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Improving a bridge fatigue life prediction by monitoring
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges. (Brobyggnad)ORCID iD: 0000-0002-2833-4585
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

For steel railway bridges, fatigue is the main reason for a limited service life. An initial prediction of the fatigue life is usually performed using loads and conservative assumptions stated in the governing standards. The result is used for decisions of further actions. Even if the result is an insufficient residual life, some bridges are not easy to strengthen or replace without causing large traffic disturbance. In this licentiate thesis, the real load effect is studied by monitoring a bridge during service. The aim is to improve the fatigue life prediction by reducing the uncertainties in the traffic load and finally attain a longer theoretical service life of the bridge.

A case study of the Söderström Bridge in central Stockholm, one of Sweden’s most important railway bridges, is incorporated in the studies. Previously performed theoretical assessments have shown alarming results regarding the remaining fatigue life for some of the structural members in the bridge. To verify the result and hopefully receive more favorable stress ranges, the bridge was instrumented with a monitoring system in 2008. The bridge and the monitoring campaign are thoroughly presented. Owing to the large data volume produced by the monitoring system, robust routines and procedures for quality assurance have been required. A deterministic fatigue assessment is presented based on 43 days of continuous measurements comprising more than 17 thousand train passages. Unfortunately, also this fatigue assessment indicates high fatigue damages.

A large monitoring system with many gauges enables a statistical evaluation of the quality of the measurements. By the principle of Analysis of Variance, a comparison of the stress range spectra can be performed with the aim of finding deviant spectra and corrupt gauges. An additional aspect is the length of the monitoring period, meaning the required duration for obtaining a stable result. A model for the convergence progress is proposed which could be incorporated in a monitoring system for use during service.

The extensive monitoring program of the Söderström Bridge has resulted in reliable stress range spectra. By curve fitting and goodness-of-fit tests measured spectra have been compared with known statistical distributions. These distributions can be used for future fatigue reliability assessments.

Place, publisher, year, edition, pages
Stockholm: KTH , 2010.
Series
Trita-BKN. Bulletin, ISSN 1103-4270 ; 106
National Category
Civil Engineering
Identifiers
URN: urn:nbn:se:kth:diva-28618OAI: oai:DiVA.org:kth-28618DiVA: diva2:388682
Presentation
2011-01-21, Sal B1, Brinellvägen 23, Stockholm, 13:00 (Swedish)
Opponent
Supervisors
Note
QC 20110120Available from: 2011-01-20 Created: 2011-01-18 Last updated: 2011-01-20Bibliographically approved
List of papers
1. Monitoring and enhanced fatigue evaluation of a steel railway bridge
Open this publication in new window or tab >>Monitoring and enhanced fatigue evaluation of a steel railway bridge
2010 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 32, no 3, 854-863 p.Article in journal (Refereed) Published
Abstract [en]

During routine inspections of the Soderstrom Bridge in central Stockholm, one of Sweden's most important railway bridges, cracks were found in the web of the main steel beams. The finding initiated theoretical Studies which showed that the cracks developed mainly due to poorly designed connections of the cross beams and out-of-plane bending of the web. The Studies also showed an alarming result regarding the remaining fatigue life of the stringers and the cross beams. However, no cracks or other damage have been found on these components during the inspections. To explore the differences between the theoretical indications and the inspected reality, an extensive monitoring program has been performed. This article describes the monitoring program and the analysis methods used. Some results regarding the remaining fatigue life based on measured and theoretical values are presented. (C) 2009 Elsevier Ltd. All rights reserved.

Keyword
Railway bridge, Monitoring, Bridge assessment, Fatigue, Dynamics
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-28452 (URN)10.1016/j.engstruct.2009.12.011 (DOI)000275488000021 ()2-s2.0-75749154751 (Scopus ID)
Note
QC 20110117Available from: 2011-01-17 Created: 2011-01-14 Last updated: 2017-12-11Bibliographically approved
2. Statistical evaluation of monitored data intended for fatigue reliability assessment
Open this publication in new window or tab >>Statistical evaluation of monitored data intended for fatigue reliability assessment
(English)In: Structural Safety, ISSN 0167-4730, E-ISSN 1879-3355Article in journal (Other academic) Submitted
Keyword
monitoring, analysis of variance, fatigue, stress range, railway bridge, bridge assessment
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-28617 (URN)
Note

QCR 20161212

Available from: 2011-01-20 Created: 2011-01-18 Last updated: 2017-12-11Bibliographically approved

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Leander, John

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