Hiroshi Haya

Damage Evaluation for Railway Structures by Means of Acoustic Emission

Sudden ground motions such as earthquakes sometimes cause serious damage in railway structures. For evaluating the structural integrity after the shock, damage condition of superstructures (or the upper part of substructures) is primarily investigated with the unaided eye. The results are basically subjective, and the structural integrity is evaluated only from the region that could be observed. Accordingly, in order to quantify the structural integrity objectively, an AE testing is tried to apply for the railway structures. In damaged concrete materials, it is known that secondary AE activity from existing defects are readily generated, and based on the Kaiser effect, damage degree could be quantified. In the monitoring of railway structures, however, except for AE signals from the defect, directly induced AE signals by the acceleration of the train passage could be detected. In the present paper, frequency characteristics of such AE signals as secondary AE signals and noise signals are elucidated through laboratory and in-situ experiments. The damage is quantified in an actual concrete pier based on the AE activity of raw AE data including noise signals, and extracted AE data generated from existing cracks, respectively. The results suggest that the quantitative evaluation of damage degree might be possible with the extracted AE activity, however, more data should be collected to classify damage degree reasonably. Introduction Civil structures in Japan were started to construct since 1950s to support the rapid increase of the economic and social infrastructure. At present they reached more than 50 years and aging or deterioration due to weathering, corrosion, earthquake, and so forth, have been inevitable among those. Accordingly, the maintenance of those aging structures has been becoming the key in civil engineering. As it has been expected to be a promising health monitoring technique, an Acoustic Emission (AE) technique has been studied since 1960s. Currently strong movement to make the AE monitoring standard in concrete engineering can be seen e.g., in the recommended practice for in-situ monitoring of concrete structures (NDIS 2421[1]). Since the standard was based on the laboratory studies [2], in practical AE applications however, there are some problems to be resolved. In the present paper, AE activity due to evolution of damage is shown schematically, and damage indices using in-situ AE activity are proposed. In order to extract AE signals from only defects (damaged areas), AE signals directly excited by mobile load are studied for the frequency characteristics. Finally the comparison is made in estimated damage levels between raw AE data and the extracted AE data, and the possibility for damage quantification using the AE activity is discussed. Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 1622-1630 doi:10.4028/www.scientific.net/KEM.270-273.1622

Ultrasonic velocity measurement for analysis of brick structure

In order to evaluate material properties of brick structures constructed for railroads more than one hundred years ago, ultrasonic velocity measurements were performed around Japanese island of Honshu, and relationships between ultrasonic velocity and material properties (compressive and tensile strength, and elastic modulus) of brick structure was analyzed. Ultrasonic velocity is related to mechanical properties of material; therefore strength of brick structures can be estimated from ultrasonic velocity measurements. It was found that there are significant relationships between ultrasonic velocity and material properties. Acoustic physical properties of brick structures were measured at the same time. A new cross-correlation velocity measurement method was developed. In this method, a 50-kHz Gaussian pulse was used with its spectrum is matched to the transducer bandwidth for effective enhancement of measurements in large attenuations, and received signal was cross-correlated with transmitted Gaussian pulse. This method was very much effective to noisy weak signals propagating through brick structures.