The US has 542,000 bridges that consume billions of dollars per year in construction, rehabilitation, and maintenance funds and which are the lifelines of US commerce. The 1992 ISTEA (Intermodal Surface Transportation Efficiency Act) mandates the implementation of a quantitative computerized bridge management system by 1996. A prime need of such a system are quantitative bridge inspection methods to feed accurate reliable condition information to the huge database of bridges. Nondestructive evaluation (NDE) will fill a critical need in the implementation of effective bridge management. However, many serious barriers exist to the widespread routine application of this technology to bridges. This paper provides an overview of the typical problems associated with applying NDE to bridges.

This presentation will provide examples of how the basic NDE testing and evaluation methods are employed to inspect, evaluate, and extend the service life of existing highway structures. While the examples may not represent the exact procedures employed in each of the Northeast States, they represent typical applications of the NDE methods employed in many of the states. The presentation will be limited to the application of visual inspection, dye penetrant inspection, eddy current testing, ultrasonic testing, and radiographic testing. This is not intended to imply that new technologies such as acoustic emission, ground penetrating radar, and lasers measurements are not also used by any of these states.

Radar has emerged as a valuable non-destructive test method for evaluating the condition of New Hampshire bridge decks. It allows the inspector to 'see' the top surface of the portland cement concrete deck which is typically covered with asphalt pavement. Radar is also very 'customer friendly' in that it allows inspectors to evaluate the bridge decks without closing travel lanes or otherwise impeding traffic flow in any way. This paper discusses the inspection needs of the New Hampshire Department of Transportation which necessitated the use of radar, as well as a history of its selection, development, and incorporation into New Hampshire's bridge management system.

The Pennsyulvania Department of Transportation conducted a two phase investigation of all fracture critical pin hanger assemblies between 1988 and 1991 of 23 bridges. The first phase consisted of visually inspecting and documenting the condition of the pin assemblies. The second phase involved nondestructive testing of the pins and any hanger assembly parts that the engineer requested. This testing was performed by consultant engineering firms under contract with individual Penn DOT Engineering Districts. The Mehoopany Bridge was the only structure which was tested exclusively by the department's personnel. Twenty fracture critical bridges were consequently retrofitted with support girders or rod support assemblies. The remaining three locations had the pin hanger assemblies removed and the structures were made continuous. Also, the pins were replaced at some of the 20 locations. All removed pins were requested to be retained and sent to the Department's Materials and Testing Laboratory for evaluation testing. A large number of the pins were destroyed during removal and some were discarded during construction. The following criteria was established by department personnel for MTD's testing of the pins and defect comparisons with consulting engineer's test results: 1) modified ASTM A388 standard test, using 18 degree transducer; 2) 1/16 inch saw notches used as reference standard; 3) straight beam and angle test probes for UT of in-place pins; 4) 45 degree and 70 degree angle beam bore hole test probe for verification of pin defects.

The New Jersey Department of Transportation effectively uses radiographic testing techniques to evaluate in-place aluminum overhead sign structures. When structures have been damaged, or when serviceability has been questioned, this nondestructive evaluation technique has resolved questions regarding the type and extent of damage. It has also contributed to determinig the optimum remedy. This paper describes the specific techniques used.

As the infrastructure of the United States gets older and as competition for funds increases, organizations in charge of bridge repair and rehabilitation must look for new and innovative technolgies to determine the best use of their existing funds. To do this, the transportation industry must constantly be looking for new technologies and for new and innovative applications of existing technologies. As our knowledge of structures increases, so does our need for exacting testing. Through nondestructive evaluation, valuable information is acquired which assists personnel involved in bridge inspection, bridge management, bridge design, budgeting, and in providing for public safety and protecting the public investment with respect to bridges.

Corrosion of steel reinforcing bars in concrete bridge structures due to the intrusion of chloride ions from seawater or de-icing salts affects many structures in the nation's highway system. Over the past decade cathodic protection has evolved as a promising technology for arresting corrosion. The development of materials, equipment, and methods for applying cathodic protection is in a dynamic state. Through cooperative efforts with academia, industry, and the engineering community, the Florida Deparment of Transportation has developed several innovative corrosion protection systems which incorporate technologies from a wide variety of specialty areas including telemetry, photovoltaics, polymers, and specialty components developed as part of the national defense program. This paper provides an overview of corrosion and cathodic protection technology and focuses on the potential for adaptation of existing technologies into preservation of highway bridge structures.

Throughout the nation there are a number of bridges that for one reason or another, are posted for lower than original design loads. In many cases the proper strength rating of a bridge cannot be achieved by the present methods of analysis. In most cases the bridge is small and may be on an off system road so that it doesn't seriously impact the commercial users. This paper presents the nondestructive method used in Florida for evaluating the strength of existing bridges. The method allows a satisfactory overall strength evaluation of any bridge under question. The experience gained from these tests indicate that load limitations imposed by theoretical analyses are not representative of the structures' real capacities. Proof loading has consistently indicated that structures have greater residual strength. The paper illustrates the use of bridge load testing as a tool for nondestructive evaluation of old or newly constructed prestressed concrete bridge. The load testing procedure, data acquisition, and evaluation of two bridges are presented.

In cooperation with the Federal Highway Administration, the California Department of Transportation launched a full-scale dynamic testing program of seismic isolation and energy dissipation systems. This program is the first of its kind in the United States and in the world. Over a dozen companies from five countries are participating in the testing program, which will lead to uniform guidelines for prototype and verification testing as well as design guidelines and contract specifications for each of the different systems. This paper provides an overview of the testing program, the evaluation process, and the various organizational and technical issues involved in this massive project.

The Department of Transportation for the State of California (Caltrans) abides by the regulations of the Federal Highway Administration's National Bridge Inspection Standards section 650.305 that states that bridges are to be inspected at regular intervals not to exceed two years. The Division of Structures, Office of Structures Maintenance and Investigations is responsible for the inspection of approximately 26,000 bridges in California. Approximately 3,100 of these are steel bridges and of these, 1,000 have fracture critical members. Fracture critical members are tension members of a bridge whose failure will probably cause a portion of, or the entire bridge, to collapse. In 1980, the Division of Structures established a category 'A' inspection program which identified what fracture critical features were on the steel structures. All of the 'ingredients' are present for steel structures to develop cracks. The age of the structures has increased along with the average daily truck traffic and their loads. The material properties required in the 1950s and 1960s did not have requirements for fracture toughness. Proper welding procedures/quality remain a challenge to achieve today, and those structures that are 30 to 40 years old were not immune to this problem. Caltrans has 12 districts in the state with at least two area bridge maintenance engineers (ABME) per districts. Caltrans requires that the ABME be a licensed civil engineer. The ABME faces a heavy responsibility when inspecting fracture critical members. The ABME is not trained in different methods of nondestructive evaluation (NDE), which is not unusual for an engineer graduating from a four-year engineering curriculum. Beginning in 1985, the Welding and Metals Technology Branch of the Transportation Laboratory assisted the Division of Structures in the inspection of these fracture critical features using NDE methods. As of 1990, the Welding and Metals Technology Branch's Fracture Critical Inspection Team accompanies AMBEs on their scheduled category 'A' inspections.

Many freeways in California have storm water pumping plants located near a bridge structure to dewater depressed sections of the freeway. The Ravenswood Slough Pumping Plant is located near the Dumbarton Bridge, which links southerm Alameda County on the east to San Mateo County on the west (an 8,600 foot long structure, which carries over 50,000 vehicles daily). This pumping plant is the largest State-maintained pumping facility and drains all storm water into the San Francisco Bay for the City of Menlo Park.

Caltrans has shown that gamma-gamma logging is a viable, nondestructive method for detecting defects in drilled shaft bridge foundations. These defects, if left undetected, could contribute to early failure during an earthquake. This form of nondestructive testing is required by Caltrans for all drilled shafts constructed by slurry displacement methods, and is a proven technology in the field. This paper will provide an overview of Caltrans nondestructive testing practices and presents a case study demonstrating defects which can be discovered during construction.

The purpose of this paper is to give the reader a brief insight into the Kansas Department of Transportation (KDOT) Bridge Inspection Program. The State of Kansas has 25,580 bridge length structures within its boundaries used to carry vehicle traffic or pedestrians, excluding railroad. This total ranks third within the nation according to the November issue of 'Better Roads.' The total number of structures listed includes 20,453 structures owned by local governments, 340 structures owned by the Kansas Turnpike Authority, and 4,787 structures owned by the KDOT. This paper will deal specifically with the KDOT structures only.

In 1978, Wisconsin Department of Transportation discovered major cracking on a two-girder, fracture critical structure, just four years after it was constructed. In 1981, on the same structure, now seven years old, major cracking was discovered in the tie girder flange of the tied arch span. This is one example of the type of failures that transportation departments discovered on welded structures in the 1970's and '80's. The failures from welded details and pinned connections lead to much stricter standards for present day designs. All areas were affected: design with identification of fatigue-prone details and classification of fatigue categories; material requirements with emphasis on toughness and weldability; increased welding and fabrication standards with licensure of fabrication shops to minimum quality standards including personnel; and an increased effort on inspection of existing bridges, where critical details were overlooked or missed in the past. FHWA inspection requirements for existing structures increased through this same time period, in reaction to the failures that had occurred. Obviously, many structures in Wisconsin were not built to the standards now required, thus the importance for quality inspection techniques. The new FHWA inspection requirements now being implemented throughout the nation require an in-depth, hands-on type inspection at a specified frequency, on all fracture critical structures. Wisconsin Department of Transportation started an in-depth inspection program in 1985 and made it a full time program in 1987. This program included extensive nondestructive testing. Ultrasonic inspection has played a major role in this type of inspection. All fracture critical structures, pin and hanger systems, and pinned connections are inspected on a five-year cycle now. The program requires an experienced inspection team and a practical inspection approach. Extensive preparation is required with review of all design, construction, and maintenance documents. An inspection plan is developed from the review and downloaded to a laptop computer. Inspection emphasis are on 'hands on' visual and nondestructive evaluation. Report documentation includes all design plans, pictorial documentation of structural deficiencies, nondestructive evaluation reports, conclusions, and recommendations. Planned changes in the program include implementation of an engineering work station as a 'single source' information file and reporting file for the inspection program. This would include scanning all current information into the file such as design, construction, and maintenance history. It would also include all inspection data with pictures. Inspections would be performed by downloading data onto a laptop and then uploading after completion of inspection. Pictures and nondestructive data would be entered by digital disks.

Post tensioning work on the Kellogg Flyover Project included top deck and pier diaphragm transverse post tensioning cables. Also included were draped and negative moment area longitudinal post tensioning cables. My observations during inspecting this work raised questions in my mind regarding possible improvements in the operation which would be possible if enhancements in equipment and/or materials were available. In this paper, I will describe areas in which improved equipment and/or materials would have saved time and money in constructing the project. I will also briefly discuss where nondestructive testing might be helpful in assessing the long term performance of the structures post tensioning system.

The Ministry of Transportation, Ontario has taken a leading role in applying the latest technology to the rehabilitation of bridge decks by developing a system called Deck Assessment by Radar Technology (DART). Impulse radar signals propagate through the bridge deck materials and reflect wherever there is a change in the dielectric properties of the propagation medium. This change in dielectric constant is usually an indication of: an interface, such as the asphalt-concrete boundary; or, a layer of reinforcement; or damaged structure, such as a delamination. In this paper, temporal waveforms obtained from real bridge decks are presented and spectral plots are employed to gain insight to the signal properties. A methodology for the detection of delamination is presented which evaluates the shape of the reflection at the concrete boundary. The results from two actual surveys are presented which highlights measurements of asphalt thickness, cover over reinforcement, and detection of delaminations obtained by DART survey. It is demonstrated that DART survey provides predictions very close to actual deck conditions.

Detection of steel bars embedded inside concrete for reinforcement has been one of the major goals of nondestructive testing methods for concrete. The use of radar in detecting steel bars is advantageous due to the sensitivity of electromagnetic waves to metallic objects and the versatility in using appropriate electromagnetic wave polarization waves to metallic objects and the versatility in using appropriate electromagnetic wave polarization with respect to the orientation of the bars. However, obtaining imagery of steel bars inside a lossy medium such as concrete requires sophisticated problem solving approaches including understanding of the electromagnetic properties of concrete, identification of proper radar measurement parameters as center frequency and bandwidth, and development of image reconstruction algorithms. This paper presents experimental results of radar measurements of laboratory size concrete specimens with or without steel bars. Sample radar imagery processed from raw measurement data is provided with discussion.

Ground penetrating radar (GPR) has been developed and used successfully for bridge deck and roadway condition assessment. In the past, GPR interpretation has been done manually by trained engineers and technicians with the aid of standard signal processing techniques. This method of collection produced vast quantities of data, and the interpretation required a great amount of time. Recently, parallel processing in the form of artificial neural networks (ANNs) has been applied to the interpretation of GPR condition assessment data from highways. This paper introduces general strategy for using ANNs for the interpretation of GPR data. Results of applying this strategy to bridge deck condition assessment data are also given.

During the early 1980's, the Transportation Research Board (TRB) of the National Research Coimcil, under the sponsorship ofthe Federal Highway Administration (FHWA) and with the cooperation ofthe American Association of State Highway and Transportation Officials (AASHTO) undertook a thorough study of the deterioration of the nation's highway and bridge infrastructure system. The study recommended that a Strategic Highway Research Program (SHRP) be initiated to focus research and development activities that would make major contributions to improving highway transportation. The study report published as TRB Special Report 202 during 1984, emphasized six research areas, with the Long Term Pavement Perfonnance (LTPP) program as one ofthe key research areas. During 1985 and 1986, the detailed research programs were developed for SRRP by independent contractors. The detailed programs were published in May 1986 as a TRB Report entitled, "Strategic Highway Research Program - ResearchPlans." The Long Term Pavement Performance was envisioned as a comprehensive program to satisfy "the total range of pavement information needs." It draws on "technical knowledge ofpavements presently available and seeks to develop models that will better explain how pavements perform. It also seeks to gain knowledge of the specific effects on pavement performance of various design features, traffic and environment, use of various materials, construction quality, and maintenance practices." As sufficient data becomes available with time, analysis will be conducted by various agencies to provide better performance prediction models for use in design and pavement management, to provide much better understanding of the effects of many variables on pavement performance, and to provide new techniques for pavement design and construction. This paper focuses on one phase of the program -pavement instrumentation. Prior to limiting the focus, a brief overview ofthe overall LTPP program is presented

Determining a bridge structure's existing conditions and load carrying capacity often requires more complete data than can be gathered by visual observation and simple measurements. This is true below water as well as above. Various nondestructive testing techniques may be utilized underwater to gather such detailed data. Techniques to be addressed in this paper include ultrasonic nondestructive testing of timber and correlation to destructive and partially destructive testing, pulse velocity of concrete, ultrasonics in steel inspection, and an example of the underwater usage of diver-carried ground penetrating radar.

Stay cables of cable-stayed bridges have corrosion protection systems that can be elaborate. For example, such a system may simply consist of one or several coats of paint, or--more complex--of plastic pipes that are wrapped with tape and filled with grout. Frequently, these corrosion protection systems prevent visual inspections. Therefore, alternative nondestructive examination methods are called for. For example, modern dual-function electromagnetic (EM) instruments allow the simultaneous detection of external and internal localized flaws (such as external and internal broken wires and corrosion piting) and the measurement of loss of metallic cross-sectional area (typically caused by external or internal corrosion or wear). Initially developed for mining and skiing applications, these instruments have been successfully used for the inspection of stays of cable-stayed bridges, and for the inspection of guys of smoke stacks, flare stacks, broadcast towers, suspended roofs, etc. As a rule, guys and bridge cables are not subjected to wear and bending stresses. However, their safety can be compromised by corrosion caused by the failure of corrosion protection systems. Furthermore, live loads and wind forces create intermittent tensile stresses that can cause fatigue breaks of wires. This paper discusses the use of dual-function EM instruments for the detection and the nondestructive quantitative evaluation of cable deterioration. It explains the underlying principles. Experiences with this method together with field inspection results will be presented.

Ground penetrating radar has been developed as an economical alternative for evaluating pavement layer properties and estimating quantities of deterioration in bridge decks. These highway applications are based on the use of vehicle-mounted radar systems traveling at normal driving speed. Surveys are conducted without lane closures, and extensive coverage can be obtained in a short survey period. Customized software has been specifically developed to handle and interpret the large quantities of data collected by this system. Two integrated software systems have been developed and extensively tested for pavement layer thickness and bridge deck condition evaluation. PAVLAYER, for pavements, has demonstrated an accuracy of +/- 7% for asphalt layer thickness evaluation based on tests on 150 pavement sections and correlation with over 700 cores. DECAR, for evaluating quantities of deteriorated concrete in bridge decks, has demonstrated an accuracy of +/- 4.4% of the total deck area based on ground truth evaluation of 64 bridge decks. The paper describes the details of the hardware and software components and the analytic methods used in these two systems. Also presented are descriptions of three field evaluation programs, in which the PAVLAYER and DECAR results are correlated with ground truth. Typical output and ground truth correlations are presented.

Dual-band infrared (DBIR) thermal imaging is a promising, noncontact, nondestructive evaluation tool to evaluate the amount of deteriorated concrete on asphalt-covered bridge decks. We conducted proof-of-principle demonstrations to characterize defects in concrete structures which could be detected with DBIR thermal imaging. We constructed two identical concrete slabs with synthetic delaminations, e.g., 1.8-in. thick styrofoam squares, implanted just above the 2-in. deep steel reinforcement bars. We covered one of the slabs with a 2-in. layer of asphalt. We mounted the DBIR cameras on a tower platform, to simulate the optics needed to conduct bridge-deck inspections from a moving vehicle. We detected 4-in. implants embedded in concrete and 9-in. implants embedded in asphalt-cevered concrete. The midday (above ambient) and predawn (below ambient) delamination-site temperatures correlated with the implant sizes. Using DBIR image ratios, we enhanced thermal-constrast and removed emissivity-noise, e.g., from concrete compositional variations and clutter. Using the LLNL/VIEW code, we removed the asphalt thermal-gradient mask to depict the 4-in. deep, 9- in. square, concrete implant site. We plan to image bridge deck defects from a moving vehicle for accurate estimations of the amount of deteriorated concrete impairing the deck integrity. Potential longterm benefits are affordable and reliable rehabilitation for asphalt-covered decks.

This paper describes an instrumentation technique for 'reading' multiple fiber Bragg grating strain sensors, and focuses on a prototype system designed and built for the FHWA for multipoint monitoring of strain in concrete structures.

Surface crack detection in metallic structures is an important issue in many environments (such as steel bridge members) and industries. A relatively new microwave method of detection using an open-ended rectangular waveguide has shown great practical promise. This method is quite versatile and may be applied to long, finite, filled, and covered cracks. Furthermore, crack dimensional analysis is also possible with this method. The measured and theoretical results of several exposed, filled, and covered cracks/slots are shown in this paper. Furthermore, a new theoretical approach to model the interaction of the waves incident at the waveguide aperture and a metal surface with a crack are very briefly mentioned as well. The results show the utility of this method for detecting filled and covered cracks as well as cracks separated from the waveguide aperture by a slight amount of airgap (i.e. noncontact approach).

The development of a series of wideband acoustic emission sensor/preamplifier systems is described. Key design factors are discussed along with the actual design and characterization of the sensors. These new sensors with integral amplification are out-of-plane, displacement response sensors nearly independent of frequency over a range from a slow as 30 to 50 kHz up to 1.2 MHz. The sensor design includes electromagnetic shielding and mechanical protection of the sensitive elements. More importantly, these practical sensors have signal-to-noise sensitivity that is equivalent to typical commercial resonant sensor/preamplifier systems operating from 100 kHz to 300 kHz. A mounting fixture for the sensors has also been developed.

The Federal Highway Administration has sponsored the development of a new system for fatigue crack detection and quantification of fatigue cracks in steel bridges. The NDE technology selected for the new system is based on earlier studies that have identified the best methods for this task. The new system that has been developed is based on previous work which produced two portable instruments that were field tested but were not widely accepted. The best characteristics from these systems have been integrated into a single instrument, using portable computer technology and adapted to the bridge inspection environment. The new system, which has come to be known as the New Ultrasonic-Magnetic Detection System (NUMAC), is configured as a backpack with a heads-up display that leaves the inspectors hands free to climb the structure and to view the inspection site simultaneously while viewing the ultrasonic or magnetic signals. The operation of the system controlled with a mouse or a keyboard. Importantly, the accuracy and repeatability of the NUMAC is combined with the ability to store inspection data. The stored data can be used to document condition, demonstrate and identity important trends, and efficiently channel resources. The flexibility of the portable computer based NDE system is intended to provide a basic, reliable and cost- effective instrument for steel bridge inspection.

Lawrence Livermore National Laboratory is developing a prototype imaging radar for inspecting steel reinforced concrete bridge decks. The system is designed to acquire synthetic aperture radar data and provide high-resolution images of internal structure, flaws, and defects enabling bridge inspectors to nondestructively evaluate and characterized bridge deck condition. Concrete delamination resulting from corrosion of steel reinforcing bars (rebars) is an important structural defect that the system is designed to detect. The prototype system uses arrays of compact, low-cost micropower impulse radar (MIR) modules, supported by appropriate data acquisition and storage subsystems, to generate and collect the radar data, and unique imaging codes to reconstruct images of bridge deck internals. In this paper, we provide an overview of the prototype system concept, discuss its expected performance, and present recent experimental results showing the capability of this approach to detect thin delamination simulations embedded in concrete.

In order to assess the structural integrity of bridges, an accurate and cost effective measurement technology is required to ensure their safe and reliable operation. Over 60,000 of the nation's steel highway bridges have been classified as structurally deficient. The objective of this paper is to assess the applicability of a new ultrasonic measurement technology as an effective measurement technique and viable tool for the structural engineering community. Laboratory tests comparing the ultrasonic and traditional strain gage measurement technique show a correlation coefficient of 0.993. Preliminary field test data collected on a portside crane compare both measurement technolgies. The resulting conclusion is that the ultrasonic technique is comparable in performance to the traditional strain gage measurment technolgy, and offers a portable, cost effective method for evaluating bridge, crane, and other types of structural members.

I am pleased to welcome you to this timely and informative conference organized by The International Society for Optical Engineering (SPIE). As Conference Chair, I am very pleased, but not at all surprised, by your interest and enthusiastic response: Over 300 participants are contributing over 210 technical papers to six topical conferences.

the role of the National Laboratory in technology transfer is to help industry implement the latest technology. The National laboratory must have a unique capability that does not compete with tax paying companies. Typically a National Laboratory will demonstrate the benefit of applying NDE to a company's production line. The company then contracts with a vendor to supply a production inspection system based on the laboratory's demonstration. Both the company and the vendor benefit from the participation with the National Laboratory. The company improves the quality of its products and the vendor has a new product to market. The purpose of this paper is twofold: (1) to present a brief overview of NDE capabilities and application activities within the National Laboratory System and (2) to identify NDE point-of- contacts at each laboratory.

The infrastructure in the United States and the world is aging. There is an increasing awareness o the need to assess the severity of the damage occurring to our infrastructure. Limited resources preclude the replacement of all structures that need repairs or have exceeded their lifetimes. Methods to assess the amount and severity of damage are crucial to implementing a systematic, cost effective approach to repair and/or replace the damaged structures. The challenges of inspecting aging structures without impairing their usefulness rely on a variety of technologies and techniques for nondestructive evaluation. This paper will briefly describe several nondestructive evaluation technologies that re required for inspecting a variety of systems and structures.

There is no doubt that our aging or inadequate infrastructure is in trouble. Since engineers believe that we're dealing with 'a series of accidents just waiting to happen,' significant failures in the past support this theory. The Hartford Civic Center, the Kansas City Hyatt Regency, and the Mianus River Bridge are just a few examples of past failures that were all unexpected. These and other catastrophic failures confirm the problems that exist in our infrastructure due to poor design, deterioration, lack of inspection, overloading, inadequate maintenance, and the 'low-bid' syndrome. Finding and correcting all the problems amy be an impossible task, but through the use of current nondestructive evaluation methodology, the risks of failure can be minimized.

This plenary presentation provides a big-picture perspective on the role of NDT/NDE technologies in addressing infrastructure needs, and NDE technology application opportunities in the National Technology Policy context. I will then focus on the Research and Special Program Administration regulatory responsibilities and research coordination activities relevant to the subject of NDE. Finally, on behalf of the Department of Transportation, I will discuss our strategic priorities in R&D and infrastructure renewal. Other DOT participants in this conference--representing the Federal Highway Administration, Federal Aviation Administration, Federal Rail Administration, and our maritime modes--will provide a window on the diverse NDE-related research and technology programs related their missions.