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Monitoring and enhanced fatigue evaluation of a steel railway bridge
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges. (Brobyggnad)ORCID iD: 0000-0002-2833-4585
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.ORCID iD: 0000-0002-8926-2140
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.ORCID iD: 0000-0002-5447-2068
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.

Place, publisher, year, edition, pages
2010. Vol. 32, no 3, 854-863 p.
Keyword [en]
Railway bridge, Monitoring, Bridge assessment, Fatigue, Dynamics
National Category
Civil Engineering
Identifiers
URN: urn:nbn:se:kth:diva-28452DOI: 10.1016/j.engstruct.2009.12.011ISI: 000275488000021Scopus ID: 2-s2.0-75749154751OAI: oai:DiVA.org:kth-28452DiVA: diva2:388359
Note
QC 20110117Available from: 2011-01-17 Created: 2011-01-14 Last updated: 2013-09-17Bibliographically approved
In thesis
1. Improving a bridge fatigue life prediction by monitoring
Open this publication in new window or tab >>Improving a bridge fatigue life prediction by monitoring
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:nbn:se:kth:diva-28618 (URN)
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
2. Refining the fatigue assessment procedure of existing steel bridges
Open this publication in new window or tab >>Refining the fatigue assessment procedure of existing steel bridges
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis treats the fatigue assessment process of steel bridges. The purpose is to identify areas with potential of enhancement with an overall aim of attaining a longer service life. The aging bridge stock in Sweden and in many other developed countries is an impending economical burden. Many bridges have reached their expected service life and increased axle loads, speeds, and traffic intensity further accelerate the deterioration. An immediate replacement of all our bridges approaching their expected service life will not be possible. For economical and environmental reasons, effort should be put on extending the theoretically safe service life as far as possible.

 Fatigue is one of the major reasons limiting the service life of steel bridges .A specific example is the Söderström Bridge in Stockholm, Sweden. Fatigue cracks have been found in the webs of the main beams and theoretical assessments have shown an exhausted service life. As a mean to reduce the uncertainties in the theoretical assessments a monitoring campaign was started in 2008 and continued in periods until 2011. The first continuous period of 43 days of measurements in 2008 forms the experimental foundation for this thesis.

A fatigue life prediction involves (i) an estimation of the load effect, (ii) an estimation of the resistance, and (iii) the selection of a prediction model. This thesis treats in some sense all three of them. Considering part (i), the load effect, a theoretical study on the influence of dynamics has been performed. The quasi static approach suggested in the standards does not necessarily reflect the true dynamic behavior of the structure. Performing a dynamic moving load analysis gives for all cases studied a more favorable fatigue life. A further enhancement of the assessment is to perform in situ measurements. The uncertainties related to dynamics, loads, and structural behavior are thereby captured in the response. Routines for processing the measured response and performing life predictions are treated, moreover the quality of the measured response.

The resistance, part (ii), in form of the fatigue endurance has a funda- mental influence on the fatigue life. As an attempt to reach a more adequate fatigue endurance a refined assessment of a typical joint is performed using linear elastic fracture mechanics (LEFM). A descriptive detail category is suggested which renders a somewhat more favorable resistance.

Part (iii), the prediction model, is treated considering the safety format. A reliability-based model is suggested which enables a consideration of the uncertainties in each stochastic variable. Thereby, all aforementioned parts and uncertainties can be combined within the same prediction. The reliability-based model is used for a code calibration of partial safety factors to be used in semi-probabilistic assessments according to the standards.

The implementation of the suggested procedures is shown with a numerical example. The outcome should not be generalized but the example clearly shows an increase in fatigue life with the proposed enhancements of the assessment procedure.

 

 

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013
Series
Trita-BKN. Bulletin, ISSN 1103-4270 ; 118
Keyword
Fatigue, Steel bridges, Assessment, Reliability, Monitoring, Utmattning, stålbroar, bärighetsberäkning, tillförlitlighet, mätningar, Söderström, getingmidjan
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-127707 (URN)
Public defence
2013-10-11, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20130917

Available from: 2013-09-17 Created: 2013-09-04 Last updated: 2013-09-17Bibliographically approved

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Leander, JohnAndersson, AndreasKaroumi, Raid

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