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Reliability Assessment of the Dynamic Behavior of High-Speed Railway Bridges Using First Order Reliability Method
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.ORCID iD: 0000-0002-8453-8937
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges. Swedish Transport Administration.ORCID iD: 0000-0002-8926-2140
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.ORCID iD: 0000-0002-5447-2068
2020 (English)In: Proceedings of the 11th International Conference on Structural Dynamics, / [ed] M. Papadrakakis, M. Fragiadakis, C. Papadimitriou, Athens, Greece, 2020, Vol. 2, p. 3438-3450, article id 18654Conference paper, Published paper (Refereed)
Abstract [en]

The operational speed of the trains is intended to be significantly increasedforthcoming; which consequently questions the safety level of the current design conceptsconcerning different performance limits. Thus, the reliability of the simply supportedsingle-span bridges is assessed in the current article adopting the first-order reliabilitymethod (FORM) approach. In this regard, the dynamic response of the aimed bridges isinvestigated under the passage of a series of moving loads using available closed-form solutions in the literature. Hereof, axle load, car body/train configuration, flexural rigidity,damping, mass and model uncertainties are considered as random variables; while traintrack-bridge interactions are neglected and the procedure is repeated for a wide range ofspan lengths and train velocities. Then, the safety index corresponding to each case isevaluated by considering running safety as the limit state function; where, the bridge deckvertical acceleration is taken as the capacity of the system. The outcomes are presentedas average probability of exceeding the limit state versus train speed and categorized basedon span lengths.

Place, publisher, year, edition, pages
Athens, Greece, 2020. Vol. 2, p. 3438-3450, article id 18654
Series
EASD Procedia
Keywords [en]
High-Speed Railway Bridges, Bridge Dynamics, Structural Reliability, First Order Reliability Method, Running Safety, Serviceability Limit State
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering, Structural Engineering and Bridges; Civil and Architectural Engineering
Identifiers
URN: urn:nbn:se:kth:diva-287539DOI: 10.47964/1120.9282.18654OAI: oai:DiVA.org:kth-287539DiVA, id: diva2:1509871
Conference
Eurodyn 2020, 11th International Conference on Structural DynamicsAthens, 23-26 November, 2020.
Projects
Shift2Rail
Note

Not duplicate with DiVA 1552464

QC 20201216

Available from: 2020-12-14 Created: 2020-12-14 Last updated: 2024-03-21Bibliographically approved
In thesis
1. Reliability-Based Assessment and Optimization of High-Speed Railway Bridges
Open this publication in new window or tab >>Reliability-Based Assessment and Optimization of High-Speed Railway Bridges
2021 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Increasing the operational speed of trains has attracted a lot of interest in the last decades and has brought new challenges, especially in terms of infrastructure design methodology, as it may induce excessive vibrations. Such demands can damage bridges, which in turn increases maintenance costs, endangers the safety of passing trains and disrupts passenger comfort. Conventional design provisions should therefore be evaluated in the light of modern concerns; nevertheless, several previous studies have highlighted some of their shortcomings. It should be emphasized that most of these studies have neglected the uncertainties involved, which preventsthe reported results from representing a complete picture of the problem. In this respect, the present thesis is dedicated to evaluating the performance of conventional design methods, especially those related to running safety and passenger comfort, using probabilistic approaches. To achieve this objective, a preliminary study was carried out using the first-order reliability method for short/medium span bridges passed by trains at a wide range of operating speeds. Comparison of these results with the corresponding deterministic responses showed that applying a constant safety factor to the running safety threshold does not guarantee that the safety index will be identical for all bridges. It also shows that the conventional design approaches result in failure probabilities that are higher than the target values. This conclusion highlights the need to update the design methodology for running safety. However, it would be essential to determine whether running safety is the predominant design criterion before conducting further analysis. Therefore, a stochastic comparison between this criterion and passenger comfort was performed. Due to the significant computational cost of such investigations, subset simulation and crude Monte-Carlo (MC) simulation using meta-models based on polynomial chaos expansion were employed. Both methods were found to perform well, with running safety almost always dominating the passenger comfort limit state. Subsequently, classification-based meta-models, e.g. support vector machines, k-nearest neighbours and decision trees, were combined using ensemble techniques to investigate the influence of soil-structure interaction on the evaluated reliability of running safety. The obtained results showed a significant influence, highlighting the need for detailed investigations in further studies. Finally, a reliability-based design optimization was conducted to update the conventional design method of running safety by proposing minimum requirements for the mass per length and moment of inertia of bridges. It is worth mentioning that the inner loop of the method was solved by a crude MC simulation using adaptively trained Kriging meta-models.

Abstract [sv]

Att öka tågens hastighet har väckt stort intresse under de senaste decennierna och har medfört nya utmaningar, särskilt när det gäller broanalyser, eftersom tågen inducerar stora vibrationer. Sådana vibrationer kan öka underhållskostnaderna, äventyra säkerheten för förbipasserande tåg och påverka passagerarkomforten. Konstruktionsbestämmelser bör därför utvärderas mot bakgrund av dessa problem; dock har flera tidigare studier belyst några av bristerna i dagens bestämmelser. Det bör understrykas att de flesta av dessa studier har försummat de osäkerheter som är involverade, vilket hindrar de rapporterade resultaten från att representera en fullständig bild av problemet. I detta avseende syftar denna avhandling till att utvärdera prestandan hos konventionella analysmetoder, särskilt de som rör körsäkerhet och passagerarkomfort, med hjälp av sannolikhetsmetoder. För att uppnå detta mål genomfördes en preliminär studie med första ordningens tillförlitlighetsnmetod för broar med kort/medellång spännvidd som passeras av tåg med ett brett hastighetsspektrum. Jämförelse av dessa resultat med motsvarande deterministiska respons visade att tillämpa en konstant säkerhetsfaktor för verifieringen av trafiksäkerhet inte garanterar att säkerhetsindexet kommer att vara identiskt för alla broar. Det visar också att de konventionella analysmetoderna resulterar i brottsannolikheter som är högre än målvärdena. Denna slutsats belyser behovet av att uppdatera analysmetoden för trafiksäkerhet. Det skulle emellertid vara viktigt att avgöra om trafiksäkerhet är det dominerande designkriteriet innan ytterligare analyser genomförs. Därför utfördes en stokastisk jämförelse mellan detta kriterium och kriteriet för passagerarkomfort. På grund av den betydande. analystiden för sådana beräkningar användes delmängdssimulering och Monte-Carlo (MC) simulering med metamodeller baserade på polynomisk kaosutvidgning. Båda metoderna visade sig fungera bra, med trafiksäkerhet som nästan alltid dominerade över gränsningstillståndet för passagerarkomfort. Därefter kombinerades klassificeringsbaserade metamodeller som stödvektormaskin och beslutsträd genom ensembletekniker, för att undersöka påverkan av jord-brointeraktion på den utvärderade tillförlitligheten gällande trafiksäkerhet. De erhållna resultaten visade en signifikant påverkan och betonade behovet av detaljerade undersökningar genom ytterligare studier. Slutligen genomfördes en tillförlitlighetsbaserad konstruktionsoptimering för att föreslå ett minimikrav på erforderlig bromassa per längdmeter och tröghetsmoment. Det är värt att nämna att metodens inre loop löstes med en MC-simulering med adaptivt tränade Kriging-metamodeller.

Place, publisher, year, edition, pages
Sweden: KTH Royal Institute of Technology, 2021. p. 83
Series
TRITA-ABE-DLT ; 2133
Keywords
High-speed railway bridges, Bridge dynamics, Running safety, Passenger comfort, Structural reliability, Meta-models, Surrogate models, Adaptive sampling, Reliability-based design optimization, Höghastighetsjärnvägsbroar, Brodynamik, Trafiksäkerhet, Passagerarkomfort, Konstruktioners tillförlitlighet, Metamodeller, Surrogatmodeller, Adaptiv sampling, Tillförlitlighetsbaserad designoptimering
National Category
Engineering and Technology Civil Engineering Infrastructure Engineering
Research subject
Civil and Architectural Engineering, Structural Engineering and Bridges
Identifiers
urn:nbn:se:kth:diva-301318 (URN)978-91-7873-977-6 (ISBN)
Presentation
2021-10-01, Videolänk https://kth-se.zoom.us/j/64754196008, Du som saknar dator /datorvana kontakta Raid Karoumi raidk@kth.se / Use the e-mail address if you need technical assistance, Stockholm, 13:00 (Swedish)
Opponent
Supervisors
Note

QC 20210910

Available from: 2021-09-10 Created: 2021-09-07 Last updated: 2022-06-25Bibliographically approved
2. Improving the Dynamic Design Philosophy of High-Speed Railway Bridges Using Reliability-Based Methods
Open this publication in new window or tab >>Improving the Dynamic Design Philosophy of High-Speed Railway Bridges Using Reliability-Based Methods
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Modern railway infrastructures, especially bridges, are exposed to significant vibrations with potential safety implications. In this context, previous studies have shown the inconsistency and inadequacy of some conventional design methods necessitaing them to be improved. The assessment of safety inherently deals with uncertainties. Therefore, the current study is dedicated to this objective using reliability-based methods. Of the various possible failure modes, the investigations presented here are limited to running safety and passenger comfort. The investigation of these limit-states requires constructing complex computational models with train-track-bridge interaction capabilities. However, the application of these computationally intensive models in the context of structural reliability does not appear to be feasible. Simplifying the system, the vertical acceleration and the deflection of the bridge serve as implicit limit-state measures. Initially, using First Order Reliability Method (FORM) revealed limitations in the application of the current safety factor, resulting in inconsistent reliability indices. Therefore, probabilistic design curves are proposed, defining minimum required bridge mass and stiffness based on cross-section types, span configurations and train speeds. These results are obtained by formulating a FORM-based optimization. Subsequently, the results are used to investigate the sensitivity of the estimated failure probabilities with respect to the contributing basic random variables. Acknowledging the limitations of FORM, surrogate-assisted simulation-based reliability assessments were used for further investigations. A comparison of the performance of widely used regression-based surrogate models under an identical active learning scheme showed the superior performance of the Kriging method over the others. Within areliability-based design optimization framework, this Kriging model facilitates the generation of new probabilistic design curves. This is achieved by reformulating the conventional method to account for the dependency between design variables using the copula concept. In addition, the surrogate model aided in calibrating the safety factor associated with the vertical acceleration threshold, leading to a proposal of 1.38 as a new safety factor. Subsequently, the influence of soil-structure interaction on the estimated reliability indices is evaluated using an ensemble of classification-based surrogate models. Results highlighted its beneficial contribution in terms of increased damping for shorter spans, countered by adverse effects due to frequency shortening in longer bridges. Finally, the epistemic uncertainties arising from the limited knowledge of the vertical acceleration threshold are investigated. It is found that neglecting these uncertainties can lead to an overestimation of allowable train speeds by about 13%.

Abstract [sv]

Moderna järnvägsbroar utsätts för betydande säkerhetsrelaterade vibrationer. Tidigare studier har visat att vissa konventionella dimensioneringsmetoder är inkonsekventa och otillräckliga, vilket kräver förbättringar. Säkerhetsbedömning handlar i grunden om osäkerheter. Därför ägnas den föreliggande studien åt detta mål med hjälp av tillförlitlighetsbaserade metoder. Undersökningarna här begränsas till trafiksäkerhet och passagerarkomfort som möjliga dimensioneringsvillkor. Undersökningen av dessa gränstillstånd kräver komplexa beräkningsmodeller som beaktar tåg-spår-bro-interaktion. Att använda beräkningsintensiva modeller för strukturell tillförlitlighet verkar inte genomförbart. Genom förenklingar av systemet kan vertikal acceleration och nedböjning ansättas som mått för implicita gränsvillkor. Inledningsvis visade användningen av första ordningens tillförlitlighetsmetod (FORM) begränsningar i tillämpningen av nuvarande säkerhetsfaktor, vilken resulterade i inkonsekventa säkerheter. För att adressera detta föreslås probabilistiska dimensioneringskurvor, som definierar minsta erforderliga bromassa och styvhet baserat på tvärsnittstyper, spannkonfigurationer och tåghastigheter. Dessa resultat erhålls genom att formulera en FORM-baserad optimering. Därefter används resultaten för att undersöka känsligheten hos de uppskattade brottsannolikheterna med avseende på de ingående grundläggande stokastiska variablerna. Med tanke på begränsningarna med FORM användes simulering-baserade tillförlitlighetsbedömningar med hjälp av surrogatmodeller för fortsatta undersökningar. I en jämförelse av kända regressionsbaserade surrogatmodeller, under identiska inlärningsförutsättningar, visade Kriging-metoden överlägsen effektivitet. Inom ramen för en tillförlitlighetsbaserad optimering underlättar denna Kriging-modell framtagningen av nya probabilistiska designkurvor. Detta uppnås genom en ny formulering av metoden där korrelationen mellan de stokastiska variablerna beaktas med hjälp av Copula-funktioner. Dessutom användes surrogatmodellen till att kalibrera säkerhetsfaktorn som är associerad med gränsvärdet för vertikal acceleration, vilket ledde till ett förslag på 1,38 som ett nytt värde för säkerhetsfaktorn. Därefter utvärderas påverkan av jord-strukturinteraktion på uppskattad säkerhet med hjälp av en samling av klassificeringsbaserade surrogatmodeller. Resultaten visar interaktionens bidrag i form av ökad dämpning för kortare spann, motverkad av negativa effekter på grund av frekvensförkortning hos längre broar. Slutligen utforskas de epistemiska osäkerheterna behäftade med den begränsade kunskapen om gränsvärdet för vertikal acceleration. Det konstateras att försummelse av dessa osäkerheter kan leda till en överskattning av tillåtna tåghastigheter med cirka 13%.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2024. p. 93
Series
TRITA-ABE-DLT ; 246
Keywords
High-speed railway bridges, Bridge dynamics, Running safety, Passenger comfort, Structural reliability, Surrogate models, Active learning, Reliability-based design optimization, Partial safety calibration, Epistemic uncertainties, Höghastighetsjärnvägsbroar, Brodynamik, Trafiksäkerhet, Passagerarkomfort, Konstruktioners tillförlitlighet, Surrogatmodeller, Aktivt lärande, Tillförlitlighetsbaserad optimering, Kalibrering av partialkoefficienter, Epistemiska osäkerheter
National Category
Civil Engineering Infrastructure Engineering Mechanical Engineering
Research subject
Civil and Architectural Engineering, Structural Engineering and Bridges
Identifiers
urn:nbn:se:kth:diva-344610 (URN)978-91-8040-880-6 (ISBN)
Public defence
2024-04-26, Kollegiesalen, Brinellvägen 8, KTH Campus, https://kth-se.zoom.us/j/67332931197, Stockholm, 13:00 (English)
Opponent
Supervisors
Projects
IN2TRACK2IN2TRACK3IAM4RAIL
Note

QC 240325

Available from: 2024-03-25 Created: 2024-03-21 Last updated: 2024-04-03Bibliographically approved

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Allahvirdizadeh, RezaAndersson, AndreasKaroumi, Raid

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