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Seasonal effects on the stiffness properties of a ballasted railway bridge
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.ORCID iD: 0000-0002-5447-2068
2013 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 57, p. 63-72Article in journal (Refereed) Published
Abstract [en]

In this article it is shown empirically that ballasted bridges in cold climates can exhibit a step-like variation of their natural frequencies as the yearly season changes. The bridge under study was observed to have significantly higher natural frequencies (as much as 35%) during the winter months compared to the summer. This variation was rather discrete in nature and not proportional to temperature. Furthermore the increase in natural frequencies took place only after the temperatures had dropped below 0 °C for a number of days. It was thus hypothesized that this change in natural frequencies was due to changes in the stiffness parameters of some materials with the onset of frost. In low temperature conditions not only the mean value of the measured frequencies increased, but also their variance increased considerably. Given the large spread of the measured natural frequencies, the stiffness parameters were assumed to be stochastic variables with an unknown multivariate distribution, rather than fixed values. A Bayesian updating scheme was implemented to determine this distribution from measurements. Data gathered during one annum of monitoring was used in conjunction with a finite element model and a meta model, resulting in an estimation of the relevant stiffness parameters for both the cold and the warm condition.

Place, publisher, year, edition, pages
2013. Vol. 57, p. 63-72
Keywords [en]
Railway bridges, Dynamics, Ballasted track, Seasonal effects, Bayesian updating, Markov-Chain Monte-Carlo Sampling
National Category
Infrastructure Engineering
Research subject
Järnvägsgruppen - Infrastruktur
Identifiers
URN: urn:nbn:se:kth:diva-132254DOI: 10.1016/j.engstruct.2013.09.010ISI: 000330488800006Scopus ID: 2-s2.0-84885204016OAI: oai:DiVA.org:kth-132254DiVA, id: diva2:659329
Funder
EU, FP7, Seventh Framework Programme, 286276
Note

QC 20131205

Available from: 2013-10-25 Created: 2013-10-25 Last updated: 2017-12-06Bibliographically 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. p. x, 58
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
2. Application of monitoring to dynamic characterization and damage detection in bridges
Open this publication in new window or tab >>Application of monitoring to dynamic characterization and damage detection in bridges
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The field of bridge monitoring is one of rapid development. Advances in sensor technologies, in data communication and processing algorithms all affect the possibilities of Structural Monitoring in Bridges. Bridges are a very critical part of a country’s infrastructure, they are expensive to build and maintain, and many uncertainties surround important factors determining their serviceability and deterioration state. As such, bridges are good candidates for monitoring. Monitoring can extend the service life and avoid or postpone replacement, repair or strengthening works. The amount of resources saved, both to the owner and the users, by reducing the amount of non-operational time can easily justify the extra investment in monitoring.

This thesis consists of an extended summary and five appended papers. The thesis presents advances in sensor technology, damage identification algorithms, Bridge Weigh-In-Motion systems, and other techniques used in bridge monitoring. Four case studies are presented. In the first paper, a fully operational Bridge Weigh-In-Motion system is developed and deployed in a steel railway bridge. The gathered data was studied to obtain a characterization of the site specific traffic. In the second paper, the seasonal variability of a ballasted railway bridge is studied and characterized in its natural variability. In the third, the non-linear characteristic of a ballasted railway bridge is studied and described stochastically. In the fourth, a novel damage detection algorithm based in Bridge Weigh-In-Motion data and machine learning algorithms is presented and tested on a numerical experiment. In the fifth, a bridge and traffic monitoring system is implemented in a suspension bridge to study the cause of unexpected wear in the bridge bearings.

Some of the major scientific contributions of this work are: 1) the development of a B-WIM for railway traffic capable of estimating the load on individual axles; 2) the characterization of in-situ measured railway traffic in Stockholm, with axle weights and train configuration; 3) the quantification of a hitherto unreported environmental behaviour in ballasted bridges and possible mechanisms for its explanation (this behaviour was shown to be of great importance for monitoring of bridges located in colder climate) 4) the statistical quantification of the nonlinearities of a railway bridge and its yearly variations and 5) the integration of B-WIM data into damage detection techniques.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. p. x, 65
Series
TRITA-BKN. Bulletin, ISSN 1103-4270 ; 126
Keywords
Structural health monitoring, Traffic monitoring, Bridge monitoring, Bridge Weigh-In-Motion, BWIM, Damage detection, Suspension bridge bearings, Axle loads, Dynamics, Temperature effect
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-150804 (URN)
Public defence
2014-09-19, Sal F3, Lindstedtsvägen 26, Sing-Sing, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20140910

Available from: 2014-09-10 Created: 2014-09-10 Last updated: 2014-09-10Bibliographically approved

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