NDT in Grouted PT Inspection NDT in Grouted PT Inspection for Bridges for Bridges
PTI Technical Conference & ExhibitionPTI Technical Conference & Exhibition
Miami, FLMiami, FL
May 8, 2007May 8, 2007
HongHong--gang Cao gang Cao
CTLGroupCTLGroup
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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The NDT Applications in PT The NDT Applications in PT inspection:inspection:-- Locating embedded tendonsLocating embedded tendons
-- Evaluation of void in grouted tendonsEvaluation of void in grouted tendons
-- Locating break and crack along tendon Locating break and crack along tendon strand / wire near anchoragestrand / wire near anchorage
-- Inspection of cable condition through Inspection of cable condition through videoscopevideoscope
-- Corrosion inspectionCorrosion inspection
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Currently available techniques:Currently available techniques:
Impact Echo methodImpact Echo method
Impulse Radar or Ground Penetrating Radar Impulse Radar or Ground Penetrating Radar (GPR)(GPR)
Ultrasonic Pulse Echo Ultrasonic Pulse Echo
VideoscopeVideoscope examinationexamination
Others, e.g. XOthers, e.g. X--Ray, magnetic flux leakage, Ray, magnetic flux leakage, etc. etc.
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Void Detection Using Impact Void Detection Using Impact Echo MethodEcho Method
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Project 1 Project 1 –– Bridge GirderBridge Girder
•• A 11A 11--span bridge supported by 9 parallel span bridge supported by 9 parallel precastprecast postpost--tensioned girders in each spantensioned girders in each span
•• 20 years old20 years old
•• 99 nos. of beams in total99 nos. of beams in total
•• Single postSingle post--tensioning tendon in each beamtensioning tendon in each beam
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Web Web -- Plate structurePlate structure
Single TendonSingle Tendon
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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PP--Wave Speed:Wave Speed:
T = 0.19 mT = 0.19 m
ffT T = 8.8 kHz (Test on = 8.8 kHz (Test on solid concrete portion)solid concrete portion)
VpVp =2 * T * f=2 * T * fTT / 0.96 / 0.96 ≈≈3400 m/s 3400 m/s 0
50
100
150
200
250
0 5000 10000 15000 20000 25000 30000 35000
Frequency (Hz)
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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If fully grouted:If fully grouted: ffT T = 8.8 kHz (8.3 kHz used) = 8.8 kHz (8.3 kHz used) ffsteelsteel = 13.9 kHz= 13.9 kHz
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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If empty:If empty: ffT T < 8.8 kHz (or 8.3 kHz)< 8.8 kHz (or 8.3 kHz)ffvoidvoid = 26.7 kHz= 26.7 kHz
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Results:Results:
•• 2200 points were tested in 99 beams 2200 points were tested in 99 beams
•• Two completely ungrouted tendon as Two completely ungrouted tendon as well as more than 20% partially well as more than 20% partially grouted ducts were notedgrouted ducts were noted
•• Boroscope examination was performed Boroscope examination was performed to verify the findingsto verify the findings
•• Overall success rate 80%Overall success rate 80%
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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IE Experience:IE Experience:
•• Good for plate type structure: slab, wall Good for plate type structure: slab, wall ……..
• Single tendon
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Void Detection Using GPRVoid Detection Using GPR
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Project 2Project 2–– External TendonExternal Tendon
•• Two similar mileTwo similar mile--long long bridgesbridges
•• 237 external cables or 237 external cables or 5,180 m (17,000 ft)5,180 m (17,000 ft) in in lengthlength
•• PE pipe diameter 4.5 in.PE pipe diameter 4.5 in.
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Traditional way:Traditional way:
Visual inspection + mechanical Visual inspection + mechanical soundingsounding
CTL approach:CTL approach:
Impulse Radar + visual inspection + Impulse Radar + visual inspection + mechanical soundingmechanical sounding
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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TTmm = C / (4f = C / (4f √ε√ε))
εε = 5 to 12= 5 to 12
f = 1.5 x 10f = 1.5 x 1099 HzHz
TTmm = 22 mm = 22 mm Or Or
13% section area 13% section area
POLYETHYLENE PIPE
POST-TENSIONED STRANDS
22mm MIN.
GROUT
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Radar Testing Along External Ducts
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Empty duct Grouted
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Partially grouted
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Results:Results:
•• Approximately 2% of total cable length Approximately 2% of total cable length was empty or partially groutedwas empty or partially grouted
•• Majority of the voids found by sounding Majority of the voids found by sounding method was not seen by Radar. method was not seen by Radar. Boroscope examination proved only Boroscope examination proved only thin void or delamination between PE thin void or delamination between PE duct and grout.duct and grout.
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Experience:Experience:Pros Pros ––
•• Radar finding important or significant voidRadar finding important or significant void
•• Save by using a costSave by using a cost--effective repair effective repair approachapproach
Cons Cons ––
•• Relatively expensive (time consuming) in Relatively expensive (time consuming) in inspectioninspection
•• WonWon’’t work on galvanized steel sheathing or t work on galvanized steel sheathing or other metallic base materialother metallic base material
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Strand / Wire Break Inspection Strand / Wire Break Inspection --Ultrasonic PulseUltrasonic Pulse--EchoEcho
MethodMethod
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Typical ResultsTypical Results
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Ultrasonic PulseUltrasonic Pulse--EchoEcho
High frequency transducer capable of High frequency transducer capable of locating fine cracklocating fine crack
Typically effective over 4 to 5 ft at end Typically effective over 4 to 5 ft at end of Strandof Strand
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Intrusive InspectionIntrusive Inspection
Seeing is Believing !
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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•• 500 ft long ramp500 ft long ramp
•• More than 100 tendonsMore than 100 tendons
•• BoroscopeBoroscope inspection through each inspection through each jointjoint
Project 3 Project 3 –– Video Scope InspectionVideo Scope Inspection
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Tendon Layout plan – Half of the Bridge deck
1000 drill holes along segmental joints, 7/8 in. in 1000 drill holes along segmental joints, 7/8 in. in diameterdiameter
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Drilling process:Drilling process:
•• Drilling holes using a template based Drilling holes using a template based on construction drawingon construction drawing
•• Unsuccessful near anchor zone Unsuccessful near anchor zone
•• GPR does the workGPR does the work
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Tendon Ducts
GPR Survey
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Use of Videoscope:Use of Videoscope:
•• 6mm diameter flexible tube, 10 ft long6mm diameter flexible tube, 10 ft long
•• TwoTwo--men crew completed survey in men crew completed survey in two weekstwo weeks
•• Video recording functionVideo recording function
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Summary:Summary:
•• NDT techniques available in PT NDT techniques available in PT InspectionInspection
•• They do the job if used properlyThey do the job if used properly
•• Experience mattersExperience matters
•• Realistic expectationRealistic expectation
2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO
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Thank YouThank You
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