SUB-TASK 2.1: LABORATORY-SCALE
INVESTIGATIONS
LABORATORY-SCALE DESCRIPTION
•
•
Ninety one laboratory-scale specimens were subjected to
multiple damage-heat straightening repair cycles
Focused on A36 and A588 steels due to the availability of
material as apposed to older A7 and A373
–
–
–
•
•
A36 - closest in chemical compositions as A7 and A373
A588 - third most relevant steel type from database
Some A7 steel specimens were acquired from the web of a
W24x76 steel beam
Test specimen-test areas damage by uniaxial tensile
forces and repaired with uniaxial compressive forces and
by applying strip heats
Material samples taken from the test areas to obtain
statistically significant structural properties and fracture
toughness
NOTES ON TESTING APPROACH
Two methods were considered
(Method 1)
t
Damage Force (Pd)
Restraining Force (Pr)
PROBLEMS WITH METHOD 1
•
The specimen cross-section and length are subjected to different
magnitudes of damage strain, restraining stress, and heat
straightening repair.
•
Hinders obtaining several material specimens subjected to
consistent damage-repair magnitudes and testing them to obtain
statistically significant structural properties.
METHOD 2
Damage
Repair Force
Force(P(P
r )d )
•
Specimen test-areas are subjected to
consistent damage strains,
restraining stresses, and heat
straightening repair.
•
Several material specimens are
obtained from the test-areas and
Test
tested to obtain statistically significant Area
structural properties.
•
Method 2 was chosen in this
research project.
Strip Heat
TEST MATRIX – 91 TOTAL SPECIMENS
•
A36 – 28 Specimens
• Three damage strains (d) – 30y, 60y , or 90y
• Two restraining stresses (y) – 0.25 y or 0.50y (0.40 y or 0.70 y for d = 30y)
• Number of damage-repair cycles (Nr) – 1, 2, 3, 4, or 5
•
A588 – 30 Specimens
• Three damage strains (d) – 20y, 40y , or 60y
• Two restraining stresses (y) – 0.25y or 0.50y
• Number of damage-repair cycles (Nr) – 1, 2, 3, 4, or 5
•
A7 – 17 Specimens
• Three damage strains (d) – 30y, 60y , or 90y
• Two restraining stresses (y) – 0.25y or 0.50y
• Number of damage-repair cycles (Nr) – 1, 3, or 5
• Three maximum heating temperatures
•
Overheated A36 – 16 Specimens
• Two damage strains (d) – 60y or 90y
• Two restraining stresses (y) – 0.25y or 0.50y
• Number of damage-repair cycles (Nr) – 1 or 3
• Two maximum heating temperatures - 1400F or 1600F
TEST SPECIMEN DETAILS
A36 and A588 steel
A7 steel
8.00
2.13 3.75 2.13
7.875
1.63
3.38
2.06 3.75 2.06
f = 1.1875
2.00
3.38
16.88
3.38
13.25
3.75
3.75
3.25
46.25
3.25
39.00
5.00
3.75
3.75
16.88
3.38
f = 1.1875
13.25
3.38
3.38
1.63
2.00
Test specimen thickness = 1.00 in.
f = 1.1875
Test specimen thickness = 0.45 in.
MATERIAL COUPONS FROM TEST AREAS
(A36 and A588 Specimens)
End A
End A
3.25 in.
3.25 in.
1
1
2
2
3
3
YY
1.0 in.
2.165 in.
2.165 in.
1.375
1.375
XX
0.75
0.75
0.394
0.394
1
2
3
0.25 in.
0.5 in.
3.25 in.
Cross-section
at End
EndAA
Cross-section at
0.5
0.5
5
5
6
1.0 in.
6
0.75
0.75
0.394 0.394 0.394
0.394 0.394 0.394
End B
End B
0.75
0.75
Tension
Coupons
0.394
0.394
0.394
4
5
6
3.25in
.
Cross-section
atEnd
End B
Cross-section
at
0.75 in.
4
2.165 in.
2.165 in.
4
0.75 in.
2.25
2.25
0.5
0.5
1.375
1.375
5.0 in.
5.0 in.
Charpy
Specimens
0.394
0.75 in.
0.394 0.394 0.394
0.394 0.394 0.394
0.75 in.
0.75
0.75
0.5 in.
TEST SETUP
Concrete Blocks
Top Beam
Test
Specimen
Hydraulic
Actuator
Split-flow
valve
Bottom Beam
Electric Pump
Pressure Gage
Needle Valve
DAMAGE CYCLE-INSTUMENTATION
•
•
•
Pressure transducers to measure actuator pressures
Two longitudinal strain gages in test area
Two displacement transducers to measure average
strain
Gage – front
Gage -back
TEST
AREA
5.0 in.
Test-Area
3.25 in.
Two displacement transducers to measure
average strains in test area
EXPERIMENTAL DAMAGE BEHAVIOR
(SPECIMEN A36-60-50-3)
70
Stress-strain of undamaged uniaxial tension test
60
Cycle 3-Average Strains
50
Stress (ksi)
Cycle 2 Average Strains
40
Cycle 1-Longitudinal Strain Gages
(Back (gray) and Front (red))
30
Cycle 1-Average Strain
20
Specimen A36-60-50-3
Target d = 0.080 in/in
10
0
0
0.01
0.02
0.03
0.04
0.05
Strain
(mm/mm)
Strain
(in/in)
0.06
0.07
0.08
0.09
REPAIR CYCLE-INSTRUMENTATION
•
•
•
Pressure transducers to measure actuator pressures
Infrared thermometer to measure surface temperature
Two displacement transducers to measure displacement
between top and bottom beam.
Infrared thermometer used to
measure temperature on all sides
Two displacement transducers to monitor movement
during heat straightening
EXPERIMENTAL REPAIR BEHAVIOR
(SPECIMEN A36-60-50-3)
5000
4500
Left Displacement*10000 (in)
4000
3500
Right Displacement
*10000 (in)
3000
2500
Pressure (psi)
Temperature (F)
2000
1500
1000
500
0
0
500
1000
1500
2000
2500
Time (s)
3000
3500
4000
4500
5000
REPAIR DESCRIPTION
Applying the Strip Heat
Monitoring the Surface Temperature
COLOR OF STEEL AT ELEVATED
TEMPERATURES
1200F
1400F
1600F
UNIAXIAL TENSION RESULTS (A36)
d = 30y d = 30y d = 60y d = 60y d = 90y d = 90y
r =0.40y r =0.70y r =0.25y r =0.50y r =0.25y r =0.50y
1.20
ELASTIC MODULUS
1.10
1.00
0.90
0.80
1.30
Ratio of Yield Stress to Undamaged Material
Ratio of Elastic Modulus to Undamaged Material
1.30
0.70
1.20
YIELD STRESS
1.10
1.00
0.90
0.80
1 2 3 4 5
1 2 3 4 5
1 2 3 4 5
1 3 5
1 2 3 4 5
1 2 3 4 5
Number of damage-repairs (Nr)
d = 30y d = 30y d = 60y d = 60y d = 90y d = 90y
r =0.40y r =0.70y r =0.25y r =0.50y r =0.25y r =0.50y
1.20
ULTIMATE STRESS
1.10
1.00
0.90
0.80
0.70
1.30
Ratio of %Elongation to Undamaged Material
Ratio of Ultimate Stress to Undamaged Material
d = 60y d = 90y d = 90y
d = 60y
r =0.25y r =0.50y r =0.25y r =0.50y
0.70
1 2 3 4 5
1.30
d = 30y d = 30y
r =0.40y r =0.70y
1 2 3 4 5
1 2 3 4 5
d = 30y d = 30y
d = 60y
r =0.40y r =0.70y r =0.25y
1 2 3 4 5
1 3 5
1 2 3 4 5
d = 60y d = 90y d = 90y
r =0.50y r =0.25y r =0.50y
1.20
DUCTILITY
% ELONGATION
1.10
1.00
0.90
0.80
0.70
1 2 3 4 5
1 2 3 4 5
1 2 3 4 5
1 2 3 4 5
1 3 5
Number of damage-repairs (Nr)
1 2 3 4 5
1 2 3 4 5
1 2 3 4 5
1 2 3 4 5
1 2 3 4 5
Number of damage-repairs (Nr)
1 3 5
1 2 3 4 5
DUCTILITY OF A36, A588, AND A7 STEEL
d = 60y
r =0.25y
1.10
d = 60y d = 90y d = 90y
r =0.50y r =0.25y r =0.50y
1.00
Ratio of %Elongation to Undamaged Material
d = 30y d = 30y
r =0.40y r =0.70y
A36 STEEL
0.90
0.80
0.70
0.60
0.50
d = 30y d = 30y d = 60y
r =0.40y r =0.70y r =0.25y
d = 60y d = 90y d = 90y
r =0.50y r =0.25y r =0.50y
1.00
A588 STEEL
0.90
0.80
0.70
0.60
0.50
1 2 3 4 5
1 2 3 4 5
1 2 3 4 5
1 2 3 4 5
1 2 3
1 2 3 4 5
1 2 3 4 5
1 2 3 4 5
1.10
1 2 3 4 5
d = 30y d = 30y
r =0.40y r =0.70y
d = 60y
r =0.25y
d = 60y d = 90y d = 90y
r =0.50y r =0.25y r =0.50y
1.00
A7 STEEL
0.90
0.80
0.70
0.60
0.50
1
3
5
1 2 3 4 5
Number of damage-repairs (Nr)
Number of damage-repairs (Nr)
Ratio of %Elongation to Undamaged Material
Ratio of %Elongation to Undamaged Material
1.10
1
3
5
1
3
3*
5
1
3
Number of damage-repairs (Nr)
5
1
3
1
3
1 2 3 4 5
1 2 3 4 5
CONCLUSIONS–STRUCTURAL PROPS.
• Multiple damage-heat straightening repair cycles have a
slight influence (±15%) on the elastic modulus, yield stress,
ultimate stress, and surface hardness of A36, A588, and A7
bridge steels
• The yield stress and surface harness increase slightly and
the ultimate stress and elastic modulus are always within
±10% of the undamaged values
• However, the % elongation of damaged-repaired steel is
influenced significantly
• The ductility (% elongation) of A36 and A588 steel
decreases significantly but never lower than minimum
values according to AASHTO requirements
• The ductility of A7 steel subjected to five damage-repair
cycles is extremely low
2.25
d = 30y r = 0.40y
2.00
Fracture Toughness/ Toughness Undamaged A36
Fracture Toughness/ Toughness Undamaged A36
2.25
Fracture Toughness/ Toughness Undamaged A36
FRACTURE TOUGHNESS RESULTS (A36)
d = 30y r = 0.70y
1.75
1.50
1.25
95% high
95% high
1.00
Mean
Mean
0.75
95% low
0.50
0.25
95% low
0 = undamaged
0.00
0
1
2
3
4
5
0
1
2
Number of damage-repairs (Nr)
d = 90y r = 0.25y
2.00
1.75
3
4
5
d = 90y r = 0.50y
95% high
Mean
Mean
0.75
0.50
95% low
0.25
0.00
95% low
0 = undamaged
0
1
3
5
0
1
2
Number of damage-repairs (Nr)
3
4
5
d = 60y r = 0.50y
1.75
95% high
95% high
1.50
1.25
Mean
1.00
Mean
0.75
95% low
0.50
95% low
0.25
0 = undamaged
0.00
0
1
2
3
4
5
0
1
2
3
Number of damage-repairs (Nr)
4
5
• The 95% CI Low, mean, and 95% CI high toughness
values of the damaged-repaired specimens were
normalized with respect to the undamaged mean
toughness of the corresponding steel.
1.25
1.00
d = 60y r = 0.25y
2.00
• Fracture toughness of damaged-repaired specimens
analyzed statistically  mean toughness and 95%
confidence interval (CI) high and low toughness values
95% high
1.50
2.25
4
• The normalized fracture toughness values for the
damaged-repaired specimens are shown and the
effects of parameters d, r, and Nr are evaluated.
CONCLUSIONS - A36 FRACTURE TOUGHNESS
•
The fracture toughness of A36 steel is much lower
than the undamaged fracture toughness
•
Mean fracture toughness of specimens damaged
to 30y becomes less than 50% after two damagerepair cycles
•
The fracture toughness of specimens damaged to
60y becomes less than 50% after three damagerepair cycles
•
Mean fracture toughness of specimens damaged
to 90y was found to have significant scatter
•
Higher restraining stress appear to decrease the
fracture toughness slightly
CONCLUSIONS - A588 FRACTURE TOUGHNESS
• The fracture toughness of damaged-repaired A588
steel is greater than or close to the undamaged
fracture toughness in several cases
• The fracture toughness never decreases below
50% (even after five damage-repair cycles)
• Increasing the restraining stress reduces the
fracture toughness of A588 steel significantly
CONCLUSIONS - A7 FRACTURE TOUGHNESS
• The fracture toughness of A7 steel decreases with an
increase in r and Nr and with a decrease d
• The fracture toughness of steels damaged to 30y
reduces to 50% of the undamaged toughness after
three damage-repairs
• The fracture toughness of specimens damaged to 60y
and repaired with 0.25y is excellent. However,
increasing r has a significant adverse effect on the
fracture toughness
• The fracture toughness of specimens damaged to 90y
is close to the undamaged toughness after three
damage-repair cycles
SUB-TASK 2.1: LARGE-SCALE
INVESTIGATIONS
LARGE-SCALE DESCRIPTION
•
•
•
Six beam specimens were subjected to three damageheat straightening repair cycles
Two beam specimens were made of A7, two made of A36,
and two made of A588
Beams subjected to weak axis bending by applying
concentrated forces at midspan
–
–
–
•
•
Similar to damage induced to the bottom flange of a composite
beam impacted by an over-height truck
Two flanges could be used for the removal of material samples as
apposed to one flange
Easier to conduct, control, and repeat in a laboratory type setting
as compared to the composite beam damage
Repair conducted by applying half-depth Vee heats along
the damaged area of the beam
Results of material testing used to validate the
conclusions and recommendations of Sub-task 2.1
LARGE-SCALE TEST MATRIX
For each steel type, one damage-repair parameter was altered among
the two specimens. The parameters were chosen from the results of
laboratory-scale testing.
d / y
Specimen ID
p (in)
Mr / Mp-y
Tmax (°F)
Cycle # 
1
2
3
1
2
3
1
2
3
1, 2, 3
A7-Beam 1
30
30
30
0.25
0.50
0.25
2.2
2.2
2.2
1200
A7-Beam 2
90
60
60
0.50
0.50
0.50
8.5
5.9
5.9
1200
A588-Beam 1
40
20
20
0.25
0.25
0.25
4.9
2.1
2.1
1200
A588-Beam 2
40
20
20
0.50
0.50
0.50
4.9
2.1
2.1
1200
A36-Beam 1
30
30
30
0.25
0.50
0.25
3.1
3.1
3.1
1200
A36-Beam 2
30
30
30
0.25
0.50
0.25
3.1
3.1
3.1
1400
 d / y is the ratio of the damage strain in the extreme tension fiber to the
yield strain
 Mr / Mp-y is the ratio of the restraining moment in the heated steel to the
weak-axis plastic moment capacity of the section
 p is the plastic displacement at the point of loading after unloading
 Tmax represents the maximum heat temperature at the vee heat location
LARGE-SCALE TEST SETUP
•
Before damage - indicating instrumentation
Longitudinal strain
gage locations
Rotation
Meter
Rotation Meter
Quarter 6 in.
Displacement
Transducer
Infrared Thermometer
•
Quarter 6 in.
Displacement
Transducer
Midspan 12 in.
Displacement
Transducer
After damage – indicating key elements of test setup
Support
Column
Support
Column
Threaded Rod
Beam Specimen (A7-Beam 2)
p = 8.5 in
d = 90 y
Loading Beam
Hydraulic Actuator
LOADING FRAME
(a)
(b)
(h)
(c)
(d)
(e)
(f)
(g)
(i)
Elevation View
ELEVATION
VIEW
a)
b)
c)
d)
Top Plates
Semi-Circular Contact Shafts e)
f)
0.75 in. Threaded Rods
Side VIEW
View
SIDE
g)
Beam Specimen
Semi-Circular Contact Shafts h)
i)
Loading Beam
Hydraulic Actuator
2.5 in. Threaded Rod
Structural Plates and Nuts
DAMAGE CYCLES
•
•
•
The damaging (upward) force was applied by the
hydraulic actuator pushing the loading beam against the
flanges
Load was applied monotonically until the strain in the
extreme tension fiber reached d from earlier table
Instrumentation included:
–
–
–
–
Pressure transducers to measure actuator pressures
Six longitudinal strain gages at midspan to measure strains at the
top, bottom, and at bf / 3 from the top on both flanges
Four displacement transducers to measure midspan and quarter
deflections
Four rotation meters used to measure the end rotations
DISPLACEMENT DATA AT MIDSPAN
WHILE DAMAGING (A36-Beam 1)
500
Damage Cycle 3
400
Load (kN)
Damage Cycle 2
300
Damage Cycle 1
200
100
0
0
20
40
60
Displacement (mm)
80
100
REPAIR CYCLES
•
•
•
•
The restraining (downward) force was applied by the
hydraulic actuator pulling down on the loading beam with
additional attachments
Two researchers applied Vee heats simultaneously to both
flanges, spaced along the entire damaged region
Heats were applied until the deflection of the beam was
within 1/16 in. of the deflection before damage
Instrumentation included:
–
–
Pressure transducers to measure actuator pressures
–
Four displacement transducers to measure midspan and quarter
deflections
–
Four rotation meters used to measure to measure end rotations
Infrared thermometer used to measure the surface temperature of
the Vee heat
VEE HEAT LOCATIONS AND
NOMENCLATURE
9.46 in.
4.50 in.
4.50 in.
L5 L4 L3 L2
L1 C R1
40.00 in.
R2 R3 R4 R5
MATERIAL COUPSONS FROM BEAMS
•
Three flat tensile
coupons removed from
the back flange
(Flange A) of each
beam specimen
Tensile
CouponsFrom
from Flange A
a) a)
Tensile
Specimens
A
8.00 in
2.50 in
4.50 in
X
Y
Z
0.75 in
0.75 in
0.75 in
L1
C
R1
9.00 in
•
Twelve charpy
specimens removed
from the mid thickness
of the front flange
(Flange B) along the
center of Vee heats
L1, C, and R1
CharpySpecimens
SpecimensFrom
fromFlange B
b)b)Charpy
Flange B
2.165 in
2.25 in
4.50 in
2.165 in
2.165 in
L1-1
C-1
R1-1
0.394 in
L1-2
C-2
R1-2
0.394 in
L1-3
C-3
R1-3
0.394 in
L1-4
C-4
R1-4
0.394 in
L1
C
9.00 in
R1
Y
1.15
0.96
1.02
0.94
-
Z
1.20
0.94
1.03
0.80
-
Average
1.14
0.95
1.03
0.85
1.12
1.03
-
0.84
-
NORMALIZED STRUCTURAL PROPERTIES
1
Results are normalized to theA588-Beam
statistical
mean structural
X
0.94
1.00
0.90
properties of undamaged steel
from
the
same
plate
Y
0.96
0.99
0.92
Specimen /Coupon
y / yo
E / Eo
u  uo
e / eo
Hd / Hdo
A7-Beam 1
Z
Specimen
/Coupon
Average
A7-Beam
1 2
A588-Beam
XX
1.07
y 0.99
/ yo
1.01
E1.00
/ Eo
0.98
u0.93
 uo
0.79
e 0.89
/ eo
Hd0.95
/ Hdo
1.01
0.97
0.94
1.02
1.01
0.89
1.02
0.90
0.96
1.02
0.96
0.93
--
X
1.16
1.01
1.01
0.96
-
Y
1.16
0.94
1.02
0.96
-
YY
1.16
0.89
1.16
0.94
Z
1.25
0.93
1.06
0.81
-
ZZ
1.25
1.08
0.93
0.98
1.06
0.99
0.81
0.81
--
Average
1.19
0.96
1.03
0.91
1.07
Average
Average
1.19
0.97
0.96
0.99
1.03
0.92
0.91
0.92
1.07
0.94
--
A7-Beam
2 1
A36-Beam
A7-Beam 2
X
1.07
0.95
1.03
0.80
-
XX
1.07
1.07
0.95
1.00
1.03
0.98
0.80
0.97
--
Y
1.15
0.96
1.02
0.94
-
YY
1.15
1.07
0.96
0.93
1.02
0.96
0.94
0.94
--
Z
1.20
0.94
1.03
0.80
-
ZZ
1.20
1.07
0.94
1.04
1.03
0.98
0.80
0.88
--
Average
1.14
0.95
1.03
0.85
1.12
Average
Average
1.14
1.07
0.95
0.99
1.03
0.97
0.85
0.93
1.12
1.10
A588-Beam
A36-Beam 21
A588-Beam 1
X
0.94
1.00
0.90
1.03
-
XX
0.94
1.21
1.00
1.04
0.90
1.05
1.03
0.89
--
Y
0.96
0.99
0.92
0.84
-
YY
0.96
1.16
0.99
0.97
0.92
0.99
0.84
0.69
--
Z
1.07
1.01
0.98
0.79
-
ZZ
1.07
1.10
1.01
0.98
0.98
0.98
0.79
0.79
--
Average
0.99
1.00
0.93
0.89
0.95
Average
Average
1.16
0.99
1.00
1.00
1.01
0.93
0.79
0.89
0.97
0.95
A588-Beam 2
A588-Beam 2
X
0.89
0.97
0.89
1.02
-
X
0.89
0.97
0.89
1.02
-
Y
0.94
1.02
0.90
0.93
-
Y
0.94
1.02
0.90
0.93
-
Z
1.08
0.98
0.99
0.81
-
Z
1.08
0.98
0.99
0.81
-
CONCLUSIONS – STRUCTURAL PROPERTIES
•
•
•
Damage-heat straightening repair cycles do not have a
significant influence on the yield stress, elastic modulus,
ultimate stress, or surface hardness of steel ( 15%)
Damage-repair cycles reduce the percent elongation
(ductility) of A7 and A36 steel
For A588, damage-repair cycles slightly increase the
percent elongation of the outmost (X) specimen and
decrease the percent elongation of the middle (Y) and
innermost (Z) specimens
NORMALIZED FRACTURE TOUGHNESS
Results are normalized to the statistical mean fracture toughness of
undamaged steel from the same flange plate
Location
L1
1
2
3
4
Avg.
0.73
0.23
0.19
0.12
0.32
1
2
3
4
Avg.
3.08
3.07
2.77
1.47
2.60
1
2
3
4
Avg.
1.53
1.48
0.38
0.24
0.91
C
R1
A7-Beam 1
0.13 0.25
0.07 0.14
0.14 0.13
0.09 0.12
0.11 0.16
A588-Beam 1
3.08 3.08
3.05 3.07
2.63 3.05
1.26 1.36
2.51 2.64
A36-Beam 1
0.36 2.18
1.53 0.83
0.36 1.44
0.25 0.36
0.62 1.20
Avg.
L1
0.37
0.15
0.15
0.11
0.20
2.03
2.42
1.04
0.13
1.40
3.08
3.07
2.82
1.37
2.58
3.08
3.06
1.36
1.09
2.15
1.36
1.28
0.73
0.28
0.91
2.07
2.52
2.07
1.01
1.92
C
R1
A7-Beam 2
1.07
2.85
0.84
0.89
0.12
0.88
0.22
0.18
0.56
1.20
A588-Beam 2
3.06
3.01
2.87
2.72
1.25
1.11
0.77
1.07
1.99
1.97
A36-Beam 2
4.61
4.05
3.19
4.23
1.24
2.43
0.40
1.64
2.36
3.08
Avg.
1.98
1.38
0.68
0.18
1.05
3.05
2.88
1.24
0.98
2.04
3.57
3.31
1.91
1.02
2.45
CONCLUSIONS – FRACTURE TOUGHNESS
•
•
•
•
•
The fracture toughness of A7-Beam 1 subjected to Nr=3 and d=30y
is much lower than the undamaged toughness. The mean fracture
toughness of A7-Beam 2 compares favorably with the undamaged
toughness. However, some variability is seen in the results and the
toughness of material closer to the flange-web junction (k-region) is
much lower
Damage-repair cycles increase the fracture toughness of A588 steel
significantly to the ranges of 272-308% for the outermost two rows of
charpy specimens. The fracture toughness values were smaller for
charpy specimens closer to the flange-web junction
The overall fracture toughness of A36-Beam 1 is comparable to the
undamaged toughness. However, significant variability exists
The fracture toughness of A36-Beam 2 increased significantly. The
increase ranges from 101-460% of the undamaged toughness. There
was one low value (40%)
None of the significant conclusions and recommendations from the
laboratory-scale testing (Sub-task 2.1) were altered by the results from
the large-scale testing
QUESTIONS, COMMENTS, AND
DISCUSSION?