Operational Modal Analysis on a Tied-Arch Railway Bridge

A case study to determine the natural frequencies and mode shapes from in-situ accelerational measurements

Master thesis (2022)

Authors

M. Benschop Civil Engineering & Geosciences

Contributors

E. Lourens Dynamics of Structures - CEG (supervisor 1)
A. Cabboi Mechanics and Physics of Structures - CEG (supervisor 1)
Coen van der Vliet ARCADIS Nederland (supervisor 1)
Faculty
Civil Engineering & Geosciences
Copyright: © 2022 Michiel Benschop
Dynamics of Structures Railway bridge Frequency Domain Decomposition Operational Modal Analysis Arch bridge
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Published Date

18-10-2022

Language

English

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Faculty

Civil Engineering & Geosciences

Abstract

Due to increasingly efficient engineering of the last decades, the design process for civil structures is heading in the direction of optimal solutions. Among other things, the reduction in self-weight enhances the susceptibility to dynamic loads. As the process for the determination of realistic modal parameters from a digital model often diverges from the reality, the uncertainties should be investigated. This research aims to gain knowledge on the accuracy and stability of such modal parameter estimates.

A case study is investigated to determine modal parameters for a realized tied-arch railway bridge. The desired modal properties include the natural frequencies, mode shapes and damping parameters. The frequency domain decomposition (FDD) method is applied on a set of accelerational measurements to determine the modal parameters.
Four dominant frequencies are identified and investigated, from which the most dominant operational deflection shapes are extracted. The overall response of the structure shows great similarities with the expected mode shapes for similar bridge types. The computed modes show signs of complex behaviour, due to the characteristics of the load or the structure. An effective method to reduce uncorrelated noise is the application of an autocorrelation function (ACF) to the time domain signals, before execution of the FDD. Prior to the computation of the final results related to the case study, a simplified test case is considered to validate correctness of the FDD implementation.