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Use of Nondestructive Testing in Bridge Inspection and Evaluation Practice Sreenivas Alampalli, Ph.D., P.E., MBA The role of infrastructure in modern societies is multifaceted, as noted in President Obama’s inaugural speech on January 20, 2009: “We will build the roads and bridges, the electrical grids and digital lines that feed our commerce and bind us together.” Bridge and highway infrastructure are not viewed as just a means to move people and goods from one place to another, but also as a backbone of commerce. Thus, mobility, reliability, economic advantage, and security, as well as safety, are all becoming important performance measures for owners in a resource-constrained environment. At the same time, new materials and innovative construction methods are also becoming popular for the advantages they offer, such as quick construction to minimize traffic interruptions. Preserving the infrastructure of the United States is dependent on the successful implementation of advanced technology, such as nondestructive testing (NDT) methods and engineering structural health concepts, into routine evaluation to implement objective decision-making processes for effective asset management. Even though visual inspection is still predominantly used, bridge inspection techniques and technologies have been ever-evolving since the National Bridge Inspection Standards (NBIS) were established by the Federal Highway Administration (FHWA) over 50 years ago. The origins of current bridge inspection practices can be traced to the collapse of the Ohio River Bridge (known as the “Silver Bridge”) between Point Pleasant, West Virginia, and Kanauga, Ohio, in 1967. Following this tragedy, which killed 46 people, the FHWA Act of 1968 led to the establishment of NBIS, which led to systematic periodic inspections by qualified personnel and is the basis for the current NBIS. The NBIS has been modified several times, including after the failure of the Mianus River Bridge in Greenwich, Connecticut, and the Schoharie Creek Bridge near Fort Hunter, New York, which led to fracture-critical and underwater bridge inspections with established intervals. As technology has advanced, so have the tools and techniques that have become available to a bridge inspector. Periodic visual inspection, with qualified and trained inspectors using prescribed manuals and methods, is the primary technique used to perform bridge inspections. Standard bridge inspection is performed using a two-tier process: routine inspection that can trigger more detailed “in-depth” or “special” inspection. In addition to these procedures, analytical ratings of bridge load capacity are
Figure 1. Use of Infrared Thermography for detecting delamination between fiber reinforced polymers and concrete.
Vol 24, 3 2019
carried out as needed to reflect the bridge condition observed during the inspection, and inspection of underwater structures is performed generally by divers at least once every 60 months. Nondestructive evaluation (NDE) methods are becoming popular for augmenting visual inspections. Even though routine inspection essentially consists of common tools, for the last two decades or more, these have been supplemented by some very basic testing tools such as a chain drag and hammer for concrete members and dye penetrant and magnetic particle testing for steel members. Ultrasonic testing is used routinely as a second level of NDE when inspectors request further investigation, as well as during steel member fabrication. During the last decade, the use of ground penetrating radar (GPR) for evaluating bridge deck condition for planning further repair and rehabilitation actions has been increasing steadily. With the use of new materials such as fiber-reinforced polymers for bridge decks and concrete member wrapping, use of NDT methods, such as thermal/infrared testing, is also used for construction quality control as well as for periodic inspection (Figure 1). Each of the NDE methods has its own advantages and disadvantages for infrastructure inspection. Combining several methods may yield higher reliability of the results by taking advantage of the efficiencies of individual methods. Type, location, accessibility, and condition of a bridge as well as the type of inspection are some of the factors that determine what techniques are used. Table 1 presents a brief synopsis of typical bridge elements and some of the standard inspection and NDE tools available to address the concerns previously described. Additionally, there are several systems that can be used to monitor a bridge to provide real-time data and alert the owner of such things as failure of load-carrying members, excessive rotation or displacement of an element, overload in a member, crack growth, scour around bridge piers, or occurrence of a significant flood event. The type of information provided is typically very specific and provides data on isolated areas or members of the bridge. The most practical of these systems are being used by owners during “in-depth” or “special” inspections or implemented for long-term monitoring. The technology in this sector is advancing rapidly with more and more owners starting to experiment and incorporate these into their asset management practices. Future trends include: • More widespread use of NDE systems as part of visual inspection, such as use of augmented reality and technology fusion for data visualization (Figure 2). • Use of advanced multi-sensor robotic platforms (Figure 3), such as unmanned ground-based systems (UGS), unmanned aerial systems (UAS), and unmanned water-based systems (UWS). Automation in both multi-sensor data collection and data processing has resulted in near real-time data images. • Large-scale wired and wireless sensor networks for bridge structural health monitoring (SHM). • Use of artificial intelligence (AI) and deep learning for data analysis. • Remote sensing using satellite-based technologies for system-wide monitoring of the structural assets as a first level of monitoring.
