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Improving the Dynamic Design Philosophy of High-Speed Railway Bridges Using Reliability-Based Methods
KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad. (Division of Structural Engineering and Bridges)ORCID-id: 0000-0002-8453-8937
2024 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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%.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2024. , s. 93
Serie
TRITA-ABE-DLT ; 246
Nyckelord [en]
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
Nyckelord [sv]
Höghastighetsjärnvägsbroar, Brodynamik, Trafiksäkerhet, Passagerarkomfort, Konstruktioners tillförlitlighet, Surrogatmodeller, Aktivt lärande, Tillförlitlighetsbaserad optimering, Kalibrering av partialkoefficienter, Epistemiska osäkerheter
Nationell ämneskategori
Samhällsbyggnadsteknik Infrastrukturteknik Maskinteknik
Forskningsämne
Byggvetenskap, Bro- och stålbyggnad
Identifikatorer
URN: urn:nbn:se:kth:diva-344610ISBN: 978-91-8040-880-6 (tryckt)OAI: oai:DiVA.org:kth-344610DiVA, id: diva2:1846168
Disputation
2024-04-26, Kollegiesalen, Brinellvägen 8, KTH Campus, https://kth-se.zoom.us/j/67332931197, Stockholm, 13:00 (Engelska)
Opponent
Handledare
Projekt
IN2TRACK2IN2TRACK3IAM4RAIL
Anmärkning

QC 240325

Tillgänglig från: 2024-03-25 Skapad: 2024-03-21 Senast uppdaterad: 2024-04-03Bibliografiskt granskad
Delarbeten
1. Reliability Assessment of the Dynamic Behavior of High-Speed Railway Bridges Using First Order Reliability Method
Öppna denna publikation i ny flik eller fönster >>Reliability Assessment of the Dynamic Behavior of High-Speed Railway Bridges Using First Order Reliability Method
2020 (Engelska)Ingår i: Proceedings of the 11th International Conference on Structural Dynamics, / [ed] M. Papadrakakis, M. Fragiadakis, C. Papadimitriou, Athens, Greece, 2020, Vol. 2, s. 3438-3450, artikel-id 18654Konferensbidrag, Publicerat paper (Refereegranskat)
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.

Ort, förlag, år, upplaga, sidor
Athens, Greece: , 2020
Serie
EASD Procedia
Nyckelord
High-Speed Railway Bridges, Bridge Dynamics, Structural Reliability, First Order Reliability Method, Running Safety, Serviceability Limit State
Nationell ämneskategori
Infrastrukturteknik
Forskningsämne
Byggvetenskap, Bro- och stålbyggnad; Byggvetenskap
Identifikatorer
urn:nbn:se:kth:diva-287539 (URN)10.47964/1120.9282.18654 (DOI)
Konferens
Eurodyn 2020, 11th International Conference on Structural DynamicsAthens, 23-26 November, 2020.
Projekt
Shift2Rail
Anmärkning

Not duplicate with DiVA 1552464

QC 20201216

Tillgänglig från: 2020-12-14 Skapad: 2020-12-14 Senast uppdaterad: 2024-03-21Bibliografiskt granskad
2. Probabilistic dynamic design curves optimized for high-speed reinforced concrete railway bridges using first order reliability method
Öppna denna publikation i ny flik eller fönster >>Probabilistic dynamic design curves optimized for high-speed reinforced concrete railway bridges using first order reliability method
(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Abstract [en]

Increasing the operating speed of trains in modern railway networks can induce greater actions on the infrastructure than was previously the case. This is due, in particular, to the occurrence of the resonance phenomenon in railway bridges, which is the focus of this article and was not traditionally considered as a concern. In this context, the vibrations experienced by bridges, both vertical accelerations and displacements, are limited by design regulations to ensure that the safety of train passages over bridges and the comfort of passengers are guaranteed. However, previous studies have shown that the conventional dynamic design methods do not always result in conservative designs, nor is the achieved safety always consistent. Therefore, a probabilistic approach is adopted in this study to optimize the cross-section properties of various railway bridges in a widedesign range including section types, span lengths, and number of spans. For this purpose, an iterative line search based optimization problem is formulated to minimize the depth of the cross-sections under consideration and consequently the linear mass of the bridges. Meanwhile, the associated failure probabilities of the above dynamic limit states are constrained to be less than the desired level of safety by incorporating them in to the optimization constraint. In this regard, First Order Reliability Method (FORM) is adopted to perform reliability analyses. Thus, the obtained results are presented in the form of design curves that may assist designers to select minimum cross-section dimensions satisfying the desired level of safety in terms of dynamic limit states. This objective can be achieved using the proposed design curves without the need to construct associated complex computational models and perform computationally expensive dynamic analyses.

Nyckelord
High-speed railway bridges, Bridge dynamics, Running safety, Passenger comfort, Design curve, Structural reliability, FORM
Nationell ämneskategori
Infrastrukturteknik
Forskningsämne
Byggvetenskap, Bro- och stålbyggnad
Identifikatorer
urn:nbn:se:kth:diva-344607 (URN)
Projekt
IAM4RAIL projec
Anmärkning

QC 20240321

Tillgänglig från: 2024-03-21 Skapad: 2024-03-21 Senast uppdaterad: 2024-03-21Bibliografiskt granskad
3. Applicability of meta-model assisted reliability assessment for dynamic problems: a comparison between regression-based methods
Öppna denna publikation i ny flik eller fönster >>Applicability of meta-model assisted reliability assessment for dynamic problems: a comparison between regression-based methods
2023 (Engelska)Ingår i: Proceedings 14th International Conference on Applications of Statistics and Probability in Civil Engineering, ICASP14, Trinity College Dublin , 2023Konferensbidrag, Muntlig presentation med publicerat abstract (Refereegranskat)
Abstract [en]

There is a growing intent among engineers, stakeholders, and decision makers to use probabilistic methods for infrastructure assessment or design objectives. However, the corresponding limit state for such problems usually requires the construction of complex computational models, usually using commercial software without parallelization capability. Such a requirement makes performing reliability analysis computationally prohibitive, which is even more challenging for dynamic problems, since a very short time step is required to obtain sufficiently accurate predictions. This concern has led to several methods being proposed to surrogate the limit state function with a generally black box called a meta-model. A variety of them, such as Kriging, Polynomial Chaos Expansion (PCE), Artificial Neural Networks (ANN), and response surfaces (e.g., polynomial, spline, or radial-base functions), have been adopted for this purpose. These meta-models are typically trained on a limited data set collected by computing the true responses of carefully selected input variables. Their applicability for assessing the probability of failure has been studied individually in the literature for both benchmark and practical problems. However, as far as the authors are aware, no comparison has been made between them for dynamic problems. This comparison needs to be made from the point of view of both accuracy and performance (number of calls to the limit state function). In this context, this paper takes a systematic approach to evaluate their performance under identical conditions, i.e., with similar training datasets. For this purpose, the dynamic response of railway bridges with different spans excited by the passage of trains with a wide range of speeds is used as a reference problem.

Ort, förlag, år, upplaga, sidor
Trinity College Dublin, 2023
Nationell ämneskategori
Infrastrukturteknik
Forskningsämne
Byggvetenskap, Bro- och stålbyggnad
Identifikatorer
urn:nbn:se:kth:diva-337404 (URN)
Konferens
14th International Conference on Applications of Statistics and Probability in Civil Engineering, ICASP14, Dublin, Ireland, July 9-13, 2023
Anmärkning

QC 20231004

Tillgänglig från: 2023-10-02 Skapad: 2023-10-02 Senast uppdaterad: 2024-03-21Bibliografiskt granskad
4. Improved dynamic design method of ballasted high-speed railway bridges using surrogate-assisted reliability-based design optimization of dependent variables
Öppna denna publikation i ny flik eller fönster >>Improved dynamic design method of ballasted high-speed railway bridges using surrogate-assisted reliability-based design optimization of dependent variables
2023 (Engelska)Ingår i: Reliability Engineering & System Safety, ISSN 0951-8320, E-ISSN 1879-0836, Vol. 238, artikel-id 109406Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Operating high-speed trains imposes excessive vibrations to bridges raising concerns about their safety. In this context, it was shown that some conventional design methods such as those related to the running safety suffer from a vague scientific background questioning their reliability or optimality. Therefore, the current article is devoted to updating the conventional design methodology, using Reliability-Based Design Optimization (RBDO) to propose the minimum allowable mass and stiffness which assures satisfying the target reliability. These proposed minimum design values can conceptually replace the conventional partial safety factor-based design method for running safety without the need for dynamic analysis. If the mass and stiffness resulting from the control of other limit states meet the proposed minimum values, the desired target reliability for running safety will be assured. This is achieved by adaptively training Kriging meta-models as a surrogate for the computational models decoupling the RBDO problem. In this regard, a new stopping criteria is proposed using mis-classification ratio of the cross-validated model; which reduces the generalization error of the trained meta-model and consequently the estimated failure probability. Moreover, due to the dependence of the design variables, the Copula concept is used to refine the augmented space and reformulate the RBDO problem.

Ort, förlag, år, upplaga, sidor
Elsevier BV, 2023
Nyckelord
Active learning, Adaptive sampling, Bridge dynamics, Copula function, Dependent variables, High-speed railway bridges, Kriging, Meta-modelling, Reliability-based design optimization
Nationell ämneskategori
Teknisk mekanik
Identifikatorer
urn:nbn:se:kth:diva-331438 (URN)10.1016/j.ress.2023.109406 (DOI)001021234800001 ()2-s2.0-85161610804 (Scopus ID)
Anmärkning

QC 20230710

Tillgänglig från: 2023-07-10 Skapad: 2023-07-10 Senast uppdaterad: 2024-03-21Bibliografiskt granskad
5. Partial safety factor calibration using surrogate models: An application for running safety of ballasted high-speed railway bridges
Öppna denna publikation i ny flik eller fönster >>Partial safety factor calibration using surrogate models: An application for running safety of ballasted high-speed railway bridges
2024 (Engelska)Ingår i: Probabilistic Engineering Mechanics, ISSN 0266-8920, E-ISSN 1878-4275, Vol. 75, artikel-id 103569Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Traditionally, regulations employ semi-probabilistic methods with partial safety factors to control design limits. Calibrating these partial safety factors involves estimating the target reliability level and optimizing the partial safety factor values in order to minimize the deviation of the safety index between the considered design scenarios and the target value. This procedure necessitates performing a demanding amount of reliability analyses and is often carried out for simplified design situations. Therefore, high computational costs must be accepted for design problems formulated with complex computational models. This study implements a meta-modeling approach based on active learning in the partial safety calibration procedure, enabling its application to computationally intensive problems. Subsequently, the approach is applied to the running safety of ballasted high-speed railway bridges. This limit state implicitly accounts for the phenomenon of ballast destabilization, the occurrence of which disturbs the load path from the rail level to the bridge structure. The dramatic increase in train operating speeds in recent decades has increased the possibility of this design limit state being violated due to resonance. Despite the evident safety concerns, the adopted safety factors appear to be solely based on engineering judgments rather than calibration through higher-level reliability analysis. Therefore, the proposed calibration method is employed to determine the corresponding partial safety factors for various maximum allowable operating train speeds. The newly calibrated partial safety factors allow for a permissible maximum vertical acceleration of the bridge deck approximately 25% higher than the conventional design approaches. Therefore, incorporating these factors into the design procedure may lead to the construction of lighter bridges.

Ort, förlag, år, upplaga, sidor
Elsevier BV, 2024
Nyckelord
Active learning, Bridge dynamics, High-speed railway bridges, Kriging, Meta-modeling, Partial safety factor calibration, Running safety
Nationell ämneskategori
Infrastrukturteknik
Identifikatorer
urn:nbn:se:kth:diva-342141 (URN)10.1016/j.probengmech.2023.103569 (DOI)2-s2.0-85180810123 (Scopus ID)
Anmärkning

QC 20240115

Tillgänglig från: 2024-01-15 Skapad: 2024-01-15 Senast uppdaterad: 2024-03-21Bibliografiskt granskad
6. Reliability assessment of running safety criteria of railway bridges considering soil-structure interaction effects using ensemble of classification-based surrogate models
Öppna denna publikation i ny flik eller fönster >>Reliability assessment of running safety criteria of railway bridges considering soil-structure interaction effects using ensemble of classification-based surrogate models
(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Abstract [en]

The increasing speeds of modern trains lead to excessive vibrations on the bridges, which have the potential to destabilize the ballast particles of the track. The occurrence of this phenomenon not only increases the track maintenance cost, but can also disrupt the load path from the rail level to the bridge deck, posing a risk to the train running safety. The design regulations indirectly control this limit-state by limiting the vertical acceleration of the bridge deck to a threshold value. The assessments pertaining to this purpose often neglect the soil-structure interaction (SSI) effects considering that as a conservative assumption. Such effects can positively contribute by increasing the system damping, but they can also increase the bridge flexibility making it more susceptible to vibrations. Therefore, this study investigates the influence of considering/disregarding SSI effects on the running safety criterion using a probabilistic methodology. The results are classified based on the maximum permissible train speeds and the bridge span length. Due to the high computational costs of the reliability analyses, the limit-state is approximated by an ensemble of classification-based surrogate models using the stack-generalization concept. Subsequently, the upper/lower bounds of the failure probability in the presenceof SSI effects are compared with those obtained for simply-supported bridges. It is pointed out that neglecting SSI effects for shorter span bridges may lead to an underestimation of system safety. For longer span bridges, however, this may lead to an overestimation of safety, which means that a non-conservative system can be designed.

Nyckelord
Running safety, Soil-structure interaction effects, High-speed railway bridges, Ensemble of surrogate models, Active learning, Binary classification surrogate
Nationell ämneskategori
Infrastrukturteknik
Forskningsämne
Byggvetenskap, Bro- och stålbyggnad
Identifikatorer
urn:nbn:se:kth:diva-344608 (URN)
Projekt
IAM4RAIL projec
Anmärkning

QC 20240321

Tillgänglig från: 2024-03-21 Skapad: 2024-03-21 Senast uppdaterad: 2024-03-21Bibliografiskt granskad
7. Surrogate-assisted investigation on influence of epistemic uncertainties on running safety of high-speed trains on bridges
Öppna denna publikation i ny flik eller fönster >>Surrogate-assisted investigation on influence of epistemic uncertainties on running safety of high-speed trains on bridges
2024 (Engelska)Ingår i: Probabilistic Engineering Mechanics, ISSN 0266-8920, E-ISSN 1878-4275, Vol. 75, artikel-id 103559Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The operational safety of high-speed trains traversing ballasted bridges is contingent upon the prevention of the ballast destabilization, which can interrupt load transfer from the rail to the bridge. Current design regulations indirectly address this limit-state by specifying a threshold value for the vertical acceleration of the superstructure. This value represents the condition at which the inertial forces induced by train passage exceed the resistive forces. However, this approach is based on limited experimental data and the influence of numerous parameters remains unexplored. As a result, reliability analyses pertaining to running safety are hampered by a lack of knowledge, leading to greater epistemic uncertainties. In this study, the impact of such uncertainties on this dynamic system is investigated using surrogate-based Imprecise Structural Reliability Analysis (ISRA). For this purpose, parametric probability boxes are used to represent lower and upper bounds of the cumulative distribution function for basic random variables with epistemic uncertainties and surrogate models are adaptively trained to reduce computational costs. The obtained results show that neglecting the influence of epistemic uncertainties can lead to permissible operating train speed higher than the speed corresponding to the desired reliability level. In this study, an overestimation of about 13% was observed on average. Furthermore, the rough analyses carried out show that taking epistemic uncertainties into account can lead to a reduction of the system characteristic safety factor by up to 30%. This significant reduction underlines the importance of expanding the available knowledge on the phenomenon of ballast instability.

Ort, förlag, år, upplaga, sidor
Elsevier BV, 2024
Nyckelord
Aleatory uncertainty, Epistemic uncertainty, High-speed railway bridges, Imprecise Structural Reliability Analysis, Kriging, Probability-box, Running safety, Surrogate models
Nationell ämneskategori
Infrastrukturteknik
Identifikatorer
urn:nbn:se:kth:diva-341453 (URN)10.1016/j.probengmech.2023.103559 (DOI)001126380100001 ()2-s2.0-85178381569 (Scopus ID)
Anmärkning

QC 20240108

Tillgänglig från: 2024-01-08 Skapad: 2024-01-08 Senast uppdaterad: 2024-03-21Bibliografiskt granskad

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