5/20/2013 - Post-Tensioning Institute

1 5/20/20131 Infrastructure GroupMistras Confidential Information Infrastructure GroupOutline Methods Acoustio/Ultrasonics Radiography Acoustic Emission Systems and Software Large SHM Project (Hammersmith Flyover) wire Break P T Monitoring Experience Summary Chloride contaminated grout discovered on suspected 34 bridges in P T Tendons Tendons failures on several US bridges and in Europe Some only 7 and 15 years old. In the UK corroding internal tendons have closed a major London bridge Tendons designed to be maintenance free but difficult to inspect Common tendon problems are corrosion from contaminates, voids and wire breaks. Utilized many NDT and SHM (Structural Health Monitoring) experience in research Methods discussed P T Tendon inspection and SHM were: Ultrasonics, Phased Array Ultrasonics, Radiographic, Computed Digital Radiography, Ground Penetrating Radar, Magnetic Particle, Magnetic Flux Leakage, Eddy Current, Electromagnetics, Vibration and Strain Gages, Acoustic Emission and Infrared Thermography.

2 Magnetic Flux Leakage has shown promise for metals loss and has been published in the past by University of Wisconsin. We investigate five other methods/technologies. This presentation discusses non invasive technologies for P T Tendon inspection and Bridge, 34 others being checked for possible structural defectsGrout used to protect steel cables may be contaminated with corrosive compound1. Acousto/Ultrasonics technology was developed by the Army Corp of Engineers for detecting voids in concrete columns wrapped with FRP. This system uses a rolling sensor and a B scan imaging system to give a less experience operator a color coded view of voids in the Active Corrosion Detection: Acoustic Emission (AE) has been used in the petroleum industry to locate and map active corrosion in steel tank bottoms.

3 The chemical industry adapted a portable version. A tendon can be monitored with this portable AE system to see if there is active corrosion. 3. Long term AE monitoring: is used regularly to detect wire breaks as recommended in NCHRP 353 and NCHRP 534. Recent full scale field and lab data and monitoring results. One of which is the largest known P T Tendon monitoring project for the Hammersmith Flyer Over Bridge for internal tendons wire The last sections will discuss two radiographic techniques and detecting voids. Voids contain oxygen, which lead to corrosion and wire breaks. Real Time RTComputed Radiography *Not discussed Magnetic Flux Leakage, Documented over 10 years for metal loss on tendon (University of Wisconsin). Attempted to develop to replace high tech coin tappers Acousto Ultrasonics (AU) active non destructive testing method.

4 The AU method is the combination of Acoustic Emission (AE) method and Ultrasonic method. Waveform analysis techniques of AE method and applies typical through transmission mode of Ultrasonics. The AU system using a function generator board at the frequency range of 100 1000 kHz, depending on the structure under test. Receivers record the propagating pulse signal in the path of pulser receiver. The acquired waveforms are processed to estimate signal properties such as arrival time, amplitude, shift in the dominant frequency. Any change in signal properties indicates the variation of pulser receiver path as compared to the baseline. If there is no change in the characteristics of pulser receiver path, waveform signature will be the same as the baseline. If there is any change in the path, the change is detected using the waveform signature characteristics, such as amplitude, peak frequency.

5 Showed promising results in lab on sample Test at FDOT on their lab tendon did not work ODOT research canceled Figure 8: Rolling Acousto/Ultrasonic ProbesMistras Confidential Information 5/20/20132 Infrastructure Group Foam clearly visible with Real Time RT Scanning for voids at about 2 MPH Accessibility to tendonsFoam inserted into tendon and RT imagine for foamMistras Confidential Information Acoustic emission is a global passive inspection methodMistras Confidential Information 5/20/20133 Adjustable ThresholdTime of HitDurationRise TimeCountsAE Amplitude 23 Different Features Hits Events Rise Time Counts to Peak Duration Amplitude Energy Average Frequency Initialization Freq Frequency Centroid Reverberation Freq Peak Freq Absolute Energy Signal Strength Partial Power 1 Partial Power 2 Partial Power 3 ASL Counts RMS Waveform Streaming Waveform 100 dB0 dB40 dBAE Signal 10 Million Samples/Second 80 db Dynamic

6 Range 100 Microseconds AE signal (absolute energy)1010109108107106105104103102 CorrosionMetal fatigueComposite damageConcrete micro fractureWire breaks Post tensioned concrete Suspension bridgesLead BreakReference ASTM STP 908 Fundamental Aspects of Acoustic Emission Applications to the Problems Caused by Corrosion Active Corrosion Monitoring with Acoustic Emission Mistras Confidential Information Energy, Counts,Frequency,Amplitude, etc Classifier Bad AE dataGood AE dataSensor SystemSensor SystemSensor SystemMistras Confidential Information 5/20/20134 Software Automated to filter wire break signal from other data Seven step AE Filter Reduces Report and Analysis TimeEMAIL from system, -----Original Message-----From: 11 August 2012 09:35To: HumberSubject: Humber6: Sensor Connection Status Change detectedDo not reply to this Humber6:The following sensor(s) are now connected: 88-----Original Message-----From: 11 August 2012 01:35To: HumberSubject: Humber6: Sensor Connection Status Change detectedDo not reply to this Humber6:The following sensor(s) are now disconnected.

7 88 American Society for Testing and Materials (ASTM) American Society of Mechanical Engineers (ASME) The Society of the Plastics Industry (SPI) United States Department of Transportation (DOT) Federal Rail Authority (FRA)/Association of American Railroads (AAR) Society of Automotive Engineers Nuclear Regulatory Commission Compressed Gas Association American Petroleum Association American Society for Nondestructive Testing (ASNT) The European Working Group on Acoustic Emission (EWGAE) The Japanese Society for NDI (NDIS) UK Health and Safety Executive DGZfP (German Society for Non Destructive Testing) AFNOR (French Association for Standards)5/20/20135 Results: Typically 1 hr. test 2 channels Sample 20ft of tendon in an hours Attenuation test with lead pencil, 20 dB loss Impressed current inducted corrosion is detectable More research Tendon needs to be tested under load and with active corrosionMistras Confidential Information Also University of Texas Austin, Dr.

8 Wheat and othersAcoustic Emission Monitoring Mistras Japan (NPA) has had third party verification tests of our post-tension wire break Test Japanese Public Highways Corporation in 2001-2002. First stage trials carried out on parallel wire cables and wound wire rope (Macalloy bars) Ducts with differing percentages of grout. Failures were induced by mechanical cutting and also corrosion; using corrosion cells placed over exposed sections of cable wire breaks (2mm in diameter) detected and located in all grouting levels. Mistras proceeded with long term monitoring of two P-T bridges Second stage evaluation and system calibration using a post tension concrete test block cemented to the concrete box girder bottom flange. wire breaks induced by corrosion cell mounted over an exposed section of cable.

9 Readily detected and located. Location accuracy ~2-4% of sensor spacing wire break detection 82% and 86% in strand cables and parallel wire cable respectively Mistras co-wrote technical paper with the Japanese Highways Agency Detection and Evaluation of Failures in High Strength Tendon of Pre-stressed Concrete Bridges by Acoustic Emission , located in Appendix up for tests5/20/20136 Evaluation of AE wire Break Detection with Japan Highways Public CorporationTest beam specimensSensor 110,000 Sensor 2225027503250250250 wire break due to corrosion of a strand(19 wires) wire break due to corrosion of parallel wire cable(12 cables)Fully groutedUnbondedPartly groutedAE Location on beam (m)Number of eventsFully groutedPartially groutedUnbondedPT beam Software Automated to filter wire break signal from other data Seven step AE Filter Reduces Report and Analysis TimeMonitor Results from bridges5/20/20137 Reinforced concrete balanced cantilever beam supports with a single central column.

10 Deck spine and wings are hollow pre stressed concrete design. Concrete post tension 17 span, 4 lane bridge 300 AE sensors and Strain gages Contracted for SHM System to detect and locate post tension wire breaks and measure deterioration and structural movement. SHM System uses a combination of acoustic emission wire break sensors, displacement transducers, resistance strain gauges, inclinometers, and thermocouples Networked stations and uses lasers/prisms along the length of the flyover 450 sensors, largest bridge monitoring in UK. Installation commenced in April 2010 and took 8 weeksAE Triangulated the break to within 4 (100mm) of the physical break and to the correct tendon group5/20/20138 Strain Vibration Seismic movement Acoustic Emission Tilt / Rotation 3D movement Displacement Temperature / Weather Video/stillMistras Confidential Information Alerts & AlarmsMistras Confidential Information wire Break Reporting Concrete wire break monitoring on the M56, Bridge in Manchester England 88 channel MISTRAS AE system Installed January 2011 $300k system/installation and year monitoring/reporting and sensor Forty five years of corrosive road salt draining onto one side of an overpass History of trucks hitting its underside 53 foot long, 60 ton concrete beam Rated 4 on a scale of 1 to 10 a few months prior to collapse Combination of age, wear and tear in the structure, a history of being hit by trucks and.