This paper presents how one university is addressing the problems of our deteriorating and failing infrastructure. Results of two recent questionnaires reveal that State Highway Agencies are beginning to shift their priorities to emphasize inspection and rating of infrastructure. While both public and private practices are responding, education as a whole tends to remain fixed to traditional analysis and design courses. While traditional courses are essential, new trends must be periodically injected into the curriculum. This paper will show the efforts of the Denver campus of the University of Colorado to educate both undergraduate and graduate engineers in these non-traditional aspects of Civil Engineering. The 3- credit course titled Condition Assessment and Failure Analysis of Civil/Mechanical Infrastructure included such topics as nondestructive evaluation (NDE), lock and dam inspections, bridge maintenance and inspection, structural failure analysis, vehicle accident reconstruction, engineering ethics, and the law. The design of new structures is being overshadowed by the need to maintain and rehabilitate existing structures. In addition, valuable educational material is found in our record of past engineering failures. It is hoped that by publishing information on this course other higher learning institutions will be encouraged to educate students as to the trends that are occurring in practice.

Wisconsin Department of Transportation implemented a Fracture Critical & Specialized Inspection Program in 1987. The program has a strong emphasis on Nondestructive Testing (NDT). The program is also completely computerized, using laptop computers to gather field data, digital cameras for pictures, and testing equipment with download features. Final inspection reports with detailed information can be delivered within days of the inspection. The program requires an experienced inspection team and qualified personnel. Individuals performing testing must be licensed ASNT (American Society for Nondestructive Testing) Level III and must be licensed Certified Weld Inspectors (American Welding Society). Several critical steps have been developed to assure that each inspection identifies all possible deficiencies that may be possible on a Fracture Critical or Unique Bridge. They include; review of all existing plans and maintenance history; identification of fracture critical members, identification of critical connection details, welds, & fatigue prone details, development of visual and NDE inspection plan; field inspection procedures; and a detailed formal report. The program has found several bridges with critical fatigue conditions which have resulted in replacement or major rehabilitation. In addition, remote monitoring systems have been installed on structures with serious cracking to monitor for changing conditions.

Since 1985, Florida Department of Transportation (FDOT) has been conducting non-destructive testing (NDT) to evaluate the load carrying capacity of existing bridges. This paper describes the procedure of load rating existing bridges through non-destructive load testing. The application of field testing eliminates some unnecessary retrofitting/demolishing and identifies the unsafe bridges for public safety.

This paper summarizes the results of a series of impulse response tests on inaccessible drilled shafts constructed at the National Geotechnical Experimentation Site (NGES) at Northwestern University. The drilled shafts are 610 to 910 mm in diameter and 12 to 27 m long, and are covered by pile caps up to 1.5 m thick. Results of tests on drilled shafts obscured by the pile caps have shown that useful information can be obtained below a 'cutoff frequency' which is defined by the propagation velocity and the geometries of the intervening structure and the deep foundation. An extension of the conventional impulse response method using multiple geophones is described which makes interpretation of responses from the foundation easier by minimizing the effects of surface waves on the processed signals. Superposing the velocity responses from each geophone allows the reflections from the deep foundation to be more easily identified.

The FHWA project 'Dynamic Bridge Substructure Evaluation and Monitoring System' was conceived to use dynamic characteristics of the bridge substructure to determine the condition of the foundation and to identify the type of the underground substructure (deep or shallow foundation). The determination of the foundation condition will be used to quantify losses in foundation stiffness caused by seismic and scour events. The dynamic characteristics of natural frequencies and mode shapes are extracted from the experimental data and compared with the computer simulation results. The computer simulations are based on a 3-D finite element modeling with Super-Soil-Structural (SSS) elements. The stiffness and mass of these Super-Soil-Structural elements are indicative of the foundation conditions which may be quantified by structural parameter identification techniques. Discussed in this paper are experimental test setups and initial test results for three kinds of foundation conditions at the Trinity River Bridge in Liberty County, Texas.

Evaluation of bridge substructures for vulnerability to scour or other potential sources of damage requires knowledge of foundation conditions beneath piers and abutments that are often unknown. This paper presents a potential method for determining unknown foundation conditions which is simple and inexpensive. The method is based on strain and rotation measurements which are used to compute a stiffness matrix for the unknown foundation. The stiffness coefficients in the matrix are then matched with values previously determined for known foundations. The objective of the reported work has been to demonstrate the feasibility of this method. Finite element models for representing pile and spread footing conditions have been used to characterize the difference in stiffness properties between the two foundation types. Field measurements of strains, displacements, and rotations have been taken on two bridges in Massachusetts: one with a spread footing and the other with a pile foundation. Parameter estimation models have been developed and used in conjunction with this field data to calculate the foundation stiffness properties. The paper describes the models, the numerical results, and the results of field testing.

This paper presents work in progress toward the development of a bridge condition assessment system. The system combines remote laser vibration sensing technology and a strain-energy- based damage detection algorithm. The results from vibration tests conducted on laboratory specimens with different degrees of damage are presented. The vibration signatures are acquired using Scanning Laser Vibrometers (SLV). The extracted mode shapes from these tests are then used in the damage detection algorithm. The preliminary results indicate that the strain energy differences are highly sensitive to damage, and can be used to locate and distinguish progressive damages. The combination of SLV technology and the damage detection algorithm makes remote sensing attractive for the monitoring and inspection of structures. Finite element simulation of a progressive damage at a single location is also presented to illustrate the sensitivity of the algorithm to increasing damages.

This paper presents results from testing several suspender ropes of the Delaware Memorial Bridge using vibration measurements and a non-destructive evaluation (NDE) instrument called the Axial Load Monitor (ALM). The testing consisted of measuring the frequencies of suspender ropes and determining their tension levels. Results were compared to theoretical predictions. This paper presents the results of the testing and discusses the problems associated with vibration measurements on actual bridges.

There is no single attribute which can always predict structural deterioration. Accordingly, we have developed a scheme for monitoring a wide range of incipient deterioration parameters, all based on a single motion sensor concept. In this presentation, we describe how an intrinsically low power- consumption fiber optic harness can be permanently deployed to poll an array of optical sensors. The function and design of these simple, durable, and naturally digital sensors is described, along with the manner in which they have been configured to collect information for changes in the most important structural aspects. The SIMS system is designed to interrogate each sensor up to five-thousand times per second for the life of the structure, and to report sensor data back to a remote computer base for current and long-term analysis, and is directed primarily towards bridges. By suitably modifying the actuation of this very precise motion sensor, SIMS is able to track bridge deck deflection and vibration, expansion joint travel, concrete and rebar corrosion, pothole development, pier scour and tilt. Other sensors will track bolt clamp load, cable tension, and metal fatigue. All of these data are received within microseconds, which means that appropriate computer algorithm manipulations can be carried out to correlate one sensor with other sensors in real time. This internal verification feature automatically enhances confidence in the system's predictive ability and alerts the user to any anomalous behavior.

The issues of processing, evaluation, experimental testing, and modeling of smart fiber reinforced polymer (FRP) composite materials are discussed. The specific application in view is the use of smart composite reinforcements for a monitoring of innovative bridges and structures. The pultrusion technology for the fabrication of fiber reinforced polymer composites with embedded fiber optic senors (Fabry Perot and Bragg Grating) is developed. The optical sensor/composite material interaction is studied. The tensile and shear properties of the pultruded carbon/vinylester and glass/vinylester rods with and without optical fibers are determined. The microstructural analysis of the smart pultruded FRP is carried out. The interfaces between the resin matrix and the acrylate and polyimide coated optical fibers are examined and interpreted in terms of the coatings's ability to resist high temperature and its compatibility with resin matrix. The strain monitoring during the pultrusion of composite parts using the embedded fiber optic sensors was performed. The strain readings from the sensors and the extensometer were compared in mechanical tensile tests.

In recent years, fiber-wrapping technique has become increasingly popular for retrofitting of existing bridge pier columns in seismic zones. By the way of confinement, the external jacket enhances strength, ductility and shear performance of the column. However, since state of the concrete core is not visible from outside of the jacket, it is of great necessity to develop proper non-destructive methods to evaluate structural integrity of the column. Extensive research on FRP-confined concrete at the University of Central Florida has shown that failure of such hybrid columns is often accompanied by considerable audible and sub-audible noise, making acoustic emission (AE) a viable NDE technique for retrofitted columns. Acoustic emission from fiber-wrapped concrete specimens were monitored. A total of 24 concrete specimens with two types of construction (bonded and unbonded) and four different number of layers (1, 3, 5 and 7) were tested under uniaxial compression. All specimens were made of S-glass fabric and polyester resin with a core diameter of 6' and a length of 12'. Some of the specimens were subjected to cycles of loading and unloading to examine the presence of the Kaiser and the Felicity effects. A 4-channel AEDSP-32/16 (Mistras-2001) machine from Physical Acoustics Corp. was used for the experiments. Results indicate that AE energy and the number of AE counts can both be good representatives for the response of confined concrete. Further, plots of AE energy versus load follows the same bilinear trend that has been observed in the stress-strain response of such specimens. Finally, Felicity effect was observed in all composite specimens.

Rapid advancements with respect to utilization of polymeric composite materials for bridge components is occurring. This situation is driven primarily by the potential improvements offered by these materials with respect to long term durability. However, because of the developmental nature of these materials much of the materials characterization has involved short term testing without the synergistic effects of environmental exposure. Efforts to develop nondestructive evaluation procedures, essential for any wide spread use in critical structural applications, have been consequently limited. This paper discuses the effort to develop NDE methods for field inspection of hybrid glass and carbon fiber reinforced vinyl ester pultruded 'double box' I beams that are installed in a small bridge over Tom's Creek, in Blacksburg, Virginia. Integrated structural element sensors, dormant infrared devices, as well as acousto-ultrasonic methods are under development for detecting and monitoring the occurrence and progression of life limiting deterioration mechanisms.

Because of corrosion evidence, an aggressive environment and aging effects on a post tensioned beam substructure and its superstructure, a non destructive testing of a bridge was performed. The same kind of experimental work was carried out on another bridge of very similar structural characteristics but shorter lifetime. The experimental setup and testing procedures are described. Transducers of displacements and accelerometers were used to register the movements induced by static and dynamic loads on both superstructures. Results of field tests are presented in terms of maximum static and dynamic displacements, time histories and frequency functions. These latter are used to derive characteristic dynamic parameters of the superstructures and identify associated modal shapes. The experimental response of both bridges is compared. Mathematical models of the superstructures were prepared and calibrated with the results of the experimental testing program. Currently design live loads were applied on the calibrated models and their responses were evaluated and compared. From the analysis of the experimental and analytical work, a structural safety evaluation of the superstructures was done.

The purpose of this paper is to describe existing problem areas in the manufacturing and erecting of variable message signs (VMS) on cantilever truss units. VMS are electronic message boards that are rectangular in shape and weigh between 3,000 and 5,000 pounds. The structures that were inspected for this paper are part of the Route 80 Magic Project and the Traffic Signal Contract #25 (Route 37).

As the population of the nations steel highway structures grow older each year, problems associated with structural details are discovered and must be addressed. Some details are fatigue sensitive and others carry load in a manner not originally intended by the designers. To solve or prevent these problems, it is necessary to understand the magnitude and nature of the stress flow at the problem area. With this information we can develop details that are less sensitive to fatigue, and design them to carry the appropriate loads. In Michigan, several methods are being used to measure strain and analyze stress in highway structures. A few of the technologies used are; electrical resistance strain gages, vibrating wire sensors, and photoelastic coatings. This paper discusses Michigan's experience with these technologies in two applications where they have been useful in analyzing Michigan's link plate details.

Wisconsin Department of Transportation implemented an Anchor Bolt Inspection Program and Sign Bridge Inspection Program in 1990 for cantilever & overhead sign structures, high mast light towers, interstate light towers, and signal masts. All cantilever & overhead sign structures and high mast light towers have been inspected in-depth 'hands on' during this time period while implementation of inspection continues for interstate light towers and signal masts. The program requires an experienced inspection team and a practical inspection approach. Inspection preparation includes review of all background information such as design plans, design computations, construction plans, shop plans, and maintenance history. An inspection plan is developed. Special emphasis is placed on determining type of structure, type of material, welding details. For anchor bolts, type of material, cut or rolled threads, type of coating, and method of placement are important issues. Inspection emphasis are on 'hands on' and Nondestructive evaluation. Special emphasis is placed visual conditions of sign structures and anchor bolts (cut or rolled threads, straightness, corrosion, nut tension, etc.) along with ultrasonic inspection. This program places a strong emphasis on Non Destructive Testing (NDT), especially ultrasonic. Procedures and inspection calibrations for anchor bolts, are developed from similar anchor bolt geometry and material type. Cut notches are placed in the anchor bolts at locations of possible failure. NDT inspection calibrations are performed from these bolts. Report documentation includes all design plans, pictorial documentation of structural deficiencies, sketches, nondestructive evaluation reports, conclusions, and recommendations. This program has been successful in locating critical cracks and failed members on existing sign structures and new sign structures less than six months old. Also, failed anchor bolts and critical cracks have been located on high mast light towers.

During the winter snow storm of January 7 and 8, 1996 failure occurred to a number of the highway lighting assemblies on the adjacent projects of Route 147, Section 1C and Route 147 Section 1E. These projects are located in Cape May County along the shore area. Eight LES-45 expressway poles attached to transfer bases type TB-17 located on the ground blew down on the Route 147, 1E project, while six L8S-40 lighting poles with shoe bases mounted to bridge parapet of Route 147, 1C blew down (14 in total). The poles fell on the roadway. Had it not been for the storm keeping traffic off the roads damage may have occurred to vehicles and vehicle occupants. Visual inspections by the Resident Engineer of the projects revealed that the damage to the poles and bases was general. Wind velocities recorded by the Weather Bureau and the Coast Guard indicated that wind speeds of more than 50 m.p.h. were reached during the storm. The lighting assemblies are expected to withstand 85 m.p.h. sustained winds and 104 m.p.h. gusts. The New Jersey Department of Transportation, Bureau of materials was requested to conduct an investigation to determine the probable cause of the failures to the LES-45 and L8S-40 lighting assemblies. They were further required to determine a means of inspecting non-failing assemblies for future prevention of these assemblies failing.

There are forty weathering steel bridges in service in Idaho as of August 1995, and more are planned for construction in the near future. Although problems with corrosion have been reported nationwide in the past, there is the potential for financial savings in the construction and maintenance of the unpainted weathering steel bridges if good, long range performance can be attained. The Idaho Transportation Department (ITD) conducted a study of a representative group of twelve weathering steel bridges to determine their present condition, including corrosion effects. The objective was to initiate any potential necessary changes in the design, construction and maintenance of the weathering steel bridges that are now in the planning stage. This paper will review the findings of the investigation and provide plate thickness measurements data, obtained by nondestructive testing (NDT), using ultrasonic gage. It has been observed that weathering steels develop a protective oxide coating which shields the underlying steel base from corrosion when certain conditions are met. The unpainted weathering steel on the inspected twelve Idaho bridges is found to be performing well. The continued use of weathering steel bridges in Idaho is recommended.

Pin and hanger connections can sometimes lock up due to corrosion. As the stresses in the connection are cycled due to thermal expansion and contraction of the bridge, fatigue cracking and failure may occur. We constructed an apparatus to simulate a locked-up pin and hanger connection. It consists of a 12 tooth spline bolted to the base of a mechanical testing machine. Hangers were mounted on the spline, which constrains their ends against rotation. The free ends of the hangers were loaded by the test machine's piston. We performed proof of concept tests of a method to detect stresses in pin and hanger connections prior to cracking. The method uses the fact that stress causes change in sound velocity. We propagated shear waves polarized parallel and perpendicular to the hanger axis. The normalized difference in shear wave velocities is called the birefringence. We measured the birefringence near the outer fibers of the hangers, at midsection. We simulated 3 scenarios: continuous monitoring of hanger status; intermittent monitoring from a known initial state; measurement with no a priori knowledge of hanger status. Good agreement with strain gauge data was obtained for all three scenarios.

A computer algorithm that uses raytracing to simulate the ultrasonic inspection of a pin with and without scanning will be described. This algorithm allows the users to simulate the location and orientation of a crack, or wear groove, in the pin and model the ultrasonic reflections that will occur during inspection. The procedure is part of a larger effort to improve the reliability and interpretation of ultrasonic inspection results from steel bridge pins. The simulated results are compared with actual scan results obtained using an automated scanning system on a reference pin with slag and crack imperfections.

In this paper, results of a research project sponsored by the Federal Highway Administration (FHWA) on a non-destructive method for measurement of stay cable forces in cable-stayed bridges are presented. This project included development and verification of specific analytical and experimental procedures for measurement of stay cable forces. In one set of procedures, a single laser vibrometer is used to measure low- level cable vibrations due to ambient (wind and traffic) excitation. The laser device allows rapid measurement of cable vibrations at distances of up to several hundred feet. Procedures are also developed for utilization of accelerometers attached to cables. Contact sensors are more appropriate when long-term remote monitoring is desired. Measured natural frequencies of vibration are related to cable tension through a mathematical formulation developed during the course of this study. This formulation includes the effects of cable sag-extensibility, bending stiffness, various boundary conditions, intermediate springs or dampers, etc. This method can also be used during construction in lieu of the 'lift off' method. The accuracy and effectiveness of this methodology was tested in the laboratory on a scaled model of a cable, and on two cable-stayed bridges. This ability to rapidly measure stay cable forces provides an opportunity for global condition assessment of these major structures.

By adapting a method developed to monitor the failure of post- tensioning cables, it is determined that continuous acoustic monitoring of large suspension cables and cable stays is effective in detecting single wire breaks. This will likely offer a practical method to assist bridge engineers in managing suspension bridges and cable-stay bridges. The practicality of awaiting individual wire failures with computer-based monitoring equipment differs from most acoustic emission work. In continuous monitoring, the signals obtained are not the result of deliberate changes in the stress on an element, but result when the wire breaks spontaneously and suddenly releases the energy stored when cables are placed under load. The acoustic event caused by the failure of a singe wire in the cable is sufficiently large that it can be distinguished from background noise. The identification of the cause of each event and the location of the source of the event should allow targeted and informed repair of broken elements. This paper describes installation methods and challenges, reporting protocols, a description of equipment, software, operations methodologies, and other enabling technologies.

This paper describes a new approach to nondestructive and quantitative characterization of residual and applied stress (absolute stress) on wire rope and steel cable. Examples are given from both field work as well as laboratory tests, including stress characterization of post-tensioning cables, bridge suspension cables, wire rope and thin strand steel wire. The approach is based on x-ray diffraction techniques. A detailed description of the results and the methodologies used to obtain them are provided.

This paper describes the evaluation and improvement of a Dual Band Infrared (DBIR) thermal imaging system developed by Lawrence Livermore National Laboratory (LLNL), under the sponsorship of Federal Highway Administration (FHWA). DBIR thermal imaging system is a nondestructive evaluation technique which has the potential of detecting delaminations in concrete bridge decks, with and without asphalt overlays. The system consist of two infrared scanners, one operating at a wavelength of 3 - 5 micrometer and the other at a wavelength of 8 - 12 micrometers. The scanners are mounted in front of a vehicle and are microprocessor controlled from inside the vehicle. The vehicle is driven at a speed of 40 km/hr and a typical bridge deck can be scanned in less than 5 minutes, with a low level of traffic control.

In 1995 and 1996, the Idaho Transportation Department (ITD) conducted a series of ground-penetrating radar (GPR) surveys as a nondestructive testing (NDT) method to evaluate the thickness of asphalt and Portland cement concrete (AC/PCC) pavements in Idaho. GPR surveys employed both air-coupled and combination air and ground coupled systems with their associated equipment and software. A total of 30 miles of AC/PCC pavements were evaluated by GPR surveys. The results obtained were correlated with the site-specific ground-truth data from borings. Knowledge of pavement layer thickness is needed to predict pavement performance, establish load carrying capacities and develop maintenance and rehabilitation priorities. In addition, for new construction, it is important to ensure that the thickness of materials being placed by the contractor is acceptably close to specification. Core sampling and test pits are destructive to the pavement system, expensive, time consuming and intrusive to traffic. The objective of the ITD study was to evaluate, compare and assess the ability of these two GPR systems to accurately measure the thickness of multiple pavement layers, and document the data nondestructively. This paper reviews the findings of these surveys and provides statistically based data for both AC and PCC pavements. The overall study has shown that reasonably accurate, dependable determination of pavement thickness can be achieved by using GPR survey for conditions encountered in Idaho.

This paper presents the development of ground-penetrating radar bridge deck inspection systems sponsored by the Federal Highway Administration. Two radar systems have been designed and built by Lawrence Livermore National Laboratory. The HERMES bridge inspector (High-speed Electromagnetic Roadway Mapping and Evaluation System) is designed to survey the deck condition during normal traffic flow. Thus the need for traffic control during inspection is eliminated. This system employs a 64 channel antenna array covering 1.9 m in width with a sampling density of 3 cm. To investigate areas of a bridge deck that are of particular interest and require detailed inspection a slower, cart mounted radar has been produced. This system is named PERES (Precision Electromagnetic Roadway Evaluation System). The density of data coverage with PERES is 1 cm and an average or 100 samples is taken at each location to improve the signal to noise ratio. Images of the deck interior are reconstructed from the original data using synthetic aperture tomography. The target of these systems is the location of steel reinforcement, corrosion related delaminations, voids and disbonds. The final objective is for these, and other non-destructive technologies, to provide information on the condition of the nation's bridges so that funds will be spent on the structures in most need of repair.

A research project is described involving a comparison of different non-destructive test methods for concrete bridges. A cooperative test series was started with the aim to compare and evaluate the performance and benefits of the latest technical developments in this field. For this purpose test specimens with localized defects were produced. Different modifications of radar, ultrasonic-echo and impact-echo methods were investigated. Including two- and three- dimensional reconstruction models. The experiments were accompanied by numerical simulation of the propagation of sound waves and microwaves. The results showed that the radar and the ultrasonic methods were efficient tools to locate the tendon ducts accurately if the reinforcing bars were not to narrowly spaced. The ultrasonic imaging methods were capable of identifying injection and compaction faults in a blind test. The good performance of the impact-echo method with regard to locating tendon ducts which was claimed in several publications could not be validated in the present investigations. The simulation models provided valuable information on how to improve the experimental test program and its evaluation.

There is an urgent need for fast, reliable, non-destructive test methods to measure permeability and resistivity of concrete in the field, in order to assess the performance of concrete structures and confirm the benefits of the use of new materials. The application of high performance concrete for rehabilitation of corrosion-damaged highway structures and for new bridge construction has increased in Ontario over the past few years. High performance concrete, containing supplementary cementing materials such as silica fume, typically has lower permeability and higher electrical resistivity than conventional concrete. Since 1993, the R&D staff of the Ontario Ministry of Transportation (MTO) has been evaluating various non-destructive in-situ techniques to measure the permeability and resistivity of concrete. This paper describes two methods used by MTO to measure the permeability of concrete: surface water absorption and air permeability techniques; and presents the methods used to measure the concrete electrical resistivity, chloride movement in the concrete, and corrosion activity of the embedded steel. Many of the tests were performed on both the conventional and high performance concrete. Some of these techniques can be potentially used as quality assurance tools for assessing the quality, performance and durability of concrete in the field.

Acoustic emission is an important global nondestructive test method widely used to evaluate the structural integrity of metals and fiber reinforced plastic structures. However, in concrete, application of the technology is still at the experimental stage. Microcracking and crack growth are the principal sources of emission in concrete. Bond failure, anchor slippage, and crack rubbing are also sources of emission. Tension zone cracking in reinforced concrete is a significant source of emission and has made application of the technique to concrete structures difficult. The paper describes acoustic emission monitoring of full-scale prestressed concrete girders and a reinforced concrete frame during loading. The tests on the prestressed concrete girders showed three sources of emission: shear-induced cracking in the web, flexural cracking at the region of maximum moment, and strand slippage at the anchorage zone. The reinforced concrete frame was monitored with and without concrete shear panels. The research was directed to early detection of the cracks, signature analysis, source location, moment tensor analysis, and development of criteria for acoustic emission inspection of concrete structures. Cracking of concrete in the tension areas of the reinforced concrete sections was an early source of emission. More severe emission was detected as damage levels in the structure increased.

There is a need for non-destructive evaluation (NDE) techniques which can effectively determine the extent of damage (cracking) in concrete structures. Non-destructive, one-sided surface wave attenuation measurement is a very sensitive and practical tool for such characterization. A technique for practical determination of frequency-dependent surface wave attenuation is introduced and demonstrated to be sensitive to damage in free concrete slabs. A theoretical model for the attenuation response in undamaged free slabs is introduced and shown to accurately predict experimentally obtained responses in concrete within certain frequency limits. The theoretical model is then used to investigate the practical application of the attenuation technique to concrete pavement NDE in terms of slab depth and subbase conditions. Theoretically obtained data are presented for a variety of pavement types. Based on the presented results of the theoretical model, conclusions concerning practical application of the technique to pavement inspection are given.

A research project was undertaken by the The University of Texas at Austin's Center for Transportation Research to assess the condition and remaining life of a large section of Runway (RW) 17R-35L and taxiway L at Dallas/Fort Worth International Airport. Concrete fatigue was determined from fatigue testing of RW core samples and from deflection data obtained from an experimental testing device called the Rolling Dynamic Deflectometer (RDD). The RDD is a truck-mounted device that measures continuous deflection profiles of pavements. The RDD appears to be a very promising device for use in pavement performance analysis. The RDD gives much more comprehensive deflection data than devices currently in use such as the Falling Weight Deflectometer and the Dynaflect and the data collection procedure is quicker and more efficient. Additionally, continuous deflection profiles provide more ways of assessing the in-place structural adequacy of pavements. For this research, RDD data from one section approximately 305 m (1000 ft.) was selected to illustrate several possible ways to analyze the data. Due to the large amount of data collected by sampling every 152 mm (6 in.) on a runway over a mile in length, a program called RDD3 was developed to perform the analysis. Results of this analysis are presented here.

Magnetostrictive sensors (MsS) provide a noncontact means to transmit and detect elastic waves in a ferromagnetic material. This paper reports results of using MsS for the evaluation of debonding between seven-wire prestressing strands and concrete. Two MsS configurations are described. One uses a coil that encircles the strand, and the other does not. The advantage of the encircling coil is higher sensitivity; the advantage of the other is that it can be operated from the concrete surface and does not necessarily require removal of concrete. The results showed a correlation between signal attenuation and bond quality. The guided wave speed was also found to be inversely proportional to the bond quality.

An instrument has been developed to estimate stress levels in prestress strands in existing members. The prototype instrument applies a lateral load to an exposed prestressing strand and measures the resulting displacements. The instrument was calibrated for 0.5-inch (12.7 mm) diameter seven-wire strand with exposed lengths of 1.5 feet (0.46 m) to 3.75 feet (1.14 m). It was tested to determine its accuracy, precision, and usefulness in the field. Strand forces were consistently estimated to within ten percent of the actual load. The device was also utilized in the placement of strand splices and was found to be more reliable in checking induced strand tensions than the standard torque wrench method.

This paper addresses a study, funded by the Federal Highway Administration (FHWA), the U.S. Department of Transportation (DOT), that is currently underway at the University of Wisconsin-Milwaukee. The objective of the study is to develop an automated non-destructive testing system based on the magnetic flux leakage principle that would allow assessment of the condition of reinforcing and prestressing steels in concrete bridge components. Corrosion or cracking of steel within concrete members will be detected and evaluated. The system will be used as a self clamping and moving sensing device that can be installed on a concrete girder. Data from the sensing device is transmitted via a wireless communication system to data recording/analysis equipment on the ground. The sensing device may also be operated manually to allow inspection of local areas such as the end bearing or cable anchorage locations in cable bridges. Through performing a correlation analysis of recorded data, an assessment of the condition of the member under test is made. Reference data base for the correlation analysis is established through laboratory and field testing with known conditions.

In order to accurately assess the fatigue life of asphalt concrete pavements, an in-situ field evaluation method must be used so that factors which cannot be accounted for in the lab are considered. Surface wave testing is employed in this research to nondestructively monitor sensitive structural changes in the asphalt surface layer of pavements in the field. Microcrack damage growth and healing are investigated on pavement test sections at the Minnesota Road Research Facility (Mn/Road) by way of surface wave testing. One of the mechanisms which cannot be simulated accurately in the lab is healing of asphalt concrete during rest periods. Healing of the asphalt pavement test sections at Mn/Road following a 24 hour rest period was quantified using wavespeed measurements. These measurements show that a significant amount of healing is occurring and can be detected using stress wave testing. Several signal processing methods are used to evaluate the microcrack damage growth and healing in the asphalt pavement sections. The 'apparent' modulus is computed from the velocity of wave propagation and used to quantify damage in the pavements. Attenuation of the stress waves is also calculated for damage assessment. It is discovered that attenuation parameters in the frequency domain are more sensitive than wavespeed calculations in the time domain, but contain significantly more variability.

The Fort Worth District of the Texas Department of Transportation (TxDOT) has used Ground Penetrating Radar (GPR) data extensively for pavement condition assessment and pavement rehabilitation type selection. GPR is a non- destructive testing technique that can determine pavement layer thicknesses as well as the presence of excessive moisture or excessive air voids in pavement layers. This paper describes four case studies where TxDOT personnel used GPR data to make pavement rehabilitation and assessment decisions.

Distributed damage mechanisms, such as delayed ettringite formation (DEF) and alkali-silica reactivity (ASR) can cause cracking and premature deterioration of concrete structures. The focus of the authors' research has been to determine whether transient stress waves can be used for assessing the amount of damage present in plate-like concrete sections. Results obtained from numerical, laboratory, and field studies are presented. Finite element analyses were performed to study the effects caused by distributed damage on propagation stress waves. Laboratory studies involved the use of accelerated damage specimens for performing tests for detecting changes in physical properties over time, impact-echo tests, and neutron radiography to quantify the amount of cracking present in a specimen. A correlation was made between damage predictions obtained from impact-echo signals and the actual amount of cracking as determined from radiographs. A field study on concrete box beams suffering deterioration caused by distributed damage mechanisms was performed to demonstrate the feasibility of the methods for quantifying damage in actual concrete members. These studies demonstrated that impact-echo signals can be used to detect and quantify the amount of distributed damage in concrete sections. Guidelines for determining the amount of damage using impact-echo signals are presented. For the first time, engineers have a tool for assessing the amount of damage in concrete structures with distributed cracking.

California has about 24,000 publicly owned bridges that require routine structural evaluations to comply with National Bridge Inspection Standard (NBIS) mandates. Of these, about 800 are identified as possessing fatigue prone or fracture critical details requiring thorough tactile investigations. Gaining access to bridge elements to perform these investigations has become increasingly difficult and costly. The traditional uses of under bridge inspection trucks, lift equipment and rigging are economically and practically limited by bridge size, structure type, traffic demands and support costs. In some cases, bridges that have become damaged by earthquakes cannot safely support the loads of heavy personnel lift equipment. The California Department of Transportation (Caltrans)'s Office of Structural Materials and Office of Structure Maintenance and Investigations evaluated the use of rock climbing and mountaineering techniques as an alternative means of gaining access for bridge inspections. Under a small research grant, a bridge climbing training course was developed through a local University of California outdoor recreation group and 7 engineers and technicians were initially trained. A comprehensive Code of Safe Practices was created and standards of training, procedures and equipment required for bridge inspections were established. A successful climb investigation on a large, previously inaccessible arch bridge was completed at the end of the training that proved the techniques safe, economical and effective. Within one year, 20 bridge maintenance engineers were trained, and a formal program was established to organize, schedule, equip and certify engineers and technicians for bridge climbing. Several other offices within Caltrans as well as the California Department of Water Resources have since adopted these techniques for specialized structural inspection tasks. Climbing techniques are now used routinely in California as an alterative means of gaining access to bridges and structures, and over 100 bridges have been identified as those where climbing is the only means available to perform structural investigations.

A microwave-based approach under development for detecting corrosion of rebar is described. The rebar inside the concrete is heated with an induction heater and then the surface temperature of the rebar inside the concrete is probed using a microwave reflectance method. This is in contrast to infrared thermographic approaches which monitor the surface temperature of the concrete and are dependent on waiting for considerable lengths of time for heat flow from the rebar to the concrete surface. Results will be presented for a series of test specimens produced by deliberately corroding rebar inside concrete in the laboratory. Microwave thermoreflectance measurements made in a 5 second measurement time are compared with conventional thermographic measurements of the temperature distribution at the concrete surface which require a 10 minute measurement time. Theoretical results are also presented of the predicted temperature versus time curves expected for rebar inside concrete with and without air defects at the rebar-concrete interface. These results predict that a rebar-concrete interface could be distinguished from a rebar-air interface with only 1 second of heating. The theoretical results further show that the presence of an air layer of finite thickness between rebar and concrete after about 2 seconds could be detected with a 2 second heating time.

Falling weight deflectometor (FWD) has been frequently used to evaluate structural integrity of pavement. The device applies an impulsive force on the surface of pavement and measure surface deflections at several locations including the place of loading. Although the test is dynamic, the data is regarded as pseudo-static data. According to common practice, using the peak load and the corresponding peak deflections, layer moduli are estimated in a static domain such that the measured peak deflections coincide with the corresponding calculated deflections based on the assumption of the theory of linear elasticity. This paper presents a method to back calculate layer moduli in dynamic domain such that the histories of both measured and calculated responses corresponding to the impulsive force coincide. Pavement is modeled by an axisymmetric linear elastic system. FEM is utilized coupled with Ritz vector to reduce a matrix and thus to improve computational efficiency. The backcalculation algorithm used is the Gauss-Newton method coupled with a truncated singular value decomposition.

This paper discusses operational issues which affect the reliability and affordability of Global Positioning System (GPS)-based structural deformation monitoring systems. Two primary differences between GPS and most other sensors commonly used are the amount of data generated and the complexity of data processing functions. If these functions are not handled appropriately, operational costs can outweigh the relative benefits of GPS and make the system unaffordable. However, a significant amount of automation can be designed into the system to minimize labor costs and risk of human error.

Long-term continuous monitoring may be helpful in periodic evaluation of structures, decision-making for preventative maintenance, and examining new design techniques. Remote bridge-monitoring systems are expected to be useful in future bridge inspection and management. Reliability of data- collection systems, sensors, and communication systems in the service environment is critical for successful field operation. This paper briefly describes a study undertaken by New York State Department of Transportation to investigate reliability of a state-of-the-art bridge-monitoring system available at the inception of that study and to examine its utility for continuous monitoring of bridge structures.

The development of a retrofit design aimed at retarding or eliminating fatigue crack growth in a large bridge can be a very difficult and expensive procedure. Analytical techniques frequently do not provide sufficient accuracy when applied to complex structural details. The Infrastructure Technology Institute (ITI) of Northwestern University, under contract to the California Department of Transportation (Caltrans), recently applied experimental state-of-the-art NDE technology to the Interstate 80 bridge over the Sacramento River near Sacramento, California (Bryte Bend). Acoustic emission monitoring was applied in conjunction with strain gage monitoring to aid in characterizing the retrofits' effect on existing active fatigue cracks. The combined test results clearly showed that one retrofit design was superior to the other.

The relations between data from test methods and conditions in bridge elements are considered. NDE methods are joint applications of a test and a basis for interpretation of data obtained in the test. Correct assessments of conditions of elements depend on the inaccuracy and variability in test data and on the uncertainty of correlations between attributes (what is measured) and conditions (what is sought in the inspection). A full description of the performance of NDE methods considers the relation of test data to conditions of elements. The quality of the test itself is important, but equally important is the interpretation that occurs after the test. The effects of variability in test data and uncertainty in correlations of attributes and conditions are presented in three examples of field testing methods.

The highway system in the United States includes nearly 577,000 bridges, the majority of which were built during two major bridge building periods -- just before World War II (1930s) and in the first two decades of the Cold War (1950s and 1960s). Given the age and increased usage of these bridges over the years, many now require substantial maintenance to satisfy their desired level of service. The complex task of allocating scarce funds for the repair, maintenance, and rehabilitation of this large number of bridges led to the development of several optimization studies and two major bridge management system, namely BRIDGIT and Pontis. Pontis has emerged as the system of choice for all states in the Nation. At this time over 40 highway agencies continue to license, evaluate and implement the current AASHTOWARE Program, Pontis V. 3.2. However, all data currently required by Pontis to assess the structural stability and resulting suggestions for repair and maintenance of bridges are based on visual inspection and judgement. Consequently, all suggestions are based on that visual inspection. This paper discusses development of a plan for how non-destructive evaluation (NDE) data can be used to provide more information than visual inspection.

On-line, continuous monitoring technologies of a rigorous and objective nature are sought to quantitatively identify and evaluate the condition or health of highway structures over their useful lifetime. A global bridge evaluation methodology is under development based upon the structural identification concept, employing modal testing, truckload testing, and instrumented monitoring as its principal experimental tools. Test results are transformed to either modal flexibility or the unit influence line, which have been demonstrated to be conceptual, quantitative, comprehensive, and damage-sensitive signatures. Four test sites were tested, monitored, and studied in order to classify their similar bride-type-specific behavior mechanisms and to validate the performance of the implemented methodology. Practical, type-specific procedures for instrumented monitoring and nondestructive evaluation can then be developed for the whole group or type of highway bridges.

This paper describes a load test performed on a bridge that has a deflected steel I-beam. The test was conducted using acoustic strain gauges. Results from the test were used to evaluate the extent of composite action between the deck and the beams thereby eliminating speculation in the load rating analysis of the structure.

In diagnosing the structural health of a steel highway bridge it is important to determine accumulated fatigue damage as well as the maximum load capacity of the structure. Dynamic stress measurement required in determining accumulated fatigue damage has been demonstrated by the SonicForce^R Acoustic Strain Gauge. Current research and development is focused on non-intrusive assessment of relative dead load. Under a Cooperative Research and Development Agreement (CRADA), SonicForce^R together with the National Institute of Standards and Technology (NIST) located in Boulder, Colorado is presently developing ultrasonic instrumentation to map these dead load stresses. This paper presents a case study of the use of the Acoustic Strain Gauge as a fatigue damage diagnostic tool, and presents a new product, the Acoustic Load Gauge (ALG), that utilizes a non-contact ultrasonic technology to measure relative Dead Load stresses in steel bridges.

A large percentage of the nation's bridges are classified as structurally deficient or functionally obsolete. Many bridges are classified as such due to the bridge's load rating. However, the vast majority of bridges are not actually tested to determine their load capacity. In general, actually testing a structure to determine the load rating is time consuming and expensive. As a result only a low number of bridges can be tested. A main time consuming portion of the load test is the setup of conventional instrumentation to monitor the status of the bridge under test. Typically strain gages and LVDT (or similar) deflection transducers are used. Instrumentation which would allow rapid load testing of bridges is currently being developed and tested at the Federal Highway Administration. This instrumentation includes wireless data acquisition systems interfaced with clamp-on strain gages, which can be placed at a measurement location in a matter of minutes. Also, the instrumentation includes a remote laser- based deflection measurement system. The combination of the two types of instrumentation, wireless data acquisition and laser-based deflection measurements, has the potential to allow a greater number of structures to be load rated giving a more accurate picture of the health of the nation's bridges.

All welding and fabrication procedures for steel structures within the state of Texas are in accordance with the ANSI/AASHTO/AWS D1.5 Bridge Welding Code or the ANSI/AASHTO/AWS D1.1 Structural Welding Code. To meet the stringent requirements imposed by these codes on inspection personnel, a certification program was developed and implemented. This program provides for the required training, testing, qualification, and certification of the nondestructive testing personnel, and the training necessary to become a Certified Welding Inspector (CWI). following is an overview of that program.

Timber bridges are very common in state and rural highway systems. According to the National Bridge Inventory (NBI), there are 41,743 timber bridges in the United States and another 42,102 bridges with timber decks as a part of the superstructure. As these bridges age, there is a critical need for reliable inspection and assessment methods for evaluating timber members. Under an FHWA mandate, these bridges also need to be evaluated for scour susceptibility. Knowledge of the length of timber piles supporting the bridge is a vital component in calculating scour resistance of a bridge. However, records of timber pile lengths are often nonexistent or incomplete due to the construction practices for timber piles. This paper presents nondestructive evaluation (NDE) techniques used for assessing timber piles on 10 bridges in Clallam County, Washington. Stress wave velocity and resistance drilling techniques were used to determine the presence of and quantify the extent of decay in the piles. A longitudinal stress wave technique was used for determining the length of timber piles. Determination of piles with decay aided in establishing maintenance and repair needs on the bridge substructures. Pile length estimates enabled Clallam County Road Department to determine the scour-susceptibility of these bridges.

Pile tip elevations are unknown for nearly half of Georgia's 14,500 bridges. Since the length of a pile is directly related to its capacity, and ultimately, to a bridge's load capacity, the need for a straightforward, effective, and inexpensive method to determine pile embedment lengths is apparent. If the top of the pile is exposed and free to be impacted and instrumented, the task is relatively simple. The exposed pile top is impacted axially, and the resulting longitudinal wave motion is monitored and used to calculate the pile lengths. However, such piles rarely exist in bridge structures, and the more common case is that the tops of the piles are cast into the bent cap. This lack of access poses a challenging problem when trying to nondestructively ascertain the length of pile that is embedded in the surrounding soil. Although soil borings and other intrusive tests are capable of determining pile tip elevations, the time and cost of performing these tests on a large number of bridges is prohibitive. The research project described here uses flexural waves, induced by exciting piles laterally, to determine the unknown embedment lengths. Modal analysis techniques are employed to quantify the difference in modal characteristics (natural frequencies, damping, and mode shapes) of piles with differing lengths, to create a modal model of the system, and finally to back-calculate the unknown pile embedment lengths.