Since 2008, the following projects have been completed by the Nondestructive Evaluation (NDE) Laboratory:

The Evaluation of Section Loss Due to Corrosion in Single and Multiplate Gusset Connections Using Nondestructive Technologies (NDT) provided an initial examination of the capabilities of NDT systems for the inspection of steel truss gusset plates. The study focused on two ultrasonic testing systems: 1) a phased array ultrasonic system, and 2) a conventional single-element dry-coupled ultrasonic system. The results from tests on single plates ranging from 0.36 to 0.74 inches in thickness and with various geometries of section loss were presented and compared. A feasibility study for the inspection of hidden corrosion in multiplate gusset plate connections was also presented.

The Steel Bridge Testing Program (SBTP) focused on detecting and characterizing fatigue cracks on steel girders at high-stress or critical detail locations where the presence of growing cracks is possible. In addition, locations with high concentrations of stress, particularly at steel weldments and sharp corners, were of interest. Several advanced commercially available crack detection and crack growth detection (i.e., crack monitoring) technologies were evaluated through an in-depth laboratory testing, phase I. In phase II, testing of these technologies was conducted in the field and at actual bridge sites.

The objective of the Load and Resistance Factor Rating (LRFR) Procedures for the Response-Based Rapid Load Rating of the Steel Bridges project was to develop procedures and tools (e.g., hardware, software, algorithms, and equations) for converting field strain measurements into load rating for bridges that have calculated load ratings requiring them to be posted. The objective was to improve existing ratings of deficient steel bridges to benefit from field measurements representing the actual bridge response to actual bridge loads, and from Load and Resistance Factor Design (LRFD)/LRFR reliability theory. This response-based approach expedites load testing and rating, and alleviates the expense and logistics of conducting a bridge load test, the need to collect detailed traffic, and the development and execution of a calibrated finite element model and analysis of the bridge.

The objective of the LRFR Procedures for Response-Based Rapid Load Rating of Prestressed Concrete Bridges project was to produce an LRFR procedure and tools (e.g., hardware, software, algorithms, and/or equations) for converting field strain measurements into load rating for prestressed concrete bridges that have calculated load ratings requiring them to be posted. Additionally, the objective was to improve existing ratings of deficient prestressed concrete bridges to benefit from field measurements representing the actual bridge response to actual bridge loads, and from LRFD/LRFR reliability theory. This response-based approach will expedite load testing and rating, and alleviate the expense and logistics of conducting a bridge load test, the need to collect detailed traffic, and the development and execution of a calibrated finite element model and analysis of the bridge.

The objective of the Study of Local Vibrations in Stressed Steel Beams was to validate protocols for the selection and placement of sensors and data acquisition to effectively monitor salient features of local vibratory response in a steel beam in flexure and to test the ability to analyze vibratory response signature under controlled impact loading and isolate salient modes, and finally to quantify the correlation and variability between vibratory response and flexural stress magnitude.

The FAST NDE Lab initiated the development of InfoTechnology, a web tool for assisting bridge practitioners with the proper selection of NDE technologies for the condition assessment of  highway infrastructures, including bridges, pavements, and tunnels. This tool provides information about  the target of investigation, description, physical principle, data acquisition, data processing, data interpretation, advantages, and limitations of a broad range of NDE technologies. The current version supports NDE technology search based on the asset type (i.e., bridges, pavements, or tunnels) or material (i.e., concrete, steel, or timber).

A study was completed on the Performance Evaluation of Bridge Weigh-in-Motion (WIM) Systems. The objectives of this project are to identify and compare the accuracy of WIM systems for bridge applications. This evaluation will compare capabilities with respect to providing repeatable, research-quality measurements of axle weight and spacing, vehicle speed, and identification of vehicle classification for trucks as they pass over bridge structures.

An effective and promising solution to the time-consuming process of inspecting highway structures using conventional acoustic techniques is to eliminate the need for physical contact between the sensors and a structure through the application of contactless acoustic sensors. In the study, Robotic Air-Coupled Acoustic Array for High Speed Nondestructive Evaluation of Highway Structures, researchers at the FHWA’s Advanced Sensing Technology (FAST) NDE laboratory used contactless acoustic receivers to develop a noncontact, air-coupled acoustic array to inspect bridge decks. This air-coupled system is mounted on a robotic platform for the high-speed inspection of bridge decks. The hardware and software parts of the device are substantially improved to reduce noise, and accurately measure the acoustic response of concrete. The device uses 40 microelectromechanical systems (MEMS) microphones to capture stress waves, which are further analyzed to evaluate the phase velocity and impact-echo response of concrete. This air-coupled system is mounted on a robotic platform for the high-speed inspection of bridge decks.

A study was completed to explore the use of unmanned aerial systems (UAS) to support bridge inspection. The study assessed UAS platforms and sensors used to assist or augment inspections, the data-collection needs that UAS can meet, and the means and methods for managing the tremendous amount of data that can be collected by UAS-mounted sensors. The study also illustrated real-world applications of UAS for bridge inspections, and the results of both field and laboratory testing geared toward establishing standards and requirements for UAS sensors that will ensure quality inspection products. This study will be informative to bridge owners, engineers, and inspectors as well as UAS operators with an interest in bridge inspections. Additionally, the information in the report may be of interest to UAS sensor and system manufacturers as they continue to advance the technologies for the benefit of the transportation infrastructure industry.

A study was completed to evaluate integrating both nondestructive evaluation (NDE) data and field data from structural health monitoring (SHM) to obtain load ratings that reliably represent a bridge’s load-carrying performance. The load rating is one of the most common methodologies for evaluating the load carrying performance of a bridge, whereby the capacity of individual members is compared to the dead-load and live-load demands. This work provides guidance on how to integrate both nondestructive evaluation (NDE) data and field-data from structural health monitoring (SHM) to obtain load ratings that more reliably represent a bridge’s load-carrying performance.

A study was completed on the evaluation of concrete bridge deck overlays using nondestructive evaluation techniques.  The goal of this study was to identify and describe the effective and promising NDE techniques that can inspect a concrete bridge deck through various types of overlays, and detect and characterize deterioration in deck overlays.

The FAST NDE lab evaluated two magnetic-based NDE systems for corrosion detection in prestressed and post-tensioned tendons and anchorage zones. For the external tendons, two types of magnetic main flux method (MMFM) systems—a solenoid type and a permanent magnet type—were validated in the laboratory and in the field. The solenoid-type MMFM system was the most accurate NDE method. For corrosion detection in prestressed concrete structures, the Magnetic Flux Leakage (MFL) technique was evaluated. This project led to the design and fabrication of a robotic transport system (the robotic rover) that facilitates the scanning of the underside of PS concrete bridge I-girders with a newly developed magnetic flux leakage (MFL) NDT system (the payload). The NDT payload (magnets/sensors assembly) uses the magnetic flux leakage concept to detect corrosion of prestressing steel within concrete. The robotic rover and NDT payload are designed and fabricated as two modular sub-systems that operate independently. This concept allows the new NDT payload to be easily removed and replaced with another payload sub-system equipped with a different NDT device/concept to facilitate complimentary NDT assessment of PS concrete I-girders in bridges.

A study was completed to develop recipes for concrete reference specimens representing at least four common problems in concrete structures, and to develop a framework for a quantitative performance comparison of NDE methods for concrete bridges. These four testing problems include corrosion (or section loss) of reinforcement or prestressed tendons embedded in concrete, vertical cracks, delamination, and honeycombs. The recipe procedures are being defined and established in a way that the reference specimen is easily reproducible in any laboratory. These specimens can be utilized for comparing service providers, comparing methods, validation, benchmarking research and development, definition of test task, specification of work, training, and certification.