An Investigation into Upward Tie Movements at Railroad Bridge Approaches in Time and Frequency Domains

Abstract

This manuscript presents time and frequency domain analyses of transient track displacements recorded under train passage at an instrumented bridge approach. Emphasis has been given to excessive upward tie movements that were recorded at the Near-Bridge Location (NBL), but not at the Open-Track Location (OTL). First, the displacement and acceleration time histories are analyzed in the time domain to identify different events associated with the tie lifting phenomenon. Next, the displacement and acceleration time histories are analyzed in the frequency domain to identify dominant frequencies governing the tie vibration at both NBL as well as OTL. A theoretical approach based on train dimensions and operating speed has been adopted to demarcate the dominant tie vibration frequencies associated with the passage of the train. The field data at NBL is observed to have two additional frequencies, 7.4 Hz and 9.2 Hz, that cannot be accounted for by the theoretical calculations. The upward movement of the tie has been linked to the vibration amplitude at 7.4 Hz. Therefore, the authors have emphasized the importance of combined time- and frequency-domain analysis while studying the transient track deformation trends at bridge approaches.

Keywords: Track Transition, Bridge Approach, Differential Movement, Frequency Domain, Upward Movement