Diagnostic procedures play an important role in performing a condition survey of a structure. Specialized tests are used during a field survey to supplement visual observations. The tests provide valuable information regarding the internal condition of the structure and quality of the construction materials. The tests also help in determining the extent of damage, if any. Recently, a team of consulting engineers performed a study to determine the remaining capacity of the Brooklyn Bridge approaches for the Department of Transportation, City of New York. Using advanced diagnostic procedures such as impact-echo and flatjack testing, additional information was gathered to assist in the study. Impact-echo testing was helpful in identifying the condition of the brick soffits which were covered with pneumatically- applied concrete, and flatjack testing was useful in determining in-situ compressive strength and compression modulus of the brick masonry. The paper describes the work and the testing results.

Nondestructive methods are increasingly being used in the USA for evaluation of our aging infrastructure. One of the areas of concern is he determination of conditions of unknown bridge foundation. Foremost is the need to determine the foundation depth, followed by foundation type, geometry, and subsurface conditions. Recently, a comprehensive evaluation was made of potential NDT technologies that have relevance to this problem in the NCHRP 21-5 project 'Determination of Unknown Subsurface Bridge Foundations'. This paper presents the test results of a research study on the applicability of using borehole-based nondestructive test (NDT) techniques for the determination of unknown subsurface bridge foundations. The results included in this paper are from the three borehole-based NDT techniques of parallel seismic test, borehole sonic test, and borehole radar test. The parallel seismic method was found to have the broadest application to the investigations of concrete, timber, and steel bridge substructures.

This paper presents a new product, the SonicForce Acoustic Strain Gauge (ASG), that utilizes a non-contact ultrasonic technology to measure applied strain requiring no paint removal and minimal surface preparation. After an overview of the ultrasonic technology is presented the results of a diagnostic test utilizing a prototype of the ASG will be discussed. The purpose of this test was to validate the ASG as being functionally equivalent to the resistance strain gauge, and to demonstrate a cost effective enabling technology to the civil and structural engineering communities. The diagnostic tests program was supervised by Dr. Abba Lichtenstein in accordance with accepted guidelines contained in the manual for 'Rating Bridges Through Testing'. FOr the purpose of this study the bridge superstructure was modeled and structural loading profiles were determined using both resistive and acoustic strain measurement techniques. Measured strains as determined by the ASG were compared to theoretical loads in order to determine if the rodeo gulch superstructure was operating in a safe and reliable manner. Additionally, under the direction of Phil Fish, two pre-production ASGs were used to monitor accumulated cyclic loading. These test data presented as a time series strip chart and rainflow histogram.

To understand the dielectric properties of PCC and better correlate them with type and severity of PCC internal defects, a study was conducted to evaluate PCC complex permittivity and magnetic permeability over a wideband of frequencies using both time domain and frequency domain techniques. Three measuring devices were designed and fabricated: a parallel plate capacitor, a coaxial transmission line, and transverse electromagnetic (TEM) horn antennae. The TEM horn antenna covers the microwave frequencies. The measurement technique involves a time domain setup that was verified by a frequency domain measurement. Portland cement concrete slabs, 60 by 75 by 14 cm, were cast; defects include delamination, delamination filled with water, segregation, and chloride contamination. In this paper, measurements using the TEM horn antennae and the feasibility of detecting flaws at microwave frequency are presented.

The feasibility of characterizing the severity of corrosion in reinforcing bars and prestressing strands was investigated using the magnetostrictive sensor (MsS) technique and time-frequency analysis. Relatively high bandwidth elastic waves were generated and detected in these steel members using the MsS technique. The detected signals wee then analyzed for their dispersion characteristics and attenuation with time-frequency analysis. In both rebars and strands, the wave attenuation was found to increase with an increased degree of corrosion. Wave attenuation was found to increase significantly when strands and rebar were cast in concrete. Initial studies showed that low frequencies will be needed to operate over a significant distance in concrete.

As part of an ongoing inspection and maintenance program for the prestressed, post-tensioned concrete runway extension decks at La Guardia Airport, a state-of-the-art method known as x-ray diffraction was utilized to non-destructively measure stresses in existing post-tensioning tendons. A review of the theory of x-ray diffraction stress measurement is given and a case study of the first known application of x-ray diffraction stress measurement to in-situ post- tensioning as undertaken by the Port Authority at La Guardia Airport is presented.

Fracture mechanics can be used to evaluate the consequence of having a crack in a bridge structure. To do so requires that the stress state near the crack be known including the contribution of residual and fabrication stresses. In general these must be measured. Stress causes a small but measurable change in the speed of sound in many materials. Hence measurement of velocity in a bridge provides a means to determine all the components of stress. This concept has been demonstrated in laboratory situations by various researchers. Here we report results from field tests on actual bridges. The stress in flange and web regions of two bridges was measured with ultrasonics. In the first bridge we determined the residual stress in the girders. The second bridge was an integral backwall bridge with no expansion joints. It had been instrumented at time of construction. Strain gage readings indicated compressive stresses near yield. Ultrasonic measurements showed the bridge to be safe. Subsequent replacement of suspect electronics in the monitoring instrumentation verified the ultrasonic results to be safe.

There are 590,232 federally reported bridges in the US with 186,733 or 31.6 percent being defined as substandard. Developing new methods for inspection and evaluation of bridges has recently received considerable attention. The characterization of aging responses in structural materials entails establishing the fundamental relationships between service and environmental exposure and material properties. Service failures due to inaccurate characterization of aging responses might result in costly repair or premature component replacement. A novel portable/in-situ stress- strain microprobe (SSM) system was developed to use an automated ball indentation technique to nondestructively measure yield strength, true-plastic-strain curve, strength coefficient, strain-hardening-exponent, and to estimate fracture toughness. Example test results on metallic structural components and samples are given in this paper and a video demonstration will be presented at the conference. The SSM technology will allow: 1) establishing current key mechanical properties which are needed as input for various damage prediction models as well as to re- evaluate the safety factors used for bridges, and 2) periodic monitoring of aging bridges to develop correlations between the SSM-measured mechanical properties and the damage accumulation as a function of bridge service usage.

In 1990, Wisconsin Department of Transportation found a high mast light pole with two of six anchor bolts failed. This failure along with published reports from Michigan DOT about anchor bolt failures on cantilever sign structures, raised concern about the quality and condition of anchor bolts on the Wisconsin DOT system. Wisconsin Department of Transportation implemented an Anchor Bolt Inspection Program in 1990 for cantilever sign structures, high mast light towers, 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 material type, cut or rolled threads, and type of coating for anchor bolts. Inspection emphasis are on "hands on" and Nondestructive evaluation. Special emphasis is placed on visual conditions of 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 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 failed anchor bolts and critical cracks before failure of an entire structure.

Concrete overlays with thickness ranging between 25 mm and 300 mm are frequently used to restore and strengthen existing concrete pavements and bridge approach slabs. Differences in the strengths and elastic moduli of the overlay and the substrate, as well as the cleanliness and roughness of the interface between the two layers affect the medium and long term performance of these structures. Debonding at the interface, excessive tensile stresses at the base of the overlay and delamination within the upper layer are commonly occurring problems. If these defects are not detected and corrected in god time, the deterioration of the overlay under the action of heavy axle loads is rapid and becomes expensive to fix. Nondestructive methods are required to identify the budding problems of the type described above, by surveying overlay systems quickly and economically. Stress wave methods for flaw detection in concrete structures and foundations have shown great promise in recent years. The Impact-Echo test has been applied successfully to many diverse concrete material problems. The Impulse Response test is proven in the detection of flaws in deep concrete foundations, as well as the location of poor support conditions beneath and delaminations within concrete slabs on grade. This paper presents a case study where both methods were used to examine a stepped concrete overlay on approach slabs to bridge decks on a heavily trafficked interstate highway. The two test methods are briefly described, and a comparison is drawn emphasizing the advantages and disadvantages of both techniques.

In this paper, a novel pavement distress detection algorithm based on fuzzy logic is proposed. The idea of the proposed method is based on the fact that the crack pixels in pavement images are 'darker than their surroundings and continuous'. First, the proposed method determines how much darker the pixels are than the surroundings. This is done by determining the brightness membership function for gray levels in the difference image. Then, we check the connectivity of he darker pixels to eliminate the pixels which lack of connectivity. Finally, image projections are employed to classify cracks. The experimental results have shown that the cracks are correctly and effectively detected by the proposed method. The main advantages of the proposed method are: 1) It can correctly find out thin cracks even from very noisy pavement images. 2) It can be operated automatically. 3) The efficiency and accuracy of the proposed algorithm are superior. 4) Application-dependent nature, instead of image-dependent, will simplify the design of the system.

Falling weight deflectometer (FWD) test is employed by many state highway agencies for the nondestructive evaluation of pavement layers moduli. The accuracy of test results changes significantly for different pavement systems and may results in misleading conclusions. In this study, explicit finite element analysis was used to investigate the behavior of pavement layers under the action of an impact load. The time dependent dynamic responses of origin and flexible pavements were compared and significant differences in behavior were observed. Analysis of the time-histories of vertical deformations propagating through the pavement depth reveals that the displacements measured on the surface layer at standard FWD sensors' positions may not be indicative of the displacements of underlying layers. Computer results are provided for the extreme cases of fully bonded and unbonded pavement layers' interfaces. The results of the analysis reveal that the dynamic displacement patterns are much more complicated than the static ones. Animation of the model results indicates that near-surface pavement layers may behave as a set of composite plates resting on an elastic foundation in absence of bonds between the layers interfaces. If there are strong bonds, the near surface layers behave as a single composite solid resting on elastic foundation.

The need for effective design in the nation's highways is greater now, more than ever, due to shrinking funds for new construction and rehabilitation/maintenance practices and the need to preserve the lands that are not now part of the roadway system. Most of the nation's highways were constructed within the last 30 years and many of these are due for significant rehabilitation and even reconstruction. Thus, the need to infuse robust design methods into these rehabilitation and reconstruction strategies is paramount. Currently, methods for cost allocation for pavement rehabilitation/maintenance activities and pavement management estimations are based on empirical and semi- empirical founded predictions that come up short, particularly when the roadway i subjected to multi-axle, heavy weight vehicles. Additionally, materials currently used int he construction of the pavement structure do not always behave in an elastic manner and the ability to predict the pavement response in the presence of other than elastic material behavior is essential. Finally, prediction of pavement states of distress based on empirical methods and elastic material behavior are inadequate, particularly when heavy weight vehicular traffic is involved. This paper includes descriptions of the overall methodology for pavement design and the unique requirements for the design and implementation of the structural and environmental sensing elements. Description of the mechanistic aspects in the software for the structural and material models is discussed and comparison of predicted and field measured results are presented.

Conventional visual and manual pavement distress analysis approaches are very costly, time-consuming, dangerous, labor-intensive, tedious, subjective, having high degree of variability, unable to provide meaningful quantitative information, and almost always leading to inconsistencies in distress detail over space and across evaluations. In this paper, a novel system for multipurpose automated real-time pavement distress analysis based on fuzzy logic and neural networks will be studied. The proposed system can: provide high data acquisition rates; effectively and accurately identify the type, severity and extent of surface distress; improve the safety and efficiency of data collection; offer an objective standard of analysis and classification of distress; help identify cost effective maintenance and repair plans; provide images and examples through information highway to other user/researchers; provide image/sample back for training or as the benchmark for testing new algorithms. The proposed system will reduce the cost for maintenance/repair greatly, and can contribute to other research in pavement maintenance, repair and rehabilitation.

Nondestructive testing of pavements plays an important role int he management of pavement infrastructure. A new technique for continuous profiling of pavements is under development. This technique involves the Rolling Dynamic Deflectometer (RDD). The RDD is a large truck on which a servo-hydraulic vibrator is mounted. The vibrator is used to apply large vertical dynamic loads to the pavement. The resulting dynamic displacements are sensed with rolling sensor. A description of the RDD and procedures used to analyze RDD data are discussed herein. The results of continuous RDD profiling of rigid pavements are presented. These results show that continuous stiffness profiles of displacement per given load of origin pavements can be used to characterize: 1) the pavement stiffness and its longitudinal variation; 2) the location of transverse cracks and joints; 3) the efficiency of transverse cracks and joints; 4) the efficiency of longitudinal joints; and 5) the lateral variation in average mid-span stiffness. Two significant benefits of continuous RDD profiles which are clearly shown are: 1) softer versus stiffer areas are clearly delineated and 2) the variation in joint efficiency is readily identified.

We demonstrated dual-band infrared (DBIR) thermal imaging at the Grass Valley Creek Bridges near Redding, CA. DBIR thermal imaging is an enabling technology for rapid, reliable, bridge deck inspections while minimizing lane closures. The bridge-deck inspections were conducted from a mobile DBIR bridge inspection laboratory during November 2- 3, 1995. We drove this self-contained unit at limited highway speeds over 0.4 lane miles of bridge deck. Using two thermal IR bands, we distinguished delaminations from clutter. Clutter, or unwanted thermal detail, occurs from foreign materials or uneven shade on the bridge deck surface. By mapping the DBIR spectral-response differences at 3-5 micrometers and 8-12 micrometers , we removed foreign material clutter. By mapping the deck diurnal thermal inertia variations, we removed clutter from uneven shade. Thermal inertia is a bulk deck property, the square root of thermal conductivity X density X heat capacity. Delaminated decks have below-average thermal inertias, or above-average day-night temperature excursions. Compared to normal deck areas, delaminated deck areas were typically 2 or 3 degrees C warmer at noon, and 0.5 degrees C cooler at night. The mobile DBIR bridge inspection laboratory is currently undergoing extensive testing to examine bridges by the Federal Highway Administration.

This study presents the findings on the use of ground penetrating radar (GPR) to nondestructively assess the condition of bridge decks and pavements with and without asphalt overlay including the thickness effects. Several concrete bridge deck and pavement specimens with varying internal conditions such as with/without reinforcement and with/without delaminations were tested under laboratory conditions. In order to assess the effect of asphalt overlay on the detectability of subsurface delaminations, asphalt layers with thickness ranging from 1 inch to 3 inches were poured on the specimens and tested using GPR. The study also included specimens with debonding at the asphalt/concrete interface. Individual radar waveforms and color intensity plots from these specimens were compared to study the effect of anomalies on the radar waveforms.

Sonic and ultrasonic methods are excellent tools for diagnosis of problems with concrete slabs and bridge decks. However, it is important to fully understand the limitations of these methods. The conditions where these methods are most effective and those where the methods may not yield satisfactory results are presented. More importantly, cases when an integrated approach can be the best solutions are also outlined. This paper serves as a guideline for practitioners with a practical understanding of the methods to assess the theoretical and experimental limitations of these methods.

Corrosion of rebar in concrete bridges causes subsurface cracks and is a major cause of structural degradation that necessitates repair or replacement. Early detection of corrosion effects can limit the location and extent of necessary repairs, while providing long-term information about the infrastructure status. Most current detection methods, however, are destructive of the road surface and require closing or restricting traffic while the tests are performed. A ground-penetrating radar imaging system has been designed and developed that will perform the nondestructive evaluation of road-bed cracking at traffic speeds, i.e., without the need to restrict traffic flow. The first-generation system consists of an offset-linear array of 64 impulse radar transceivers and associated electronics housed in a trailer. Computers in the trailer and in the towing vehicle control the data acquisition, processing, and display. Cross-road resolution is three centimeters at up to 30 cm in depth, while down-road resolution depends on speed; 3 cm below 20 mph up to 8 cm at 50 mph. A two-meter-wide path is inspected on each pass over the roadway. In this paper, we describe the design of this system, show preliminary results, and lay out its deployment schedule.

A small span bridge that has suffered corrosive deterioration of a number of the steel structural members is in the process of being rehabilitated with glass and carbon fiber reinforced, pultruded polymer structural beams. As part of a comprehensive research program to develop methods for modeling long term durability of the composite material, nondestructive evaluation if being used to provide a preliminary assessment of the initial condition of the beams as well as to monitor the deterioration of the beams during service.

This paper presents a qualitative health monitoring technique to be used in real-time damage evaluation of civil infrastructures such as bridge joints. The basic principle of the technique is to monitor the structural mechanical impedance which will be changed by the presence of structural damage. The mechanical impedance variations are monitored by measuring the electrical impedance of a bonded piezoelectric actuator/sensor patch. This mechanical- electrical impendance relation is due to the electromechanical coupling property of piezoelectric materials. This health monitoring technique can be easily adapted to existing structures, since only a small PZT patch is needed, giving the structure the ability to constantly monitor its own structural integrity. This impedance-based method operates at high frequencies, which enables it to detect incipient-type damage and is not confused by normal operating conditions, vibrations, changes in the structure, or changes in the host external body. This health monitoring technique has been applied successfully to a variety of light structures. However, the usefulness of the technique for massive structures needs to be verified experimentally. For this purpose, a 500 lb quarter-scale deck truss bridge joint was built and used in this experimental investigation. The localized sensing area is still observed, but the impedance variations due to incipient damage are slightly different. The localized sensing area is still observed, but the impedance variations due to incipient damage are slightly different. Nevertheless, by converting the impedance measurements into a scalar damage index, the real- time implementation of the impedance-based technique has been proven feasible.

We describe a fiber optic Bragg grating distributed strain sensor system for large scale structural monitoring applications, such as bridge monitoring. The system is capable of assessing both long term static structural loading changes and dynamic/modal behavior of the structure using two different optical interrogation schemes to address the same sensor array. The system has been used to monitor over 45 sensors attached to or embedded in a single-lane bridge span, for damage assessment.

The University of Melbourne in collaboration with VicRoads, the road and bridge authority in the state of Victoria, has performed a series of static and dynamic tests to evaluate the in-service condition of a number of bridges of different design. From this experience, a strategy for a routine bridge testing procedure has emerged, the presentation of which is the main subject of this paper. The strategy presented involves the selective use of the following methods and techniques: 1) Measurements: vibration response to ambient/traffic excitation, Modal Testing using impact deices and/or shakers. 2) Modal parameter estimation from experimental measurements. 3) FEM modeling: development of generic parametric FEM models of standard/typical designs, and special models. 4) Correlating FEM models and experimental results: updating FEM model parameters, identification of bridge support conditions, estimation of effective stiffness of aged materials and structural elements. 5) Detection of structural faults: simple methods and advanced techniques if required. 6) Prediction of bridge load carrying capacity using verified FEM model: use in re- rating bridges and as a basis or a substitute for proof load testing. The outline of the strategy together with a brief description of the elements above is given. The motivation for the work presented in this paper was to select the state of the art engineering tools to assist relevant authorities in the decision processes necessary for implementing a cost- effective maintenance and replacement policy for the ageing bridge stock.

The coherent laser radar bridge measurement system (CLBM) developed by Coleman Research Corporation provides unique non-contact capability to measure dead load contours, live load deflections, and modal frequencies. There data are vital for non-destructive evaluation of structures such as bridges. The CLBM is programmable to make these measurements at numerous predetermined points on the structure automatically. The CLBM makes its measurements at standoff distances up to 100 feet and no instrumentation needs to be mounted on the structure. This paper presents a summary of the system and compares field data obtained using the CLBM with similar data obtained using traditional contact displacement and accelerometer instrumentation.

A new method to detect and localize structural flaws, mode signature analysis, has been developed and demonstrated on a large realistic model bridge. The presence and location of flaws are detected by analyzing the vibrational response of the structure at a single, fixed point to an impulse excitation at a different fixed point. The localization method has successfully pinpointed a defect with a resolution of approximately 4 cm when both the impulse- excitation source and the point at which the vibration is monitored are located several tens of cm away from the defect. The detection method has been demonstrated by 1) contact measurements made by an accelerometer mounted on the structure and 2) remotely, from the time-dependent Doppler shift of a laser beam reflected from the structure. After the accelerometer signal, proportional to acceleration, is integrated to produce a signal proportional to velocity, it is found to be essentially identical to the remotely observed laser-vibrometer signal. Data analysis illustrates the tradeoff between maximizing the probability that an existing flaw is detected and minimizing the probability that a structure that is in good condition is misdiagnosed as faulty.

The Connecticut Department of Transportation (ConnDOT) has undertaken a major initiative to install permanent remotely- accessible monitoring systems on seven in-service highway bridges. These systems will consist of either a Roadway Weather Information System (RWIS), or Structural Monitoring System (SMS), or both, depending on the structure type and/or location. The RWIS provides weather related information regarding the pavement on and off the structure and ambient weather conditions at the bridge site. Systems like this are commercially available and in use throughout the country assisting transportation agencies in performing winter maintenance operations. The SMS is the product of cooperative research at the University of Connecticut and ConnDOT. The University has specified, installed and operated a prototype vibrational-based monitoring system on tow in-service bridges during separate year-long studies. The planned SMS, modeled after the prototype, includes accommodations for a variety of sensors including strain, tilt, structural temperature and vibration. The ultimate goal of this work is to develop a generic platform for a remote bridge monitoring system which can be adapted to any bridge with any combination of sensors and sensor types. Such a system would benefit both the safety and management of these structures. Current activity along with background information are discussed.

This paper deals with the identification of the dynamic behavior of bridges under ambient excitation. The technique here presented allows the estimation of modal parameters using transient data excitations, i.e., the vehicle passage, without requiring any traffic limitation, this fact representing a consistent advantage of the motorway companies. In this paper, the wavelet transform as a time- frequency distribution is proposed for system identification under different traffic conditions: particularly, it is shown how the wavelet analysis of the free response of a real system allows the estimation of natural frequencies, viscous damping ratios and mode shapes with a good precision. The accuracy of this identification technique is firstly proved performing the analysis on a mathematical model of a multi-supported beam with moving loads, simulating a bridge excited by traffic; finally, the acceleration responses from a real bridge, the Queensborough Bridge in Vancouver, Canada, under ambient excitations, are successfully analyzed. The results obtained using this procedure show a good agreement with those already presented in other papers referred to the dynamic identification of the same Queensborough Bridge and reported in references.

The US Department of Transportation sought out the development of technologies to enhance infrastructure health monitoring. Specifically, the agency requested methods to improve data collection of sensor measurements over distributed points on highway bridges. The current methods of data collection used hard wire connections for data transmission, which resulted in increased labor and installation cots. Furthermore, the hardwire connections hinder the mobility of the data collection units and the ability to quickly measure a number of distributed points. In response to this problem, Invocon, Inc. designed a static, wireless, data acquisition and communications network as an experimentation tool to evaluate the performance of bridge structures under transient loads. The network incorporates two-way, RF, spread spectrum communications between distributed noes or units and a central collection unit. Spread spectrum technology reduces potential interference from other RF source while operating at low transmit power levels that preserve battery life and will not interfere with other communications.

This paper presents an application of experimental modal analysis testing technique for evaluating the structural properties of Fuge's bridge--a reinforced concrete (RC) bridge continuous over three spans which has been in-service since 1915 and later widened in 1939. The technique was able to identify the departure from the encastre support condition at the abutments and the damping properties for most significant modes of vibration. Result for the experimentally identified modal characteristics enabled the construction of a reliable finite element method model that could then be used with some degree of confidence for the prediction of the structural behavior of the bridge and its load carrying capacity. The advantages of dynamic testing as a tool for the identification of the in-service conditions of ageing bridge superstructures has been clearly demonstrated from this experience.

This paper describes a new thermal method, coating tolerant forced diffusion thermography, specifically designed to inspect large steel bridge structures. Coating tolerant thermography separates the effects of structural defects and variations in emissivity. The technique is a derivative of force diffusion thermography which uses patterned radiation to force heat flow in-plane to specifically target cracks. This paper presents the fundamentals of coating tolerant forced diffusion thermography including the mathematical bases for the separation of thermal gradients and emissivity gradients. Also presented are case studies including the inspection of a bridge girder.