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Application of the continuous wavelet transform on the free vibrations of a steel-concrete composite railway bridge
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.ORCID iD: 0000-0002-5447-2068
2011 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 33, no 3, 911-919 p.Article in journal (Refereed) Published
Abstract [en]

In this article, the Continuous Wavelet Transform (CWT) is used to study the amplitude dependency of the natural frequency and the equivalent viscous modal damping ratio of the first vertical bending mode of a ballasted, single span, concrete steel composite railway bridge. It is shown that for the observed range of acceleration amplitudes, a linear relation exists between both the natural frequency and the equivalent viscous modal damping ratio and the amplitude of vibration. This result was obtained by an analysis based on the CWT of the free vibrations after the passage of a number of freight trains. The natural frequency was found to decrease with increasing amplitude of vibration and the corresponding damping ratio increased with increasing amplitude of vibration. This may, given that further research efforts have been made, have implications on the choice of damping ratios for theoretical studies aiming at upgrading existing bridges and in the design of new bridges for high speed trains. The analysis procedure is validated by means of an alternative analysis technique using the least squares method to fit a linear oscillator to consecutive, windowed parts of the studied signals. In this particular case, the two analysis procedures produce essentially the same result.

Place, publisher, year, edition, pages
2011. Vol. 33, no 3, 911-919 p.
Keyword [en]
Railway bridges, Steel concrete composite bridge, Train induced vibrations, Continuous wavelet transform, System identification
National Category
Civil Engineering
Identifiers
URN: urn:nbn:se:kth:diva-31633DOI: 10.1016/j.engstruct.2010.12.012ISI: 000287901300021Scopus ID: 2-s2.0-79251597214OAI: oai:DiVA.org:kth-31633DiVA: diva2:405470
Note
QC 20110322Available from: 2011-03-22 Created: 2011-03-21 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Essential modelling details in dynamic FE-analyses of railway bridges
Open this publication in new window or tab >>Essential modelling details in dynamic FE-analyses of railway bridges
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The increased need to reduce the use of fossil fuels imposes higher demands on the efficiency of rail transportation. Therefore, an improved knowledge regarding the dynamic properties of railway bridges and infrastructure for railway traffic in general is required. Typically, increased train speed, longer trains and increased axle loads increase the dynamic response in railway bridges. Modelling details for bridge structures such as the flexibility of the foundations, radiation damping in the subsoil and the embankments as well as hysteretic effects in bridge bearings and the track superstructure are typically neglected. The reason for this is that suitable models which consider the influence of such effects in engineering calculations have not yet been implemented in the effectual design codes. This thesis is mainly based on a case study of a ballasted, simply supported steel-concrete composite bridge, which shows a considerable variation in the natural frequencies and damping ratios depending on the amplitude of vibration. Furthermore, the natural frequencies were found to increase significantly during the winter. It is well known that the dynamic properties of typical civil engineering structures are dependent on the amplitude of vibration. However, the fact that certain railway bridges exhibit such non-linear behaviour also for very small amplitudes of vibration has been shown only during later years. This has been verified by means of measurements of the free vibrations after train passages on three typical Swedish beam bridges for railway traffic. Possible sources to this amplitude dependency have been identified primarily in the bridge bearings and the track superstructure. Models of these structural components, based on the so called Bouc-Wen model, have been implemented in a commercial finite element program and was used in a preliminary study. The results indicate that roller bearings and pot bearings can give rise to a non-linear mode of vibration, characterised by two different states. At very small amplitudes of vibration (. 0:1m=s2), no movement over such bearings occur (state 1) since their initial resistance to motion is not overcome. Depending on parameters such as the longitudinal stiffness of the foundations and substructures, the beam height over the supports as well as the bearing type, there is an amplitude of vibration at which the initial resistance to motion is completely overcome (state 2). The bearings are then free to move, with a resistance characterised by the kinematic friction (pot bearings) or the rolling resistance (roller bearings). During the transition from state 1 to state 2, the frequency decreases continuously towards an asymptotic value and the damping initially grows considerably, from a value which corresponds quite well to the recommendations of the Eurocodes and then returns to a value similar to that in state 1. The preliminary study indicates that it is possible to design certain bridges so that this increase in damping is optimal over the relevant range of amplitudes of vibration.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. x, 58 p.
Series
Trita-BKN. Bulletin, ISSN 1103-4270 ; 120
National Category
Infrastructure Engineering
Research subject
Järnvägsgruppen - Infrastruktur
Identifiers
urn:nbn:se:kth:diva-132298 (URN)
Public defence
2013-11-01, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20131025

Available from: 2013-10-25 Created: 2013-10-25 Last updated: 2013-10-25Bibliographically approved

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