Modal Identification of a Railway Bridge Under Train Crossings: A Comparative Study

The existing railway bridge infrastructure of Europe is aging rapidly. Yet, rapid increases in technology and consumption bring about higher demands on railway bridges in the form of higher train speeds and axle loads. In order to ensure the safety of railway infrastructure, their dynamic response must be studied in detail and health be monitored. Vibration signatures of railway bridges are commonly used to fulfill these tasks. In particular, ambient or free vibration signals measured on railway bridges are utilized to determine their dynamic characteristics and, subsequently, to update the finite element models. However, the effects of train crossings on the dynamic behavior of bridges have not been investigated thoroughly via experimental testing. This study investigates the modal identification results of a five-span reinforced concrete railway bridge under different vibration sources. Specifically, it focuses on the variations in the dynamic behavior of the bridge observed under train crossings and those obtained from ambient vibrations. The bridge, whose dynamic response is under scrutiny, presents peculiarities in terms of its boundary conditions. They significantly differ from the original design and affect the dominant dynamic response. Fifty train crossing cases are examined, and their results are compared to those obtained using ambient and free vibrations. The results highlight the importance of bridge-train interaction and the influence of the structure's higher vibration modes. The implications of this interaction for model updating and damage detection are also addressed.