Methods for Extending the Service Life of Railway Bridges Using Active Elements

• Development of an active vibration mitigation system for steel trough bridges using boundary actuation
• Numerical and experimental investigations on the service life extension of steel trough bridges
• Comparison of the active system with state-of-the-art damping systems

A significant proportion of railway bridges in Germany and across Europe will reach the end of their planned service life within the coming decades, while at the same time the demands on rail transportation continue to increase. Train passages generate periodic loads that are primarily responsible for the excitation of structural vibrations. The relevant excitation frequencies depend on the respective train configuration and train speed. These cyclic loadings directly contribute to the fatigue of the structures and gradually reduce their load-bearing capacity over time. As a consequence, existing railway bridges often need to be replaced by new structures, particularly when repair and maintenance measures are no longer economically or technically feasible. However, demolition and reconstruction are associated with considerable economic costs, operational restrictions, and additional environmental impacts. Therefore, strategies for vibration reduction and, consequently, for extending the service life of existing structures are becoming increasingly important.

One promising strategy for extending the service life of railway bridges is the retrofitting of existing structures with active elements. This approach enables a targeted and active influence on the dynamic behavior of the structure without introducing significant additional weight.

Within the scope of this research project, the concept is investigated both experimentally and numerically using a steel trough bridge crossing the river Spree near Cottbus (see figure above). The active elements are integrated at the supports of the bridge.

The figure above illustrates that the existing bridge bearing, shown in green, is supplemented by a hydraulic cylinder. Due to its eccentric arrangement relative to the bridge support, the actuator can introduce an actively controllable boundary moment into the structure. This makes it possible to actively reduce vibrations caused by different train types and therefore by different excitation frequencies.

An important research question concerns the placement of the actuators. In order to minimize retrofitting efforts in future applications, the project investigates actuation applied at only one end of the steel trough bridge. Particular attention is given to the influence of unilateral actuation on higher asymmetric bending and torsional modes. For comparison, a configuration with actuation at both ends of the bridge is also examined. For both variants, the required actuation effort as well as the constraint forces introduced into the structure by the actuation are evaluated. In addition, the design of the support for the hydraulic cylinder and the anchorage of the large expected actuator forces represent significant engineering challenges.

Another important aspect of the project is the comparison with state-of-the-art damping systems. The active system is compared with passive, semi-active, and active tuned mass damper systems. The primary evaluation criterion is the achievable extension of the service life. The comparison is carried out both numerically and experimentally.

The research project is conducted in cooperation with academic and industrial partners. The University of Stuttgart Institute of System Dynamics is responsible for the control design of the active system. DB InfraGO AG and German Center for Rail Traffic Research provide the bridge for the investigations and contribute expertise in the field of train load modeling. Liebherr-Components Kirchdorf GmbH develops the required actuators. Maurer Engineering GmbH contributes its expertise in the field of vibration damping systems for bridges and the design of bridge bearings.

Project title:
Transfer Project T1 – Methods for Life Time Extension of Railway Bridges with Active Elements
Funding:
German Research Foundation (DFG), Colloborative Research Center CRC1244: "Adaptive Hüllen und Strukturen für die gebaute Umwelt von morgen", GEPRIS project number 279064222
Project partner:
Institut für Systemdynamik (ISYS), Universität Stuttgart
Cooperation partner:
DB InfraGo AG, Cottbus
Liebherr-Components Kirchdorf GmbH, Kirchdorf
Maurer Engineering GmbH, München
Deutsches Zentrum für Schienenverkehrsforschung beim Eisenbahn-Bundesamt, Dresden