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|Federal Highway Administration > Publications > NDEC News > Evaluation of NDE Technologies for Fatigue Crack Detection|
Publication: Volume 3, Issue 1
Date: March 2010
Evaluation of NDE Technologies for Fatigue Crack Detection
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According to the National Bridge Inspection Standards requirements, all publicly owned highway bridges (including steel bridges) that are longer than 20 ft (6 m) undergo an inspection at least once every 24 months. The United States has approximately 200,000 steel bridges; however, the inspection of steel bridges is primarily visual, followed by magnetic particle or dye penetrant inspection for validation purposes. The Federal Highway Administration (FHWA) Nondestructive Evaluation (NDE) Center is undertaking a program to evaluate NDE technologies and demonstrate advanced methods offering better accuracy, wider ranges of applicability and reduced costs.
The Steel Bridge Testing Program addresses the inspection issues in steel bridges that are primarily focused on detection and monitoring of fatigue cracks. The cyclic loads that bridges are subjected to over their lifetimes due to varying traffic patterns can result in fatigue cracks. Advanced NDE technologies can provide valuable information on the location of cracks, geometric features of cracks, and the status (active or stable) of cracks. The program has two phases: Phase I evaluated NDE technologies in a laboratory setup, and Phase II will involve field inspections of bridges. The NDE technologies were classified into two categories: crack detection technologies, and crack monitoring technologies. The crack detection technologies currently being evaluated under this program are the phased array ultrasonic testing (PAUT) systems, and the eddy current array sensors (ECAS). The electrochemical fatigue sensors (EFS) and acoustic emission (AE) systems are evaluated as a part of the crack monitoring technologies.
Figure 1. Graph. Composite Scan Image from PAUT System.
PAUT systems are advanced ultrasonic inspection systems that can electronically steer and focus ultrasonic beams. This steering capability enables the user to inspect components without moving the probe. In addition, the commercial probes currently available, enable probe selection based on the thickness of the component under inspection and the accuracy of flaw sizing needed. PAUT systems are designed to locate and size surface and subsurface cracks, and can also be used to detect porosity and lack of fusion in welds. PAUT systems offer a variety of scanning options that include linear, sectorial, lateral, combination, and depth focusing.
Developing a New NDE Tool for Rapid Load Testing of Highway Bridges
Data from the National Bridge Inventory indicate that the Nation has a large population of bridges with an average age of 42 years. There is an urgent need to quickly measure the load rating of these aged bridges. The FHWA NDE Center is working to develop an NDE tool for rapid bridge load rating applications. The research will integrate microwave interferometric radar scanning, and advanced chaos theory analysis techniques into a unique, rapid, detecting system, which can collect bridge responses remotely from large numbers of critical locations and conduct advanced analysis to determine a bridge load rating.
Microwave interferometric radar scanning is a ground based radar device that can measure wide areas, and remotely monitor vibrations of a bridge structure under various loading conditions. Chaos theory analysis is a new technique that uses modern nonlinear chaotic dynamics, information theory, and topologic dynamics analysis for extracting nonlinear system invariants for structural health condition monitoring applications. These nonlinear system invariants can be used to characterize the inherent nonlinear behavior of a general nonlinear system and reveal potential local instabilities due to changes in aging structures.
The focus of this research is to develop a working NDE screening tool for rapid bridge load rating applications. FHWA NDE Center staff will use the microwave interferometric radar scanning technique to collect real-time bridge vibrations under various load conditions from large numbers of critical locations on a bridge structure. The staff then will use chaos theory analysis to conduct advanced analysis to provide rapid condition assessment, and determine a bridge load rating. The development of such a new NDE system will simplify the bridge load rating process and provide better information in revealing bridge load behaviors and capacities.
Figure 2. Graph. An example of chaos
theory analysis of bridge vibrations to
Figure 3. Photo. The research
concept—rapid load rating application using a new NDE detecting
Figure 6. Photo. Bridge deck specimen with reinforcing bars.
Figure 7. Photo. Prestressed concrete specimen with untensioned tendon strands.
Figure 8. Photo.
Half-automated scanner with bridge deck specimen with reinforcing
bars (top) and specimen with
A data acquisition system was set up to monitor the corrosion process by collecting potential, current, resistance, and temperature data—including that from an embedded anodeladder system. The methods used for half-automated NDT structural health monitoring consist of half-cell potential, an advanced ultrasonic linear array for early crack detection, 0.9 and 2.3 GHz ground penetrating radar (GPR), a 10 GHz microwave camera, and infrared thermography with induction heater. Using induction thermography, the rebar can be heated in the concrete by using an alternating current electrical induction heater, external to the concrete structure. The half-automated NDE scanner system setup in the NDE Center with support of upward vertical motion (UVM) is shown in figure 8.
The main goal of this study is to promote the use of NDE as a tool for bridge maintenance and preservation by performing periodic baseline NDE measurements.
NDE Center Program Manager
Federal Highway Administration
Tel: (202) 493-3082
NDEC NEWS is the newsletter of the Federal Highway Administration's (FHWA) Nondestructive Evaluation (NDE) Center.
The FHWA NDE Center was established in 1998. The objective of the NDE Center is to improve the state of the practice for highway bridge inspection. The NDE Center is a resource for State transportation agencies, industry, and academia involved in the development and testing of innovative NDE technologies. The NDE Center provides State highway agencies with independent evaluation and validation of NDE technologies, develops new NDE technologies, and provides technical assistance to States exploring the use of these advanced technologies. The NDE Center uses a series of unique resources to assess the factors affecting the reliability and performance of NDE systems.
The NDE Center is located at the Turner-Fairbank Highway Research Center in McLean, VA. To supplement the capabilities of these laboratory facilities, a series of bridges located in northern Virginia and southern Maryland are used to conduct field investigations. In addition, a collection of component test specimens are used in various test programs.
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Topics: Research, Infrastructure, Nondestructive Evaluation, Testing
Keywords: Research, Infrastructure, Nondestructive Evaluation, Testing