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Trafikverket förfogar över närmare 4000 järnvägsbroar i olika skick och ålder runt om i landet. Beståndet är i ständigt behov av underhåll och erfordrar kontinuerliga kontroller. Den här rapporten är utformad som en skadeutredning på en enkelspårig järnvägsbro söder om Solvarbo i Säter kommun. Järnvägsbron är i drift och här passerar över 10 000 tåg/år. Allt från snabbtåg till godståg. Bron är av typ balkbro, fritt upplagd över väg. Rapporten är gjord i samråd med företaget Reinertsen Sverige AB. En utredning av bron utfördes 2013 av Reinertsen Sverige AB i vilken beskrivs att ena landfästet kläms mot överbyggnaden till följd av rörelse. De skador som då noterades var att de rörliga lagren var kraftigt snedställda, överbyggnaden var i kontakt med grusskifte samt att en avsevärd uppsprickning av landfäste hade skett. Skadorna bedömdes påverka konstruktionens funktion och ansågs behöva en fortsatt utredning där brons rörelser och skador studeras mera för att kunna ta ställning till framtida åtgärder. Målet med detta arbete är att analysera hur bron har förändrats sedan upprättandet samt att besvara vad som kan ha föranlett förändringarna. Rapporten tas fram som underlag för att kunna ta ställning till framtida åtgärder enligt ovanstående. För att fastställa hur bron rört sig utfördes en inmätning med en totalstation. Därefter upprättades aktualiserade ritningar över bron som sedan jämfördes med befintliga originalritningarna. För att visa vad som kan föranlett förflyttningen gjordes en glidningskontroll med olika laster. Utöver det utfördes en kartläggning av skador på konstruktionen som sedan utvärderades. Jämförelsen visar en kraftig förflyttning av det östra landfästet mot det västra. Rörelsen av landfästet har gjort att de båda frontmurarna lutar i vertikalled.  Glidningskontrollen slår fast att det inte föreligger risk för glidning av enbart jordtryck men att det föreligger risk för glidning vid belastning av tåg samt bromskraft från tåg. På grund av slitage samt bristande underhåll har skador åsamkats på konstruktionen. De synliga skador som återfunnits på bron är sprickor, kalkutfällningar, snedställning av lager samt korrosion av lager och synlig armering. Det som kunde fastställas är hur bron har förflyttat sig i horisontal- och vertikalled och att en orsak till det östra landfästets förflyttning är de horisontella krafter som de passerande tågen för med sig. Genom att undersöka de skador som uppkommit på bron och jämföra dessa med de krav som Trafikverket har på sina broar kunde det fastställas att några av dessa skador beror på bristande underhåll. / The Swedish Transport Administration manage nearly 4,000 railway bridges in different condition and age around the country. These bridges is in constant need of maintenance and requires continuous inspections. This thesis is designed as a damage investigation on a single-track railway bridge south of Solvarbo in Säter municipality. The railway bridge is in operation and serves over 10,000 trains a year, everything from speed trains to freight trains. The bridge is built as a beam bridge, simply supported over a road. The report is made in consultation with the company Reinertsen Sweden AB. An investigation of the bridge was carried out in 2013 by Reinertsen Sweden AB, which describes that the abutments lean onto the superstructure due to motion. The damage noted was that the movable bearings are seriously tilted, the superstructure is in contact with the breast wall and several cracks were found on the abutment. These damages were considered to affect the function of the structure and found needing further investigation to consider possible future actions. The objective of this thesis is to analyze how the bridge has changed since it was built and to find what may be the underlying causes to these changes. The report is aimed to constitute a foundation and a decision basis for further measures. To determine how the bridge has moved a surveying with a total station was performed. Thereafter updated drawings of the bridge were established and later compared with the existing original drawings. To understand why the bridge has moved a sliding control was performed with different loads. In addition an inspection of structural damages was carried out and evaluated. Comparing the drawings showed a significant displacement of the eastern abutment towards the western. The movement of the abutment has made the two bearing walls tilt. The sliding control showed that there is no risk of sliding when only earth pressure is considered, but when loads of the trains are applied there is a risk of sliding. Wear of the bridge has caused several damages in the bridge structure. The visible damages found were cracks, efflorescence, bearing misalignment and corrosion of bearings and visible reinforcement. What could be determined was that the bridge has moved horizontally and vertically and one reason for the movement in the eastern abutment could be the horizontal forces brought by a passing train. By examining the damage caused to the bridge and compare them with the requirements of the Swedish Transport Administration it could be established that some of these damages have raised due to lack of maintenance.

A significant portion of the reinforced concrete railway bridges in Sweden are reaching their designed lifespan and are scheduled to be demolished and replaced in the upcoming years. To limit the econom-icand environmental impact related to the replacement of existing railway infrastructure, a comprehen-siveevaluation of their capacity is required with the aim of extending its lifespan. In fact, experimental evidence has shown that some of these bridges may have a higher capacity than previously determined due to the conservative assumptions used during their design. The proper stress distribution pattern at the ballast-concrete interface is among the factors that need to be studied, as research on the topic has shown that some of the available guidelines to calculate it can produce conservative results. In this paper, available analytical models for computing the internal forces in concrete bridges due to train axle loads are compared to a numerical model calibrated using the experimental results obtained from the test of ballasted reinforced concrete trough bridge, a typical structural type found in Sweden, and existing research. As a first step, a literature review of existing numerical modeling strategies for ballast-edconcrete railway structures (e.g., finite element models, discrete element models, and their combina-tion)is conducted. Then, the most appropriate numerical modelling strategy is identified and used to develop the numerical model of the bridge, including the ballast. Finally, results of contact pressure and vertical stresses in the numerical model are compared to those obtained analytically.

The work reported in this thesis presents a general overview of the dynamic response of short-span railway bridges considering soil-structure interaction. The study aims to identify the effect of the surrounding and underlying soil on the global stiffness and damping of the structural system. This may lead to better assumptions and more efficient numerical models for design.A simple discrete model for calculating the dynamic characteristics of the fundamental bending mode of single span beam bridges on viscoelastic supports was proposed. This model was used to study the effect of the dynamic stiffness of the foundation on the modal parameters (e.g. natural frequency and damping ratio) of railway beam bridges. It was shown that the variation in the underlying soil profiles leads to a different dynamic response of the system. This effect depends on the ratio between the flexural stiffness of the bridge and the dynamic stiffness of the foundation-soil system but also on the ratio between the resonant frequency of the soil layer and the fundamental frequency of the bridge. The effect of the surrounding soil conditions on the vertical dynamic response of portal frame bridges was also investigated both numerically and experimentally. To this end, different numerical models (i.e. full FE models and coupled FE-BE models) have been developed. Controlled vibration tests have been performed on two full-scale portal frame bridges to determine the modal properties of the bridge-soil system and calibrate the numerical models. Both experimental and numerical results identified the substantial contribution of the surrounding soil on the global damping of short-span portal frame bridges. A simplified model for the surrounding soil was also proposed in order to define a less complicated model appropriate for practical design purposes. / <p>QC 20180315</p>

This thesis concerns dynamic Soil-Structure Interaction (SSI) analysis of portal framerailway bridges. Dynamic problems are common for bridges used for high speedrailway traffic. The passing trains induce harmonic loads on the bridges causingvibration amplitudes that may cause damage to the bridge structures and userdiscomfort.Previous studies have shown that the effects of SSI are substantial for short spanportal frame bridges. The damping ratio of the system is greatly increased due to theenergy dissipation properties of the surrounding soil causing significant changes in thedynamic response of the structure. Therefore, it is of interest to investigate the effectsof SSI for portal frame bridges with longer spans.Two case study bridges with span lengths of approximately 16m have been investigatedin detail in this study. Dynamic analyses of the bridges and train passage simulationshave been performed. The results show that SSI significantly increases the dampingratio which leads to lower vibration amplitudes. It is also possible to draw theconclusion that more accurate results are achieved when modeling fixed foundationsrather than using static spring foundations to replicate the stiffness of the subsoil.Moreover, a simplified modeling approach accounting for the effects of SSI is proposed.The proposed method provides satisfactory results, but more future work may increasethe quality of the results further. To validate the conclusions from this study, a proposalfor experimental validation is presented. Performing full-scale dynamic tests on thestudied bridges would enable further comparison and validation of the results.

As rail transportation is significantly more virtuous than airplanes or cars in terms of greenhousegases emissions, its development is being encouraged in several European countries, includingSweden. In addition, the development of railway lines on which trains can travel at higher speeds ismade in Sweden with the integration of existing infrastructure. On railway bridges, an increased trainspeed potentially leads to an increase in vibrations during passage, for which the structure may not bedesigned. It is therefore essential to know the dynamic properties of the structures used.Several studies highlight the influence of friction phenomena in sliding bearings on the dynamicproperties of bridges equipped with them. This Master Thesis is based on previous works that led tothe development of a finite element modelling the friction mechanisms that occur in these bearings.The friction occurring between a PTFE sliding plate and a steel surface is thus modelled using the Bouc-Wen model, a model for hysteresis phenomena. The finite element was developed as a Fortransubroutine, which can be integrated into the finite element calculation software Abaqus as a "userdefinedelement". It allows friction to be modelled along the longitudinal direction of the bridge onlyand can therefore only be used in two-dimensional models. The user-defined element is also based ona model that takes into account the influence of contact pressure and sliding velocity on the steel-PTFEcoefficient of friction. As several studies indicate, contact temperature can also have a significantinfluence on the value of the coefficient of friction but is not taken into account in the current model.In this project, the previously developed finite element was therefore generalized to account forfriction in both directions of the sliding plate by the means of a two-dimensional generalization of theBouc-Wen model. Based on experimental data available in scientific literature, the model forcalculating the coefficient of friction was also extended to take into account the influence of thecontact temperature. In addition, a model to update the contact temperature based on the theory ofsurface heating of semi-infinite bodies has been incorporated. Finally, this thesis presents theintegration of this updated finite element on three-dimensional models of the Banafjäl Bridge, locatedin northern Sweden. Simulations to estimate the fundamental frequencies and resonance modes ofthe structure as well as the temperature increase that can occur in a bearing during the passage of atrain were carried out on this model.

The diploma thesis is focused on the design of a new steel structure of a single-track railway bridge with bottom bridge deck. The solved bridge construction is located on line No. 123 between Nemšová and Trenčianska Teplá at the point, where the line crosses over the river Váh. The existing bridge on the line has a span of 50 + 50 + 50 + 50 m. The assignment was processed in five variants of a steel bridge structure with a bottom orthotropic deck. Each variant has a different static system, a different number of fields and a different type of superstructure. The comparison of variants was performed using multicriterial evaluation based on selected criteria. The most suitable variant was elaborated in more detail. The calculations were performed according to valid ČSN EN standards.

The subject of the diploma thesis is the design and check of the supporting structure of the railway bridge on the line Brno - Česká Třebová. The bridge carries a double-track railway line across Šámalova Street in Brno. The span of the bridge is 16.58 m, the length of the supporting structure is 17.1 m and the width in cross section is 17.81 m. Two variants of the supporting structure have been developed. The first variant is a bridge with a composite supporting structure, the second variant is a bridge with concreted steel girders. A technical report and drawing documentation are prepared for the selected variant.

At the moment of writing, an expansion of the Swedish railway network has started, by constructions of new lines for high-speed trains. The aim is to create a high-speed connection between the most populous cities in Sweden - Stockholm, Göteborg and Malmö, and the rest of Europe. Thereby, the likelihood of faster, longer and heavier foreign trains crossing the Swedish lines is increased. However, this could be problematic since the dynamic response in railway bridges and, consequently, the risk of resonance increases with increasing train speeds. Bridges are usually designed based on contemporary conditions and future requirements are rarely considered, due to e.g. cost issues. Prospectively, the dynamic performance of existing bridges may become insufficient. Hence, the current expansion of the high-speed railway network results in an increased demand of innovative design solutions for new bridges and cost-efficient upgrading methods for existing lines. The aim of the present thesis is to propose a vibration mitigation strategy suitable for new and existing high-speed railway bridges. The main focus is a retrofit method with fluid viscous dampers installed between the bridge superstructure and the supports, which is intended to reduce the vertical bridge deck acceleration below the European design code limits. Furthermore, the intention is to investigate the efficiency of such a system, as well as to identify and analyse the parameters and uncertainties which could influence its functionality. In order to examine the applicability of the proposed retrofit, case studies, statistical screenings and sensitivity analyses are performed and analysed. Two different models, a single-degree-of-freedom system and a finite element model, are developed and compared. From the different models, it is possible to study the influence from the damper parameters, the variability of the material properties and different modelling aspects on the bridge response. After the installation of the fluid viscous dampers, it is found that the acceleration level of the bridge deck is significantly reduced, even below the design code requirements. / I skrivande stund har en utbyggnad av det svenska järnvägsnätet initierats. Målet är att skapa en höghastighetsanslutning mellan de folkrikaste städerna i Sverige - Stockholm, Göteborg och Malmö, och vidare ut i Europa. Därmed ökar sannolikheten att snabbare, längre och tyngre utländska tåg korsar de svenska järnvägslinjerna. Dock kan detta bli problematiskt i och med att järnvägsbroars dynamiska respons och, följaktligen, risken för resonans ökar med ökad tåghastighet. Broar dimensioneras ofta utifrån nuvarande förutsättningar och hänsyn tas sällan till framtida hållbarhetskrav, exempelvis p.g.a. kostnadsbesparingar. Ur ett framtidsperspektiv kan därför det dynamiska beteendet hos befintliga broar komma att bli otillräckligt. Utbyggnaden av höghastighetsnätverket ökar därmed behovet av innovativa konstruktionslösningar för nya broar och kostnadseffektiva uppgraderingsmetoder för befintliga sträckor. Syftet med föreliggande avhandling är att föreslå en metod för att minska de vibrationsnivåer som kan uppstå i både nybyggda och befintliga järnvägsbroar för höghastighetståg. Huvudfokus är en eftermonteringsmetod med viskösa dämpare, som har installerats mellan brons överbyggnad och landfästen, för att minska brobanans vertikala acceleration under gällande europeiska dimensioneringskrav. Vidare avses att undersöka effektiveteten av ett sådant system, samt att identifiera och analysera de parametrar och osäkerheter som kan påverka dess funktionalitet. Fall- och parameterstudier, samt statistiska metoder används och utvärderas för att undersöka tillämpbarheten av den föreslagna vibrationsdämpningsmetoden. Två olika modeller, ett enfrihetsgradssystem och en finit elementmodell, har skapats och jämförts. Utifrån dessa modeller kan påverkan av dämparens parametrar, variabiliteten hos materialegenskaperna och behandlingen av olika modelleringsaspekter studeras. Från resultaten är det tydligt att brobanans accelerationsnivå avsevärt reduceras efter monteringen av viskösa dämpare, till och med under dimensioneringskraven. / <p>QC 20170425</p>

In the field of structural dynamics, a broader knowledge about relevant phenomena that affect the dynamic behavior of railway bridges is vital for structural engineers and design code administrators. The knowledge might benefit in an increased understanding of e.g. the resonance phenomena, and in improvements of the existing design codes. A phenomenon that has received more attention in recent times is the so called soil-structure interaction (SSI), as it may significantly contribute to the stiffness and damping of a structural system. Previous investigations have suggested that the influence of SSI might be crucial for short and relatively stiff structures such as portal frame bridges. Yet, this effect is usually neglected due to the lack of simple models and guidelines. Dynamic analyses have been performed on a short-span closed portal frame railway bridge, situated on the Bothnia Line, where the effect of the surrounding and underlying soil and the ballasted track, has been investigated. This has been accomplished through the adoption of multiple boundary conditions to consider different forms of soil-structure interactions. The vertical bridge response has been studied by numerical three-dimensional models, both with full FE-models and simplified models appropriate for practical design purposes. More specifically the natural frequencies and damping ratios have been scrutinized. Theoretically, it has been identified that the contribution of the soil on the global damping is largely influential, as it has been indicated that the damping ratio of the fundamental bending mode is seven times greater than the, in this case, significantly conservative recommended design value. Furthermore, SSI has shown to increase the natural frequencies which consequently shifts the critical resonant speed, allowing for higher speeds. The bridge response is predominantly affected by the backfill soil, yet the modal damping contribution is equally substantial from the backfill and the subsoil. Moreover, it has been established that the proposed simplified model is promising and in good agreement with the full model. It has also been resolved that train passages on the surrounding soil play an important role on the dynamic bridge response. Unfortunately, the simplified model has proven to be incapable of considering these train loads, implying that further development is needed to attain an adequate model that may be implemented for portal frame bridges of short span. Applying only elastic constraints on the vertical degree of freedom at the foundation is a simplified modeling approach that fails to capture the soil behavior in an accurate manner, and is therefore not recommended for future research projects. While on the subject of future investigations, the effect of SSI should be studied on other bridges to externally validate the obtained results. / Inom strukturdynamik är det essentiellt att erhålla en bredare kunskap om relevanta fenomen som kan påverka det dynamiska beteendet av järnvägsbroar. Detta gäller för både yrkesverksamma ingenjörer och administratörer av normer och standarder för att få en ökad förståelse av exempelvis resonansfenomen samt för revidering och förbättring av befintliga normer. Ett fenomen som på senare tid har fått mer uppmärksamhet är den så kallade jord-struktur interaktionen eftersom den kan ha en signifikant inverkan på styvheten och dämpningen av ett system. Tidigare undersökningar har tytt på att effekten av jord-struktur interaktionen kan vara avgörande för korta och relativt styva broar som exempelvis plattrambroar. På grund av bristen på enkla modeller och riktlinjer är denna effekt ofta försummad. Dynamiska analyser har utförts på en kort sluten plattrambro belägen på Botniabanan, där påverkan av motfyllningen, underliggande jorden och det ballasterade spåret har utretts. Detta har åstadkommits genom att beakta olika randvillkor för att ta hänsyn till diverse former av jord-struktur interaktioner. Den vertikala responsen i bron har studerats genom tredimensionella numeriska modeller både med detaljerade FE-modeller och med praktiskt lämpade förenklade modeller, där i synnerhet egenfrekvensen och dämpningskvoten har analyserats. Bidraget från jorden har påvisat sig ha en avsevärd inverkan på den globala dämpningen då det framgick att dämpningskvoten för den fundamentala böjmoden är sju gånger större än det, i denna fallstudie, betydligt konservativa rekommenderade dimensioneringsvärdet. Dessutom har jord-struktur interaktionen lett till ökade egenfrekvenser som följaktligen skiftat den kritiska resonanshastigheten vilket tillåter högre hastigheter. Motfyllningen har haft en avsevärd effekt på responsen av bron, medan bidraget till ökningen i modala dämpningen har fördelats lika mellan motfyllningen och underliggande jorden. Vidare är den föreslagna förenklade modellen lovande och i god överenstämmelse med den detaljerade modellen. Det har även konstaterats att tågpassager på motfyllningen spelar en viktig roll för den dynamiska responsen. Dessvärre har den förenklade modellen misslyckats med att ta hänsyn till dessa tåglaster, vilket indikerar att en vidareutveckling krävs för en implementerbar adekvat modell för plattrambroar av korta spännvidder. Ett förenklat modelleringsalternativ är applicering av enbart elastiska randvillkor i den vertikala frihetsgraden av bottenplattan. Detta alternativ har visat sig vara otillräckligt för att efterlikna den underliggande jordens beteende och undanbedes för framtida studier. På tal om framtida projekt bör jord-struktur interaktionen utredas på andra broar för att externt validera resultaten.