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Overview of FHWA Research on NDE Techniques for Cable-stayed and
Post-tensioned Bridge Tendons
Seung-Kyoung Lee Manager of Coatings and Corrosion Laboratory
Turner-Fairbank Highway Research Center Federal Highway Administration
May 24, 2010 (AASHTO T-9)
Overview of FHWA Research onOverview of FHWA Research on NDE Techniques for CableNDE Techniques for Cable--stayed and stayed and
PostPost--tensioned Bridge Tendonstensioned Bridge Tendons
Seung-Kyoung Lee Manager of Coatings and Corrosion Laboratory
Turner-Fairbank Highway Research Center Federal Highway Administration
May 24, 2010 (AASHTO T-9)
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Presentation OutlinePresentation Outline
• Research Background
• Laboratory Evaluation
• Field Trial of Magnetic Main Flux Method (MMFM)
at the Varina-Enon Bridge, VA
• Planned Field Trial of MMFM at the Luling Bridge, LA
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Research BackgroundResearch Background
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Corrosion of Post-Tensioned TendonsCorrosion of Post-Tensioned Tendons
After 16 Years, Niles Channel Bridge, Keys, FL (1999)
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Corrosion of Post-Tensioned TendonsCorrosion of Post-Tensioned Tendons
Niles Channel Bridge, Keys, FL
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Corrosion of Post-Tensioned TendonsCorrosion of Post-Tensioned Tendons
After 13 Years, Sunshine Skyway Bridge, Tampa, FL (2000)
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Sunshine Skyway Bridge, Tampa, FL
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After 6 years, Mid-Bay Bridge, Destin, FL (2000)
Corrosion of Post-Tensioned Tendons
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Mid-Bay Bridge, Destin, FL
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Corroded Post-Tensioned Tendons
Corroded Post-Tensioned Tendons
After 17 years, Varina-Enon Bridge, Richmond, VA (2007)
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Laboratory Evaluation ProgramLaboratory Evaluation Program
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Artificial Defects by Saw CutsArtificial Defects by Saw Cuts
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Artificial Defects by Impressed CurrentArtificial Defects by Impressed Current
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Artificial Defects for Internal PT TendonsArtificial Defects for Internal PT Tendons
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Internal PT TendonsInternal PT Tendons
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NDE Technologies EvaluatedNDE Technologies Evaluated
• Ultrasonic and Sonic Echo/Impulse Response (SE/IR)
• Magnetostrictive Sensor (MsS) Technology for Guided Long-Range Waves
• Microwave Thermoreflectometry
• Remnant Magnetic System
• Magnetic Main Flux Method (MMFM)
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Lab TestsLab Tests
[Ultrasonic]
[Sonic Echo/Impulse Response]
Permanent magnets
MsS ribbon coils
[Magnetostrictive Sensor Guided-Wave]
[Remnant Magnetic]
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FindingsFindings
• None of the NDE systems was able to detect artificial defects
in the internal PT tendons.
• Presence of grout in the external PT tendons made
propagating signals attenuate significantly and resulted in
most NDE technologies ineffective.
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Magnetic Main Flux Method (MMFM)Magnetic Main Flux Method (MMFM)
Carlton Lab at Columbia University
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MMFM PrincipleMMFM Principle
N Pole S Pole
Area S
Flux φ
Area S’
Flux φ’
Normal Section
Corroded Section
Magnetic Flow磁束
全磁束検出波形
損傷部モデル
損傷部と検出波形サーチコイルSearch Coil
Damage Model
Detecting Wave
Flux
* The absolute value of metallic area can be evaluated by * The absolute value of metallic area can be evaluated by measuring the parameter measuring the parameter ΔΔØØ..
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MMFM System ComponentsMMFM System Components
Wire/StrandWire/StrandSearch CoilSearch Coil
Hall Effect Hall Effect SensorSensor
Constant DC
P.C.P.C.
Gauss Meter
Electrical Cable Electrical Cable
MagnetizerMagnetizer
Flux Meter Data
Recorder
PolaritySwitch
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MMFM on PT Tendons – 1st GenerationMMFM on PT Tendons – 1st Generation
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Magnetic Flux Chart of Specimen AMagnetic Flux Chart of Specimen A
Estimation of Section Loss (%) 0.2 2.0 0.2
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Autopsy Result of Specimen AAutopsy Result of Specimen A
Estimation (%) 99.8 98.0 99.8Actual (%) 99.8 87.6
(16.5 wires) 99.8
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MMFM on PT Tendons – 2nd GenerationMMFM on PT Tendons – 2nd Generation
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Test Results – Linear RegressionTest Results – Linear Regressiony = 0.999x - 0.1935
R2 = 0.9918
88
89
90
91
92
93
94
95
96
97
98
99
100
88 89 90 91 92 93 94 95 96 97 98 99 100
Remaining Cross- sectional Area (%)
Rate
of
Mag
netic
Flu
x (%
)
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Findings - MMFMFindings - MMFM
• MMFM was determined to be the most accurate NDE
system in the lab study.
• Great potential for detecting insidious corrosion in the
external PT tendons, stay cables, and suspension cables.
• It was decided to verify the MMFM technology through field
trials on two bridges with known problems.
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MMFM Field Trial at Varina-Enon Bridge, VA (April 27 – May 1, 2010)
MMFM Field Trial at Varina-Enon Bridge, VA (April 27 – May 1, 2010)
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Preparation & Getting to the Test AreasPreparation & Getting to the Test Areas
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Preparation & Getting to the Test AreasPreparation & Getting to the Test Areas
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Test AreaTest Area
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Magnetizer SetupMagnetizer Setup
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Dummy Wire AttachmentDummy Wire Attachment
¼ in. wire
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MMFM TestingMMFM Testing
[Scan Measurement] [Point Measurement]
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Raw MMFM Data (Screen Shots)Raw MMFM Data (Screen Shots)
[Scan Measurement] [Point Measurement]
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Distance Measurement Distance Measurement
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Magnetizer RemovalMagnetizer Removal
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AutopsyAutopsy
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Temporary RepairsTemporary Repairs
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P14S13TE-3
0.2% section loss estimated
by MMFM
Very minor corrosion possible
by MMFM
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P14S13TE-3
Autopsy-1
Autopsy-3
[Autopsy-1]
[Autopsy-3]
P14S13TE-3
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Autopsy Results (P14S13TE-3, Autopsy-1)Autopsy Results (P14S13TE-3, Autopsy-1)
1,000 mm(39.4 in.)
(No corrosion observed)
(No corrosion observed)
(Minor corrosion observed)
(Minor corrosion observed)
Wall
Wall
Wall
Wall[Wall]
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Autopsy Result (P14S13TE-3, Autopsy-3)Autopsy Result (P14S13TE-3, Autopsy-3)
Strands embedded in good condition grout and no corrosion observed [a small nick was found on a wire that was probably created during the excavation work]
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P14S13TE-1
No corrosiondamage detected by MMFM
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P14S13TE-1
Autopsy-2
P14S13TE-1
[Autopsy-2]
No excavation was made because of a low possibility of discovering corrosion problem.
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P14S13TE-2
No corrosiondamage detected by MMFM
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P14S13TE-2
P14S13TE-2
No excavation
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P12S11TE-2
No corrosiondamage detected by MMFM
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P12S11TE-2
P12S11TE-2Autopsy-4
[Autopsy-4]
Strands were fully embedded in grout and no excavation was made.
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P12S12TW-3
0.6% section loss estimated
by MMFM(1 wire broken)
0.3% section loss estimated
By MMFM
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P12S12TW-3 (Uncovered Condition)
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Autopsy Results (P12S12TW-3, Autopsy-5)Autopsy Results (P12S12TW-3, Autopsy-5)
~810 mm (32 in.) from wall ~1,900 mm (75 in.) from wall
2,110 mm (83 in.) from wall
[Wall]
[Partial section loss observed on
several wires]
[Partial section loss observed on
several wires]
[1 wire brokenand heavy
section lossobserved
on several wires]
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Preliminary FindingsPreliminary Findings
• It was observed that MMFM was able to identify intact areas
and locations having corrosion damage that ranged from
approximately 0.2 % to more than 0.75 % section loss.
• This finding is consistent with the lab results in that the same
lowest detection resolution (0.2 %) was verified during this
field trial.
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Preliminary Findings - ContinuedPreliminary Findings - Continued• However, it could not measure section loss accurately when
a wire was corroded in two (not critical, same issue observed in the lab testing).
• Also, there are discrepancies of up to 20 in. between actual
location of a corrosion damage and where MMFM data
suggested. It might be due to errors in distance
measurements. It needs further investigations.
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Preliminary Findings - ContinuedPreliminary Findings - Continued• The current MMFM system demonstrated promising results
of being a fully operable field NDE technology.• A more efficient field MMFM system needs to be improved at
least in the following areas: – Improved cable winding and unwinding methods for the magnetizer – Precise measurement of magnetizer’s travelling distance,– Magnetizer’s better riding ability on the tendons– Self-propelled magnetizer (?)
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MMFM Field Trial at Luling Bridge, LAMMFM Field Trial at Luling Bridge, LA
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Luling Bridge (Hale Boggs Memorial Bridge)Luling Bridge (Hale Boggs Memorial Bridge)
• Opened in 1983
• Weathering steel
• 1st
cable-stayed over Miss. river
• 2,745 ft. long (1,222 ft. main span)
• 39 out of 72 cables were rated critical
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Planned Field TestingPlanned Field Testing
Scan length/cable = ~20 ft.
Magnetizer
Electrical winch
• No. of cables to be inspected = 3-5• No. of autopsy samples = three 10-ft. sections• Removed samples will be transported to FHWA Corrosion Lab for detailed autopsy
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Thank you!Any Questions?
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