| 1. |
- Mathern, Alexandre, 1986
(författare)
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Addressing the complexity of sustainability-driven structural design: Computational design, optimization, and decision making
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Being one of the sectors with the largest environmental burden and high socio-economic impacts sets high requirements on the construction industry. At the same time, this provides the sector with great opportunities to contribute to the globally pursued sustainability transition. To cope with the increasing need for infrastructure and, at the same time, limit their sustainability impacts, changes and innovation in the construction sector are required. The greatest possibility to limit the sustainability impact of construction works is at the early design phase of construction projects, as many of the choices influencing sustainability are made at that point. Traditionally, an early choice of a preferred design is often made based on limited knowledge and past experience, considering only a handful of options. This preferred design is then taken on to the successive stages in the stepwise design process, leading to suboptimization. Alternatively, many different design choices could be considered and evaluated in a more holistic approach in order to find the most sustainable design for a particular application. However, finding design solutions that offer the best sustainability performance and fulfil all structural, performance and buildability requirements, require methods that allow considering different design options, analysing them, and assessing their sustainability. The aim of this thesis is to explore and develop methods enabling structural engineers to take sustainability objectives into account in the design of structures. Throughout this thesis, a number of methods have been explored to take sustainability aspects into account in the structural design process. As a first step, highly parameterized computer codes for sustainability-driven design have been developed. These codes interoperate with FE analysis software to automatically model and analyse design concepts over the whole design space and verify compliance with structural design standards. The codes were complemented with a harmonized method for life cycle sustainability performance assessment, in line with the state-of-the-art standards. Here, sustainability criteria were defined covering environmental, social, economic, buildability and structural performance for multi-criteria assessment of design concepts. To identify the most sustainable designs within the set, multi-objective optimization algorithms were used. Algorithms that address the high expense of constraint function evaluations of structural design problems were developed and integrated in the parameterized computer codes for sustainability-driven design. To ensure the applicability and validity of these methods, case studies based on real-world projects and common structural engineering problems were used in this thesis. Case studies for bridges and wind turbine foundations as well as a benchmark case of a reinforced concrete beam were investigated. The case studies highlight the potential of the methods explored to support the design of more sustainable structures, as well as the applicability of the methods in structural engineering practice. It is concluded that it is possible and beneficial to combine computational design, life cycle sustainability assessment, and multi-objective design optimization as a basis for decision making in the design phase of civil engineering projects. A wide adoption of such a sustainability-driven design optimization approach in structural engineering practice can directly improve the sustainability of the construction sector.
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| 2. |
- Robuschi, Samanta, 1991
(författare)
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Natural corrosion in reinforced concrete structures
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Among the threats to the durability of concrete structures, corrosion of the reinforcement bars is undoubtedly the most common one. Corrosion damages impair safety and durability of infrastructure, and assessment of the safety is challenging due to the complex nature of the corrosion process. Furthermore, research on the topic often requires adapting results from short-time laboratory tests, where corrosion of the reinforcement bars is induced using impressed current, to the reality of existing structures. The use of impressed current results in differences in type and distribution of corrosion products. Naturally corroded specimens are hence the necessary bridge between the knowledge acquired from artificially corroded specimens and the application to real structures. This works investigates the structural effects of natural, chloride-induced corrosion in reinforced concrete structures. Specifically, three research questions were investigated. First, the bond and anchorage of naturally corroded plain bars was studied using 3-point bending and pull-out tests. The tests were designed to be applied to specimens taken from a decommissioned bridge from the 1930s. The bond capacity of plain bars was observed to be significantly higher than in results obtained from laboratory tests on similar bars. Significant factors influencing the effect of corrosion damages on the bond were casting position and presence of stirrups. Finite element analyses were used to further investigate the bond-slip behaviour of the tested specimens. The results highlighted the effect of the loss of bond at yielding on the structural behaviour of the specimens. The second question looked into the characteristics of the corrosion products and the surrounding concrete; this is relevant to assess corrosion damages in existing structures. Neutron imaging and X-ray computed tomography were used to obtain qualitative and quantitative data on corrosion damages in a naturally corroded specimens, including iron to rust ratio. Comparison with an artificially corroded specimen showed differences in distribution of the corrosion products. Finally, possible correlations between transversal cracks and corrosion damages was investigated. A dataset was compiled from experiments available in literature. In the selected studies, corrosion of the steel reinforcement resulted from exposing laboratory specimens, pre-cracked in 3-point bending, to chloride environments. No clear correlation between surface crack width and corrosion characteristics was found, but corrosion pits were shown to likely appear in the proximity of transveral cracks. To conclude, this work highlights the complexity of the corrosion process and argues that a thorough understanding of the material and environmental characteristics influencing this process is necessary to properly assess existing structures. Tests on naturally corroded structures are a fundamental step towards acquiring this knowledge.
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| 3. |
- Sciegaj, Adam, 1990
(författare)
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Multiscale Modelling of Reinforced Concrete Structures
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Concrete cracks at relatively low tensile stresses; cracks open up for ingress of harmful substances, negatively affecting the durability of reinforced concrete structures. Crack widths are thus limited in the design codes, and accurate predictions are needed, especially for large reinforced concrete structures such as bridges or nuclear reactor containment buildings. On the one hand, cracking of concrete, constitutive behaviour of steel, and the bond between them must be accounted for in order to properly describe crack growth. On the other hand, explicitly resolving these features in large structures could prove computationally intractable. This thesis concerns multiscale modelling of reinforced concrete structures. More specifically, different two-scale models, based on Variationally Consistent Homogenisation (VCH), are developed. In these models, the response of a Representative Volume Element (RVE) is upscaled to a few popular structural models: a homogenised solid in plane stress, the effective Euler-Bernoulli beam and the effective Kirchhoff-Love plate. The effective response of the RVE is defined through a boundary value problem, for which different types of boundary conditions are developed and discussed. Furthermore, in order to allow for reinforcement slip transfer across the large-scale elements, a novel macroscopic reinforcement slip field is introduced. The developed two-scale models are used to analyse reinforced concrete deep beams subjected to membrane loads, reinforced concrete beams subjected to uniaxial tension and bending, and reinforced concrete panels subjected to combinations of membrane and bending loads. The results show that the general structural behaviour is reflected well by the multiscale models compared to single-scale analyses. By enriching the model with a macroscopic reinforcement slip field prescribed at the boundary of the RVE, the crack width predictions given by the two-scale models are improved and localisation of effective strain is observed at the large-scale. However, the results were dependent on the large-scale mesh and RVE sizes. In order to improve the objectivity of the model, a novel boundary condition type, prescribing the effective slip in the volume of the RVE, was developed. The macroscopic reinforcement slip became no longer RVE-size dependent, and the maximum crack width predictions were more consistent and showed a smaller variance for different large-scale meshes and sizes of RVEs. In conclusion, the developed two-scale models allow for the analysis of a wide range of reinforced concrete structures, and show potential in saving computational time in comparison to single-scale analyses.
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| 4. |
- Ekström, Daniel P T, 1976
(författare)
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Integrated structural and construction engineering – A study of project team performance in Swedish bridge design
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Swedish Transport Administration (STA) ambitiously strives to increase the level of productivity and innovation within its operations while meeting and surpassing national sustainability objectives. In this effort, the STA has concluded that climate gas emissions from construction, operation, and maintenance of the infrastructure must be reduced for Sweden to maintain its position as a pioneer and to reach both national and global climate goals. Emissions from road, rail, and other civil works is mainly related to the production of construction materials, such as construction steel, concrete and reinforcement in bridges, retaining walls, and other structures. For bridges, normally designed for a long service-life, the environmental impact of all stages after realization is greatly dependent on and constrained by decisions made during design and construction of the structure. To succeed in realizing effectiveness in bridge construction project is only possible by close cooperation between all project participants, i.e. client, consultant(s), and contractor(s). The construction industry is often described as complex, multidisciplinary, and project-focused but with no clear boundaries of who actually owns processes and, consequently, the development of them. The overall purpose of this research is, therefore, to contribute to framing a systematic and holistic design approach fostering many kinds of project-settings and pre-requisites. This research aims to further understand how to introduce construction knowledge in the early design stages through utilizing an approach with integrated projects teams. The thesis is based on several studies exploring how integration is related to the bridge construction process and the key features are for such integration. Further, this thesis explores the prevailing interprofessional dialogue in the Swedish bridge construction process and how this may both support and hinder knowledge and experience transfer in the interprofessional interface. Given the complexity in construction today, all participants involved, individually, will lack some pieces of the puzzle, but that collectively, they can gather their knowledge and resources to achieve success for all parties involved. When integration is seen from this perspective, the following key features crystallize; skills to collaborate and communicate; interdependency between the parties; importance for the structural engineer to receive feedback from, and to have a dialogue with, the contractors; teams to be provided with the right people. The contribution of this thesis is that it provides further knowledge to develop and improve the contemporary approach in the design and construction of bridges.
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| 5. |
- Persson, Peter
(författare)
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Vibrations in a Built Environment : Prediction and Reduction
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Vibrations in a built environment can exceed the requirements for sensitive equipment in a building or can cause annoyance to residents. Hence, there is often a need for reducing such vibrations. The vibrations can originate from ambient sources such as motorway traffic, or from internal sources such as people walking inside the building. Disturbing vibrations can be reduced by reduction measures. Vibration-reduction measures can be evaluated numerically, with for instance the finite element method, to avoid construction of expensive mock-ups. In the thesis, large finite element models involving several physical domains (e.g. road, soil, bedrock, and building parts) were developed to study the effect of vibration-reduction measures.Ground vibrations can be reduced by installing a wave barrier between an external source and a receiver. As concluded in the thesis, an empty barrier (i.e. a trench) installed in the soil has the ability to reduce the ground-vibration level by approximately 60%. If the barrier contains a solid material, however, the level of reduction is reduced to approximately 30%. At long distances, at around 500 m and longer, from the vibration source, an amplification in vibration is observed. At such distances, moreover, the ground motion follows the motion of the bedrock. Another example of a wave obstacle that is studied in the thesis involves shaping the landscape surrounding a building. The topsoil that is usually transported from the construction site can be used to construct hills and valleys that constitute the shaped landscape. However, this can result in anything from an appreciable reduction to an appreciable amplification in the ground-vibration levels, depending on how the landscape is formed. If constructed properly, the reduction in the level of vibration can reach approximately 35%. Vibrations from both external and internal sources can be reduced by modifying the properties of the concrete slabs and the soil underneath. The soil properties can be improved by mixing the soil with a binder, in order to stiffen the soil. Is is shown in the thesis that by using stabilised soil underneath a concrete slab, vibrations originating from motorway traffic can be reduced by almost 60%, and up to 80% for an internal pedestrian load. By using a time-efficient numerical model developed in the thesis, the effect by using different positions for the supports of a water-pipe system on vibrations transmitted to other parts of buildings was studied. Because frequency peaks can be avoided, a marked change of vibration characteristics can be achieved. A reduction of more than 60% in the transmitted vibrations was observed. The general methods and measures presented in the thesis are exemplified by the conceptual design process of the MAX IV Laboratory, a vibration-sensitive research facility. This laboratory exhibited the phenomena needed for selecting it as a comprehensive example case.
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| 6. |
- Stojanovski, Todor
(författare)
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Urban Form and Mobility - Analysis and Information to Catalyse Sustainable Development
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Urban transportation today consumes scarce resources of fossil fuels and it is a major cause for environmental damage and accelerating climate change. To achieve sustainable mobility in the cities, it is necessary to improve energy efficiency and lower carbon emissions through the promotion of walking, cycling and especially public transportation.The urban form and the embeddedness of automobility is a challenging obstacle on the way towards sustainable mobility and cities. Many neighbourhoods and cities, particularly in developed countries like Sweden, were specifically designed and developed to accommodate the private car, individual mobility and freedom of movement. It is impossible to walk or cycle and the public transportation is not competitive. The lack of mobility choices in these neighbourhoods and cities hinders the possibilities to shift towards more sustainable travel alternatives. Urban designers and planners can help with redesigning these neighbourhoods and creating urban forms that encourage walking, cycling and increased use of public transportation if they are aware about the possible modal shares, energy efficiency, environmental performance and carbon implications of transportation in existing and newly planned neighbourhoods.This Doctoral Thesis examines Swedish urbanisation and the historical integration of public transportation in competition with other transportation modes. It analyses emergence of typical neighbourhoods that oriented towards walking (the pre-industrial city), to public transportation (the industrializing city), to the private automobile (the modern/industrial city) and ultimately to a wide range of mobility choices (the postmodern/post-industrial city with sustainable city neighbourhoods). It investigates furthermore the effect of urban form variables (including neighbourhood type) on travel (modal shares of public transportation). Based upon this empirical knowledge, the Doctoral Thesis proposes a mobility choices model based on urban form and accessibility factors commonly used in urban planning, design and development practices. The mobility choices model produces heat maps and visually informs about the integration with walking, cycling, public transportation and private car, modal shares, carbon emissions and transportation energy use. This information can (potentially) trigger urban transformation or redesign car-oriented neighbourhoods to better integrate energy efficient and environmentally friendly mobility alternatives and catalyse the development of more sustainable cities.
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| 7. |
- Khajehei, Hamid, 1987-
(författare)
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Data-driven models for railway track geometry maintenance
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Railways are currently experiencing higher demands on safety, infrastructure performance, network capacity and service quality, etc. As a result, a high level of track availability, service quality and infrastructure robustness against unexpected events is required, at reduced cost, to meet the demands. The track geometry is one of the critical parameters influencing the performance of the infrastructure and the capacity and quality of service of the railway network. The track geometry continuously degrades and deviates from the designed level over time and under the influence of various factors. A poor track geometry negatively affects the ride quality and passenger comfort and increases the risk of train derailment. To ensure a safe and reliable track for the trains, the track geometry should be kept in an acceptable condition. This necessitates the development of an applicable and effective tamping regime, as the main maintenance action for track geometry rejuvenation. An effective tamping regime enables enhancement of the availability and safety performance of the track, to control the track degradation and to restore the damaged track to an operational state, at the lowest possible cost. The purpose of the research conducted for this thesis was to develop data-driven methodologies and optimization approaches for the development of a plan for predictive railway track geometry maintenance. First, a study was carried out to investigate the application of artificial neural networks to estimation of the track geometry degradation rate in spatial space by considering the operational and constructional covariates. In addition, the relative importance of the observed covariates for the track geometry degradation was also explored. The results showed that the maintenance history, the degradation value after tamping and the frequency of the trains passing along the track were the most important covariates affecting the track geometry degradation rate. Second, a case study was performed on a heavy haul railway line to analyse the isolated twist and longitudinal level defects. A data-driven model was developed to predict the occurrence of track geometry defects. A machine learning technique, namely the RUSBoost algorithm, was used to classify the track sections into healthy and unhealthy track sections. In order to capture information about the shape of the defects, first- and second-order derivatives of the track irregularities were used. The observed anomalies in the conducted case study in the pattern of the track geometry degradation were also explored. It was found that applying a combination of the kurtosis and the standard deviation to represent the track quality is beneficial for identifying the anomalies in the trend of geometry defects. Third, a simulation-based framework was developed with the aim of allocating an effective maintenance limit by assessing the effect of different maintenance limits on the total maintenance cost. The results showed that it is not one value only, but a range of values for the maintenance limits which can be selected to minimize the total maintenance costs. However, by considering the safety aspects of track geometry maintenance, it is suggested that one should select the lower bound of the range of cost-effective limits for maintenance planning. Finally, an optimization model was developed to schedule track tamping activities with the aim of minimizing both the track geometry maintenance costs and the number of unplanned maintenance actions. The proposed model enables infrastructure managers to examine the effect of different scenarios for the control and management of isolated defects on the track geometry condition and the maintenance cost. The results obtained in the present research are highly relevant for specific industrial challenges and are expected to enhance the capability of infrastructure managers to make effective and efficient decisions when developing their planning and scheduling of the tamping regime. The results have been verified through interaction with experienced practitioners working for a major railway infrastructure manager and railway maintenance subcontractors.
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| 8. |
- Lundberg, Joacim
(författare)
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Road Surface and Tyre Interaction : Functional Properties affecting Road Dust Load Dynamics and Storage
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Luftburna partiklar (PM) är ett problem för människans hälsa, där flertalet samband mellan negativa hälsoeffekter finns mellan luftföroreningar finns, bland annat för respiratoriska sjukdomar, lungcancer och kardiovaskulära sjukdomar med flera. I länder där dubbdäck används, till exempel Sverige, Finland och Norge, och sandning av vägar och gator genomförs vintertid för att säkerställa god friktion kommer en betydande andel av partiklarna från vägslitage och nedkrossning av sand vilket bidrar till PM10. Mängden som icke-avgaspartiklar bidrar med till PM10 varierar med lägst nivåer på landsbygd och högst nivåer i vägnära miljöer.Avhandlingen har flertalet mål, där ett bredare mål är att undersöka det komplexa väg-ytadäcksystemet gällande vägslitage och dess inverkan på genererandet av slitagepartiklar och vägdamm, inklusive transporten och lagringen av vägdamm på vägytan. Avhandlingen syftar även att sätta in dessa aspekter i relation till andra lika komplexa funktionella parametrar som kommer av eller påverkas av vägyta-däckinteraktionen såsom bullergenerering, rullmotstånd och fiktion. Detta görs genom några mer specifika mål och begränsningar som beskrivs i avhandlingen. Avhandlingen har även det fundamentala syftet att agera som en start för att nå ett holistiskt helhetsgrepp för att förstå den funktionella prestandan som krävs för väg-ytadäckinteraktionen, vilket har genomförts i samarbete med Vieira och det som han publicerar i sin avhandling.Vägyta-däckinteraktionen utgörs av ett komplex kontaktsystem, som påverkas av både däckegenskaper och vägens egenskaper, dels ingående material och vägytans karaktär, samt omkringgivande miljö och eventuella mellanlager av till exempel vatten, slask, snö, is eller sand och grus med mera.Slitlagret, eller vägbeläggningen, har flera funktioner som beror på de ingående materialens egenskaper. Beläggningen måste motstå flertalet olika nedbrytningsprocesser, inklusive stensläpp, olika typer av deformation, olika typer av sprickor och slitage från dubbdäck bland annat.Beläggningens konstruktion och trafikens sammansättning och egenskaper påverkar även partikelgenereringen, där beläggningsegenskaperna som styr nötningsmotståndet mot dubbdäckslitage även påverkar genereringen av slitagepartiklar.Andra aspekter som påverkas av vägyta-däckinteraktionen är genereringen av buller och fordonets rullmotstånd. Buller har likt partiklar negativa hälsoeffekter och vägyta-däckinteraktionen är den dominerande källan till trafikbuller från ungefär 15 - 25 km/h för lätta fordon och från ungefär 30 - 35 km/h för tunga fordon. Flertalet mekanismer ger upphov eller förstärker bullret, och flera är kopplade till ytans beskaffenhet såsom makrotexturen. Rullmotstånd är omvandlingen av mekanisk energi till värme för ett rullande däck och påverkas av både däckets och vägytans deflektion och deformation, och påverkas även av vägytans beskaffenhet av t.ex. ojämnheter och makrotexturen. Rullmotståndet ör kopplat till bränsleförbrukningen och därigenom till avgasemissioner. En annan funktionell egenskap för vägytan är friktionen som påverkas av vägytans beskaffenhet av både mikro- och makrotexturen.Det finns flertalet åtgärder för att minska vägdamm och PM10. Åtgärderna kan vara preventiva eller avhjälpande. I avhandlingen beskrivs åtgärder riktade mot att förändra trafiksituationen och däckanvändningen, byte av vägbeläggning, städning av vägytan och dammbindning.Flertalet metoder har använts i studierna som diskuteras i avhandlingen och består av en storskalig vägsimulator, användandet av lasermätsystem för bestämning av vägslitage respektive textur, dels en prediktionsmodell för dubbdäcksslitage och den nordiska NORTRIP-modellen för modellering av icke-avgasemissioner från vägtrafik. Även ett kommersiellt trafiksystem har nyttjats samt en metod för att bestämma dubbdäcksandelen av trafiken. Vägdamm har samlats in och kvantifierats genom användandet av WDS (Wet Dust Sampler) metoden och det insamlade dammet har beskrivits och karakteriserats med hjälp av en laboratoriemetod och med hjälp av lasergranulometri. Turbiditet har även använts som en approximation av vägdammsförrådet.Fem artiklar finns bifogade till avhandlingen. Den första handlar i korthet om en kalibrering av den svenska prediktionsmodellen för dubbdäckslitage av vägar och dess effekt på NORTRIP-modellen, där slitagemodellen är implementerad. Den andra artikeln handlar om olika vägbeläggningars makrotextur och hur olika mått kan användas för att beskriva den potentiella lagringsförmågan. Den tredje artikeln undersöker WDS-metoden, dels beträffandes dess prestanda gällande vatten samt dels hur detta teoretiskt påverkar eventuella dammförluster. Den fjärde artikeln handlar om den rumsvariationen och tidsvariationen av vägdamm för sex vinter- och vårsäsonger i Stockholm för flera gator med ABS (AsfaltsBetong, Stenrik)-beläggningar. Den femte artikeln genomförde en liknande undersökning under en vinter- och vårsäsong i Linköping för en dubbeldränerande beläggning och för en ABS-beläggning som agerade referens. Resultaten jämfördes med resultaten i Stockholm när det var möjligt.Resultaten visar att slitagemodelleringen överskattade slitaget med ungefär 50%, vilket ledde till att NORTRIP-modellen överskattar bidraget från dubbdäckslitage till partikelemissionerna, vilket inte var förvånande. Dock är det inte troligt att NORTRIP-modellen får motsvarande minskning då vägyta-däckinteraktionen är komplex och flertalet aspekter påverkar slitaget och den efterföljande genereringen och lagringen av vägdamm, såsom polering av vägytan, ökat slitage vid våt vägbana med mera.Resultaten från undersökningen med WDS-metoden visar att metoden verkar fungera väl, givet begränsningarna som fanns i studien. Den största vattenförlusten verkar vara det vatten som lämnas kvar på ytan. Det verkar även som att det mesta av dammet samlas upp. Diskussionen tar även upp hur WDS-metoden använder sig av vatten och vilka för- och nackdelar detta har jämfört med en torr metod.Resultaten från undersökningarna om rumsvariationen och tidsvariationen av vägdammsförrådet i Stockholm visade att det fanns skillnader mellan olika säsonger, och att det fanns en skillnad mellan dammängderna i hjulspåren och mellan hjulspåren. I vissa fall syntes även skillnader mellan de undersökta gatorna med stora variationer, vilket kunde förväntas då dammförrådet beror på trafiksammansättningen, mängden fordon, vägdriften, deposition av material på ytan och meteorologin. Ett annat resultat var att en ökande makrotextur verkade resultera i ett högre dammförråd. Generellt var makrotexturen lägre mellan hjulspåren och högre i hjulspåren, vilket ej var förvånande på grund av trafikens inverkan på texturutvecklingen. Detta var dock enbart uppmätt vid ett tillfälle. Omläggningen av en ABS-beläggning till en mer slittålig ABS-beläggning genomfördes, med ett högre dammförråd som följt jämfört med före omläggningen, samtidigt som okulärbesiktning av vägytan antydde att makrotexturen ökat. Dock kan detta ha påverkats av ett högre slitage vilket inträffar under en beläggnings första vintersäsong på grund av ett extra initialslitage. Resultaten i Linköping visade liknande tids- och rumsvariation som i Stockholm för den undersökta ABS-beläggningen. Vidare diskuterades även hur den dränerande beläggningens konstruktion inverkar på partiklarnas transportprocesser. I jämförelsen föreslogs även att dammbindningen och städningen i Stockholm påverkar dammförrådet, då dessa åtgärder saknas i Linköping, vilket möjligtvis reflekteras i vägdammsförrådet i och mellan hjulspåren.En diskussion förs kring hur olika texturmått kan användas för att karakterisera vägytans textur och hur detta kopplar till dammförrådet, samt vad som kan vara lämpligt att initialt använda, även om det påpekas att måttet som bör användas inte nödvändigtvis är upptäckt än.Diskussionen tar även upp avsaknaden av ett holistiskt helhetsgrepp gällande vägyta-däckinteraktionen som tar samtidig hänsyn till effekter såsom slitagepartiklar, buller och rullmotstånd. Det verkar finnas några åtgärder som kan vara av intresse för att förbättra minst två aspekter samtidigt, till exempel användandet av en dubbeldränerande beläggning eller texturoptimering. En diskussion förs mellan för och nackdelar gällande de olika mekanismerna som påverkar de olika effekterna, samt hur vissa mekanismer bör undersökas närmare utifrån andra perspektiv, till exempel bullermekanismer som kan vara intressanta ur partikelsynpunkt.Avhandlingen ger slutligen flera förslag till fortsatta undersökningar för att öka kunskapen. Detta gäller dels vägslitagemodellering och vägdammsmodellering där även vägytans textur bör beaktas. Vidare bör även mekanismer från andra effekter från vägyta-däckinteraktionen, till exempel de som påverkar buller, även undersökas och användas för att förklara mekanismer relaterade till vägdammsgenerering och uppvirvling. Det föreslås även flertalet gemensamma undersökningar som simultant undersöker flera aspekter, såsom till exempel buller, rullmotstånd, vägytans egenskaper, vägslitage, slitagepartiklar, vägdammsförrådet, uppvirvlingen av partiklar och friktion, vilket krävs för att slutligen åstadkomma det holistiska helhetsgreppet som krävs för att minst minimera intressekonflikter mellan olika funktionsegenskaper för vägbeläggningar.
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| 9. |
- van Eldert, Jeroen, 1987-
(författare)
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Drill Monitoring for Rock Mass Assessment in Tunnelling
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Site investigations for tunnel projects are often unable to determine rock mass conditions accurately for the entire tunnel, as these investigations obtain qualitative data for only limited parts of the tunnel. This is the case at the Stockholm Bypass project in Sweden. At two ramp tunnels, the rock mass was characterised as significantly poorer during the excavation than had been determined previously in the site investigation. In this study, Measurement While Drilling (MWD) technology was employed to characterise the rock mass for grouting purposes using extraction drill monitoring data from the grout holes. In addition, MWD data were extracted from blast holes at the entrance of one access and two ramp tunnels. The MWD data included the penetration rate and feed, percussive, rotation, and water pressure measurements at less than 3cm intervals in the drill holes. The drill rig supplier’s software was able to characterise the rock mass accurately for fracture zones, as shown in a comparison of the fracturing index of grout holes, blast holes, and the mappedrock mass structures. Since the suppliers’ software packages ignored some essential features of drilling, the study developed an improved MWD data normalisation and filtering process. This new process took the effects of different rock drills and drill rod extensions on the MWD data into account. The new normalisation and filtering process showed the capability to describe the rock mass conditions more accuratelythan the current method. A holistic approach was also developed to optimise the rock support process even further. Here, the rock mass was objectively qualified using measured drilling data instead of observations. This process correlated the fracturing index to rock mass quality and rock support requirements. Lastly, a correlation was made between the rock mass quality and the grout requirements per grout umbrella;these requirements were linked to the rock mass conditions determined by the MWD parameters. Based on these relations, a conceptual grout decision-making model was developed. The study found all-in-all tunnel practices could be improved with the implementation of MWD for rock mass characterisation and as part of a rock mass quality control plan. The MWD technology provides additional information on the rock mass and could be incorporated into the observational method for rock mass excavation.
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| 10. |
- Allahvirdizadeh, Reza
(författare)
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Improving the Dynamic Design Philosophy of High-Speed Railway Bridges Using Reliability-Based Methods
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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%.
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