhole Distance
Cx - Hor. Image Center
Cy - Vert. Image Centerk - Lens Distortion Coef.
Extrinsic Parameters:a - Rotation about Z Axis
b - Rotation about Y Axis
g - Rotation about X Axis
Xo - X Axis Offset
Yo - Y Axis Offset
Zo - Z Axis Offset
Sensor Plane
Pinhole
Optic Axis
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System calibration
Calibrations methods use a
combination of known points
from standards and
correspondence between
cameras to determine each
camera’s parameters.
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Shape Measurement
Surface in
space
Undeformed
Image Cam 1
Undeformed
Image Cam 0
Camera 1
Camera 0
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Displacement Measurement
Undeformed
Image Cam 1
Undeformed
Image Cam 0
Deformed
Image Cam 1
Deformed
Image Cam 0
Surface in
space
Camera 1
Camera 0
Displaced
location
Displacement
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Displacements to strains
Strains determined from
curve fitting local areas
of data
Local areas define a quasi
gage-length for the calculations
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Strain Example
X img (pixel)
Yim
g(p
ixe
l)
400 600 800
0
200
400
600
800
Eyy
0.185
0.16
0.135
0.11
0.085
0.06
0.035
X img (pixel)
Yim
g(p
ixe
l)
400 600 800
0
200
400
600
800
Exy
0.032
0.022
0.012
0.002
-0.008
-0.018
-0.028
-0.038
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Strain example
X img (pixel)
Yim
g(p
ixe
l)
400 600 800
0
200
400
600
800
Exx
-0.01
-0.015
-0.02
-0.025
-0.03
-0.035
-0.04
-0.045
-0.05
-0.055
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Measurement system
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Measurement system
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Panel configurations
.30 m
Local area
Global area
1.98 m
Control panel FRP panel
Local area
Global area
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Surface patterns
global pattern as imaged
from the global camerasglobal and local pattern
as imaged from the local
cameras
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Center point displacement
Center point displacement (mm)
Pre
ssu
re(k
Pa
)
0 50 100
0
5
10
15
20
25
30
35
40
control panel
FRP panel
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Control panel displacement
Animation / Video
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Out-of-plane displacements
X location (mm) -1000
-500
0
500
Y location (m
m)
-1000
-500
0
500
1000
-20
0
20
40
60
80
100
120
140
Wd
isp
lace
me
nt
(mm
)
-20
0
20
40
60
80
100
120
140
X location (mm) -1000
-500
0
500
Y location (m
m)
-1000
-500
0
500
1000
-20
0
20
40
60
80
100
120
140
Wd
isp
lace
me
nt
(mm
)
-20
0
20
40
60
80
100
120
140
Control panel FRP panel
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Initial shape (local area)
X location (mm)
0 200 400 600 800 1000
Ylo
ca
tio
n(m
m)
-1000
-800
-600
-400
-200
0
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Strain progression
Animation / Video
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Failure strains
X location (mm)
0 200 400 600 800 1000
Ylo
ca
tio
n(m
m)
-1000
-800
-600
-400
-200
0
E1
0.04
0.0375
0.035
0.0325
0.03
0.0275
0.025
0.0225
0.02
0.0175
0.015
0.0125
0.01
0.0075
0.005
0.0025
0
X location (mm)S
trip
str
ain
0 200 400 600 800-0.002
0
0.002
0.004
0.006
0.008
0.01 Y = -150 mm strip
Y = -450 mm strip
Y = -750 mm strip
strain map (1st princ. strains) strains along each FRP strip
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Failure modes
Shear-Flexure Failure – Type 1
Shear-Flexure Failure – Type 2
Shear-Flexure Failure – Type 3
*Glass only
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Phase 1 Results
Control phase 1
ultimate = 26.9 kPa
max deflection = 55.6 mm
U/C Disp
1.41 25.5
1.34 37.8
1.48 47.5
U/C Disp
1.0, 55.6
1.41 25.5
1.34 37.8
1.48 47.5
ultimate pressure/control pressure
displacement in mm
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ng
Phase 2 Results
Control phase 1
ultimate = 34.8 kPa
max deflection = 135.1 mm
ultimate pressure/control pressure
displacement in mm
U/C Disp
1.63 77.2
1.05 135.1
1.44 64.6
*
U/C Disp
1.00 135.1
0.96 59.6
1.65 75.5
0.92 125.8
*
Exp
eri
men
tal
stu
dy o
f F
RP
rein
forc
ed
co
ncre
te p
an
els
Lafa
yett
e C
oll
eg
e D
ep
t. o
f M
ech
an
ical
En
gin
eeri
ng
Conclusions
•Determine the design parameters that govern use of fiber
reinforced polymer (FRP) strips for external reinforcement of
existing concrete structures
Develop a method to apply a uniform distributed pressure load to
large (7ft x 7ft) panels of steel reinforced concrete
Adapt the digital image correlation (DIC) technique to measure
full-field displacements and strains in the panels
Acquire panel failure data for a variety of FRP reinforcement
configurations
Analyze the raw image data to obtain full-field displacements,
strains and crack patterns
•Use the data to develop design criteria for FRP reinforcement of
concrete panels
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