Monitoring Vibrations

The objective of the research was to determine the frequency and cause of resonant vibrations of truss verticals on bridge A4497 over the Missouri River in Jefferson City, MO. It was concluded that the frequency of resonant vibration events is likely 0.25 events per day or less. The vibrations are caused by average winds from the WNW/NW or SW of ~17 mph or greater, based on monitoring results. Recommendations stemming from the research were as follows: 1) The effect of the vibration events on the durability of the members should be analyzed further to determine if a retrofit is necessary. The data provided through the field monitoring should be used in the analysis; and 2) Other vertical members of a similar length should be monitored to determine if they are affected by resonant vibrations.


Field Testing of Handheld Thermography

This report is the second of two volumes that document results from the pooled fund study TPF-5 (247), Development of Handheld Infrared Thermography, Phase II. The interim report (volume I) studied the implementation of handheld thermography by participating state Departments of Transportation (DOTs). This final report (volume II) provides a summary of field testing conducted to evaluate the capabilities of two different IR imaging technologies for detecting subsurface damage in concrete. The IR-UTD technology collects thermal images over a period of time; these data are processed to measure thermal inertia of a
material. The IR-UTD technology is an entirely new approach for imaging damage in concrete structures. The IR-DSS technology automatically captures thermal images while the system is moved from one position to another. The IR-DSS technology produces images based on the radiant thermal energy from a material in the same manner as other typical thermal imaging systems. However, the IR-DSS has a unique design that allows the system to be implemented from different mobile platforms and uses a precision encoder to trigger data collection.
In general, it was found that the IR-UTD technologies had capabilities that exceeded the capabilities of conventional IR imaging. The technology provided highly accurate data that documented the size and shape of delaminations in bridge decks and other structures. The IR-UTD technology also provided data on the depth of damage and could image the structural features of a bridge.

Illuminance

Condition assessments of highway bridges in the U.S.typically rely on visual inspection for the detection and assessment of damage.  For bridge members defined as “fracture critical,” meaning the failure of the member would most likely result in the collapse of the bridge, hands-on inspections are required on a biennial basis.  These inspections assess the condition of the members, focusing in particular on the detection of cracking that could undermine the structural integrity of the bridge.  Inspections such as these are conducted at distances of ~24 inches from the surface under inspection (i.e. hands-on), and rely on the inspector’s ability to detect cracks visually.  Previous research on the reliabilityof this process has indicated that crack detectionrates are very low.  One way to improve an inspector’s ability to detect a crack is to ensure that adequate lighting is available during the inspection.  The geometric environment of a bridge is such that inspections are typically conducted in the relatively dark conditionsfound under bridges, and the low contrast provided by a crack in the steel surface may be difficult to detect under these circumstances.The FHWA study(Moore, et. al., 2001) found that inspectors that use flashlights during the inspection process have a higher likelihood of detecting cracks, although crack detection rateswerestill low.

This study  evaluated the illuminance provided by typical flashlights and assessed how that lighting may affect an inspector’s ability to detect cracks in bridges.  Currently, there are lighting standards in other industries that provide some guidance in this area.  For example,procedures for certain NDE technologies, such as magnetic particle inspection (MT), require the intensity of light on the inspection surface be at least 100fc (foot-candles)(ASTM Standard E709, 2008, “Standard Guide for Magnetic Particle Testing,” ASTM International). The Illuminating Engineering Society (IES)recommendation for office environments where low contrast or small visual tasks such as bookkeeping, accounting, or drafting, are performed is 75fc (Kaufman, J. E., J. F. Christensen, et al, 1987,IES lighting handbook: 1987 application volume). The goal of this study was to determine adequate lighting levels, spatial and contrast resolution, and overall visibility necessary for crack detection.  The second part of this research is the assessment of the performance of a series of lights in areas such as illuminance and uniformity of light, the objective being to identify commercially available lights that would be recommended for bridge inspection.

The research found that the level of  illuminance that can be called adequate for visual inspection is indeterminable due to the variance in human vision. The research process was to determine a relevant crack-opening dimension (COD) that would be considered a problem, then to determine what level of illuminance was required to sufficiently resolve a line of that width. However, the literature search indicated cracks in ferromagnetic steel can range anywhere from 10 to 1000 microns in width, with the crack opening dimension in the 10-40 micron range (Anderson et al. 2006).  None of the visual resolution test results indicated that any of the participants could resolve items below 100 microns. The issue is further complicated by the fact that the data does not highly correlate an increase in illuminance with a greater resolving  capacity for smaller objects. And while the data does correlate an increase of visual contrast with greater resolution capacity, the contrast in a bridge inspection environment is not a variable that can be greatly shifted. Therefore no illuminance level can be definitively stated to be the minimum required for the average human eye to detect significant cracks in bridge steel.

Developing Reliability-Based Bridge Inspection Practices

The objective of this research is to assess the effect of reliability-based inspection practices on current bridge inspection procedures by performing pilot studies in Texas and Oregon.

Almost all nondestructive tests (NDT) applications are characterized by noisy data, less-than-perfect detection and therefor their data do not necessarily fall into one of two obviously defined categories that can be uniquely ascribed to the presence or absence of the anomaly in question. Therefore, NDT reliability comprises two types of wrong indications: failure to give a positive indication in the presence of a defect and giving a positive indication when there is no defect (a false call). Probability of detection curve (POD) which is mostly used for the reliability of NDT assessment is not enough on its own unless the false alarm rate (FPR) is given too. Further, information given by POD is important from a safety viewpoint since the reliability is assessed by means of detection only. The probability of false calls can be presented through receiver operating characteristics (ROC) curve. This curve can provide information in terms of both detection and false calls. Indeed this information is important from a safety as well as an economic viewpoint. ROC curve is used in many fields but has never been used for the evaluation of NDT reliability. In this research, the reliability of NDT tests in detecting a different kind of anomalies in concrete bridge deck will be assessed by using ROC. The curve was found as an ideal approach to qualitatively assess the reliability of such nondestructive techniques.

A previous study’s findings can be downloaded here NCHRP Report 782

Evaluating the Reliability of Ultrasonic Testing on Welds

The objective of this research is to evaluate the reliability of the current American Welding Society procedures used for ultrasonic testing (UT) of welds by developing a timeline describing the development of UT as a common inspection tool, and comparing the current code requirements to the reliability of the results.

One of the most commonly used nondestructive testing (NDT) methods for testing materials for defects is UT. This technology relies on the principle of echo-ranging, in which a pulse of acoustic energy emitted from a transducer, propagates through a material, and is reflected from boundaries of the materials or defects within the material. Reflections are detected by the transducer and analyzed, to assess the location and extent of any indications in the material that may result from embedded defects.

The detection and analysis of defects relies in part on the experience, training and capabilities of the instructor performing the testing. Significant variation in results between different inspectors can result. For example, a study conducted in 1981 (NCHRP 242) found that the defect ratings varied by an average of 6.5 dB between different tests conducted on the same sample defects. Under current code requirements for welding (AWS D1.5), the range between acceptance and rejection for a given indication is only 4 dB. As a result, indication may be rated as acceptable by one test, and unacceptable in another, suggesting the reliability of the methodology may need to be improved.

Ultrasonic testing was developed in 1945 by Dr. Floyd Firestone, and has been implemented into the American Welding Society Code for Welding in Building Construction (AWS D1.0-69) and Specifications for Welded Highway and Railway Bridges (AWS D2.0-69). Current requirements are included in AWS D1.5, 2011. There appears to be limited previous study of the reliability of this technology as currently implemented in the AWS code. In other industries, such as aerospace and nuclear fields, extensive probability of detection (POD) studies have been used to quantify the reliability of UT procedures. However, similar studies have not been conducted previously to assess the reliability of the technology according to the AWS code procedures.

The American Welding Society Ultrasonic Testing procedure utilizes the amplitude of the reflected wave as well as the measured length of the defect to establish the severity of the defect. Because the AWS relies on the reflected amplitude, the tests are used to determine what factors impact the reflected amplitude. The tests include: length-amplitude measurement, size-amplitude measurement, transducer wedge angle-amplitude measurement, defect orientation-amplitude measurement, surface roughness-amplitude measurement, attenuation measurements and defect sizing using AWS procedure.

The equipment included an AWS ultrasonic wedge transducer, an encoder, a pulse receiver and a calibration block. The USB-UT350 Ultrasonic Pulse Receiver with A/D Converter and encoder capabilities was ordered because some tests require many waveform measurements over a given length. The S1 encoder tracks the movement of the transducer and associates a waveform with each encoder location. A sensitivity calibration block (SC) was used as a reference for each of the measurements.

Various test specimens were manufactured for test purposes. A plate with EDM cuts with known lengths and depths was created for the length-amplitude measurement. Several side-drilled holes of various diameters were drilled into a sample for the size-amplitude (Figure 1), transducer wedge angle-amplitude, and defect orientation-amplitude measurements. A plate with eight sides each with a different machined surface finish was used for the surface roughness-amplitude (Figure 2). Two plates with several EDM slots of known depths were used for the attenuation-amplitude measurements. Several fabricated defects of known location and lengths were placed in four test plates (Figure 3). Three plates with transition butt welds and one plate with standard butt weld were used.

Evaluation of Bridge Coating System Performance in Missouri

This study reports on the state of the practice for coating and overcoating of steel and evaluates the performance of existing coating in Missouri.   The following conclusions and recommendations were obtained by accomplishing the above two tasks: • An improved visual inspection procedure and associated visual guides provided through task 1 will improve the reliability of condition assessments for existing coatings systems. Implementation of the recommended procedure will improve the quality of database information available to decision makers. • The survey of the performance of coating systems used in Missouri showed that maintenance overcoating system S was effective in extending the service life of coating in many cases. The estimate of 10 to 15 years of service life for a well-applied system S coating was supported by observations in the field. However, when overcoating at locations where corrosion was very significant and drainage patterns (i.e. leaking joints) are unchanged, early system S failures were observed. This is due to the combination of existing rusting not being fully removed by the surface preparation, chlorides remaining on the surface, and the continued exposure to wet-dry cycles. • For coatings overall, the drainage of water from the deck onto the superstructure was the primary factor leading to service failure of the coating. Deterioration of the bridge deck to a poor condition is directly related to the failure of the coating system, regardless of the coating system. Coating systems with 35 to 40 years of service life were still performing well on bridges with effective drainage that kept the superstructure dry. • The contemporary coating system G was performing well in all situations observed. This modern coating is accompanied by improved designs that avoided water from the deck draining onto the superstructure. • Every coating system has pros and cons.  It is of importance to make a case-by-case study when making the decision on which type of paint should be used on a specific bridge. • Inorganic (IOZ) vs. organic zinc (OZ) primers: IOZ is good at hindering corrosion. However, OZ primer has a higher adhesive strength. • Coating system-micaceous iron oxide zinc primer with aliphatic polyurea polyaspartic topcoat resulted in a nearly equal performance: good performance on salt-fog resistance, superior resistance to UV and good freeze-thaw stability. • Aromatic polyurea can be considered to be used at locations where aesthetic appearances (color) are not a first or top priority consideration; for example, the inside surface of steel box girders. Read the complete report at:

http://library.modot.mo.gov/RDT/reports/TRyy0911/or11006.pdf

Raman Spectroscopy

This research project focused on developing methods for using Raman Spectroscopy as a tool for the nondestructive evaluation of composite materials. Changes in the Raman response due to applied strain on the material and aging effects such as stress rupture have been evaluated. Variations in elastic strain in the composite material can manifest from degradation or damage, and can be analyzed using Raman spectroscopy. The characterization of active Raman bands and the strain sensitivity of these bands for commercially available carbon and Kevlar fibers have been evaluated. These results indicate that Raman spectroscopy has some ability to make strain measurements in commercially available carbon fibers.

 

Research Projects

Tuesday, June 14th, 2016

Field Testing of Hand-Held Infrared Thermography, Phase II

The purpose of this report is to summarize field testing conducted to evaluate the capabilities of two different IR imaging […]


Tuesday, June 14th, 2016

Monitoring Vibrations on the Jefferson City Truss Bridge

The objective of the research was to determine the frequency and cause of resonant vibrations of truss verticals on bridge […]


Tuesday, February 9th, 2016

Developing a Reliability Measure for Nondestructive Testing of Reinforced Concrete

Most Nondestructive Evaluation (NDE) Technologies are characterized by noisy data and less than perfect detection characteristics. As a result, NDE […]


Tuesday, February 2nd, 2016

Ultrasonic Measurement of Stress in Gusset Plates

 The objective of this research is to develop non destructive methods for measuring the stress in steel gusset plates in […]


Tuesday, November 17th, 2015

Thermography Phase 2

  The Thermography Phase II Project (Transportation Pooled Fund project number 5-(247)) got underway in January 2012. The state of […]


Thursday, September 3rd, 2015

Developing Guidelines to Improve the Quality of Element Level Data collection in Highway Bridge Inspections

The consistency in data collection and assessment of bridge element condition is critical for supporting decision making processes ranging from […]


Wednesday, August 20th, 2014

Hybrid-Composite Girder Bridges in Missouri

Three hybrid composite beam (HCB) bridges were recently constructed in Missouri, USA. HCB is an innovative idea that incorporates traditional […]


Sunday, June 20th, 2010

Development of Hand-Held Thermography, Phase I

This study explored the application of hand-held thermographic cameras for the detection of subsurface delaminations in concrete bridges. The goal […]