Special Issue on Nondestructive Evaluation and Testing for Bridge Inspection and Evaluation

I served as the guest editor of the July/August 2010 issue of the Journal of Bridge Engineering. During the last 2 years, partly because of the failure of the I-35 Bridge in Minnesota in 2007 and other incidents, there has been significant focus and healthy discussion among bridge infrastructure stakeholders, including several elected leaders, in using nondestructive methodologies in assisting bridge inspection, evaluation, and maintenance. At present, nondestructive evaluation and testing (NDE/NDT) methods, such as ground penetrating radar and infrared thermography, are being commonly used by most transportation agencies. Several federal and state agencies are funding significant resources in developing and researching nondestructive test methods for quantitative evaluation of bridge infrastructure to augment visual inspection data. This special issue presents some of the recent advances and applications of nondestructive test methods and structural health monitoring for bridge evaluation and management.

A majority of bridge failures are attributed to scour damage that is hard to detect in real time and appropriate preventive measures that are hard to apply when scour damage is detected. Hence, scour monitoring is an important topic for transportation owners, especially during high-flood events and in coastal areas. The technical paper “Vibration-Based Method and Sensor for Monitoring of Bridge Scour” by Zarafshan et al. introduces a new fiber-optic Bragg grating (FBG) scour sensor. The scour-depth detection is based on the inverse relationship between the fundamental frequency and the length of the sensor rod embedded in the riverbed. This paper describes development of the theoretical basis for the sensor, computational methodology for detection of the riverbed foundation properties, laboratory and small-scale field verification tests, and installation and remote monitoring of scour in a multispan scour critical bridge in Illinois.

Cable-stayed bridges are increasingly popular in the United States because of their elegance and the advantages they offer for relatively long spans. When these unique bridges are built, several design assumptions are made and may have to be verified after their construction. A cable-stayed bridge was recently constructed by the Ohio Department of Transportation. Following recent trends, the stays at this bridge were built without the use of grout for the purposes of inspection and possible replacement in the future. The bridge incorporated measures put forth to mitigate stay motion. The technical paper “Cable-Stayed Bridges: Case Study for Ambient Vibration-Based Cable Tension Estimation” by Kangas et al. presents experiments that were performed to determine the viability of using traditional vibration techniques that assume an integral sheath to estimate cable tension with this new configuration. Acoustic emission (AE)-based techniques have been widely used for detecting breaks in suspension and cable-stayed bridges. The technical paper “Detection of the Presence of Broken Wires in Cables by Acoustic Emission Inspection” by Zejli et al. studies AE techniques to detect the presence and location of broken wires in anchorages.

Structural health monitoring (SHM) is becoming popular in bridge monitoring. System configuration is very important to effectively monitor performance parameters of interest. The technical paper “Measurement System Configuration for Damage Identification of Continuously Monitored Structures” by Laory et al. discusses a systematic approach to determine the appropriate number and location of sensors to configure measurement systems in which static measurement data are interpreted for damage detection using model-free (nonphysics-based) methods. A railway truss bridge in Zangenberg, Germany, is used as a case study to illustrate the applicability of this proposed approach. The technical paper “Approach to Reduce the Limitations of Modal Identification in Damage Detection Using Limited Field Data for Nondestructive Structural Health Monitoring of a Cable-Stayed Concrete Bridge” by Ismail et al. proposes a technique to reduce the limitations of modal identification in damage detection using reduced field data for nondestructive SHM of a cable-stayed concrete bridge.

Use of monitoring systems for bridge maintenance is also gaining popularity. The technical note “Automated Ice Inference and Monitoring on the Veterans' Glass City Skyway Bridge” by Kumpf et al. presents an ice inference system installed on Veterans' Glass City Skyway (VGCS) Bridge to assist the Ohio Department of Transportation in managing the response to icing events. Variation in modal properties because of the environment has to be studied before they can be correlated to possible structural damage. If variation in modal properties, caused by temperature variations to which the structure is subjected, is less than the variation caused by the damage of interest, this method cannot be reliably used for damage detection. Hence, the technical note “Effect of Temperature on Daily Modal Variability of a Steel-Concrete Composite Bridge” by Mosavi et al. investigated the effect of temperature variations on modal characteristics of a two-span, steel-concrete composite bridge in North Carolina, and addresses the extent and reason of the daily changes observed in its dynamic properties.

The deck is a major component of a bridge structure and is in direct contact with live traffic, subjected to inclement weather, and deicing salts are directly applied over it. Deck performance directly affects the durability and life-cycle costs of a bridge. The technical paper “In-Service Condition Assessment of Bridge Deck Using Long-Term Monitoring Data of Strain Response” by Ni et al. focuses on obtaining information of interest (such as peak stress distribution and dynamic internal forces) to structural engineers using data from the instrumented Tsing Ma Bridge. Inspection and evaluation considerations are very important from planning and design stages to preserve the structural health and durability while minimizing life-cycle costs. The technical paper “Damage Evaluation for Concrete Bridge Deck by Means of Stress Wave Techniques” by Shiotani et al. focuses on detection of the fatigue damage of concrete bridge decks utilizing propagation of stress waves. This experimental study concludes that by using sparsely arrayed AE technology, global integrity of bridge decks could be carried out so that local NDE methods can be employed for further investigation of areas of interest. Use of ground penetrating radar, impact echo, and infrared thermography based techniques are widely used by bridge owners to augment visual inspection data from bridge decks for informed decisions related to deck rehabilitation versus replacement. The technical paper “Nondestructive Bridge Deck Testing with Air-Coupled Impact-Echo and Infrared Thermography” by Kee et al. compares air-coupled impact echo and infrared thermography on a full-scale simulated reinforced concrete bridge deck containing simulated delamination and cracking defects. They conclude that the combination of both techniques is a practical option for consistent and rapid in situ evaluation of reinforced concrete bridge decks. The technical paper “Automatic Delamination Detection of Concrete Bridge Decks Using Impact Signals” by Zhang et al. describes the automatic impact-based delamination detection system that was developed to eliminate traffic noise by a modified version of independent component analysis. They evaluated the system using data from two bridges and found that the results were satisfactory.

Remote sensing is gaining popularity for evaluation of bridge condition, but there are several technologies available for users with varying capabilities, advantages, and disadvantages. The technical paper “Evaluation of Commercially Available Remote Sensors for Highway Bridge Condition Assessment” by Vaghefi et al. discusses evaluations of 12 potential remote sensing technologies for bridge deck and superstructure condition assessment. Each technology was rated for accuracy, commercial availability, cost of measurement, precollection preparation, complexity of analysis and interpretation, ease of data collection, stand-off distance, and traffic disruption.

Hundreds of bridges built decades ago lack foundation data, and evaluating scour potential in many of these cases has been difficult. The technical paper “Cone Penetration Test–Based Ultrasonic Probe for P-Wave Reflection Imaging of Embedded Objects” by Coe and Brandenberg presents an ultrasonic P-wave reflection imaging probe to noninvasively image the geometry of a deep foundation supporting a bridge pier. The custom transducer probe and data acquisition hardware were integrated into a system with a cone penetration testing (CPT) truck. The probe successfully imaged a pile foundation in very soft saturated clay, but not in stiffer and/or unsaturated soils. Thus, the probe could be used as a nondestructive quality assurance tool for structural elements constructed in soft saturated soils.

Detection of extent of corrosion in prestressing strands in adjacent precast prestressed concrete box-beam bridges has been a major topic of interest for all the transportation agencies because of the bridges' age, condition, and difficulty in evaluating capacity. The technical note “Field Test of Magnetic Methods for Corrosion Detection in Prestressing Strands in Adjacent Box-Beam Bridges” by Fernandes et al. reports the evaluation of magnetic flux leakage and induced magnetic field methods for condition evaluation of a bridge that was scheduled for replacement. They conclude that both magnetic field methods were able to reliably estimate corrosion by detecting the effective cross-sectional area of strand. The technical paper “Detection of Initial Yield and Onset of Failure in Bonded Post tensioned Concrete Beams” by Salamone et al. discusses monitoring of bonded post-tensioning (PT) concrete elements using the AE technique. In particular, a statistical pattern recognition technique based on a multivariate outlier analysis is presented to identify initial yielding and the onset of failure. Experimental tests on large-scale single-tendon bonded PT concrete beams subjected to multiple load cycles were presented to validate the proposed monitoring system.

Accuracy of nondestructive techniques is a subject of interest because use of these methods is being advocated more these days. The technical paper “Fatigue Reliability Updating Evaluation of Existing Steel Bridges” by Wang et al. presents a procedure for assessing and updating the fatigue reliability of existing steel bridge components using the probabilistic characteristics of the nondestructive inspection techniques, the probabilistic fatigue failure method, and the Bayes theorem. Data collected from two steel bridges were used to illustrate the fatigue reliability assessment and updating method.

It is hard to evaluate several test methods and techniques using the same test structure or the same dataset. The technical paper “Test bed for Structural Health Monitoring of Long-Span Suspension Bridges” by Xu et al. discusses establishment of an innovative test bed in a laboratory to allow researchers to recreate rational damage scenarios, to apply different sensors and sensing networks, and to test various damage detection algorithms. This test bed, composed of the delicate physical model and the updated finite-element model of a long-span suspension bridge, could solve a benchmark problem for the structural health monitoring of long-span suspension bridges. Similarly, the technical paper “Hybrid Simulation Test bed for Experimental Validation and Characterization of NDE and Sensor Technology” by Mercado and Zhang demonstrates the use of a hybrid testing setup to create a characterization test bed for more realistic evaluation of NDE and sensor technologies. A prototype bridge structure based on the Yellow Mill Pond Bridge in Connecticut was selected to demonstrate the features and issues of a hybrid simulation test bed for sensor characterization, such as flexibility in traffic-load representation and large-scale specimens, even with small testing equipment. Although a strain gauge was used to demonstrate the technology, the sensor test bed might be used for general characterization of other types of NDE devices and sensors.

All these papers present recent advances in NDE and SHM of bridge structures. All these advances show the promise in use of these technologies to improve bridge evaluation. At the same time, none of the papers discuss cost benefits (or value) of using these technologies in detail. If new technologies and methods cannot be justified based on cost-benefit analyses, progress in this field will be relatively limited. I encourage all the researchers and practitioners to work together to document the cost-benefit (or value) of the latest methods and to augment their future papers. The research should also consider the data that drive the decision making of infrastructure owners from the research planning to implementation with the focus to add value. Only then can the use of NDT/NDE and SHM in mainstream bridge engineering practice be truly advanced.

In conclusion, performance-based bridge management and risk-based inspection intervals are under consideration by regulating agencies. Innovative design and construction methodologies such as design-build and design-build-maintain approaches and innovative funding options (e.g., public-private financing) are also increasingly considered by transportation owners. NDT methodologies and SHM will play a major role in the coming years to effectively manage infrastructure. At the same time, caution is recommended before widely using any such methodology. A method should be used only after careful cost-benefit analysis to determine their value in both the short and long term.

I thank all the authors for their submissions and their patience during the review process. All the papers for the special issue were peer reviewed strictly following the ASCE Journal of Bridge Engineering peer review guidelines. I thank the paper reviewers for their valuable time spent in reviewing all the papers and providing constructive comments that enhanced the papers’ quality to maximize the benefit to the bridge engineering community. I also thank other associate editors who helped in the review process because of the large number of articles received in response to the call for technical papers. Finally, I thank the ASCE journal staff and the chief editor, Dr. Anil Agrawal, for providing required assistance in delivering this special issue on NDE/NDT for Bridge Inspection and Evaluation.