# Acoustic Emission Monitoring in Prestressed Concrete:
## 4 Results  
### Wire Breaks on Girders  
The wire breaks were generated on the girders from Stolpe, Roding, and Witzenhausen. Figure 5 shows the amplitudes for the frequency bands depending on the distance between the signal source and the sensor. Each girder (\(A\) and \(B\)) is depicted in a separate subplot. Figure 6 shows the time-domain features. In general, the attenuation profiles presented demonstrate the expected trend, where amplitudes diminish as the distance from the signal source increases. This attenuation is least noticeable at lower frequencies, where the relationship between distance and amplitude reduction can sometimes appear nearly linear. However, with an increase in frequency the amplitudes decline more sharply, leading to nonlinear profiles characterized by a steep decrease in amplitude over distances up to 3 to 4 m. Beyond this point, the slope of the decrease lessens, suggesting that the frequency components have been almost entirely filtered out. This effect varies in magnitude across different girders; for instance, it is clearly visible in the case of girder \(A\) from Stolpe, whereas it is less pronounced in girder \(A\) from Witzenhausen. The observation is similarly reflected in the time-domain features. In Figure 7, the plots each represent data from one measurement campaign conducted on one tendon per girder. The nonlinear relationship between the variables is also evident to varying degrees. Despite this nonlinearity, employing linear regression across the full range of the abscissa for calculating the attenuation coefficients is deemed sufficiently precise for each scenario, aligning with standard practices. It is important to acknowledge, however, that this methodology tends, in absolute terms, to overestimate the attenuation coefficient at greater distances. Figure 6: _Cont._In Table 2, the attenuation coefficients documented reveal that the girders from Roding exhibit the highest values, indicating a significant increase in attenuation as the frequency rises as well, with girder \(A\) being particularly notable. This is partly attributed to the shorter length of the Roding girders, which limited the range of distances between the source and sensor that could be examined. For girder \(A\), it was only possible to measure distances up to approximately 3 m, leading to an overestimation of the attenuation coefficients in this case. Due to this lack of comparability, these values were excluded from the statistical analysis presented in Section 5. Moreover, there is a considerable variation in the cross-sectional dimensions of the girders. The girders from Witzenhausen are characterized by their slender profile in the section of the wires, while the Stolpe girders feature hollow bodies that locally reduce the cross-section, as detailed in [13]. In contrast, the Roding girders are significantly more massive and contain a large number of tendons, which act as major scatterers and contribute to increased attenuation. Nevertheless, the cross-sectional dimensions are likely the critical factor influencing these observations. The geometric dimension of the cross-section becomes apparent once the spherical wavefront originating from the source encounters the component's surface. In slender components, this occurs after shorter travel distances when compared to more massive components. Subsequently, the wavefront ceases to expand, apart from reflections, and when the curvature of the wavefront decreases, it effectively transforms itself into a planar wave. This phenomenon is also observed in the literature, where the spatial resolution of the wavefront is not sufficient to be measured. Figure 6: Frequency- dependent attenuation profiles of wire break signals for the girders \(A\) and \(B\) from Stolpe (BT500) **(a,b)**, Roding **(c,d)**, and Witzenhausen (**e,f**). Figure 7: Attenuation profiles of the time-domain features peak amplitude (**a**) and energy (**b**) for wire break signals for the girders from Stolpe (BT500), Roding, and Witzenhausen.