Daniel Algernon

Bridge Inspection and Condition Assessment in Europe

The European infrastructure asset has developed historically and is characterized by nation-specific construction processes. Inspection, condition assessment, and maintenance procedures differ from country to country. Because of historical and political circumstances, national infrastructure assets are maintained at different levels, too. Since the budget for maintaining the bridge infrastructure less and less meets the demands of a growing bridge stock, bridge inspection, maintenance, and life-cycle considerations gain higher importance. The need exists to develop effective diagnosis tools for early detection of construction faults, defects, and deterioration processes during inspection, to keep the bridge infrastructure at an acceptable level, from structural safety and economic viewpoints. An overview on the latest research projects and integrated bridge management systems in Europe is given. The potentials of nondestructive testing (NDT) are presented, with special focus on technical advances of NDT applications to reinforced concrete (RC) and posttensioned concrete bridges. Although NDT is not regularly integrated in these processes, the application brings valuable information on the current condition of the inner structure in called-in special inspections. NDT-automation and the application of imaging echo methods, combined with advanced data processing, produce a surprising level of information about the inner structure of massive RC slabs up to a depth of about 60 cm. Detected inhomogeneity and scatterers of acoustic or electromagnetic waves can be visualized in vertical or horizontal slices through the structure or animations. The fusion of different three-dimensional data sets of processed data improves the interpretability and accuracy of the results.

Impact Echo Data Analysis Based on Hilbert-Huang Transform

Impact echo is an acoustic method based on the use of transient stress waves generated by an elastic impact; it is used for nondestructive testing of concrete structures. In practical applications, the signals obtained often are superimposed by further mechanical vibrations and the so-called geometry effects, which are caused mainly by surface waves. Because of attenuation in the concrete as well as the divergence of the acoustical waves, impact echo signals are transient. As a result, the frequency content changes over time. Normally the analysis is carried out on the Fourier power spectrum of the signal. However, the Fourier spectrum is still affected by the mentioned effects and has well-known deficiencies for short transient signals within longer time sweeps. Application of the Hilbert-Huang transform is presented as a refined method for the time-frequency analysis of nonstationary impact echo data. The basic properties of the method and its practical application for time-frequency analysis of impact echo data, signal filtering, and pattern identification are presented.

Rebar Detection with Cover Meter and Ultrasonic Pulse Echo Combined with Automated Scanning System

A sufficient concrete cover is essential to ensure the durability of reinforced concrete structures. Nondestructive testing methods that can measure the concrete cover are therefore promising tools. As a part of a research project funded by the Florida Department of Transportation, the capabilities and limitations of cover meter measurements in relation to this testing problem were investigated. Researchers designed a reinforced concrete test block on which properties such as rebar depth, size, and spacing and number of reinforcement layers were varied; the effects these variations had on the measurements were studied. The use of an automated testing frame consisting of two scanners that examined the test block from both sides ensured high positioning accuracy and constant quality in data acquisition and made possible the collection of the data along an extremely dense grid. In addition to the cover meter measurements, which referred only to the cover of the layer closest to the surface, ultrasonic pulse echo measurements were conducted, and a synthetic aperture focusing technique was applied to the data to make the rebars become apparent in refined B-scan images.

NDT VALIDATION FACILITY AT THE FLORIDA DEPARTMENT OF TRANSPORTATION

Acoustic as well as electromagnetic methods can provide a valuable tool for the quality assessment of concrete bridges. For the efficient application in the field, the capabilities of the different methods in solving a specific testing problem have to be known. In a research project funded by the Florida Department of Transportation (FDOT) a first stage facility for the calibration and validation of NDT methods has been established. A test frame with two automated scanners has been designed and built, in which concrete blocks with artificial defects or testing problems can be tested by NDT methods such as ultrasonic‐echo, impact‐echo, covermeter or Ground Penetrating Radar. The most relevant testing problems dealt with in this project are the location of reinforcement steel, tendon duct inspections and thickness measurements. Furthermore, the capabilities and limitations of NDT methods in determining elastic parameters have also been investigated. 2D and 3D imaging techniques as well as signal processing such as the Synthetic Aperture Focusing Technique (SAFT) applied to the data provide a vivid representation of the results and make the interpretation easier and more intuitive. The capabilities and limitations of the different methods regarding the different testing problems are discussed.Acoustic as well as electromagnetic methods can provide a valuable tool for the quality assessment of concrete bridges. For the efficient application in the field, the capabilities of the different methods in solving a specific testing problem have to be known. In a research project funded by the Florida Department of Transportation (FDOT) a first stage facility for the calibration and validation of NDT methods has been established. A test frame with two automated scanners has been designed and built, in which concrete blocks with artificial defects or testing problems can be tested by NDT methods such as ultrasonic‐echo, impact‐echo, covermeter or Ground Penetrating Radar. The most relevant testing problems dealt with in this project are the location of reinforcement steel, tendon duct inspections and thickness measurements. Furthermore, the capabilities and limitations of NDT methods in determining elastic parameters have also been investigated. 2D and 3D imaging techniques as well as signal processing ...