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  • 1.
    Andersson, Andreas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Extending the fatigue service life of a railway bridge by local approaches2013Conference paper (Refereed)
    Abstract [en]

    In this paper, fatigue assessment of a steel railway bridge is presented. The bridge is located in central Stockholm, Sweden, and is one of the most vital links for the railway network. The bridge services both freight trains and commuter trains with more than 500 passages per day. The main load bearing structure is designed as a steel grillage of welded I-beams. Fatigue critical sections have been identified at locations where secondary bracing systems are welded to the flanges of the I-beams. Both numerical simulations and extensive field measurements have shown a significant exceedance of the theoretical fatigue service life. Based on analysis of local stress concentrations, improvement of fatigue critical details have been suggested. The decrease in stress concentration is demonstrated both by numerical simulations and in-situ field measurements and shows a significant improvement when estimating the remaining fatigue service life.

  • 2. Aygul, Mustafa
    et al.
    Al-Emrani, Mohammad
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. Khalifa University of Science Research and Technology, United Arab Emirates.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    An investigation of distortion-induced fatigue cracking under variable amplitude loading using 3D crack propagation analysis2014In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 45, p. 151-163Article in journal (Refereed)
    Abstract [en]

    The distortion-induced fatigue cracks in the welded details of the Soderstrom Bridge are analytically and numerically investigated by performing 3D crack propagation analyses with variable amplitude fatigue loading. In the crack propagation analyses, the effects of bridge loading are defined on the basis of the field measurements in order to simulate crack growth and predict the residual fatigue life of the studied detail as accurately as possible. The effect of crack closure and crack direction while considering the most common criteria is also studied. The results are compared with those obtained from the crack propagation analyses with constant amplitude fatigue loading presented in Ayg l et al. [1]. The results of the crack growth simulations with variable amplitude fatigue loading have generally shown good agreement with the real crack formation and reveal that the crack growth rates are different in different directions. The crack behaviour in the damaged detail is mainly controlled by the loading and geometrical arrangement of the detail components. There is generally a significant difference between constant and variable amplitude fatigue crack growth analyses and the variable amplitude fatigue crack growth analyses yield more conservative results. The main reason for this difference is the bridge loading and the number of stress cycles defined in the analyses. The crack direction criteria studied in this investigation showed basically the same crack formation and crack growth rate.

  • 3. Aygül, M.
    et al.
    Al-Emrani, M.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Investigation of distortion-induced fatigue cracked welded details using 3D crack propagation analysis2014In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 64, p. 54-66Article in journal (Refereed)
    Abstract [en]

    The behaviour of distortion-induced fatigue cracks in welded details in an existing bridge was studied analytically by performing crack propagation analysis based on linear elastic fracture mechanics. The real load history of the bridge was obtained from strain measurements. These loads were utilised to examine the crack growth rate and the residual service life of the cracked detail. Moreover, the effectiveness, accuracy and applicability of the crack propagation analysis on bridge structures were investigated by simulating a complex case of fatigue cracking using several crack propagation analyses. The results of the analyses revealed that the fatigue crack in the studied details had significantly different crack growth characteristics in different directions. In the thickness direction, for instance, the crack was seen to propagate at a certain rate, which increased with the propagated crack from the beginning and, as expected, the crack propagation rate decreased when the crack grew longer. The crack was subsequently arrested half way through the thickness of the plate. In the longitudinal direction, the crack was not, however, arrested in the same way as in the thickness direction and it continued to propagate at a reduced yet constant crack growth rate. The results also revealed that, even though distortion-induced fatigue cracking was usually caused by a mixed-mode condition (i.e. a combination of modes I, II and III), the governing propagation mode is still mode I. Furthermore, it was also observed that the contribution of modes II and III to crack propagation was very little and dependent on the location of the propagated crack front, as well as the geometrical configuration of the cross-beam.

  • 4. Honfi, D.
    et al.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Björnsson, Í.
    Ivanov, O. L.
    Plos, M.
    Zandi, K.
    Magnusson, J.
    Lechner, T.
    Gabrielsson, H.
    Decision support for maintenance and upgrading of existing bridges2017In: IABSE Conference, Vancouver 2017: Engineering the Future - Report, International Association for Bridge and Structural Engineering (IABSE) , 2017, p. 336-345Conference paper (Refereed)
    Abstract [en]

    Maintenance of transportation infrastructure assets can be relatively expensive, since it does not only include the direct cost of interventions, but also the indirect consequences of traffic disruptions. To make optimal decisions about maintenance actions, including rehabilitation and upgrading, reliable information about the performance of existing structures is needed. However, obtaining such information might require significant efforts and can be done in various ways. The purpose of an ongoing Swedish research project BIG BRO is to develop a framework for a decision support methodology that can be used for implementing maintenance strategies for bridges on a rational basis. The present paper provides a brief overview about the project as well as describes some of the ongoing work. 

  • 5.
    Honfi, Dániel
    et al.
    RISE Research Institutes of Sweden.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Björnsson, Ívar
    Lund University.
    Decision support for bridge condition assessment2017In: SMAR 2017 Proceedings, 2017Conference paper (Refereed)
    Abstract [en]

    The paper presents the first steps of the development of a theoretical framework for a rational yet practical decision making process concerning the condition assessment of existing bridges in Sweden. The main focus is on how to choose the appropriate level of enhanced conditions assessment considering aspects of model sophistication, uncertainty consideration and knowledge content utilisation. A conceptual case study is presented exemplifying how the framework can be used to structure the assessment actions of a steel bridge subjected to fatigue deterioration.

  • 6.
    Ivar, Björnsson
    et al.
    Lund University.
    Larsson Ivanov, Oskar
    Lund University.
    Honfi, Dániel
    RISE.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Decision support framework for bridge condition assessments2019In: Structural Safety, ISSN 0167-4730, E-ISSN 1879-3355, Vol. 81Article in journal (Refereed)
    Abstract [en]

    An essential aspect in the maintenance of existing bridges is the ability to adequately and accurately assess and evaluate the condition of the structure. Condition assessments, which can be carried out in any number of ways, provide valuable information concerning the actual state of a bridge, including the severity of potential damages, and form the basis for further maintenance decisions. Any decision support concerning the management of existing structures thus requires attention towards the uncertainties associated with the assessment methods when applied in practice as well as the maintenance actions these support. These uncertainties cannot be solely described as model uncertainties but are also a result of the variation in engineering performance observed in practice. In the current paper a rational and systematic framework is presented which provides practical decision support concerning whether condition assessments are necessary, what assessment methods are recommended, if invasive actions are needed, or if some other non-invasive option may be more appropriate. The framework takes into account three main attributes of an enhanced condition assessment, namely, modelling sophistication, considerations of uncertainties and risks, and knowledge/information content. Increasing the level of one or more of these attributes may be advantageous only if the expected benefits or added value of information is considered appropriate in relation to the cost of implementation in practice. A decision making model, based on Bayesian decision theory, is adopted to evaluate this problem. Two case studies, in which the framework is applied, are provided for illustrative purposes; the first is a generic numerical example and the second a decision scenario related to the fatigue assessment of an existing railway bridge.

  • 7.
    Kullberg, Claes
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Trillkott, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Töjningsmätningar på järnvägsbro över Söderström 2008-20112011Report (Other academic)
  • 8.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Bro över Söderström : Stockholms C.-Älvsjö km 1+83: Rapport 1: Mätning och utvärdering m.a.p. utmattning2008Report (Other academic)
  • 9.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Fatigue life prediction of steel bridges using a small scale monitoring system2018Report (Other academic)
    Abstract [en]

    With an increasing number of bridges approaching their expected service life, improved and new methods for accurate assessment methods are called for. Economical restraints and sustainability reasons will not allow bridge managers to replace the numerous bridges that theoretically will be judged unsafe. As a method for refined assessment, in-service monitoring can be used to accurately determine the actual structural response. This will enable an alleviation of conservative estimates and facilitate accurate service life predictions.For fatigue assessment, the well established technique for strain measurements using electrical strain gauges can provide accurate estimations of the actual structural response. It is, however, not possible to mount gauges at all positions with critical details for large structures as bridges. The possibility of using a small scale monitoring system with few sensors has been investigated and a review of methods for predicting the response at unmeasured locations is presented in this report. A few selected methods, like multivariate regression and artificial neural networks (ANN), have been tested and evaluated on measured data from the Rautasjokk Bridge.The use of an ANN for time history prediction is demonstrated and promising results are presented. However, the predictions are sensitive to the input data and questionable results were attained when the input deviated from the training set. For predictions based on stress range spectra, multivariate linear regression constitute a robust tool and provided a high accuracy for an example from the Rautasjokk Bridge.This report also contains a presentation of the monitoring campaign of the Rautasjokk Bridge. The setup of the system and the management of data are described. The bridge is used for demonstrating the prediction methods and an advanced assessment approach based on linear elastic fracture mechanics. It enables a consideration of the measured response and a reliability based updating considering inspection results.

  • 10.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Friktionsförband under yttre dragkraft: En studie av kraftfördelning mellan skruv och plåtar2010Report (Other academic)
    Abstract [sv]

    Föreliggande studie omfattar en studie av ett förspänt skruvförband utsatt för dragkrafter.

    Enligt gällande Eurokod för dimensionering av knutpunkter och förband i stålkonstruktioner, EN 1993-1-8, beaktas en medverkande area av de sammanfogade plåtarna som är fyra gånger skruvens area. Förfarandet lämnas utan kommentarer i standarden. Med hjälp av olinjära FE-analyser studeras verkningssättet för ett förspänt skruvförband under dragning och kraftfördelningen mellan skruven och de sammanfogade plåtarna.

    Resultatet visar att den medverkande arean inte är konstant och att både de sammanfogade plåtarnas tjocklek och skruvens diameter har betydelse för sambandet. En funktion för beräkning av graden av samverkan i förbandet presenteras och är ett resultat av en statistisk utvärdering.

  • 11.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Gamla Lidingöbron: Sammanfattning av mätningar från mars 2017 t.o.m. november 20182018Report (Other academic)
    Abstract [sv]

    Gamla Lidingöbron bär spårvagnstrafiken längs Lidingöbanan, gående och cyklister över sundet mellan Ropsten och Lidingö i Stockholm. Brons tillstånd och bärförmåga har under flera år ifrågasatts då korrosion och skador har påvisats under inspektioner. Ett mätsystem har installerats som ett led i att säkerställa brons bärförmåga fram till dess att den nya bron, Lilla Lidingöbron, är färdigställd. Föreliggande rapport sammanfattar de mätningar som påbörjades 15 mars 2017 och pågår fortlöpande. Rapporten omfattar mätresultat fram till och med 19 november 2018.

    Mätsystemets uppbyggnad med givare, datainsamlingsenheter och utrustning för kommunikation finns redovisat. Vid skrivandet av denna rapport fanns 16 trådtöjningsgivare, 3 accelerometrar med tre mätriktningar vardera och en inklinometer med två mätriktningar installerade på bron. Dessutom fanns ett experimentellt system för energiinsamling installerat.

    Det resultat som redovisas är långtidsvariationen av uppmätta spänningar, accelerationer och rotationer. Dessutom visas tidshistorier för enstaka tågpassager och ackumulerade spänningskollektiv. Spänningsnivåerna baserade på de uppmätta töjningarna för tågpassagerna är som störst ca 36\,MPa. Det är betydligt lägre än den dimensionerande lasteffekten vilket tyder på att brons statiska bärförmåga är tillräcklig. Däremot kan den nedbrytning som pågår, t.ex. omfattande korrosion, i förlängningen orsaka en oacceptabelt låg säkerhet.

    Under två nätter i november 2018 genomfördes kontrollerade tester för tågpassager med hastigheter inom intervallet 5\,km/h till 50\,km/h. En statistisk analys visar att hastigheten inte är signifikant för de uppmätta spänningarna. Det betyder att hastigheten inte har kunnat visas ge några dynamiska effekter med ökande spänningsnivåer inom det beaktade intervallet.

  • 12.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Improving a bridge fatigue life prediction by monitoring2010Licentiate 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.

  • 13.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Kalibrering av lambda-metoden för dimensionering av stål- och samverkansbroar i Sverige - en förstudie2017Report (Other academic)
    Abstract [en]

    In design of new bridges for road traffic, the fatigue verification should comply with the Eurocode using the fatigue load model 3 (FLM 3) together with damage equivalent factors (lambda factors). This model has, however, been questioned in Sweden and internationally, since it has shown a different result in comparison to previous assessment methods.

    In this report, a method for calibration of the Eurocode model against governing safety demands is proposed. The method builds upon reliability analysis and traffic loads determined from BWIM measurements (Bridge-Weigh-In-Motion). The reliability based method enables an assessment against an acceptable probability of failure or the associated reliability index.

    Calculations have been performed for nine different bridge types and seven different traffic volumes. The reliability based method has been used to estimate what reliability index the Eurocode assessment model gives. The result shows a large scatter with the lowest value of β = 0,86 and the highest value of β = 4,75. This shows in itself a need of a calibration. The scatter is caused partly by differences between traffic categories, and partly by differences between span lengths.

    A future calibration should initially be focused on the number of heavy vehicles observed or estimated per year and per slow lane, Nobs, and the critical length factor λ1.

  • 14.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Refining the fatigue assessment procedure of existing steel bridges2013Doctoral 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.

     

     

     

  • 15.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Reliability evaluation of the Eurocode model for fatigue assessment of steel bridges2018In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 141, p. 1-8Article in journal (Refereed)
    Abstract [en]

    In European countries, the design of bridges is conducted following the specifications in the Eurocodes. For verification against fatigue of steel bridges, a simplified model is suggested based on a single vehicle load model together with λ factors to estimate a representative stress range. Since the release of the Eurocodes the accuracy of this format has been discussed and questioned. In the current paper, a probabilistic model for fatigue assessment is suggested estimating the load effect from bridge weigh-in-motion (BWIM) measurements. The probabilistic model has been used to estimate the reliability reached with the existing verification format for road bridges. The result shows a large scatter depending foremost on the bridge geometry and the traffic volume. A tentative calibration of the verification format has been performed and new functions for two of the λ factors have been derived. With these new functions a significant improvement in the consistency of the reliability level has been achieved. The study demonstrates the need for a more extensive calibration of the Eurocode model and indicates the parameters to focus on.

  • 16.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Utmattningskapacitet hos skruvförband för rörbroar: Analys av statisk provning som underlag för utmattningsprovning2012Report (Other academic)
    Abstract [sv]

    En statisk provning har utförts av ett skruvförband i ett rörbrosegment. Syftet med provningen är att studera provkroppens verkningssätt under belastning och för att verifiera de teoretiska beräkningsmodeller som upprättats. Denna studie ingår som en del i ett större projekt för bestämning av skruvförbandets utmattningshållfasthet. Studien avses utgöra ett underlag för den efterföljande utmattningsprovningen.

    Två teoretiska beräkningsmodeller är upprättade, en tredimensionell skalmodell och en tvådimensionell balkmodell, båda i det generella FE-programmet Abaqus. I skalmodellen är provkroppens samtliga plåtar beaktade med överlappningar och hål. Friktionslösa kontaktvillkor är föreskrivna mellan plåtarna och skruvarnas funktion är modellerade med stela förbindningar. Balkmodellen är uppbyggd utan beaktande av överlappande plåtar och skruvförband för bestämning av nominella spänningar.

    Resultatet från provningen stämmer väl överens med resultatet från skalmodellen vad gäller last-förskjutningsförhållandet och deformationerna. Även balkmodellen ger ett resultat i samma storleksordning. De under provningen uppmätta spänningarna visar inte några antydningar till spänningskoncentrationer. De nominella spänningarna från balkmodellen är något högre än vad provningsresultatet visar. Baserat på resultaten anses spänningsvidden i de efterföljande utmattningsprovningarna kunna baseras på uppmätta spänningar intill skruvförbandet. Vidare visade den statiska provningen att upplagens utformning är av stor vikt. En led erfordras i upplaget för att förhindra en excentrisk belastning av upplagsfjädrarna.

  • 17.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Al-Emrani, Mohammad
    Chalmers University of Technology.
    Reliability-based fatigue assessment of steel bridges using LEFM: A sensitivity analysis2016In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 93, no 1, p. 82-91Article in journal (Refereed)
    Abstract [en]

    The lack of an established safety format prohibits a widespread use of linear elastic fracture mechanics (LEFM) for the fatigue assessment of steel bridges. The aim of this study is to facilitate a future development of a deterministic design approach. A probabilistic sensitivity analysis has been performed to study the influence of different modeling options on the resulting time variant reliability. The analyses have been performed by the first order reliability method (FORM) together with a model correction factor. The result shows the importance of modeling the crack shape in an adequate manor and, the importance of the material parameters. Other parameters as the load sequence and the option between a linear and a bi-linear crack growth law are less important. A calculation of the omission sensitivity factors shows that the uncertainties of the material parameters in the crack growth law have the most decisive influence and, thereafter, the uncertainty of the stress intensity factor.

  • 18.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Amer, Wadi
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Pettersson, Lars
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Fatigue testing of a bolted connection for buried flexible steel culverts2017In: Archives of Institute of Civil Engineering / [ed] Arkadiusz Madaj, Iwona Jankowiak, 2017, Vol. 23, p. 153-162Conference paper (Refereed)
    Abstract [en]

    A fatigue assessment of steel structures based on the safe life approach requires a detail category representing the fatigue strength. For flexible culverts there are no matching details in the governing regulations. In this paper the testing and evaluation of the fatigue strength of a standardized bolted connection for steel culverts are presented. A test rig was designed to mimic the in-service conditions with a combination of bending moment and axial force. A total of ten specimens was tested to failure. The failure was governed cracks initiating at the indentations from the bolt heads and propagated towards the nearest edge. From the test results, an S-N curve has been derived suggesting a characteristic fatigue strength of 124 MPa at 2 million cycles and a slope of 5 in log-log scale.

  • 19.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Andersson, Andreas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Järnvägsbro under bevakning2011In: Samhällsbyggaren, ISSN 2000-2408, no 3, p. 25-29Article in journal (Other (popular science, discussion, etc.))
    Abstract [sv]

    Bro över Söderström utgör en del av den så kallade getingmidjan i Stockholm där all tågtrafik söder om Stockholms central samsas på två spår. Under rutininspektioner har ett flertal sprickor upptäcktsi bron vilket föranlett teoretiska studier av brons bärighet och kvarvarande livslängd. Avgörande för livslängden är utmattning i några av de svetsade knutpunkterna. En omfattande mätningskampanj har på uppdrag av Trafikverket utförts av avdelningen för Brobyggnad vid KTH dels för att minska osäkerheterna i de teoretiska beräkningarna och dels för att klargöra uppkomna skillnader mellandet teoretiska resultatet och den inspekterade verkligheten.

  • 20.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Andersson, Andreas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Enhanced Assessment of the Remaining Service Life of a Steel Railway Bridge2009In: Damage Assessment Of Structures VIII, Trans Tech Publications Inc., 2009, Vol. 413-414, p. 245-252Conference paper (Refereed)
    Abstract [en]

    During annual inspections of one of Sweden's most important railway bridges, the Soderstrom Bridge in central Stockholm, cracks in the web of the main steel beams have been discovered. Extensive theoretical work has been undertaken to assess the remaining service life of the bridge. Furthermore, the bridge has recently been instrumented to enhance the theoretical predictions by monitoring the real railway traffic as well as the response of the bridge. This article describes the monitoring program and the analysis methods used. Some interesting results regarding the remaining fatigue life are presented.

  • 21.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Andersson, Andreas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Monitoring and enhanced fatigue evaluation of a steel railway bridge2010In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 32, no 3, p. 854-863Article in journal (Refereed)
    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.

  • 22.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Aygül, Mustafa
    Chalmers University of Technology.
    Norlin, Bert
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Refined fatigue assessment of joints with welded in-plane attachments by LEFM2013In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 56, p. 25-32Article in journal (Refereed)
    Abstract [en]

    The fatigue life of joints with welded in-plane gusset plates is studied. The purpose is to suggest a descriptive detail category to be used in assessment of existing structures. Linear elastic fracture mechanics is used together with fictitious initial crack depths to predict the fatigue life. By calibrating the fictitious crack depths to real fatigue tests and simulating new test results, fatigue strengths dependent on the dimensions of the joint have been derived. The results show that a decreasing length and thickness of the gusset give decreasing stress intensity and higher fatigue strength. A numerical example is presented showing the merit of the proposed strengths in fatigue life.

  • 23.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Honfi, Daniel
    RISE Research Institutes of Sweden.
    Björnsson, Ivar
    Lund University.
    Risk-based planning of assessment actions for fatigue life prediction2017In: 2nd International Conference on Structural Integrity, ICSI 2017, 4-7 September 2017, Funchal, Madeira, Portugal, Elsevier, 2017, Vol. 5, p. 1221-1228Conference paper (Refereed)
    Abstract [en]

    It is vital to extend the service life of existing bridges as far as possible as a means for improved sustainability leading to reduced economic cost and resource consumption. This requirement is especially valid for bridges which are critical components of highly vulnerable infrastructure systems. Achieving this aim requires enhanced methods involving various actions and methods influencing different aspects of the assessment process. A framework is presented in this paper based on three common factors used to describe the assessment actions of existing bridges; (i) model sophistication, (ii) uncertainty consideration, and (iii) knowledge content. The framework elucidates the influence of different decisions on the assessment process and facilitates the planning of appropriate assessment actions. Furthermore, it provides a basic scheme for a risk-based decision analysis for determining suitable assessment actions or activities. A fatigue assessment of an existing bridge detail is used to demonstrate the application of the framework in practical cases.

  • 24.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Honfi, Dániel
    RISE.
    Larsson Ivanov, Oskar
    LTH.
    Björnsson, Ívar
    LTH.
    A decision support framework for fatigue assessment of steel bridges2018In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 91, p. 306-3014Article in journal (Refereed)
    Abstract [en]

    Many bridges are approaching or have already passed their expected service life. For steel bridges, fatigue is often the decisive degradation phenomenon that theoretically puts restrictions on a continued use. At the same time, fatigue is also afflicted with large uncertainties on the resistance side as well as on the action effect side. An accurate assessment of the service life will require measures outside the governing regulations but understanding what steps to take and how to consider the outcome for decisions on interventions can be a difficult task for a non-expert. This paper presents possible assessment actions and a decision support framework for rational decisions on interventions to extend the theoretical service life of existing bridges. A case study of a critical railway bridge is incorporated to demonstrate the framework. The aim is to provide a tool for bridge managers on how to evaluate and procure different assessment actions.

  • 25.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Dynamics of thick bridge beams and its influence on fatigue life predictions2013In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 89, p. 262-271Article in journal (Refereed)
    Abstract [en]

    An analytical model for moving load analysis is derived based on the Timoshenko beam theory. The model enables rapid and reliable analyses of the influence of dynamics on the fatigue life prediction of thick beams. This type of beams is typical for open deck railway bridges. The number of modes required in a modal superpositioning is studied as well as the influence of damping and support stiffness. A total of 22 bridge beams from open deck bridges presented in the literature is included in the study. The results clearly show a fundamental difference in the behaviour of one span beams and continuous beams. Especially in the case of assessment of existing bridges, the quasi static model of the Eurocode renders an excessive safety margin. For the majority of continuous beams studied, the dynamic response is lower than the static response resulting in no dynamic amplification. Such an outcome can have a substantial influence on the remaining fatigue life prediction due to the exponential relation between the stress range and the fatigue life.

  • 26.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Quality Assurance of Measured Response Intended for Fatigue Life Prediction2012In: Journal of Bridge Engineering, ISSN 1084-0702, E-ISSN 1943-5592, Vol. 17, no 4, p. 711-719Article in journal (Refereed)
    Abstract [en]

    By in situ measurements, the real distribution of stress ranges caused by service loads can be recorded. Inherent effects in the measured response as disturbance can, however, create puzzles in the interpretation of the result. In large monitoring campaigns, it is not possible to examine the result from every gauge over the whole measured period by visual control. In this paper, an approach for a quality assurance of the measured response is presented based on established statistical methods. The stress range spectra, the product of the monitoring program intended for fatigue assessment, are analyzed. The aim of the analysis is to find deviant spectra and identify corrupt gauges. An additional aspect is the length of the monitoring period, that is the required duration for obtaining a stable result. A case study of a monitored Swedish steel railway bridge is incorporated in the paper to exemplify the approaches. Some statistical distributions for the monitored stress ranges are also presented and incorporated in a fatigue assessment.

  • 27.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Rate of convergence of measured stress range spectra2012In: Bridge Maintenance, Safety, Management, Resilience and Sustainability - Proceedings of the Sixth International Conference on Bridge Maintenance, Safety and Management / [ed] Biondini, F. and Frangopol, D. M., Taylor & Francis Group, 2012, p. 3381-3386Conference paper (Refereed)
    Abstract [en]

    A fatigue assessment is afflicted with several uncertain variables. Monitoring constitutes a mean to reduce or properly estimate some of them. The subject of this paper is the measured stress range spectrum and, the required duration of monitoring to obtain convergence. A theoretical model is presented based on the Palmgren–Miner damage rule and an assumed shape of progress. The long-term monitoring campaign of The Söderström Bridge located in Stockholm, Sweden, is used as a case study. It is an open deck bridge for railway traffic subjected to high traffic intensity. The required duration of monitoring differs between different structural parts in the bridge. Stress range spectra for members with a short influence line seem to converge faster than for members with a longer influence line. For some gauge locations, a diverging shape of the spectrum has been found due to non-linear behavior of the structure. The proposed model for convergence progress is shown to give reliable predictions of the required monitoring duration. By implementing the model in the routines for data acquisition, the end time could be a variable determined during operation of the monitoring system.

  • 28.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Refined fatigue assessment of an existing steel bridge2015In: Proceeding of 13th Nordic Steel 2015 Construction Conference / [ed] Markku Heinisuo & Jari Mäkinen, Tampere: Tampere University of Technology, 2015Conference paper (Refereed)
    Abstract [en]

    This paper treats the fatigue assessment of existing steel bridges for road traffic. It is focused on the estimation of the load effect. The deterministic assessment methods suggested in governing codes are reviewed and a comparison is performed against a reliability-based assessment. The latter method enables a consideration of reduced uncertainties from measurements of the real load effect. The Vårby Bridge in Sweden, a steel–concrete composite bridge south of Stockholm, is used as a case study. The results show a considerable increase in fatigue life with the use of measurements and a reliability-based assessment. Another conclusion is that the load models in the Eurocode give an unjustified conservative result.

  • 29.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
    Statistical evaluation of monitored data intended for fatigue reliability assessmentIn: Structural Safety, ISSN 0167-4730, E-ISSN 1879-3355Article in journal (Other academic)
  • 30.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    The value of monitoring on the service life prediction of a critical steel bridge2018In: Life Cycle Analysis and Assessment in Civil Engineering: Towards an Integrated Vision: Proceedings of the Sixth International Symposium on Life-Cycle Civil Engineering (IALCCE 2018), 28-31 October 2018, Ghent, Belgium, 2018, p. 2121-2128Conference paper (Refereed)
    Abstract [en]

    This paper is focused on the service life prediction of steel bridges subjected to a combination of corrosion and fatigue. Both deterioration mechanisms are dubious to handle in theoretical assessments due to large uncertainties, on the action effect side and the resistance side. A reliability-based assessment in combination with updating considering monitoring and inspections provide an approach to reduce the uncertainties. To evaluate what assessment actions to engage, this approach has been combined with Bayesian decision theory which provides a rational basis to evaluate the value of information (VoI). The Old Liding\"{o} Bridge in Sweden is used as a case study to demonstrate the reliability-based approach. This bridge is subjected to severe corrosion and has been deemed unfit for service. However, it provides the only link to the island Liding\"{o} for the local tram and pedestrians why the bridge owner has decided to keep it in service until a new bridge is in place. To secure the safety of the bridge, recurrent inspections are conducted and discovered defects are repaired immediately. A system for continuous monitoring of critical parts was installed during the spring 2017. The bridge, the approach for assessment, and the procedure for evaluating the VoI are presented in the paper.

  • 31.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Rohner, Christian
    Uppsala universitet.
    Höglund, Joel
    SICS RISE.
    Wirström, Niklas
    SICS RISE.
    Rosengren, Peter
    CNet Svenska AB.
    Eriksson, Daniel
    CNet Svenska AB.
    Smart condition assessment, surveillance and management of critical bridges2018Conference paper (Refereed)
    Abstract [sv]

    Bridges with critical roles in heavily loaded transport infrastructures often need to be kept in service despiteknown damage and deficiencies. Closing or limiting the traffic on a bridge, leading to traffic diversions, issometimes not a feasible option. The current paper describes an approach for securing the functionalityand the safety of critical bridges by using an innovative smart system for monitoring and conditionassessment. It builds on the use of wireless sensor networks, advanced assessment methods, and cloudbased services for storage and distribution of results. This is an ongoing research project and the progressso far is presented in this paper. A case study of the Old Lidingö Bridge in Stockholm, Sweden, is used todemonstrate the approach. The monitoring system installed, devices for energy harvesting, and methodsfor condition assessment are presented. Some preliminary results on the condition of the bridge are alsopresented.

  • 32.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Rohner, Christian
    Uppsala universitet.
    Höglund, Joel
    RISE.
    Wirström, Niklas
    RISE.
    Rosengren, Peter
    CNet Svenska AB.
    Kool, Peeter
    CNet Svenska AB.
    Smart condition assessment, surveillance and management of critical bridges2019Report (Other academic)
    Abstract [en]

    Bridges with known deficiencies often have to be kept in service as they constitute links in highly stressed transport infrastructures. Disruptions in the traffic flow are often considered unacceptable. The current project was aimed at bridges with known deficiencies in particular, with the purpose of securing the serviceability and the safety using an innovative smart system for surveillance and condition assessment.

    Related to measurements and collection of data, the project has focused on wireless sensor networks. In comparison to traditional wired systems, the installation demands less resources and the locations of the sensor nodes are not restricted by cabling issues. The research activities regarding sensors have been aimed at energy harvesting and energy efficient scheduling of operations. A completely wireless installation requires local power sources as batteries with limited lifetime, which restricts the time for measurements. With the purpose of extending the lifetime, systems for energy harvesting have been evaluated as, e.g., units based on vibrations and electromagnetic waves. Another aspect is when and for how long measurements and communication should be performed. By scheduling the activities of the sensor node, the results of the project shows a potential to save energy.

    The purpose of a monitoring system is to provide data for condition assessment and damage detection. A condition assessment involves the estimation of the present safety level and a prediction of the remaining service life. Within this field, degradation models for the interaction between corrosion and fatigue have been studied, and a probabilistic model have been developed facilitating considerations of uncertainties in the measured response and in the results from inspections. The purpose of damage detection is to find anomalies in the behaviour of the structure that might be caused by damages or a change in structural behaviour. It can involve unexpected events difficult to predict in advance, but detectable by thorough investigation of measured data. A method based on machine learning and statistical inference have been developed in the project and tested on fictitious damage cases.

    If the results form a condition assessment or damage detection indicates insufficient safety, a decision has to be made on interventions. A decision support model based on Bayesian decision theory have been implemented in the project and tested on data from the Old Lidingö Bridge.

    Cloud based services have been developed to transfer data from the sensors, to the analysis parts, and on to the decision agent. The purpose was to simplify the management of large data volumes from a monitoring system and to visualize the results in a comprehensible format. Solutions for collecting, storing and sharing of data have been developed, together with a mobile app for presentation of the results.

    The objective to develop an integrated system for surveillance, sharing of data, condition assessment, and decision support is partly completed. Some parts of the integration remains to be solved before a complete solution can be launched.

  • 33.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Norlin, Bert
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Reliability-based calibration of fatigue safety factors for existing steel bridges2015In: Journal of Bridge Engineering, ISSN 1084-0702, E-ISSN 1943-5592, Vol. 20, no 10, article id 04014107Article in journal (Refereed)
    Abstract [en]

    This paper investigates the fatigue assessment of existing steel bridges. Measurements can be used to reduce uncertainties in the structural behavior and the effects of action. However, the treatment of the measured response is not clearly defined in today's codes of practice. A reliability model is suggested that treats the uncertainties for bilinear fatigue endurance and the uncertainties in the measured response. A parametric study on the modeling of the load effect is performed and shows a significant influence on the reliability. The reliability model is used for calibration of the partial safety factors in a deterministic design equation. The suggested partial safety factors enable practical use of measured stresses in the fatigue assessment of existing steel bridges. A numerical example shows the merit of the proposed model and partial safety factors as an increase in fatigue life.

  • 34.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Selén, Emma
    Stockholms läns landsting.
    The applicability of reliability-based inspection planning for steel bridges based on fatigue crack detection2017In: Safety, Reliability, Risk, Resilience and Sustainability of Structures and Infrastructure: 12th Int. Conf. on Structural Safety and Reliability / [ed] Christian Bucher, Bruce R. Ellingwood, Dan M. Frangopol, Vienna: TU Verlag an der Technischen Universität Wien , 2017Conference paper (Refereed)
    Abstract [en]

    A damage tolerance method for fatigue assessment opens the possibility of combining theoretical assessments with inspection results. This is widely accepted in the aerospace and offshore industries but is rarely implemented in the assessment of bridges. In this paper, an investigation on the applicability of a damage tolerance approach is presented for bridge specific conditions regarding geometry, loading and reliability level. A probabilistic model is defined and used for the reliability estimation. The result shows that conventional inspection methods can provide enough information to update the reliability resulting in an increased fatigue life.

  • 35.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Skoglund, Oskar
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    A calibrated verification model for fatigue assessment of road bridges2019In: Proceeding of Nordic Steel 2019, 2019Conference paper (Refereed)
    Abstract [en]

    The format suggested in the Eurocode for fatigue verification of road bridges is under scrutiny in thispaper. The model is easy to use in practice, which is important for design purposes, but its accuracyhas been questioned. For this reason, a reliability-based evaluation of the safety level has beenperformed and is briefly recapitulated in this paper. It shows a large scatter in reliability index rangingfrom unacceptably low to overly conservative. A calibration of the existing model has been performedshowing a more consistent reliability level. Results from comparisons of the existing and calibratedmodels are shown for real bridges considering the influence on design stress ranges. The results showthat the Eurocode model is conservative for short span bridges subjected to low traffic volume. Forother cases, the Eurocode model is non-conservative.

  • 36.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Svedholm, Christoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Dynamic analyses for fatigue assessment of existing steel bridges2014Conference paper (Refereed)
    Abstract [en]

    In fatigue assessments of existing bridges, the influence of dynamics is conventionally considered by a dynamic amplification factor on the static response. This quasi-static approach gives a multiplicative enlargement of the stress ranges but doesn't necessarily represent the actual dynamic response. Moving loads on a bridge usually gives a more complicated time response than the corresponding static load. Redistribution of the stress range spectrum is expected dependent on the train speed and the dynamic properties of the bridge. Typical bridge beams found in open deck steel bridges are studied using two analytical methods for analysis. The methods are based on the Euler-Bernoulli beam theory and the Timoshenko beam theory, respectively. Using both methods enable a study on the influence of shear deformation and rotational inertia. The study also comprises the discrepancies in dynamic response of simply supported beams and continuous beams. The numerical results support the use of the quasi static approach for one span beams. For continuous beams on the other hand, the quasi static approach does not correctly reflect the dynamic behavior.

  • 37.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Trillkott, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Kullberg, Claes
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Götaälvbron: Töjningsmätningar för kalibrering av beräkningsmodell2015Report (Other academic)
    Abstract [en]

    The Götaälv Bridge in Gothenburg was instrumented with strain gauges in April 2015. This report is a presentation of the measurements performed until 29 April. The measurements were performed by personnel from the Division of Structural Engineering and Bridges at KTH. The project was commissioned by the City of Gothenburg – Traffic & public transport authority through ÅF Infrastructure AB and performed in collaboration with researchers from the Division of Structural Engineering at Chalmers University of Technology.

    The monitoring system comprised 23 strain gauges divided between two areas. One between support 13 and 14 at the South Viaduct and one between support III and IV at the elevated river part. Measurements were performed at four arranged bridge openings and a calibration monitoring using two trucks with known weights. Continuous measurement was also performed during the afternoon Tuesday 28 April.

    For the bridge openings, stresses up to 5,6MPa were recorded on the elevated river part. The recorded stresses are lower than those caused by the ordinary traffic in the instrumented locations.

    The calibration measurements were performed during night using two trucks with weights of 25,0 tons and 25,1 tons, respectively. Together, they caused maximum recorded stresses of 15,4MPa for the South Viaduct and 16,8MPa for the elevated river part. Associated stress ranges were 19,4MPa and 19,8MPa, respectively. The largest values were recorded in the gauges located close to the mid spans.

    Stress range spectra are presented for the short term continuous measurement. The daily traffic gives in general lower stress ranges than the trucks used for the calibration. A large portion of the cycles are distributed over small stress ranges.

    For the gauges on the elevated bridge part, the analyses show a significant influence of dynamics on the results.

  • 38.
    Leander, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Zamiri Akhlaghi, Farshid
    Chalmers.
    Al-Emrani, Mohammad
    Chalmers.
    Fatigue reliability assessment of welded bridge details using probabilistic fracture mechanics2016In: IABSE Congress Stockholm 2016 Report: Challenges in Design and Construction of an Innovative and Sustainable Built Environment, Zürich: IABSE c/o ETH Hönggerberg , 2016Conference paper (Refereed)
    Abstract [en]

    The safe life method for the fatigue life prediction of steel bridges has for several cases been shown to render misleading results. To improve the accuracy, a probabilistic model based on linear elastic fracture mechanics (LEFM) is suggested. The model is used for a sensitivity analysis on the influence of different modelling options pertinent for a fatigue assessment of bridge details. The influence of material parameters and the crack growth threshold have been investigated. The analyses have been performed for a bridge detail frequently occurring in old steel bridges and a stress range spectrum based on measurements. The results show a significant difference in the estimated fatigue life depending on the modelling options. Furthermore, the omission sensitivity factors have been estimated for the probabilistic model showing the influence of the uncertainties of the variables and which of them that needs to be determined with care.

  • 39.
    Neves, Ana C.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Gonzalez, Ignacio
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    An approach to decision-making analysis for implementation of structural health monitoring in bridges2019In: Structural Control and Health Monitoring: The Bulletin of ACS, ISSN 1545-2255, E-ISSN 1545-2263, Vol. 26, no 6, article id e2352Article in journal (Refereed)
    Abstract [en]

    Adverse situations such as prolonged downtime of a structure, unnecessary inspections, expensive allocation of personal and equipment, deficient structural performance, or failure can be avoided by using structural health monitoring (SHM). Enhanced structural safety is the leading reason for its implementation, but one of the remaining obstacles to fully implement SHM systems deals with justifying their economic benefit. At any point in time, the preference towards one particular action depends on factors such as the probability of the triggered events and their consequences. All the possible decisions and relevant information can be illustrated by decision tree models, and the optimal decision corresponds to the one with the highest utility. Applying the Bayesian Theorem, the assumed prior probabilities of the structural state are updated in the light of new information provided by a system and the optimal decision is revised. This paper proposes a dynamic decision-making framework to manage civil engineering structures, where the ultimate goal is to achieve greater overall economy without jeopardizing safety. This paper covers a case study of a bridge where the optimal SHM and maintenance decisions are determined in the context of different scenarios in which the event probabilities and associated costs are made-up.

  • 40.
    Neves, Ana C.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    González Silva, Ignacio
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Cost-based optimization of the performance of a damage detection system2019In: Life-Cycle Analysis and Assessment in Civil Engineering: Towards an Integrated Vision - Proceedings of the 6th International Symposium on Life-Cycle Civil Engineering, IALCCE 2018, CRC Press/Balkema , 2019, p. 2103-2112Conference paper (Refereed)
    Abstract [en]

    Situations such as the collapse of civil engineering structures can be avoided if Structural Health Monitoring (SHM) systems can detect early potential failures and timely withdraw the structure from service ahead of a likely disaster. Structural safety is the leading reason for the implementation of SHM but also noteworthy is the cost reduction associated with routine maintenance and inspection. One of the remaining obstacles to fully implement SHM systems in our infrastructure deals with justifying their economic advantage. This paper proposes a rational framework for the use of SHM in the decision making process regarding the maintenance of civil engineering structures, based on the optimal setup of the damage detection system that yields the minimum associated deployment cost. Concepts such as Bayesian Theorem, Damage Index and Receiver Operating Characteristic curve are used in the proposed framework.

  • 41.
    Neves, Andreas C.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Gonzalez, Ignacio
    Sweco AB, Stockholm, Sweden..
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    A New Approach to Damage Detection in Bridges Using Machine Learning2018In: EXPERIMENTAL VIBRATION ANALYSIS FOR CIVIL STRUCTURES: TESTING, SENSING, MONITORING, AND CONTROL / [ed] Conte, JP Astroza, R Benzoni, G Feltrin, G Loh, KJ Moaveni, B, SPRINGER INTERNATIONAL PUBLISHING AG , 2018, p. 73-84Conference paper (Refereed)
    Abstract [en]

    At the same time that civil engineering structures are increasing in number, size and longevity, there is a conforming increasing preoccupation regarding the monitoring and maintenance of such structures. In this sense the demand for new reliable Structural Health Monitoring systems and damage detection techniques is high. A model-free damage detection approach based on Machine Learning is presented in this paper. The method performs on the collected feature measurements on a railway bridge, which for this study were gathered in a numerical experiment using a three dimensional finite element model. The first step of the approach consists in collecting the dynamic response of the structure, simulated during the passage of a train over the bridge, in both the healthy and damage states of the structure. The next step consists in the design and unsupervised training of Artificial Neural Networks that use as input accelerations and axle loads and compute a novelty index, called prediction error, based on a novelty detection approach. The distribution of the obtained prediction errors is statistically evaluated by means of a Gaussian Process and, after this process, damage indexes can be defined. Finally, the efficiency of the method is assessed in terms of Type I (false positive) and Type II (false negative) errors using Receiver Operating Characteristic curves. The promising results obtained in the case study demonstrate the capability of the presented method.

  • 42.
    Neves, André
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    González, I.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Structural health monitoring of bridges: a model-free ANN-based approach to damage detection2017In: Journal of Civil Structural Health Monitoring, ISSN 2190-5452, Vol. 7, no 5, p. 689-702Article in journal (Refereed)
    Abstract [en]

    As civil engineering structures are growing in dimension and longevity, there is an associated increase in concern regarding the maintenance of such structures. Bridges, in particular, are critical links in today’s transportation networks and hence fundamental for the development of society. In this context, the demand for novel damage detection techniques and reliable structural health monitoring systems is currently high. This paper presents a model-free damage detection approach based on machine learning techniques. The method is applied to data on the structural condition of a fictitious railway bridge gathered in a numerical experiment using a three-dimensional finite element model. Data are collected from the dynamic response of the structure, which is simulated in the course of the passage of a train, considering the bridge in healthy and two different damaged scenarios. In the first stage of the proposed method, artificial neural networks are trained with an unsupervised learning approach with input data composed of accelerations gathered on the healthy bridge. Based on the acceleration values at previous instants in time, the networks are able to predict future accelerations. In the second stage, the prediction errors of each network are statistically characterized by a Gaussian process that supports the choice of a damage detection threshold. Subsequent to this, by comparing damage indices with said threshold, it is possible to discriminate between different structural conditions, namely between healthy and damaged. From here and for each damage case scenario, receiver operating characteristic curves that illustrate the trade-off between true and false positives can be obtained. Lastly, based on the Bayes’ Theorem, a simplified method for the calculation of the expected total cost of the proposed strategy, as a function of the chosen threshold, is suggested.

  • 43.
    Pettersson, Lars
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Hansing, Lars
    ViaCon AB, Linköping.
    Fatigue design of soil steel composite bridges2012In: Archives of Institute of Civil Engineering, 2012Conference paper (Refereed)
    Abstract [en]

    Soil steel composite bridges are used more and more often in road and railroad bridge construction. Spans have increased and structures with spans over 20 m have been built. At the same time road designers call for lower heights of cover. At lower heights of cover the effect of concentrated loads will increase and therefore checking of the fatigue capacity is becoming more important.

    The paper presents the on-going project involving fatigue testing of bolted connections used to lap corrugated steel plates in Soil Steel Composite Bridges together with an evaluation of the detail category. The project also includes the development of a design procedure for the fatigue design of a Soil Steel Composite Bridge with low height of cover according to the Eurocode.

  • 44.
    Skoglund, Oskar
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    The impact of local geometry on the fatigue life of a welded structural detail2019In: Proceeding of Nordic Steel 2019, 2019Conference paper (Refereed)
    Abstract [en]

    Fatigue often limits the capacity of welded steel bridges, and thus often governs the amount of steel required. The fatigue life is, to a large extent, governed by stress concentrations and the magnitude is controlled by local as well as global geometry; by improving the local geometry the stress raising effects can be lowered and by increasing the global dimensions the nominal stress can be reduced. The fatigue assessment format presented in the Eurocode gives little or no room for the designer to control the local geometry of the structural detail, and is often left with increasing the overall dimensions in order to improve the fatigue life of the structure. This paper aims at investigating the possible impact on the fatigue life of welded steel structures by different weld geometries. In this paper a vertical stiffener will be studied by fracture mechanics. The study showed that significant improvements in fatigue life can be made by small changes to the weld geometry and the most pronounced effect was by changing the weld toe radius, and

  • 45.
    Skoglund, Oskar
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Optimizing the steel girders in a high strength steel composite bridgeIn: International Journal of Steel Structures, ISSN 1598-2351, E-ISSN 2093-6311Article in journal (Refereed)
    Abstract [en]

    The use of high strength steel has the potential to reduce the amount of steel used in bridges and thereby, facilitate a more sustainable construction. In this study, an optimization of a composite steel and concrete bridge is presented. The study aimed at identifying the potential benets of using high strength steel, compared to conventional steel, in terms of weight, material cost and environmental impact. The optimization routine followed what is outlined in the Eurocode and satised both ultimate and serviceability limit state conditions, with exception of fatigue. To study the inuence of fatigue a separate verication was performed on the solutions found from the optimization. The study showed that substantial savings in weight, environmental impact and material cost could be made by implementing high strength steel. However, when the fatigue verication according to Eurocode was considered, the potential benets of using steels of higher grade vanished completely.

  • 46.
    Skoglund, Oskar
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Overview of steel bridges containing high strength steel material2019In: International Journal of Steel Structures, ISSN 1598-2351, E-ISSN 2093-6311Article in journal (Refereed)
    Abstract [en]

     The use of high strength steel has the potential to reduce the amount of steel used in bridges and thereby, facilitate a more sustainable construction. A survey of existing bridges built using high strength steel is presented in this paper with emphasis on the Swedish bridge stock. The survey aimed at identifying the steel grades that were used and where in the cross-section they have been used. A case study on the inuence of fatigue shows that today's regulations make it more dicult to use high strength steel in comparison to previous regulations.

  • 47.
    Tell, Sarah
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Andersson, Andreas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges. Trafikverket.
    Mahir, Ülker-Kaustell
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges. Tyréns.
    Sensitivity analysis of a high-speed railway bridge with supplemental fluid viscous dampersManuscript (preprint) (Other academic)
    Abstract [en]

    One approach for upgrading existing high-speed bridges which are susceptible to excessive vibrations is to install damping devices. In this paper, a single-degree-of-freedom model of a simply-supported bridge with supplemental fluid viscous dampers installed between the superstructure and the abutments is derived based on an arbitrary mode of vibration. Further, to ensure the robustness of the proposed vibration mitigation method, a statistical screening of the uncertainties associated with the bridge-damper system is conducted using Monte-Carlo simulations. From this screening, it is possible to evaluate the probability of exceedance of a stipulated acceleration level, as well as studying the sensitivity of the ingoing random variables. This paper also highlights the necessity of conducting a statistical assessment to determine an estimate for the distribution of the acceleration limit and model uncertainty for dynamic analyses. The results also show that 1) the modulus of elasticity and structural damping should be treated as stochastic variables for the studied bridge, 2) it is sufficient to install damping devices only at the moveable bearing and 3) the proposed retrofit is insufficient if the friction of the moveable bearings is not overcome for the given set of damper parameters.

  • 48.
    Wallin, Joakim
    et al.
    KTH.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
    Strengthening of a steel railway bridge and its impact on the dynamic response to passing trains2011In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 33, no 2, p. 635-646Article in journal (Refereed)
    Abstract [en]

    Two different strengthening methods for a through-girder steel railway bridge are investigated. The studied structure is the Soderstrom Bridge, located in the city of Stockholm, Sweden. Due to fatigue problems, it is in need of assessment and strengthening. In one of the methods, arches are added under the bridge modifying the structural system and lowering the stress ranges for all structural members. The other method consists of prestressing the floor beams. This increases their stiffness and transforms the mean stress in the lower flanges from tension to compression. A 3D finite element model is created and verified with measurements. The different strengthening methods are tested in the model by dynamic analysis with moving train loads. The strengthening methods show some positive effect concerning the fatigue life. Changes in vertical bridge deck acceleration for high speed traffic are also presented. A comparison between the European code and the Swedish code regarding vertical bridge deck acceleration levels for high speed traffic shows large differences for the bridge.

  • 49.
    Wang, Ruoqi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Comparison of simulation methods applied to steel bridge reliability evaluations2019Conference paper (Refereed)
    Abstract [en]

    Steel bridges are in general subjected to fatigue deterioration and the structural reliability of bridges will thus reduce over time. There are multiple simulation-based procedures available to perform structural probabilistic studies with several classes of uncertainty taken into account. Since the crack propagation is highly nonlinear and the limit state function (LSF) is multi-dimensional, it imposes specific demands on the simulation methods. Monte Carlo simulation (MCS) has been widely applied in various of fields, however, it requires a great amount of samples and long computation time to reach a high level of accuracy. A more advanced method, Subset Simulation (SS), compensates this shortage. It calculates the product of conditional probabilities of several chosen intermediate failure events. In this paper, the performance of each method was evaluated and compared against fatigue deterioration for aselected bridge detail. A probabilistic model was defined and both prior and updated reliability estimation were performed. The results showed that SS is a good option to deal with fatigue problem with high nonlinearity and multi-dimensional LSF, and shows outstanding time efficiency compared to MCS to reach a comparable accuracy.

1 - 49 of 49
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