In the last decade, many advanced sensing and measurement technologies have been developed or transferred from defense use to infrastructure applications. It is now possible to measure various properties of a structural system, its elements and materials. However, the development of new technologies and tools should be considered in conjunction with fundamental changes and new paradigms as opposed to simple modifications to civil infrastructure systems engineering practice. It may be useful to start with a bold vision for an integrated bridge structural and operational management capability, and to properly design, develop, validate, demonstrate and standardize the technologies that are needed in conjunction with this vision. The term `health-monitoring', used in relation to intelligent infrastructure, will be helpful for formulating a complete and coherent vision for the bridge management of the future. The writers define `health monitoring,' as the measurement of the operating and loading environment and the critical responses of a structure in order to track and evaluate the symptoms of operational anomalies and/or deterioration or damage that may impact service or safety reliability.

The design of a microinstrument for corrosion monitoring in reinforced concrete is presented and the performance of the prototype device discussed. Sensors for the measurement of corrosion rate, corrosion potential, chloride concentration, and concrete conductivity have been developed and tested inside of model concrete slabs. The tests include electrochemical chloride driving as a method for test acceleration and wet/dry cycling. The corrosion rate and conductivity sensors perform very well, as do all aspects of the electronics. Work continues on the chloride sensor and reference electrode.

In this paper, we develop and demonstrate a nondestructive evaluation technique for corrosion detection of embedded or encased steel cables. This technique utilizes time domain reflectometry (TDR), which has been traditionally used to detect electrical discontinuities in transmission lines. By applying a sensor wire along with the bridge cable, we can model the cable as an asymmetric, twin-conductor transmission line. Physical defects of the bridge cable will change the electromagnetic properties of the line and can be detected by TDR. Furthermore, different types of defects can be modeled analytically, and identified using TDR. TDR measurement results from several fabricated bridge cable sections with built-in defects are reported.

As proliferation of structures incorporating composite materials occurs, the benefits of in-situ monitoring of the building materials in order to increase reliability and improve maintainability of the overall structure are being recognized. For example, measurement of shear-strain and load within bridge bearings can be directly related to the health and longevity of the structure. In this paper, the embedding of single and multi-axis optical fiber strain sensors within liquid molded load cells for structures such as bridges is reported. Fabrication and testing processes are presented, as well as test results.

In 1996, a concrete highway bridge near Geneva (Switzerland) was instrumented with more than 100 low-coherence fiber optic deformation sensors. The Versoix Bridge is a classical concrete bridge consisting in two parallel pre-stressed concrete beams supporting a 30-cm concrete deck and two overhangs. To enlarge the bridge, the beams were widened and the overhang extended. In order to increase the knowledge on the interaction between the old and the new concrete, we choose low-coherence fiber optic sensors to measure the displacements of the fresh concrete during the setting phase and to monitor the long term deformations of the bridge. The aim is to retrieve the spatial displacements of the bridge in an earth-bound coordinate system by monitoring its internal deformations. The vertical and horizontal curvatures of the bridge are measured locally at multiple locations along the bridge span by installing sensors at different positions in the girder cross-section. By taking the double integral of the curvature and respecting the boundary conditions, it is then possible to retrieve the deformations of the bridge. This paper presents the sensor network design and the measurements that were performed during the construction phases, during the bridge operation since it was reopened and under a recent static-loading test.

The development of quantitative damage detection and evaluation technique, and damage detection technique for invisible damages of structures are required according to the lessons from the 1995 Hyogo-ken Nanbu earthquake. In this study, two quantitative damage sensing techniques for highway bridge structures are proposed. One method is to measure the change of vibration characteristics of the bridge structure. According to the damage detection test for damaged bridge column by shaking table test, this method can successfully detect the vibration characteristic change caused by damage progress due to increment excitations. The other method is to use self-diagnosis intelligent materials. According to the reinforced concrete beam specimen test, the second method can detect the damage by rupture of intelligent sensors, such as optical fiber or carbon fiber reinforced plastic rod.

In this paper, a dynamic test performed over a bridge located in northern Italy is reported: the dynamic measures are analyzed by means of different techniques to seek for the most reliable algorithm within those appropriate for the identification of dynamic systems excited by unknown input.

Coating Tolerant Thermography's ability to differentiate between chipped paint and structural flaws has clearly been demonstrated. However, the functionality of the final inspection system requires the application of the CTT algorithm to thermal stripes. This paper describes the thermal stripe projector, sensor engines and automatic stripe identification and gradient mapping algorithms required by CTT.

Thermoelastic and photoelastic stress analysis systems effectively provide information about the sum and difference of the principal stresses, respectively. Combining these two full-field, non-contact NDE techniques allows the individual stress components to be measured. One of the main difficulties in merging these two systems is in identifying an appropriate surface coating. Thermoelasticity demands a highly emissive surface, while photoelasticity requires a strain-induced birefringent, transparent coating with a retro-reflective backing. A number of candidate coatings that are useful for combined photoelastic and thermoelastic stress measurement have been identified, with sample results given here. Issues associated with the practical implementation of combined thermoelastic and phtoelastic stress measurement are also discussed in this paper.

Composite materials are being used for bridge column seismic retrofits and to rehabilitate other concrete structures. There are three different manufacturing methods for applying composites to concrete columns which are outlined in this paper. Each method has the potential for creating debonds at the composite-concrete interface and within the composite itself. Thermography is a non-destructive evaluation technique which can be used to image debonds below the composite surface. Background fundamentals of the thermographic technique are discussed. Data from thermographic tests of a variety of retrofit applications, which include examples for each of the three aforementioned manufacturing processes, are then presented. The paper concludes with a list of issues which need to be addressed when performing a thermographic inspection in the field.

Thermographic nondestructive testing was performed on composite reinforcements applied to two concrete civil structures. Information on the types of defects which occur in these structures and their locations has led to process improvements in the application of adhesively bonded laminated composites to steel reinforce concrete structures.

The NDE Validation Center is a national resource for the independent and quantitative evaluation of existing and emerging NDE techniques. The resources of the NDE Validation Center are available to federal and state agencies, the academic community, and industry. The NDE Validation Center is designed to perform critical evaluations of NDE technologies and to provide a source of information and guidance to users and developers of NDE systems. This paper describes the resources available at the Center and the initial efforts to validate the visual inspection of highway bridges. Efforts to evaluate various NDE methods for the inspection of bridge hanger pins are also described.

Unit H4 of the ACOSTA bridge in Jacksonville, Florida is composed of steel with a composite concrete deck. The bridge, designed for AASHTO HS20 loading, was built in 1993 on a horizontal curve. However it was later discovered that the designer neglected to consider the effect of curvature in the original design. Considering the effect of curvature in the analytical load rating resulted in load rating of HS4. To resolve the concerns about the low load rating of this essentially new bridge and to establish the actual load capacity, field load testing was conducted in 1996. Critical sections along the span were instrumented with strain and deflection gauges. The bridge was incrementally loaded and all measurements were recorded at each load step. The results were used to study the behavior of the bridge. The field test results combined with analysis resulted in a higher load rating than the original analytical rating considering curvature effect.

One of the major components of an infrastructure management system is the condition assessment or deterioration modeling. With application to highway pavements and bridges, this paper presents conceptually how nondestructive evaluation (NDE) results can be utilized to provide a quantitative assessment of the infrastructure condition in a format usable for network-level pavement management systems and bridge management systems. NDE techniques typically applied to pavements include Visual Rating, Falling Weight Deflectometer, Dynaflect, Seismic Pavement Analyzer, and the Ground Penetrating Radar (GPR). Bridges can also be evaluated using the GPR. NDE is particularly useful at the network level of infrastructure management because of the mobility of conducting the tests. Detailed mechanistic methods have been suggested for NDE interpretation but this method may not be practical at network level. Interpretation of NDE results, through knowledge-based systems and intelligent databases indicate the defects and residual capacity of infrastructures. Measured physical properties and defects in the infrastructure component materials can be correlated to existing scales of condition assessment such as in the NBI and PONTIS formats for bridge management and also to an index or rating such as the PSI in highway pavements.

This study focuses on examining the behavior of rigid pavement layers during the Falling Weight Deflectometer (FWD) test. Factors affecting the design of a concrete slab, such as whether the joints are doweled or undoweled and the spacing between the transverse joints, were considered in this study. Explicit finite element analysis was employed to investigate pavement layers' responses to the action of the impulse of the FWD test. Models of various dimensions were developed to satisfy the factors under consideration. The accuracy of the finite element models developed in this investigation was verified by comparing the finite element- generated deflection basin with that experimentally measured during an actual test. The results showed that the measured deflection basin can be reproduced through finite element modeling of the pavement structure. The resulting deflection basins from the use FE modeling was processed in order to backcalculate pavement layer moduli. This approach provides a method for the evaluation of the performance of existing backcalculation programs which are based on static elastic layer analysis. Based upon the previous studies conducted for the selection of software, three different backcalculation programs were chosen for the evaluation: MODULUS5.0, EVERCALC4.0, and MODCOMP3. The results indicate that ignoring the dynamic nature of the load may lead to crude results, especially during backcalculation procedures.

Three nondestructive testing techniques were used in this study to evaluate pavement layer properties. These techniques included deflection and seismic methods. In the deflection methods, measurable surface deformations were induced using falling weight deflectometer and Dynaflect tests. These two tests utilized different schemes of dynamic loading applications to produce deflection basins from which the pavement layer properties were back calculated. Pavement properties from seismic methods were obtained from the analysis of surface waves due to transient load applications. In this study the seismic pavement analyzer (SPA) was used to determine pavement moduli values. Although the same assumptions for linear elastic behavior of pavement properties are usually assumed in all the three methods, obtained moduli values from these techniques did not conform to each other. Commonly, pavement deflection from SPA is not considered when analyzing layer properties. To narrow the gap between the obtained results, however, time-history records and frequency response functions were used to determine surface deflections from the three methods. Deflection measurements correlated with the obtained moduli values. Using these correlations, moduli values at any pavement deflection levels could be evaluated, especially at levels produced by traffic loads.

Ground penetrating radar, often used for geophysics investigation and land mine detection, has been developed as a non-destructive means of concrete bridge health monitoring for nearly a decade. However, the commercially available systems are limited to estimating the location and gross quantities of the deterioration. The objective of this research is to develop a GPR system that can provide a more accurate method for obtaining detailed information, so that the location and magnitude of the delaminations and deterioration can be decided. A frequency band of 500 MHz to 6 GHz, was used for this system. A corresponding antenna with high resolution and radiation efficiency, Good Impedance Match Antenna, was developed for this frequency range. The system is able to distinguish features that are at least 360 mm deep in concrete. The GPR system, antenna, and experimental results from field investigations are presented.

Since early 1995 the Federal Highway Administration (FHWA) has been sponsoring the development of ground-penetrating radar technology to produce a tool for the non-destructive evaluation of bridge decks. Under contract with the FHWA, Lawrence Livermore National Laboratory designed and built a system capable of recording data over a 2 meter width during normal traffic flow. The derived system is called `The HERMES Bridge Inspector' (High-speed Electromagnetic Roadway Measurement and Evaluation System) and includes a 64 channel antenna array within a 30 ft trailer. For detailed investigation of portions of a bridge deck, a robotic cart mounted radar has been developed. This cart system is named `The PERES Bridge Inspector' (Precision Electromagnetic Roadway Evaluation System). PERES records data over the chosen area by rastering a single transceiver over the road. Images of the deck interior are reconstructed from the original synthetic aperture data using diffraction tomography. The work presented herein describes the findings of initial experiments conducted to determine the inspection capabilities of these systems. Internal defects such as delaminations, voids and disbonds; and construction details including deck thickness, asphalt overlay thickness and reinforcement layout were the features targeted. The final goal is for these systems, and other non-destructive technologies, to provide information on the condition of the nation's bridges for input to bridge management systems.

We investigated the feasibility of thermal inertia mapping for bridge deck inspections. Using pulsed thermal imaging, we heat-stimulated surrogate delaminations in reinforced concrete and asphalt-concrete slabs. Using a dual-band infrared camera system, we measured thermal inertia responses of Styrofoam implants under 5 cm of asphalt, 5 cm of concrete, and 10 cm of asphalt and concrete. We compared thermal maps from solar-heated concrete and asphalt-concrete slabs with thermal inertia maps from flash-heated concrete and asphalt-concrete slabs. Thermal inertia mapping is a tool for visualizing and quantifying subsurface defects. Physically, thermal inertia is a measure of the resistance of the bridge deck to temperature change. Experimentally, it is determined from the inverse slope of the surface temperature versus the inverse square root of time. Mathematically, thermal inertia is the square root of the product of thermal conductivity, density, and heat capacity. Thermal inertia mapping distinguishes delaminated decks which have below-average thermal inertias from normal or shaded decks.

A new ground penetrating radar system was built using a controllable variable pulse-width transmitter and a new antenna design. The transmitter generates monocycle pulses with pulse widths that are continuously variable from 0.5 to 2 nanoseconds; thus, the center frequency of the pulse spectrum is variable from 500 to 2000 MHz. The antenna is relatively small and light weight and operates in both the air-coupled and ground-coupled mode. The complete prototype system, including radar control unit, antenna unit, lap-top computer, battery, and back-pack, weighs 65 pounds, is portable and easily usable by one person.

In this paper, a review is presented of various applications of the magnetostrictive sensor (MsS) technology to the nondestructive evaluation of steel reinforcing bars and seven-wire strands. MsSs have been applied to the detection of corrosion in and out of concrete, the quantification of corrosion, the detection of debonding, the measurement of tensile stress, the monitoring of concrete curing, the monitoring of wire breakage, and the location of broken or fractured wires. A review of the MsS technology is given along with an assessment of the utility of the technology in the above-mentioned applications.

The determination of concrete integrity, especially in concrete bridge decks, is of extreme importance. Current systems for testing concrete structures are expensive, slow, or tedious. State of the art systems use ground penetrating radar, but they have inherent problems especially with ghosting and signal signature overlap. The older method of locating delaminations in bridge decks involves either tapping on the surface with a hammer or metal rod, or dragging a chain-bar across the bridge deck. Both methods require a `calibrated' ear to determine the difference between good sections and bad sections of concrete. As a consequence, the method is highly subjective, different from person to person and even day to day for a given person. In addition, archival of such data is impractical, or at least improbable, in most situations. The Diagnostic Instrumentation and Analysis Laboratory has constructed an instrument that implements the chain-drag method of concrete inspection. The system is capable of real-time analysis of recorded signals, archival of processed data, and high-speed data acquisition so that post-processing of the data is possible for either research purposes or for listening to the recorded signals.

The paper describes the application of Non-Destructive Testing for the detection of ruptures in the prestressing reinforcement. These damages can be detected by the non- destructive and contactless magnetic stray field measuring method. The paper presents the underlying physical principle and the results of measurements on bridges. Furthermore, the development of a multi-channel system utilizing Superconducting Quantum Interference Devices as most sensitive magnetic field detectors will be reported. First laboratory measurements indicate the potential of this new technique.

Seismic nondestructive testing technology as used for pavement evaluation has been incorporated in two devices: the Seismic Pavement Analyzer (SPA) and the Portable Seismic Pavement Analyzer (PSPA). A few short-term projects were conducted to learn when and where the use of seismic methods is feasible. The usefulness of the test methods involved in the SPA and PSPA has been to some extent evaluated. In their present states, the SPA and PSPA seem to be emerging as valuable tools in forensic studies and the day-to-day operations of state highway agencies. The devices have been useful in understanding some of the complex mechanisms encountered in a few projects. More experience is needed to fully understand the potential and weaknesses of the devices, and further development of their software is needed. This paper presents a summary of efforts put forth to improve the SPA and PSPA for their incorporation into the activities of the highway community in maintenance, rehabilitation and construction of pavements. Several case studies that demonstrate the usefulness and shortcomings of the two devices and the methodology involved in them are presented.

The acoustic emission (AE) behavior of reinforced concrete beams tested under flexural loading was investigated to characterize and identify the source of damage. This research was aimed at identifying the characteristic AE response associated with micro-crack development, localized crack propagation, corrosion, and debonding of the reinforcing steel.

Corrosion of reinforcing steel due to the ingression of chloride ions from deicing salt and/or seawater has been a major cause of the deterioration of reinforced concrete structures. Typically reinforcing steel is protected from corrosion by the formation of passive film because of highly alkaline concrete environment. The film can be damaged with the introduction of chloride ions to concrete, then corrosion occurs. There are mainly three approaches to tackle this problem, i.e., protective coating, cathodic protection and corrosion inhibitors.