# Acoustic Emission Monitoring in Prestressed Concrete:
###### Abstract  
Acoustic emission monitoring (AEM) has emerged as an effective technique for detecting wire breaks resulting from, e.g., stress corrosion cracking, and its application on prestressed concrete bridges is increasing. The success of this monitoring measure depends crucially on a carefully designed sensor layout. For this, the attenuation of elastic waves within the structure's material is ideally determined in situ through object-related measurements (ORMs) with a reproducible signal source, typically a rebound hammer. This assumes that the attenuation coefficients derived from rebound hammer tests are comparable to those from wire breaks, thus allowing their results to be directly applied to wire break detection without further adjustments. This study challenges this assumption by analysing attenuation behaviour through an extensive dataset. Employing time-domain and frequency analysis, the research generates attenuation profiles from laboratory experiments and in situ measurements across various girders and bridge structures, extracting the slope and residual standard deviation (RSD). While generally validating this approach, the findings highlight differences in attenuation behaviour from among wire break signals and rebound hammer impulses, whereby the latter potentially underestimates the relevant attenuation of wire breaks by approximately 20%. Consequently, a transfer factor is proposed to adjust ORM results obtained with the rebound hammer for wire break scenarios. It consists of a scaling factor of 1.2 to modify the average attenuation coefficient and a constant term of \(\pm 1.0\,\mathrm{dB/m}\) to cover a 95% confidence interval, and thus, account for sample scattering. Moreover, the anisotropic attenuation behaviour across different structures was studied, showing that transverse attenuation consistently exceeds the longitudinal, significantly influenced by structural features such as voids. In prefabricated concrete bridges with in situ-cast concrete slabs, transverse signal transmission remains unhindered across multiple elements. Finally, the results provide a valuable reference for the design of sensor layouts in bridge monitoring, particularly benefiting scenarios where direct in situ experiences are lacking. acoustic emission; non-destructive testing; structural health monitoring; wire break detection; post-tensioned concrete; bridges; attenuation analysis +
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not only to prestressed concrete bridges, but also to monitor damage to cables in suspension and cable-stayed bridges [8; 9; 10; 11]. The implementation of AEM in civil engineering is mostly non-standardized, and the application of this measurement technique requires specialized expertise. This often results in contractors having difficulty verifying or evaluating the technical specifications or measurement data for plausibility. Moreover, the uniqueness of each bridge in terms of its construction and its specific loading and environmental conditions necessitates a tailored assessment approach. In combination, these aspects contribute to considerable variability in the execution and quality of technical solutions. In this context, the Acoustic Emission Testing Committee of the German Society for Non-Destructive Testing (_DGZP_) recently published guideline SE05, providing a detailed instruction manual for AEM implementation in Germany. This guideline consolidates best practices, establishes fundamental aspects, and offers a procedural guide for projects [12]. For the successful implementation of AEM, a carefully designed sensor layout for the affected structure is essential. This layout must enable the detection of wire breaks with sufficient reliability and is one of the most important prerequisites for the success of the monitoring. The design is based on three central input parameters:  
* the characteristics and intensity of the source signal;
* the material- or structure-specific attenuation;
* the intensity of the background noise to define the detection threshold.