In the practical application of the Bridge Weigh-In-Motion (BWIM) methods, the position of the wheels or axles during the passage of a vehicle is a prerequisite in most cases. To avoid the use of conventional axle detectors and bridge type-specific methods, we propose a novel method for axle detection using accelerometers placed arbitrarily on a bridge. In order to develop a model that is as simple and comprehensible as possible, the axle detection task is implemented as a binary classification problem instead of a regression problem. The model is implemented as a Fully Convolutional Network to process signals in the form of Continuous Wavelet Transforms. This allows passages of any length to be processed in a single step with maximum efficiency while utilising multiple scales in a single evaluation. This allows our method to use acceleration signals from any location on the bridge structure and act as Virtual Axle Detectors (VADs) without being limited to specific structural types of bridges. To test the proposed method, we analysed 3787 train passages recorded on a steel trough railway bridge of a long-distance traffic line. Results of the measurement data show that our model detects 95% of the axles, which means that 128,599 out of 134,800 previously unseen axles were correctly detected. In total, 90% of the axles were detected with a maximum spatial error of 20 cm, at a maximum velocity of vmax=56.3m/s. The analysis shows that our developed model can use accelerometers as VADs even under real operating conditions.

Im Artikel wird das Schwingungsantwortverhalten von Eisenbahnbrücken infolge Zugüberfahrt unter Berücksichtigung von nichtlinearen Effekten untersucht und bewertet. Die betrachteten Nichtlinearitäten beziehen sich auf die bei realen Eisenbahnbrücken festgestellte Amplitudenabhängigkeit der Eigenfrequenzen. Im ersten Teil werden die bei durchgeführten dynamischen Messungen an realen Eisenbahnbrücken detektierten Nichtlinearitäten dargestellt und diskutiert. Der Fokus liegt dabei auf einfeldrigen Stahlbetonplattentragwerken mit Schotteroberbau. Die Grundlagen des nichtlinearen Duffing‐Schwingers mit unterlinearer Federkennlinie werden dargelegt und die besonderen Effekte von nichtlinearen Schwingungen werden erläutert. Im zweiten Teil werden numerische Simulationen der Zugüberfahrten unter Betrachtung von nichtlinearen Balkenmodellen durchgeführt. Bei den Simulationsberechnungen wird die Amplitudenabhängigkeit der Eigenfrequenzen berücksichtigt und die Tragwerksantworten bei Zugüberfahrt in der Form von Resonanzkurven dargestellt. Zu Vergleichszwecken werden die Berechnungen auch an linearen Balkenmodellen mit konstanten Eigenfrequenzen durchgeführt und die sich ergebenden Abweichungen diskutiert. Der Einfluss der untersuchten Nichtlinearitäten auf das Schwingungsverhalten von Eisenbahnbrücken wird herausgearbeitet und Empfehlungen für die zukünftige Berücksichtigung dieser Effekte bei dynamischen Berechnungen der Zugüberfahrt werden angegeben.

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Abstract. The microwave interferometry is a rather new measurement method, whose functioning principle allows the non-contact synchronous acquisition of structural displacements for several points along a structure, with accuracy in sub-millimetre range at a sampling rate of up to 4 kHz. Due to the high sampling rate, the acquisition of dynamic responses is also possible. Hence, main modal structural parameters such as natural frequencies and damping ratios can be straightforwardly identified. Furthermore, the synchronous measurement of several points along the targeted object, achieved due to a range resolution of about 0.75 m, may allow the direct determination of modal shapes. Under consideration of its novel character and a lack of previous experience with respect to railway-specific tasks, the measurement method had to be subjected to a systematic and comprehensive validation process prior to a reliable implementation in everyday practice. The validation process included several parallel measurements and comparisons with conventional measurement techniques. Besides the direct verification of the quality of the results, it was used as well for defining boundary conditions and limitations of the measurement method with respect to railway-specific applications. As a result, an evaluation matrix was created, which illustrates the applicability of the microwave interferometry for different types of structures. This paper gives a brief introduction of the microwave interferometry and presents some aspects and selected results of the validation process, which was performed within a cooperation project between the TU Darmstadt (Germany) and the German Railways (Deutsche Bahn AG).

<p>In 2019, the German Federal Railway Authority commissioned the consortium TU Darmstadt, KU Leuven, AIT-Austrian Institute of Technology and REVOTEC to develop a new dynamic load model for high-speed railway bridges. It aims to cover the envelopes of the dynamic train signatures and acceleration responses for all currently operating trains and the current HSLM (high-speed load model), given in the Eurocode. In addition, the development of the new load model should also include possible configurations of fast freight trains and future train configurations. An overview of the planned content of the research project and selected results of the current work will be presented.</p>

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