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  • 1.
    Teng, Penghua
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    CFD MODELLING AND EXPERIMENTS ON AERATOR FLOW IN CHUTE SPILLWAYS2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A chute spillway is a typical component of large dams for discharging floods. Because of the high water head, the flow velocity in the chute is often in excess of 20 m/s. Consequently, the structure is usually prone to cavitation damages. Flow aeration is evidenced to efficiently eliminate or to mitigate the damages. An aerator is a device that entrains air into the water flows and is an effective technical measure to counter the cavitation damages.

    Aerator flow includes intense air-water exchange and involves a process of air entrainment, transport, and detrainment. Because of the complex phenomena, it is still a challenge to investigate the behaviors of interaction between air and water. It is fundamental to understand the flow behaviors downstream of the aerator. This thesis investigates the aerator flow features using both the Computational Fluid Dynamics (CFD) and advanced measurement techniques.

    The CFD method presents three two-phase flow models to describe the aerator flows, namely, the Volume of Fluid Model, the Mixture Model, and the Two-Fluid Model. They are applied and evaluated via practical engineering projects and experimental data. The Volume of Fluid model leads to reasonable results regarding the water flow discharge and flow fields. For predicting the air concentration distribution and air bubble transport processes, the Two-Fluid Model is superior to others because it includes forces acting on the air bubbles. However, the model still overestimates the air content near the chute bottom. Based on the aerator flow from a chute spillway in Sweden, three two-phase flow models are applied and compared.

    Physical model tests are commonly conducted to investigate aerator flow features. Because of the scale effects, the results may lead to a discrepancy in the flow behaviors compared with the prototype. Thus, CFD modeling becomes an alternative tool when seeking the reason for the difference. Based on the aerator flow in a real spillway, CFD is applied to reproduce the flow; the discrepancy between the model tests and prototype observations is evidenced. The results show similar flow features with the prototype but differ from those of the model tests. An explanation for the discrepancy is discussed in terms of flow features, effect of surface tension in model tests, and the prerequisite for air entrainment of the free-surface flow.

    Laboratory experiments are conducted to study the aerator flow in a chute. Four image-based measurement techniques-i.e., high-speed particle image velocimetry (HSPIV), shadowgraphic image method (SIM), bubble tracking method (BTM), and bubble image velocimetry (BIV)-are employed. The study focuses on issues of exploring characteristic positions of water-air interfaces, interpreting the evaluation process of air bubbles shed from the tip of the air cavity, identifying the probabilistic means for characteristic positions near the fluctuating free surface, and obtaining the flow field both water flow and air bubbles features of the aerator flow. The application of these techniques leads to a better understanding of two-phase flow characteristics of the chute aerator.

  • 2.
    Kharazmi, Parastou
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Evaluation of Innovative Rehabilitation Technologies Utilising Polymer Composites for Aging Sewer Systems2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Water and wastewater sewer system maintenance is among the costliest aspects of infrastructure investment. The replacement of deteriorated lines is a difficult and expensive process that causes community disturbance and is generally not conducted fast enough to meet demand. To keep up with the rate of deterioration, the use of alternative rehabilitation technologies using polymer linings has increased significantly in recent years, both within Sweden and worldwide. Compared to the traditional pipe replacement method, these technologies are cost-effective, create less community disturbance, and offer a quick return to the service for the line. The main function of polymeric lining is to stabilise the condition of the pipeline, eliminate deterioration, and thereby extend the pipeline’s service life. Although rehabilitation technologies employing polymeric systems have been in use for over 30 years, there have been few technical assessments of either these technologies or the materials involved. Data gathered through the evaluation of these innovative technologies can make their benefits and limitations more widely understood, and can also be used to increase the effectiveness of the rehabilitation process in future.

    The main objective of this work was to contribute to an improved understanding of the most commonly used materials and methods employed in rehabilitation of wastewater and other applicable sewer lines in residential buildings in Sweden. The primary objective was not to prove that the emerging rehabilitation technologies work, but rather to increase knowledge of their weaknesses and strengths, identify any issues, and provide a technical assessment to support realistic expectations of pipeline rehabilitation. Gathering technical information in this way will help with the planning of future investigations; moreover, collecting extensive data will help to increase the effectiveness of the renewal works, aid progress in the field, and improve predictions regarding longevity and service life.

    As pipeline rehabilitation is still considered novel, and owing to the general lack of available data on the subject, a multi-approach study was carried out: this included evaluation of the polymeric materials’ performance in the presence of deteriorative factors, assessing the in-service state of the materials and lined sewers previously installed, monitoring the level of quality control implemented during previous rehabilitation works, and evaluating the environmental impacts of using pipe-lining technologies compared to pipe replacement. The techniques discussed included rehabilitation with epoxy and polyester resin-based lining materials, applied with brush-on and spray-on techniques, and cured-in-place pipe lining (installed by sending a resin-impregnated flexible tube inside the host pipe).

    Degradation of the resin-based lining materials was investigated via artificial aging involving immersion in water at elevated temperatures. The changes in materials that occurred during accelerated laboratory aging were tracked by means of various tests, including thermal and mechanical analyses, water absorption measurements and microscopy. The analysis focused on reinforced polyester-based and toughened epoxy-based lining materials in order to gain a better understanding of their performance as pipe lining. Moreover, the previously installed lined pipes and lining materials were also studied during laboratory examinations to evaluate the in-service performance of the materials and techniques under operating conditions over time, as well as to identify common defects. The state of the materials and the lined pipe were studied by means of different investigative methods, including visual inspection, microscopy, Fourier transform infrared spectroscopy, thickness measurement, thermal and mechanical analyses. This PhD work also includes an investigation to determine the level of quality control carried during some previous rehabilitation works. Data on the quality evaluation of previous rehabilitation works were gathered during visits to the work sites, as well as by analysing lined pipes that had already been installed. Finally, a comparative life-cycle assessment was undertaken to compare the environmental impacts of pipe replacement with those of alternative innovative rehabilitations, such as CIPP and coatings with polyester and epoxy polymeric systems. Data obtained from an LCA tool were used to facilitate comparison from an environmental perspective.

    Results from artificial aging in the lab indicated that the properties of polymeric lining materials changed significantly when high temperatures were combined with water exposure. However, the aging testing conducted for this study also found that the materials performed relatively well at temperatures close to the average temperatures inside sewerage systems. The results revealed that the polyester-based lining material was less sensitive when compared with epoxy-based lining materials during stimulated aging. Moreover, results from the in-service field demonstration (involving examination of 12 samples with up to 10 years of service, including reinforced polyester and modified epoxy linings or cured-in-place pipe (CIPP) lining) showed minimal evidence that the materials underwent significant deterioration after installation; instead, a majority of the common defects were found to be related to poor-quality installation practices. Because very few field samples were available to study, conclusions regarding overall performance could not be drawn. However, there is no evidence that these materials will not perform as expected during their service life when properly installed.

    Evaluating quality control of previous rehabilitation work revealed a gap between theory and practice where the level of quality control and documentation was concerned; furthermore, it also emerged that quality control and documentation is crucial to both the prevention of common issues and the overall effectiveness of the rehabilitation. Accordingly, a series of recommendations regarding the development of comprehensive quality control and quality assurance procedures (QC/QA) are provided in this work. These recommendations highlight the aspects that are most important to consider at each of several key stages (before installation, during installation, and after rehabilitation work is completed).

    Results from comparative life-cycle assessment (LCA) showed that alternative technologies, including cured-in-place (flexible sleeve) and coating techniques, have some advantages over pipe replacement from an environmental perspective. However, the choice to use one rehabilitation technology over another is a multi-stage decision-making process that should not be based solely on a single factor.

    This PhD work promotes an improved understanding of the limitations and benefits of polymeric lining through the testing performed and analyses conducted. This work highlights the need for improved quality control, and further suggests that developing a detailed and comprehensive quality control plan for each technology would provide higher and more consistent quality overall. The study also demonstrates that the long-term strength of any rehabilitation work depends on various factors, and that selecting one method over another must be a process based on extensive knowledge and understanding of each rehabilitation technology. No evidence was found to indicate that the materials could not perform well under working conditions if selected and installed appropriately. However, a larger number of field samples with longer in-service time and a more detailed technical history, along with a more extended experimental plan for laboratory investigations based on the results of this PhD work, will allow for the gathering of the data required to answer questions regarding life expectancy with a higher degree of certainty.

  • 3.
    Prästings, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Managing uncertainties in geotechnical parameters: From the perspective of Eurocode 72019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Geotechnical engineering is strongly associated with large uncertainties. Geotechnical site investigations are made only at discrete points and most of a soil volume is never tested. A major issue is therefore how to cost effectively reduce geotechnical uncertainties with respect to structural performance. Managing the geotechnical uncertainties is thus an important aspect of the design process. Guidance on this subject is given in the European design code for geotechnical design, Eurocode 7 (EN 1997), which advocates the use of the partial-factor method, with the added possibility to use the observational method if the uncertainties are large and difficult to assess.This thesis aims to highlight, develop and improve methods to assess the quality and value of geotechnical site investigations through reliability-based design. The thesis also discusses the limitations of the deterministic partial-factor method, according to its EN 1997 definition, and how to better harmonise this design methodology with the risk-based approach of reliability-based design. The main research contributions are: (1) a presented case study showing the importance of and potential gains with a robust framework for statistical evaluation of geotechnical parameters, (2) the discussion on the limitations of the partial-factor method in EN 1997, and (3) the discussion on how to harmonise the EN 1997 definition of the partial-factor method with the risk-based approach of reliability-based design.

  • 4.
    Gasch, Tobias
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Multiphysical analysis methods to predict the ageing and durability of concrete2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    With the societal demand for sustainability and the increasing age of infrastructure, a crucial task for the civil engineering community is to improve the durability of concrete structures. This thesis aims to contribute to such development through theoretical studies using mathematical modelling and numerical simulations. During its service life, a concrete structure is subjected to many different actions, ranging from mechanical loads to chemical and physical processes. Hence, a sound modelling strategy requires multiphysics and the inclusion of coupled chemical and physical fields (e.g. temperature, moisture and cement hydration) in addition to methods that describe mechanical integrity of the material. Conditions and phenomena critical for concrete structures at hydropower facilities have been of particular interest to study.

    The thesis presents several mathematical models of various complexity to describe the multiphysical behaviour of concrete using a material point description. A significant focus is on models that describe the mechanical behaviour of concrete where aspects such as ageing, cracking, creep and shrinkage are investigated. For the creep behaviour, a state-of-the-art model based on the Microprestress–Solidification (MPS) theory is reviewed and further developed. The appended papers (III to IV) presents a mathematical framework for the modelling of durability aspects of concrete based on multiphase porous media theory. The governing equations are derived with the Thermodynamically Constrained Averaging Theory (TCAT) as a starting point. It is demonstrated how this framework can be applied to a broad variety of phenomena related to durability; from the casting and hardening of concrete to the long-term absorption of water into air-entrained concrete. The Finite Element Methods (FEM) is used to solve the proposed mathematical models, and their capabilities are verified using experimental data from the literature.

    The main research contribution is the development and evaluation of theoretical models that advance the understanding and improve knowledge of the ageing and durability of concrete and concrete structures. More precisely, it is shown how multiphysical models and the developed multiphase framework can be used to gain insights on the material behaviour of concrete at smaller scales while they are also applicable to structural-scale simulations. During all model development, the efficient solution of structural problems has been fundamental. Through case studies and several examples from the literature, it is exemplified how these models can be used to enhance the performance and thereby increase the durability of concrete structures.

  • 5.
    Zhang, Wei
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport planning.
    Planning and evaluation of autonomous vehicles in freight and public transport services2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The introduction of automation technology in transport systems brings both opportunities and challenges. The direct benefits of automation technology are obvious, for instance, reduced marginal driving cost, improved energy efficiency and increased safety. However, factors such as additional vehicle acquisition cost might hinder the implementation of autonomous vehicles, especially in the early stages when mass production is not realized yet. Besides, some benefits require large-scale applications or cooperation among multiple vehicles, while the low market penetration rate of autonomous vehicles may make system-specific benefits insignificant. Without proper planning and operation schemes, the advantages of automation technology can be cancelled out by its disadvantages. Given that the advantages of individual autonomous vehicles have been extensively explored, it is necessary to estimate the efficiency of transport systems involving autonomous vehicles. This thesis intends to solve the operation problem of autonomous vehicles in freight and public transport systems, focusing on system cost analysis.

    In freight transport, semi-autonomous truck platooning is a promising way to reduce fuel consumption. By instructing vehicles to form groups and drive together closely, the trailing vehicles experience reduced air resistance from the leading vehicle, and thus less fuel consumption. However, in practice, freight transport companies should also take time windows and transport reliability into consideration. The study answers the questions whether platoons should be formed and how significant can the savings be, considering driving cost, predefined time windows, travel time uncertainty and fuel cost. System optimization techniques, including stochastic optimization and mixed-integer linear programming, are adopted to minimize the total cost.

    In public transport, autonomous buses are assumed to save on-board crew cost, partially or fully. Similar with truck platoons, semi-autonomous buses can also form bus platoons for the purpose of eliminating the drivers from trailing buses. By contrast, fully autonomous buses are completely driverless and operates individually like conventional buses. To investigate the efficiency of autonomous buses, we compare the total cost of autonomous buses with conventional buses, where both passengers’ cost and service provider’s cost are modelled. In a general trunk-and-branches network connecting city center and suburbs, both fully autonomous bus and semi-autonomous bus systems are assessed. On a simple highly demanded corridor where demand varies during peak and off-peak hours, semi-autonomous bus platoons can be used as trains by extending its capacity in peak hours. Application of semi-autonomous vehicles are considered in traditional bus transit and BRT, by comparing with its conventional opponents.

  • 6.
    Magnusson, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Fortifikationsverket.
    Shear in Concrete Structural Elements Subjected to Dynamic Loads2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Concrete structural elements subjected to severe dynamic loads such as explosions at close range may cause shear failures. In the Oklahoma City bombing in 1995 two concrete columns on the ground level were reported to have failed in shear. Such shear failures have also been reported to occur in several experimental investigations when concrete beams and slabs were subjected to blast or impact loads. The dynamic shear mechanisms are not yet fully understood and it is therefore of research significance to further investigate these mechanisms. The main objective of the research presented in this thesis is to experimentally and theoretically analyse shear failures of reinforced concrete elements subjected to uniformly distributed dynamic loads.

    The experimental work consisted of concrete beams of varying concrete grades and reinforcement configurations subjected to blast loads. One series involved testing of steel fibre reinforced concrete (SFRC) beams and the other series involved tests with concrete beams reinforced with steel bars. The former investigation showed that SFRC beams can resist certain blast loads. In the latter investigation, certain beams subjected to blast loads were observed to fail in flexural shear while the same beams exhibited flexural failures in the static tests. Such shear failures specifically occurred in beams with relatively high reinforcement contents. With these experiments as reference, numerical simulations with Ansys Autodyn were performed that demonstrated the ability to predict flexural shear failures.

    A direct shear failure mode has also been observed in experiments involving concrete roofs subjected to intense distributed blast loads. In several cases, the roof slabs were completely severed from their supporting walls along vertical or near-vertical failure planes soon after the load had been applied. Theoretical analyses of the initial structural response of beams subjected to distributed loads were conducted with the use of Euler-Bernoulli beam theory and numerical simulations in Abaqus/Explicit. These analyses show that the initial structural response consists of shear stresses and bending moments developing at the supports. The remaining parts of the beam will be subjected to a rigid body motion. Further simulations with Abaqus shows that that dynamic direct shear failure appears to be due to a deep beam response with crushing of the compressive struts at the supports, and therefore differs from a static direct shear mode. The results also showed that parameters such as element depth, amount of reinforcement, load level and load duration played a role in developing a dynamic direct shear failure.

  • 7.
    Widström, Torun
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Simulation of historic buildings for enhancement of preservation and energy performance – issues and methods2019Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Historic buildings are often particularly poorly insulated and difficult to heat, and are also at risk for several reasons. These include potential lack of use due to low thermal comfort leading to low or no profitability, damage risks due to over and under-climatization and risks due to climate change altering the boundary conditions that they were built for.

    Building simulation can be a valuable tool with which to assess the building performance of historic buildings, it can provide a background of knowledge for the design of potential strategies, and then assess such strategies in order to facilitate the decision process. Thus, simulation can contribute to minimized energy usage and optimized preservation, and prevent the need for potentially risky full-scale experiments that could jeopardize the cultural values. Thus a wide-spread use of simulation of historic buildings would be useful. However, it is difficult to simulate historic buildings with tools and methods developed for modern buildings. This may lead to a level of uncertainty that can greatly limit the usefulness of the simulation results.

    The work of the thesis

    The aim of the work presented in this thesis is to facilitate the choice and design of strategies for enhanced energy efficiency and preventive conservation in buildings of the cultural heritage. The subject of the thesis is the use of building simulation as a tool in that context, and specifically as a tool in the hands of the consultants who should perform such investigations. The work relates to the work of practitioners in the field, as a basis for making decisions on suitable strategies for enhancing energy performance and/or damage risk mitigation, not to academic tools. The focus is on whole-building simulation, in order to be able to obtain a full picture of the building performance, including deviations in conditions between different parts of the buildings.

    The work contains several parts:

    • Investigation of tools and methods relating to the specific demands of historic buildings
    • Identification of particular issues that challenge the usefulness of the simulations
    • Investigation of the particular issues and suggestions for how to deal with them
      • Several case studies testing the usefulness of the suggestions

    Several issues have been identified and investigated:

    Issue 1: Conditions by thermal bridges

    Mould issues do not occur in mid-air, they take place on surfaces, and often at the coldest, or most extreme temperatures of the room – which is often at the thermal bridges. Hence there is a need to assess the thermal performance of the thermal bridges as soon as possible in the simulation process.

    In this thesis wall-parts mimicking the performance of geometrical thermal bridges are proposed as a way to solve the problem and to allow evaluation of the potential risk of high levels of RH at places where there are two-dimensional thermal bridges in a calculating environment that can only handle one-dimensional building parts.

    The suggested method can be implemented in most whole-building simulation environments as long as wall-parts models can be created and their surface temperatures logged in the simulations. The method can be seen as satisfactory for the cases shown in the study. It manages to include the impact of two-dimensional heat conduction and the impact of thermal inertia in one-dimensional simulations. This makes damage risk assessment, specifically mould issues, possible at the points where it is most likely to occur.

    Issue 2: The impact of the wind pressure on the air exchange rate

    In buildings with natural ventilation and irregular shapes the wind pressure coefficients have a considerable impact on the air exchange rate. If the air exchange rate in the simulation does not correspond to that of the actual building, it does not matter how correct the rest is: the energy performance cannot be correctly assessed and neither can the damage risk, since the relative humidity will not be correct either.

    To investigate the wind pressure coefficients a series of wind tunnel experiments were performed with models of Skokloster Castle: The building with surrounding vegetation and neighboring building, the building without the surrounding, and the building without surrounding and without the characteristic towers. The last one was included to test a building body resembling a simpler shape, corresponding to the models used to derive the generic wind pressure coefficients that are likely to be used if no object-specific ones are available.

    The results of the wind tunnel experiments were then analyzed and compared, to check the validity of different methods to estimate wind pressure coefficients in this case. The geometric complexity added by the towers of the studied building caused additional turbulence compared to simpler geometry. This turbulence affected the pressure coefficients which in turn influenced the air exchange rate in the rooms profoundly. The value of the investigation is the quantification of the deviations between the different models, and the consequences of simplifications of the wind pressure coefficients for the model reliability.

    Issue 3: Mould risk

    In order to visualize the potential mold risk a display method was also developed to facilitate the overview and understanding of the mold risk. The most important benefit of the method is that the most critical time periods become easy to identify. This is not a new mould risk index or mould growth prediction tool as such, but rather a way of displaying the mould risk over time, so that critical periods can be identified and the pattern of the mould growth risk can be analyzed, to facilitate the design of preventive measures.

    Issue 4: Combining complexity in the model with moisture calculations without stability issues and long run times

    Commercial tools have to specialize on certain aspects of the simulation, which makes it difficult to find a single tool that can fulfill all the requirements for being a suitable tool for simulation of historic buildings.

    In the work, a new method is suggested, which is built on dividing of the simulation process into several steps in a serial fashion. This solves the issue by adding complexity and function-nality gradually. That way calibration and error-checking is facilitated while all the desired functions are provided, and stability issues are avoided. The method is tested in a case study, it proved fast and stable, and the results displayed good correspondence to measured values.

    Conclusion

    The contribution of this work is the identification and development of simulation tools and methods that are suitable for planning retrofitting strategies in historic buildings. The simulation process of historic buildings has been analyzed and a series of demands on suitable tools formulated. The issues of thermal performance of thermal bridges and the impact of wind pressure on the air exchange rate have been investigated, leading to a series of suggested methods and tools that have been found to fulfill their purposes under the conditions that they were made for and tested in. Hence, the investigations and suggestions should be of value in the simulation of historic buildings.

  • 8.
    Wadi, Amer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Soil-Steel Composite Bridges: Research advances and application2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Soil-steel composite bridges are considered competitive structures being an economical alternative to similar span concrete bridges. This frequently stimulates practitioners to push their design limits and expand the different areas of application including their performance in sloping terrain. This also implies that most design methods are continuously being developed to address new market challenges and at the same time to seek for better design and construction.

    This thesis compiles the recent research efforts to advance the knowledge on the structural performance of soil-steel composite bridges (SSCB). The first part of the thesis investigates the performance of SSCB in sloping terrain, where numerical simulations are used to predict the behaviour of three case studies. This includes structural response under sloped soils and also avalanche loads (Paper I and Paper II). The research enabled to realize the importance of soil configuration around the wall conduit and its influence on the structural response. While the presence of surface slopes emphasizes the susceptibility of SSCB with low depths of soil cover, higher covers may help in reducing the influence of steep slopes and avalanche loads. It was also found that the downhill soil configuration has substantial effects on the flexural response. The findings of the study were also used to provide methods for preliminary estimates of normal forces under sloped soils and avalanches.

    To better understand the load bearing capacity of SSCB, the second part of this thesis deals with the behaviour of large-span structures. It includes the use of finite element method simulations (FEM) for the analysis and the prediction of a previous full-scale loading-to-failure test (Paper III). The study also presents response predictions on the ultimate capacity of a large-span structure pertaining to its ongoing preparation for a full-scale field test (Paper IV). The thesis also includes discussions and possible refinements on current design equations concerning buckling calculations and live load effects. The results of the study have allowed to realize the major role of the soil load effects on the subsequent formation of yield areas and failure loads. It is found that the load position has a direct influence on the ultimate capacity especially for large-span structures. The study also highlighted the variations in the distribution of the live load sectional forces in both the circumferential and the transverse directions of the corrugations. Furthermore, possible refinements are proposed on current design equations of which are believed closely relevant on the path for the design development of large-span structures.

  • 9.
    Wang, Cong
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Sustainable Buildings.
    Ventilation Performance in Operating Rooms: A Numerical Assessment2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Surgical site infections (SSIs) remain one of the most challenging postoperative complicationsof healthcare and threaten the lives of millions of patients each year. Current evidence hasshown a positive relationship between the airborne concentration of bacteria-carryingparticles (BCPs) in the operating room (OR) and the rate of infections. The OR ventilation iscrucial for mitigating the dispersion of airborne bacterial contaminants and thus controllingthe risk of SSIs. A variety of ventilation schemes have been developed for OR use. Each haspros and cons and may be better suited than another for operations under certain conditions.The proper functioning of OR ventilation is also affected by external and internal disruptions.By applying Computational Fluid Dynamics (CFD), the present study investigates the airflowand contaminant distribution in ORs under different conditions.The airflow distribution is of critical importance in removing or diluting airbornecontaminants. The conventional mixing ventilation is not able to reliably create an ultracleanenvironment. The usage of mixing ventilation in infection-prone surgery should be limited,especially when a large surgical team is involved. Laminar airflow (LAF) ventilation demandsa sufficient airflow rate to achieve desired performance. Temperature-controlled airflow(TAF) ventilation represents an effective ventilation scheme that can serve as an energyefficientalternative to LAF.Door openings have a detrimental impact on the microbiological cleanliness of the OR. Thetemperature in the OR and adjacent space should be well controlled to minimize the interzonalcontaminant transfer. Temporarily reducing the OR exhaust flow during door operationforms a directional airflow towards the adjacent space, which is found to be an effectivesolution to ensure the isolation.Surgical lamps serve as physical obstructions in the airflow path and significantly deterioratethe performance of LAF ventilation. It is highly recommended to improve the shape anddesign of the lamps in the LAF ventilation. TAF is found to be less sensitive to the presenceof surgical lamps in the airflow path. The buoyancy-driven airflow used by TAF is morecapable of circumventing obstacles than the inertia-driven flow used by LAF. Thermal plumesdeveloped from the surgical equipment in the OR have the potential to distort the buoyancydrivenairflow in TAF.The thesis conducts a comprehensive literature review of important topics in OR ventilation.The present study enhances the understanding of the strengths and limitations of differentventilation schemes and increases the knowledge of the design and usage of OR ventilation.

  • 10.
    Jin, Junchen
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport Planning, Economics and Engineering.
    Advance Traffic Signal Control Systems with Emerging Technologies2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nowadays, traffic congestion poses critical problems including the undermined mobility and sustainability efficiencies. Mitigating traffic congestions in urban areas is a crucial task for both research and in practice. With decades of experience in road traffic controls, there is still room for improving traffic control measures; especially with the emerging technologies, such as artificial intelligence (AI), the Internet of Things (IoT), and Big Data. The focus of this thesis lies in the development and implementation of enhanced traffic signal control systems, one of the most ubiquitous and challenging traffic control measures.

    This thesis makes the following major contributions. Firstly, a simulation-based optimization framework is proposed, which is inherently general in which various signal control types, and different simulation models and optimization methods can be integrated. Requiring heavy computing resources is a common issue of simulation-based optimization approaches, which is addressed by an advanced genetic algorithm and parallel traffic simulation in this study.

    The second contribution is an investigation of an intelligent local control system. The local signal control operation is formulated as a sequential decision-making process where each controller or control component is modeled as an intelligent agent. The agents make decisions based on traffic conditions and the deployed road infrastructure, as well as the implemented control scheme. A non-parametric state estimation method and an adaptive control scheme by reinforcement learning (RL) are introduced to facilitate such an intelligent system.

    The local intelligence is expanded to an arterial road using a decentralized design, which is enabled by a hierarchical framework. Then, a network of signalized intersections is operated under the cooperation of agents at different levels of hierarchy. An agent at a lower level is instructed by the agent at the next higher level toward a common operational goal. Agents at the same level can communicate with their neighbors and perform collective behaviors.

    Additionally, a multi-objective RL approach is in use to handle the potential conflict between agents at different hierarchical levels. Simulation experiments have been carried out, and the results verify the capabilities of the proposed methodologies in traffic signal control applications. Furthermore, this thesis demonstrates an opportunity to employ the systems in practice when the system is programmed on an intermediate hardware device. Such a device can receive streaming detection data from signal controller hardware or the simulation environment and override the controlled traffic lights in real time.

  • 11.
    Källbom, Susanna
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Characterisation of thermally modified wood for use as component in biobased building materials2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The building sector shows growing interest in biobased building materials. Wood components, here defined as ground or milled wood, i.e. by-products (residuals/residues) from wood processing, such as sawdust or shavings, are valuable raw materials for new types of durable biocomposites suitable for outdoor building applications. An important research question related to such composites is how to characterise and enhance molecular interactions, i.e. adhesion properties, between wood and binder components. Another challenge is the hygroscopicity of the wood component, which can lead to dimensional changes and interfacial cracks during exposure to varying moisture conditions. Thermal modification of wood reduces its hygroscopicity, thereby, increasing its durability, e.g. its dimensional stability and resistance to biodeterioration. The hypothesis is that the use of thermally modified wood (TMW) components in biocomposites can enhance their durability properties and, at the same time, increase the value of residues from TMW processing. The main objective of this thesis is to study and analyse the surface and sorption properties of TMW components using inverse gas chromatography (IGC), dynamic vapour sorption (DVS), X-ray photoelectron spectroscopy (XPS), and the multicycle Wilhelmy plate method. The aim is to gain a better understanding of the surface and sorption characteristics of TMW components to enable the design of optimal adhesion properties and material combinations (compatibility) for use in biocomposites, especially suitable for outdoor and moist building material applications. Samples of TMW and unmodified wood (UW) components of Norway spruce (Picea abies Karst.) and Scots pine (Pinus sylvestris L.) heartwood were prepared and analysed with respect to surface energetics, hygroscopicity, liquid sorption and resulting swelling. The work also included analysis of surface chemical composition, as well as influences of extractives and moisture sorption history. The effect of using TMW components in a wood plastic composite (WPC) exposed to a series of soaking-drying cycles in water was studied with a focus on water sorption, swelling and micromorphological changes. The IGC analyses indicate that TMW components of spruce have a more heterogeneous surface energy character, i.e. a distinctly higher dispersive part of surface energy for low surface coverages, than do UW components. This is suggested to be due to the higher percentage of hydrophobic extractives present in TMW samples. Lewis acid-base analysis indicates that both UW and TMW components from spruce have a predominantly basic character and an enhanced basicity for the latter ones. Results show that both the hygroscopicity and water liquid uptake are lower for TMW than for UW samples. Unexpectedly, a significantly lower rate of water uptake was found for the extracted UW of pine heartwood than for non-extracted samples. In the former case, this is presumably due to contamination effects from water-soluble extractives, which increase capillary flow into wood voids, as proven by a decrease in water surface tension. Water uptake as well as swelling was significantly reduced for the WPCs with TMW and hot-water extracted UW components compared with the WPCs with UW components. This reduction also resulted in fewer wood component-polymer interfacial cracks in the WPCs with the modified wood components.

  • 12.
    Tympakianaki, Athina
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport Planning, Economics and Engineering.
    Demand Estimation and Bottleneck Management Using Heterogeneous Traffic Data2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Congestion on urban and freeway networks has become a major problem, leading to increased travel times and reduced traffic safety. In order to suggest traffic management solutions to improve the transport system efficiency, it is important to capture the travel demand patterns, expressed as origin-destination (OD) matrices, and understand the mechanisms of traffic bottlenecks. The increasing availability of traffic data offers significant opportunities to effectively address these issues. The thesis uses heterogeneous traffic data to improve three important problems.

    The first problem relates to the dynamic OD estimation problem, which entails significant challenges due to its complexity. The Simultaneous Perturbation Stochastic Approximation (SPSA) algorithm has been commonly used to solve the problem, which can handle any available data that can improve the estimation accuracy. However, it encounters stability and convergence issues. The thesis proposes a general modification of SPSA, called cluster-wise SPSA (c-SPSA), that has more robust performance and finds better solutions. Its efficiency is demonstrated through simulation experiments for a network from Stockholm.

    The second problem focuses on the development of methods for utilizing heterogeneous traffic data for the analysis and management of freeway work zone and tunnel bottlenecks. Simulation is used as the means to evaluate and optimize various mitigation strategies for each case.

    The third problem analyzes multimodal impacts due to network disruptions for the case of tunnel bottlenecks, using a data-driven approach. Tunnel congestion is often dealt with temporary closures, which may cause significant disruptions. It is crucial to identify the potential multimodal impacts of such interventions so as to design efficient and proactive mitigation strategies. The thesis shows the benefits of combining multiple data sources to analyze the impacts of temporary tunnel closures for a freeway tunnel in Stockholm.

  • 13.
    Chhang, Sophy
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges. INSA de Rennes.
    Energy-momentum conserving time-stepping algorithms for nonlinear dynamics of planar and spatial Euler-Bernoulli/Timoshenko beams2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Large deformations of flexible beams can be described using either the co-rotational approach or the total Lagrangian formalism. The co-rotational method is an attractive approach to derive highly nonlinear beam elements because it combines accuracy with numerical efficiency. On the other hand, the total Lagrangian formalism is the natural setting for the construction of geometrically exact beam theories. Classical time integration methods such as Newmark, standard midpoint rule or the trapezoidal rule do suffer severe shortcomings in nonlinear regimes. The construction of time integration schemes for highly nonlinear problems which conserve the total energy, the momentum and the angular momentum is addressed for planar co-rotational beams and for a geometrically exact spatial Euler-Bernoulli beam.

    In the first part of the thesis, energy-momentum conserving algorithms are designed for planar co-rotational beams. Both Euler-Bernoulli and Timoshenko kinematics are addressed. These formulations provide us with highly complex non-linear expressions for the internal energy as well as for the kinetic energy which involve second derivatives of the displacement field. The main idea of the algorithm is to circumvent the complexities of the geometric non-linearities by resorting to strain velocities to provide, by means of integration, the expressions for the strain measures themselves. Similarly, the same strategy is applied to the highly nonlinear inertia terms. Several examples have been considered in which it was observed that energy, linear momentum and angular momentum are conserved for both formulations even when considering very large number of time-steps. Next, 2D elasto-(visco)-plastic fiber co-rotational beams element and a planar co-rotational beam with generalized elasto-(visco)-plastic hinges at beam ends have been developed and compared against each other for impact problems. Numerical examples show that strain rate effects influence substantially the structure response.

    In the second part of this thesis, a geometrically exact 3D Euler-Bernoulli beam theory is developed. The main challenge in defining a three-dimensional Euler-Bernoulli beam theory lies in the fact that there is no natural way of defining a base system at the deformed configuration. A novel methodology to do so leading to the development of a spatial rod formulation which incorporates the Euler-Bernoulli assumption is provided. The approach makes use of Gram-Schmidt orthogonalisation process coupled to a one-parametric rotation to complete the description of the torsional cross sectional rotation and overcomes the non-uniqueness of the Gram-Schmidt procedure. Furthermore, the formulation is extended to the dynamical case and a stable, energy conserving time-stepping algorithm is developed as well. Many examples confirm the power of the formulation and the integration method presented.

  • 14.
    Ignat, Razvan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Ground Improvement by Dry Deep Mixing Lime-Cement Column Panels as Excavation Support2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Many urban areas near the coastal regions of Sweden are characterized by post-glacial clay deposits with very low undrained shear strength and high compressibility. Column type ground improvement by the Deep Mixing, DM, method using a binder mixture of lime and cement is commonly used in areas with poor soil conditions due to its cost-effectiveness, predominantly for settlement reduction and to improve the stability of embankments. With increasing urbanization and infrastructural development in these areas there is great interest in the industry in extending the practice of the Deep Mixing method to include other applications such as deep excavation and temporary and permanent improvement of natural slopes. Swedish experience related to use of the DM method for excavation support is limited and the current design recommendations for DM columns installed in the passive zone are very restrictive regarding the allowable mobilized column strength, resulting in a design which is often not cost-effective.

    In order to increase the use of the method to include applications where DM columns are subjected to unloading and lateral loading conditions, the mobilized strength and stiffness properties of the columns as well as the soil-column interaction need to be reliably predicted. The main objective of this study is to present a consistent method to adequately predict the behavior of lime-cement columns installed as excavation support in the passive zone of the structure and to investigate the strength and stiffness properties of lime-cement improved clay under different unloading and laterally loading conditions together with the soil-column interaction under these conditions.

    In order to investigate the field behavior of lime-cement column panels as excavation support, two experimental full-scale tests were performed. In each of these tests, a braced steel sheet pile wall supported by panels of overlapping lime-cement columns was first excavated to a pre-determined depth and thereafter loaded to failure by stepwise increasing a load applied behind the sheet pile wall. The tests provided a case record of deformations, stresses, and pore pressure responses, and failure mechanisms of the structures focusing on the improved soil. These tests showed that column-type ground improvement installed as panels of overlapping columns in the passive zone of a sheet pile wall significantly increases stability and reduces both excavation- and loading-induced structural forces and vertical and horizontal displacements in the soil.

    This thesis also presents the results of a laboratory study involving undrained and drained isotropic consolidated triaxial compression, extension and tension tests on laboratory improved clay with a binder of lime-cement similar to that used in the experimental field tests. Based on undrained triaxial test results, a relationship between the undrained strength, effective consolidation stress, and overconsolidation ratio is presented for different stress paths to failure. From the drained triaxial tests it was found that a failure surface comprising of two failure functions, one for tension failure and one for shear failure, similar to that observed for cemented sand, is consistent with the experimental data. Finally, a 3D FE-study of the experimental field tests considering the laboratory observed stress-strain behavior and mobilized strength of lime-cement improved clay was conducted. The results of these analyses are promising and failure load, deformations and structural forces in the retaining structure were predicted reasonably well.

    Summarizing the most important findings and conclusions from this study:

    -          Lime-cement columns panels installed in the passive zone acting as excavation support for a sheet pile wall will significantly increase the stability of the structure.

    -          Lime-cement column panels installed as excavation support are effective in reducing excavation induced displacements that can be of major concern for deep excavations conducted in areas with soft clay layers.

    -          The undrained strength of lime-cement improved clay at low consolidation stresses, corresponding to approximately 10 m of depth in field conditions, is dependent of the stress path to failure and it was found to be significantly lower for unloading stress paths compared to lateral loading stress paths, i.e. stress induced anisotropy. 

    -          The Young’s Modulus of lime-cement improved clay evaluated from undrained triaxial extension tests was significantly higher, 2.7 to 4.1 times, compared to the corresponding Young’s Modulus evaluated from the undrained triaxial compression tests. Also, significantly more brittle stress-strain behaviour was observed for triaxial extension tests compared to triaxial compression tests, regardless of applied stress path to failure and type of test, i.e. undrained/drained. 

    -          Results of the Finite Element analysis of the conducted experimental tests show that the current Swedish Design Guide for lime-cement columns installed in the passive zone overestimates the material undrained strength when based on results from Unconfined Compression tests, but also significantly underestimates the material drained strength. Since the Swedish Design Guide specifies that the lowest of the undrained/drained column strength should be chosen in the design, the consequence is often a too conservative design as the strength increase in the improved clay is not properly considered.

  • 15.
    Mohammadi Mohaghegh, Ali
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Structural Properties of High-Performance MacroBasalt Fibre Concrete; Flexure, Shear, Punching Shear and Fire Spalling2018Doctoral thesis, comprehensive summary (Other academic)
  • 16.
    Khan, Abdullah
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Towards the enhanced applicability of cold mix asphalt:: An experimental study focusing on surface free energies and the breaking and coalescence of bitumen emulsions2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The environmental, social and economic sustainability of our infrastructure network is clearly of paramount importance to the road-engineering sector as well to society at large. Sustainable road materials and reduced transport of those materials therefore play a significant role. Cold mix asphalt (CMA) emulsion technology could be one of the better options for the road industry to explore more thoroughly. Given its lower start-up and equipment installation costs, lower energy consumption and reduced environmental impact, CMA should offer a reliable alternative to some of the Hot Mix Asphalt (HMA) or Warm Mix Asphalt (WMA) options. As CMA is not a new technology, there are many reasons why this material is not currently being used as extensively as it might be. Though risk adverseness of the market may be partly to blame for this, a number of technical challenges and uncertainties related to material behavior are certainly responsible. This thesis has addressed some of the important technical challenges, aiming to provide more guidance in material selection and design, and prediction of the behavior of emulsion-based CMAs. To do so, this research has focused on aspects of the correct formulation of the bitumen emulsions, how to select the correct combinations of material components, and how to control the breaking and coalescence processes in bitumen emulsions better, resulting in usable and predictable adhesive and cohesive bond strengths. Though most of the laboratory and modeling choices that were made in this thesis are based on theoretical considerations, the main contribution is the test protocol development. The systematic surface free energy measurements of the material components, combined with the test set-up to monitor controllably the breaking and coalescence behavior of bitumen droplets in an emulsified environment, gives a new way to approach the design of CMA. It is recommended that future research is focused on taking the developed protocols as a basis for enhanced mix design and making a direct link to validated long-term mechanical properties on the asphalt mixture scale.

  • 17.
    Arvidsson, Therese
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Train–Track–Bridge Interaction for the Analysis of Railway Bridges and Train Running Safety2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, train–track–bridge interaction (TTBI) models are used to study the dynamic response of railway bridges. A TTBI model considers the dynamics of the train in addition to that of the track–bridge system. The TTBI model enables the assessment of train running safety and passenger comfort. In the bridge design stage, a moving force model is instead typically used for the train load. The main aim of this thesis is to use results from TTBI models to assess the validity of some of the Eurocode design criteria for dynamic analysis of bridges.

    A 2D rigid contact TTBI model was implemented in ABAQUS (Paper II) and in MATLAB (Paper III). In Paper V, the model was further developed to account for wheel–rail contact loss. The models were applied to study various aspects of the TTBI system, including track irregularities. The 2D analysis is motivated by the assumption that the vertical bridge vibration, which is of main interest, is primarily dependent on the vertical vehicle response and vertical wheel–rail force.

    The reduction in bridge response from train–bridge interaction was studied in Papers I–II with additional results in Part A of the thesis. Eurocode EN 1991-2 accounts for this reduction by an additional damping Δζ. The results show that Δζ is non-conservative for many train–bridge systems since the effect of train–bridge interaction varies with various train–bridge relations. Hence, the use of Δζ is not appropriate in the bridge design stage.

    Eurocode EN 1990-A2 specifies a deck acceleration criterion for the running safety at bridges. The limit for non-ballasted bridges (5 m/s2) is related to the assumed loss of contact between the wheel and the rail at the gravitational acceleration 1 g. This assumption is studied in Paper V based on running safety indices from the wheel–rail force for bridges at the design limit for acceleration and deflection. The conclusion is that the EN 1990-A2 deck acceleration limit for non-ballasted bridges is overly conservative and that there is a potential in improving the design criterion.

  • 18.
    Nejad Ghafar, Ali
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    An Experimental Study to Measure Grout Penetrability, Improve the Grout Spread, and Evaluate the Real Time Grouting Control Theory2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Due to the significant influence of the grout penetrability properties on spread of grout in rock fractures, this study aimed to investigate the grout penetrability from four different aspects. In Part (a), after review of all the existing methodologies developed to measure the grout penetrability, Filter-pump and Penetrability-meter were examined against Short-slot to figure out which one is more reliable. The study decisively considered Short-slot more reliable. In part (b), the so-called varying aperture long slot (VALS), an artificial fracture with apertures of 230-10 μm, was developed to study the gout penetrability more realistically. In part (c), a low-frequency rectangular pressure impulse was introduced to improve the grout spread by successive erosion of the produced filter cakes in consecutive cycles. The results showed considerable improvement in experiments using Short-slot. The dissipation of the pressure impulses was then investigated using VALS with noticeable remaining amplitudes after 2.0-2.7 m. In part (d), VALS was once more introduced to examine RTGC theory in a fracture with variable aperture. The study showed a relatively satisfactory agreement between the experimental results and the predictions of the grout propagation using the hydraulic aperture, whereas the predictions using the mean physical aperture showed considerably faster spread.

  • 19.
    Onifade, Ibrahim
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Development of Energy-based Damage and Plasticity Models for Asphalt Concrete Mixtures2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Characterizing the full range of damage and plastic behaviour of asphalt mixtures under varying strain-rates and stress states is a complex and challenging task. One reason for this  is partly due to the strain rate and temperature dependent nature of the material as well as the variation in the properties of the constituent materials that make up the composite asphalt mixture. Existing stress-based models for asphalt concrete materials are developed based on mechanics principles, but these models are, however, limited in their application for actual pavement analysis and design since rate dependency parameters are needed in the constitutive model to account for the influence of the strain rate on the stress-based yield and evolution criteria. Till date, we are yet to arrive at simple and comprehensive constitutive models that can be used to model the behaviour of asphalt mixture over a wide range of strain-rate which is experienced in the actual pavement sections. The aim of this thesis is to develop an increased understanding of the strength and deformation mechanism of asphalt mixtures through multi-scale modeling and to develop simple and comprehensive continuum models to characterize the non-linear behaviour of the material under varying stress-states and conditions. An analysis framework is developed for the evaluation of the influence of asphalt mixture morphology on its mechanical properties and response using X-Ray CT and digital image processing techniques. The procedure developed in the analysis framework is then used to investigate the existence of an invariant critical energy threshold for meso-crack initiation which serves as the basis for the development of a theory for the development of energy-based damage and plastic deformation models for asphalt mixtures. A new energy-based viscoelastic damage model is developed and proposed based on continuum damage mechanics (CDM) and the thermodynamics of irreversible processes. A second order damage variable tensor is introduced to account for the distributed damage in the material in the different principal damage directions. In this way, the material response in tension and compression can be decoupled and the effects of both tension- and compression stress states on the material behaviour can be accounted for adequately. Based on the finding from the energy-based damage model, an equivalent micro-crack stress approach is developed and proposed for the damage and fracture characterization of asphalt mixtures. The effective micro-crack stress approach takes account of the material stiffness and a critical energy threshold for micro-crack initiation in the characterization of damage and fracture properties of the mixture. The effective micro-crack stress approach is developed based on fundamental mechanics principles and it reduces to the Griffith's energy balance criterion when purely elastic materials are considered without the need for the consideration of the surface energy and a crack size in the determination of the fracture stress. A new Continuum Plasticity Mechanics (CPM) model is developed within the framework of thermodynamics to describe the plastic behaviour of asphalt concrete material with energy-based criteria derived for the initiation and evolution of plastic deformation. An internal state variable termed the "plasticity variable" is introduced to described the distributed dislocation movement in the microstructure. The CPM model unifies aspects of existing elasto-plastic and visco-plastic theories in one theory and shows particular strength in the modeling of rate-dependent plastic behaviour of materials without the need for the consideration of rate dependency parameters in the constitutive relationships. The CPM model is further extended to consider the reduction in the stiffness properties with incremental loading and to develop a unified energy-based damage and plasticity model. The models are implemented in a Finite Element (FE) analysis program for the validation of the models. The result shows that the energy-based damage and plastic deformation models are capable of predicting the behaviour of asphalt concrete mixtures under varying stress-states and strain-rate conditions. The work in this thesis provides the basis for the development of more fundamental understanding of the asphalt concrete material response and the application of sound and solid mechanics principles in the analysis and design of pavement structures.

  • 20.
    Zmijewski, Nicholas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Effects of Watershed Dynamics on Water Reservoir Operation Planning: Considering the Dynamic Effects of Streamflow in Hydropower Operation2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Water reservoirs are used to regulate river discharge for a variety of reasons, such as flood mitigation, water availability for irrigation, municipal consumption and power production purposes. Recent efforts to increase the amount of renewable power production have seen an increase in intermittent climate-variable power production due to wind and solar power production. The additional variable energy production has increased the need for regulating the capacity of the electrical system, to which hydropower production is a significant contributor. The hydraulic impact on the time lags of flows between production stations have often largely been ignored in optimization planning models in favor of computational efficiency and simplicity. In this thesis, the hydrodynamics in the stream network connecting managed reservoirs were described using the kinematic-diffusive wave (KD) equation, which was implemented in optimization schemes to illustrate the effects of wave diffusion in flow stretches on the resulting production schedule. The effect of wave diffusion within a watershed on the variance of the discharge hydrograph within a river network was also analyzed using a spectral approach, illustrating that wave diffusion increases the variance of the hydrograph while the regulation of reservoirs generally increases the variance of the hydrograph over primarily short periods. Although stream hydrodynamics can increase the potential regulation capacity, the total capacity for power regulation in the Swedish reservoir system also depends significantly on the variability in climatic variables. Alternative formulations of the environmental objectives, which are often imposed as hard constraints on discharge, were further examined. The trade-off between the objectives of hydropower production and improvement of water quality in downstream areas was examined to potentially improve the ecological and aquatic environments and the regulation capacity of the network of reservoirs.

  • 21.
    Svedholm, Christoffer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Efficient Modelling Techniques for Vibration Analyses of Railway Bridges2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The world-wide development of new high-speed rail lines has led to more stringent design requirements for railway bridges, mainly because high-speed trains can cause resonance in the bridge superstructure. Dynamic simulations, often utilising time-consuming finite element analysis (FEA), have become essential for avoiding such problems. Therefore, guidelines and tools to assist structural engineers in the design process are needed.

    Considerable effort was spent at the beginning of the project, to develop simplified models based on two-dimensional (2D) Bernoulli-Euler beam theory. First, a closed-form solution for proportionally damped multi-span beam, subjected to moving loads was derived (Paper I). The model was later used to develop design charts (Paper II) and study bridges on existing railway lines (Paper III). The model was then extended to non-proportionally damped beams (Paper IV) in order to include the effects of soil-structure interactions. Finally, the importance of the interaction between the surrounding soil and the bridge was verified by calibrating a finite element (FE) model by means of forced vibration tests of an end-frame bridge (Paper V).

    Recommendations on how to use the models in practical applications are discussed throughout the work. These recommendations include the effects of shear deformation, shear lag, train-bridge and soil-structure interactions, for which illustrative examples are provided. The recommendations are based on the assumption that the modes are well separated, so that the response at resonance is governed by a single mode.

    The results of the work show that short span bridges, often referred to as `simple´ bridges, are the most problematic with respect to dynamic effects. These systems are typically, non-proportionally damped systems that require detailed analyses to capture the `true´ behaviour. Studying this class of dynamic system showed that they tend to contain non-classical modes that are important for the structure response. For example, the bending mode is found to attain maximum damping when its undamped natural frequency is similar to that of a non-classical mode.

  • 22.
    Gustafsson, Marcus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology. Högskolan Dalarna.
    Energy Efficient Renovation Strategies for Swedish and Other European Residential and Office Buildings2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The high energy use in the European building stock is attributable to the large share of old buildings with poor energy performance. Energy renovation of buildings is therefore vital in the work towards energy efficiency and reduced environmental impact in the EU. Yet, the strategies and energy system implications of this work have not been made clear, and the rate of building renovation is currently very low.

    The aim of this thesis is to investigate the economic and environmental aspects of energy renovation strategies, with two main objectives:

    • Renovation of Swedish district heated multi-family houses, including life-cycle cost and environmental analysis and impact on the local energy system;

    • Renovation of European residential and office buildings, including life-cycle cost and environmental analysis and influence of climatic conditions.

    Buildings typical for the respective regions and the period of construction 1945-1970 were simulated, in order to determine the feasibility and energy saving potential of energy renovation measures in European climates. A variety of systems for heating, cooling and ventilation were studied, as well as solar energy systems, with focus on heat pumps, district heating, low-temperature heating systems and air heat recovery.

    Compared to normal building renovation, energy renovation can often reduce the life-cycle costs and environmental impact. In renovation of typical European office buildings, as well as Southern European multi-family houses, more ambitious renovation levels can also be more profitable.

    Exhaust air heat pumps can be cost-effective complements in district heated multi-family houses, while ventilation with heat recovery is more expensive but also more likely to reduce the primary energy use. From a system perspective, simple exhaust ventilation can reduce the primary energy use in the district-heating plant as much as an exhaust air heat pump, due to the lower electricity use.

  • 23.
    Ghafoori Roozbahany, Ehsan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Flow behavior of asphalt mixtures under compaction2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Asphalt compaction is one of the most important phases of road construction, being the decisive phase when the structure of the asphalt pavement layer is formed. In spite of its importance, the knowledge about this construction phase is still based on empirical and technological background and therefore surprisingly limited. This lack of knowledge is also due to the fact that the existing laboratory scale compaction devices for mix design are not fully capable of simulating the field compaction. The simulation of asphalt compaction in the laboratory is normally focused on the vertical rearrangements of asphalt particles whereas the flow behavior of these particles in other directions is mostly neglected. However, existing literature suggests that the neglected flow is one of the most important factors for the quality of the road construction, particularly in special cases such as asphalt joints. Therefore, building up a better understanding of the flow behavior of asphalt mixtures subjected to compaction loads is needed for improving the quality of the pavements.

    In this study, a new test setup, the so called Compaction Flow Test (CFT), was developed to simulate the flow behavior of asphalt mixtures at early stages of compaction. In the first step, feasibility tests were performed, substituting asphalt mixtures by model materials with simple geometries and less complex properties. X-ray Computed Tomography (CT) was utilized for capturing 2D radiography images of the flow patterns in the model material during the test. Results of the CFT showed the capability of the new test setup to clearly distinguish between model mixtures with different characteristics. Hence, in the next step, the CFT was applied to real asphalt mixtures and the obtained results were found to support the findings of the feasibility tests with the model materials.

    The results from the feasibility tests encouraged examining the possible use of an ultrasonic sensor as alternative to the complex and costly X-ray imaging for flow measurements during the CFT. Hence, the CFT was used along with a distance measuring ultrasonic sensor for testing asphalt mixtures with different characteristics. The test results confirmed that an ultrasonic sensor could be effective for capturing the differences of the flow behavior of asphalt mixtures tested by the CFT. 

    In addition, a parametric study with the X-ray setup was carried out to examine the capability of the CFT in reflecting the possible changes of the flow behavior in asphalt mixtures due to the change of construction parameters such as lift thickness, bottom roughness and compaction modes. The results obtained also confirmed the capability of the CFT in showing the possible differences in the flow behavior of the mixtures under the chosen conditions.

    The encouraging results suggested that the CFT may have potential to become a simple but effective tool for assessing compactability of the mixtures on-site, right after production in an asphalt plant or before placing the mixture on the road. Hence, discrete element method (DEM) was utilized to understand both the influence of selected boundaries of the CFT and the effect of its design on the results.

    As one specific example of application, an investigation was carried out using the CFT to find the most suitable tracking method for flow measurements in the field. Based on the literature review and feasibility tests, a tracking method with the highest potential for conducting flow measurements during field compaction was introduced. X-ray radiography confirmed the validity of the results obtained with the suggested method.

    The overall results obtained from this study suggest that the recommended CFT along with the suggested field tracking method may be helpful in building up a comprehensive basis of knowledge on the flow and compaction behavior of asphalt mixtures thus helping to close the gap between the field and laboratory.

  • 24.
    Medineckiene, Milena
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology.
    Integrated decision making in civil engineering, based on multi-criteria assessment and buildings’ certification2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Significant investments are being made in the construction sector in order to raise the quality of the buildings and make them more sustainable and energy-efficient. The key aspect of these investments should be the purposeful optimization of the possible renovation and construction measures. However, this important matter usually is being pushed aside in favor of construction price and/or quality. Nevertheless, there are plenty of criteria that play a major role in building sustainable development.

    The main purpose of this study is to present a tool that combines multi-criteria decision making (MCDM) methods and building certification systems in order to make weighted decisions in complicated construction tasks. For this, a decision making model was developed with a focus on sustainability, buildings’ life cycle, MCDM methods, and building certification.

    The first section of this thesis, the introduction, discusses the importance of the investigated area, and the main objectives, tasks, and structure of the thesis.

    A literature review is presented in Section 2 – Theory. The main works in the area of sustainability, LCA, building certification, and MCDM are collected to show their role and importance and how they interact in the construction industry.

    Section 3 presents and discusses the main ideas and instructions of the proposed decision making model.

    Section 4 (Methodology) introduces the main existing and proposed techniques that I have used to implement the study.

    Sections 5 and 6 are the case studies, which demonstrate how the proposed methods can be used in practice.

    Final conclusions and recommendations are presented in Section 7.

  • 25.
    Bjurström, Henrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Non-contact surface wave measurements on pavements2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, nondestructive surface wave measurements are presented for characterization of dynamic modulus and layer thickness on different pavements and cement concrete slabs. Air-coupled microphones enable rapid data acquisition without physical contact with the pavement surface.

    Quality control of asphalt concrete pavements is crucial to verify the specified properties and to prevent premature failure. Testing today is primarily based on destructive testing and the evaluation of core samples to verify the degree of compaction through determination of density and air void content. However, mechanical properties are generally not evaluated since conventional testing is time-consuming, expensive, and complicated to perform. Recent developments demonstrate the ability to accurately determine the complex modulus as a function of loading time (frequency) and temperature using seismic laboratory testing. Therefore, there is an increasing interest for faster, continuous field data evaluation methods that can be linked to the results obtained in the laboratory, for future quality control of pavements based on mechanical properties.

    Surface wave data acquisition using accelerometers has successfully been used to determine dynamic modulus and thickness of the top asphalt concrete layer in the field. However, accelerometers require a new setup for each individual measurement and are therefore slow when testing is performed in multiple positions. Non-contact sensors, such as air-coupled microphones, are in this thesis established to enable faster surface wave testing performed on-the-fly.

    For this project, a new data acquisition system is designed and built to enable rapid surface wave measurements while rolling a data acquisition trolley. A series of 48 air-coupled micro-electro-mechanical sensor (MEMS) microphones are mounted on a straight array to realize instant collection of multichannel data records from a single impact. The data acquisition and evaluation is shown to provide robust, high resolution results comparable to conventional accelerometer measurements. The importance of a perfect alignment between the tested structure’s surface and the microphone array is investigated by numerical analyses.

    Evaluated multichannel measurements collected in the field are compared to resonance testing on core specimens extracted from the same positions, indicating small differences. Rolling surface wave measurements obtained in the field at different temperatures also demonstrate the strong temperature dependency of asphalt concrete.

    A new innovative method is also presented to determine the thickness of plate like structures. The Impact Echo (IE) method, commonly applied to determine thickness of cement concrete slabs using an accelerometer, is not ideal when air-coupled microphones are employed due to low signal-to-noise ratio. Instead, it is established how non-contact receivers are able to identify the frequency of propagating waves with counter-directed phase velocity and group velocity, directly linked to the IE thickness resonance frequency.

    The presented non-contact surface wave testing indicates good potential for future rolling quality control of asphalt concrete pavements.

     

  • 26.
    Heng, Piseth
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Simplified mechanical models for the nonlinear dynamic analysis of elasto-plastic steel structures impacted by a rigid body2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Buildings subjected to impact and explosion are usually studied using large scale and highly nonlinear finite element model which are time-consuming. The first part of the thesis deals with the development of simple and accurate models for evaluating the nonlinear inelastic behaviour of steel frame structures subjected to impact. The research work in this part has produced four simplified models. The first model concerns with a 4DOF model that reproduces the behaviour of the impacted column. The restraining effect from the rest of the structure is modelled by an elastic spring, a head mass and a static load applied at the top of the column. In the second model, the impacted column is then further simplified using a SDOF model. The behaviour of the SDOF model is governed by an analytical force-displacement expressions of the column loaded by a located force. The maximum displacement of the impacted column can also be determined explicitly by adopting an energy-equivalent approach. Afterwards, in an effort to model the whole structure, two finite element models are developed. For these models, a co-rotational super-element that consists of a beam element and two generalized elasto-plastic hinges is obtained by performing a static condensation. An elastic flexible beam element is used in the first finite element model, whereas a rigid beam element is considered in the second one.

    In these models, inelasticity is concentrated at generalized elasto-plastic hinges which are modelled by combined axial-rotational springs. The behaviour of the hinges is uncoupled in the elastic range while an axial-bending interaction is considered in the plastic range making it possible to reproduce a wide range of cross-sections and joints. In addition, unilateral contact between rigid point masses is considered and the energy loss during impact is accounted by means of a restitution coefficient following Newton’s impact law. Energy-momentum scheme is used to solve the equations of motion produced by these models.

    The second part of the thesis concerns with the performance of the connectors in composite steel-concrete slabs under explosion. The purpose is to determine residual capacities of the shear connectors after being damaged by explosion using large-scale pull-out and push-out experimental tests and finite element simulations.

  • 27.
    Peñaloza, Diego
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. RISE - Research Institutes of Sweden.
    The role of biobased building materials in the climate impacts of construction: Effects of increased use of biobased materials in the Swedish building sector2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A significant share of the global climate change impacts can be attributed to the construction sector. One mitigation strategy is increasing the use of biobased materials. Life cycle assessment (LCA) has been used to demonstrate the benefits of this, but forest complexities create uncertainty due to omission of key aspects. The aim of this thesis is to enhance understanding of the effects of increasing use of biobased materials in climate change mitigation of construction works with a life cycle perspective. Non-traditional LCA methodology aspects were identified and the climate impact effects of increasing the use of biobased materials while accounting for these was studied. The method applied was dynamic LCA combined with forest carbon data under multi-approach scenarios. Diverse case studies (a building, a small road bridge and the Swedish building stock) were used. Most scenarios result in impact reductions from increasing the use of biobased materials in construction. The inclusion of non-traditional aspects affected the results, but not this outcome. Results show that the climate mitigation potential is maximized by simultaneously implementing other strategies (such as increased use of low-impact concrete). Biobased building materials should not be generalised as climate neutral because it depends on case-sensitive factors. Some of these factors depend on the modelling of the forest system (timing of tree growth, spatial level approach, forest land use baseline) or LCA modelling parameters (choice of the time horizon, end-of-life assumptions, service life). To decrease uncertainty, it is recommended to use at least one metric that allows assessment of emissions based on their timing and to use long-term time horizons. Practitioners should clearly state if and how non-traditional aspects are handled, and study several methodological settings. Technological changes should be accounted for when studying long-term climate impacts of building stocks.

  • 28.
    Deckner, Fanny
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Vibration transfer process during vibratory sheet pile driving: from source to soil2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Vibratory driven sheet piles are a cost-effective retaining wall structure, and in coming decades the continued use of this method will be crucial for minimising costs within the construction sector. However, vibratory driven sheet piles are a source of ground vibrations, which may harm structures or induce disturbance. Most urban construction projects face strict limits on permissible vibration level. Being able to reliably predict the expected vibration level prior to construction is therefore highly important. Reliable prediction demands a profound knowledge of the vibration transfer process, from source to point of interest. This thesis focuses on clarifying the vibration transfer process and will serve as a platform for the future development of a reliable prediction model. The vibration transfer process is divided into two main parts: vibration source and vibrations in soil. The different parts in the vibration transfer process are studied and investigated with the help of a literature review, field tests and numerical modelling. Within the scope of this thesis, three field tests have been conducted and a new instrumentation system has been developed. The new instrumentation system enables recording of both sheet pile vibrations and ground vibrations at depth during the entire driving. The field tests aimed to study the vibration transfer from sheet pile to soil and the vibration transfer within a sheet pile wall, as well as the wave pattern in soil. To study sheet pile behaviour during driving a numerical model was developed, which is also meant to serve as a basis for further studies. The main scientific contribution of this thesis is the identification of the sheet pile behaviour during driving. For practical application, the main contribution is the development of an increased knowledge of the vibration transfer process from source to soil, together with the new instrumentation system and the development of the numerical model.

  • 29.
    Namutebi, May
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    An investigation into some aspects for foamed bitumen technology2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Despite applications of foamed bitumen technology in pavement construction in various places around the world, there are still several aspects about this technology that are not clear. In addition, knowledge on foamed bitumen technology is mainly empirical and lacks scientific basis. This study addresses some of the aspects for foamed bitumen technology such as: Investigation of any effects in binder composition during the production process for foamed bitumen; assessment of the effect of bitumen source on foamed bitumen characteristics; development of a rational method to optimise foamed bitumen characteristics and conditions; evaluation of aggregate particle coating within foamed bitumen mixes; further improvements in the mix design procedure specifically the method of compaction and optimum bitumen content determination stages are suggested.  Fourier transform infrared spectroscopy techniques were used to investigate any changes in bitumen composition after the production process of foamed bitumen. Fourier transform infrared tests were done on foamed bitumen and neat bitumen specimens for two bitumens with similar penetration grades. Foamed bitumen characteristics of three bitumens were established by producing foamed bitumen at temperatures of 150ºC up to 180ºC and foamant water contents of 1, 2, 3, 4 and 5%. From the analysis of variation of foamed bitumen characteristics (maximum expansion ratio and half-life) at different temperatures a new method based on the equi-viscous bitumen temperature to optimize foamed bitumen conditions and characteristics was proposed. Rice density and surface energy concepts were used to evaluate aggregate particle coating with foamed bitumen. A granite aggregate divided into three different size fractions and three sets of foamed bitumen produced from three bitumen penetration grades were used. A gyratory laboratory compaction procedure for laterite gravels treated with foamed bitumen was established using the modified locking concept. Three laterite gravels with different chemical composition were mixed with foamed bitumen produced from one penetration bitumen grade. The resulting mixes were compacted up to 200 gyrations and the corresponding compaction curve defined in terms of height versus number of gyrations noted. In addition, the optimum moisture content requirements at the modified locking point were determined. 3D packing theory concepts, primary aggregate structure porosity and an indirect tensile strength criteria were employed to determine optimum bitumen content for foamed bitumen mixes.  Fourier infrared techniques revealed that foaming did not cause any changes in the bitumen chemistry, implying that the foamed bitumen production process may possibly be a physical process. Characterisation of foamed bitumen produced from three bitumen penetration grades showed that foamed bitumen characteristics (maximum expansion ratio and half-life) were mainly influenced by binder viscosity rather than the source. The equi-viscous temperature seemed to provide a suitable criterion at which foamed bitumen with optimum characteristics could be produced. Rice density results showed that aggregate size fraction, binder expansion ratio and viscosity influenced aggregate particle coating. For the coarser aggregate fraction, results revealed that binder coating seemed to be mainly influenced by temperature. Whilst for fine aggregate fraction the coating was mainly influenced by surface area. Surface energy results revealed that foamed bitumen exhibited better coating attributes than neat bitumen. A new laboratory compaction procedure for laterite gravels treated with foamed bitumen based on the modified locking point was developed. The modified locking point represents the state at which maximum aggregate particle interlock occurs when mixes are compacted in the field. It is based on the iii analysis of the rate of change for the gyratory compaction curve. The compaction curve in this case is defined in terms of compaction height versus number of gyrations. Gradation analysis beyond the modified locking point showed that aggregate particle breakdown occurred. Analysis of the optimum moisture at the modified locking point revealed that the moisture conditions were less than the aggregate optimum moisture conditions. It is recommended that this point be used to determine the optimal compaction characteristics of foamed bitumen mixes.  Aggregate structure porosity and an indirect tensile strength criteria can be used to determine the bitumen content that could be used in design of foamed bitumen mixes. This would reduce the amount of resources required since the bitumen content could be estimated prior to carrying out the actual laboratory work given that the aggregate grading is known. The aggregate structure can be divided (based on 3D packing theory) into oversize, primary, and secondary structures. The primary structure is mostly responsible for carrying loads whilst the secondary structure fills the voids within the primary structure and provides support to the primary structure. The aggregate size particles constituting the primary structure are deduced as a function of standard sieve sizes using the packing theory concepts. The minimum sieve size for the primary structure is proposed as 1 mm. The oversize structure consists of aggregate particles whose size is greater than the maximum size for the primary structure. The secondary structure consists of aggregate particles whose size is below the minimum size for the primary structure. The primary aggregate structure porosity can be used to establish the starting bitumen content; the bitumen content at which this porosity is 50% is chosen as the initial bitumen content. Indirect tensile strength values corresponding to 50% primary porosity are determined as well as the bitumen contents and compared against the recommended minimum values.

  • 30.
    Sadrizadeh, Sasan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology.
    Design of Hospital Operating Room Ventilation using Computational Fluid Dynamics2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The history of surgery is nearly as old as the human race. Control of wound infection has always been an essential part of any surgical procedure, and is still an important challenge in hospital operating rooms today. For patients undergoing surgery there is always a risk that they will develop some kind of postoperative complication.

    It is widely accepted that airborne bacteria reaching a surgical site are mainly staphylococci released from the skin flora of the surgical staff in the operating room and that even a small fraction of those particles can initiate a severe infection at the surgical site.  Wound infections not only impose a tremendous burden on healthcare resources but also pose a major threat to the patient. Hospital-acquired infection ranks amongst the leading causes of death within the surgical patient population. A broad knowledge and understanding of sources and transport mechanisms of infectious particles may provide valuable possibilities to control and minimize postoperative infections.

    This thesis contributes to finding solutions, through analysis of such mechanisms for a range of ventilation designs together with investigation of other factors that can influence spread of infection in hospitals, particularly in operating rooms.

    The aim of this work is to apply the techniques of computational fluid dynamics in order to provide better understanding of air distribution strategies that may contribute to infection control in operating room and ward environments of hospitals, so that levels of bacteria-carrying particles in the air can be reduced while thermal comfort and air quality are improved.

     A range of airflow ventilation principles including fully mixed, laminar and hybrid strategies were studied. Airflow, particle and tracer gas simulations were performed to examine contaminant removal and air change effectiveness. A number of further influential parameters on the performance of airflow ventilation systems in operating rooms were examined and relevant measures for improvement were identified.

    It was found that airflow patterns within operating room environments ranged from laminar to transitional to turbulent flows. Regardless of ventilation system used, a combination of all airflow regimes under transient conditions could exist within the operating room area. This showed that applying a general model to map airflow field and contaminant distribution may result in substantial error and should be avoided.

    It was also shown that the amount of bacteria generated in an operating room could be minimized by reducing the number of personnel present. Infection-prone surgeries should be performed with as few personnel as possible. The initial source strength (amount of colony forming units that a person emits per unit time) of staff members can also be substantially reduced, by using clothing systems with high protective capacity.

    Results indicated that horizontal laminar airflow could be a good alternative to the frequently used vertical system. The horizontal airflow system is less sensitive to thermal plumes, easy to install and maintain, relatively cost-efficient and does not require modification of existing lighting systems. Above all, horizontal laminar airflow ventilation does not hinder surgeons who need to bend over the surgical site to get a good view of the operative field.

    The addition of a mobile ultra-clean exponential laminar airflow screen was also investigated as a complement to the main ventilation system in the operating room. It was concluded that this system could reduce the count of airborne particles carrying microorganisms if proper work practices were maintained by the surgical staff.

    A close collaboration and mutual understanding between ventilation experts and surgical staff would be a key factor in reducing infection rates. In addition, effective and frequent evaluation of bacteria levels for both new and existing ventilation systems would also be important.

  • 31.
    Hai, Lu
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Service and Energy Systems.
    Energy Quality Management for Building Clusters and Districts Using a Multi-Objective Optimization Approach2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    As society develops, energy needs and the warnings of global warming have become main areas of focus in many areas of human life. One such aspect, the building sector, needs to take responsibility for a significant portion of energy use. Researchers need to concentrate on applying innovative methods for controlling the growth of energy use. Apart from improving energy efficiency by reducing energy use and improving the match between energy supply and demand, energy quality issues have become a key topic of interest. Energy quality management (EQM) is a technique that aims to optimally utilize the exergy content of various renewable energy sources. The evaluation of the optimum energy systems for specific districts is an essential part of EQM.

    The optimum energy system must follow the concept of “sustainability.” In other words, the optimization process should select the most suitable energy systems, which fulfill various sustainable requirements such as high energy/exergy performance, low environmental impacts and economic cost, as well as acceptable system reliability. A common approach to dealing with complex criteria involves multi-objective optimization, whereby multi-objective optimization is applied in the context of EQM of building clusters and districts (BCDs). In the present thesis, a multi-objective optimization process is proposed that applies a genetic algorithm (GA) to address non-linear optimization problems. Subsequently, four case studies are used to analyze how the multi-objective optimization process supports EQM of BCDs. Detailed information about these cases is provided below:

    1. Basic case (UK): This case is used to investigate the application possibility of the approach in BCD energy system design and to analyze the optimal scenario changes, along with variations of optimization objective combinations. This approach is proven to be time-effective

    2. Case 1 (Norway): The use of renewable energy sources can be highly intermittent and dependent on local climatic conditions; therefore, energy system reliability is a key parameter be considered for the renewable energy systems. This section defines system reliability as a constraint function and analyzes the system changes caused by the varying reliability constraints. According to the case, system reliability has been proven to be one of the most important objectives for the optimization of renewable energy systems.

    3. Case 2 (China): In this section, the approach is applied in order to search for the optimal hybrid system candidates for a net-zero exergy district (NZEXD) in China. Economic analysis is included in this case study. Through the optimization process, the proposed approach is proven to be flexible and capable of evaluating distinct types of energy scenarios with different objective functions. Moreover, the approach is able to solve practical issues, such as identifying the most feasible options to the stepwise energy system transition for a specific case.

    4. Case 3 (China): This section makes two major contributions. The first is to test the expansibility of inserting additional objectives into the approach; a parametric study is then applied to investigate the effects of different energy parameters. The second contribution is the conclusion that the optimum energy systems might vary significantly, depending on certain parameters.

    According to the analyses in these case studies, the multi-objective optimization approach is capable of being a tool for future BCDs’ energy system design. It should also be noted that the findings from the case studies – especially the parametric study – might provide some interesting research topics for future work.

  • 32.
    Wersäll, Carl
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Frequency Optimization of Vibratory Rollers and Plates for Compaction of Granular Soil2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Vibratory rollers are commonly used for compaction of embankments and landfills. This task is time consuming and constitutes a significant part of most large construction and infrastructure projects. By improving the compaction efficiency, the construction industry would reduce costs and environmental impact.

    This research project studies the influence of the vibration frequency of the drum, which is normally a fixed roller property, and whether resonance can be utilized to improve the compaction efficiency. The influence of frequency on roller compaction has not before been studied but the concept of resonance compaction has previously been applied successfully in deep compaction of fills and natural deposits.

    In order to examine the influence of vibration frequency on the compaction of granular soil, small-scale compaction tests of sand were conducted under varying conditions with a vertically oscillating plate. Subsequently, full-scale tests were conducted using a vibratory soil compaction roller and a test bed of crushed gravel. The results showed that resonance can be utilized in soil compaction by vibratory rollers and plates and that the optimum compaction frequency from an energy perspective is at, or slightly above, the coupled compactor-soil resonant frequency. Since rollers operate far above resonance, the compaction frequency can be significantly reduced, resulting in a considerable reduction in fuel consumption, environmental impact and machine wear.

    The thesis also presents an iterative equivalent-linear method to calculate the frequency response of a vibrating foundation, such as a compacting plate or the drum of a roller. The method seems promising for predicting the resonant frequency of the roller-soil system and can be used to determine the optimum compaction frequency without site- and roller-specific measurements.

  • 33.
    Ferdos, Farzad
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Internal Erosion Phenomena in Embankment Dams: Throughflow and internal erosion mechanisms2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

     In this study, two major internal erosion initiation processes, suffusion and concentrated leak mechanisms, which lead to both defect formation in a dam’s body and its foundation and high throughflow in dams subjected to internal erosion were studied. This understanding has the potential to facilitate numerical modelling and expedite dam safety assessment studies. 

    The throughflow properties of coarse rockfill material were studied by; analysing filed pump test data, performing extensive laboratory experiments with a large-scale apparatus and numerically simulating the three-dimensional flow through coarse rock materials, replicating the material used in the laboratory experiments.

    Results from the tests demonstrate that the parameters of the nonlinear momentum equation of the flow depend on the Reynolds number for pore Reynolds numbers lower than 60000. 

    Numerical studies were also carried out to conduct numerical experiments. By applying a Lagrangian particle tracking method, a model for estimating the lengths of the flow channels in the porous media was developed.  The shear forces exerted on the coarse particles in the porous media were found to be significantly dependent on the inertial forces of the flow.

    Suffusion and concentrated leak mechanisms were also studied by means of laboratory experiments to develop a theoretical framework for continuum-based numerical modelling. An erosion apparatus was designed and constructed with the capability of applying hydraulic and mechanical loading. Results were then used to develop constitutive laws of the soil erosion as a function of the applied hydromechanical load for both suffusion and concentrated leak mechanisms. Both the initiation and mass removal rate of were found to be dependent on the soil in-situ stresses.

    A three-dimensional electrical-resistivity-based tomography method was also adopted for the internal erosion apparatus and was found to be successful in visualising the porosity evolution due to suffusion.

  • 34.
    Wang, Qian
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology.
    Low-temperature Heating in Existing Swedish Residential Buildings: Toward Sustainable Retrofitting2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    As an energy-efficient alternative in cold climate countries such as Sweden, low-temperature heating (LTH) technology has shown promising advantages and shortcuts to contribute to the efficiency of heat supply, as well as to the overall sustainability of building performance. The goal of this thesis is to contribute to the development of methodologies and modeling tools to support sustainable retrofitting in the Swedish housing stock. A combination of three integrated modeling techniques was developed. The main focus of this work was implementing LTH in retrofitting practice. The principle of the developed methods can be regarded as a top-down approach, underpinning the general definition of LTH and sustainability criteria. It was found that a preliminary compilation and investigation of the building typology could simplify the retrofitting decision-making. Also, 36–54% of final energy savings could be achieved in studied housing archetypes by effective energy retrofitting. Combining LTH radiators with ventilation heat recovery showed the largest contributions. Below 30 W/m2 (12 W/ m3) heating demand, both radiators (ventilation radiators and baseboard radiator) could work as LTH. These reduced supply temperatures further improved the COP of air-source heat pumps by approximately 12% - 18%. For retrofitting of conventional radiators, there was no concrete evidence to support Type 22 having higher thermal efficiency than Type 21, for the Swedish climate and heating seasons. The achievements and full potential of implementing LTH in retrofitting were found to require not only efficient radiators, but also a well-designed package – insulation, piping, pumping and energy supply system - that suited the current heating demand of the building, given the local climate condition.

    However, it should also be highlighted that retrofitting incorporating all evaluated measures would not always yield higher long-term economic profits among different archetypes. It is important to find the trade-off between cost-effectiveness and energy savings in similar archetypes - instead of using a “one size fits all” types of solution. For conventional retrofit measures, such as insulations of building envelopes, it was necessary to evaluate the embodied energy during the whole retrofitting process.

  • 35.
    Dinegdae, Yared H.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Mechanics-based Design Framework for Flexible Pavements2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Load induced top-down fatigue cracking has been recognized recently as a major distress phenomenon in asphalt pavements. This paper presents a mechanics-based design framework in load and resistance factor design (LRFD) format for the top-down fatigue cracking performance evaluation of flexible pavements. This was achieved by enhancing further the hot mix asphalt fracture mechanics (HMA-FM) model through the incorporation of mixture morphology influence on key fracture properties, and incorporating partial safety factors to account for variabilities and uncertainties. The analysis framework was calibrated and validated using pavement sections that have high quality laboratory data and well documented field performance histories. Moreover, as traffic volume was identified in having a dominant influence on predicted performance, a further investigation was performed to establish and evaluate truck traffic characterization parameters effect on predicted results.

    A two-component reliability analysis methodology, which uses central composite design (CCD) based response surface approach for surrogate model generation and the first order reliability method (FORM) for reliability estimation was used for the development of the LRFD mechanics-based design framework. The effectiveness of the design framework was investigated through design examples, and the results have shown that the formulated partial safety factors have accounted effectively the variabilities involved in the design process. Further investigation was performed to establish the influence design inputs variabilities have on target reliabilities through case studies that combine input variabilities in a systematic way. It was observed from the results that the coefficient of variation (COV) level of the variability irrespective of the distribution type used have a significant influence on estimated target reliability.

  • 36.
    Hailesilassie, Biruk
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Morphology Characterization of Foam Bitumen and Modeling for Low Temperature Asphalt Concrete2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Development of new asphalt technologies to reduce both energy consumption and CO2 production has attracted great interest in recent years. The use of foam bitumen, as one of them, is attractive due to the low investment and production cost. Formation and decay of foam bitumen is a highly dynamic temperature dependent process which makes characterization difficult. In this thesis, new experimental tools were developed and applied for characterizing the foam bitumen during the hot foaming process. 

    One of the main goals of this study was to improve understanding and characterization of the foam bitumen formation and decay. X-ray radiography was used to study the formation and decay of foam bitumen in 2D representation. The results demonstrate that the morphology of bubble formation depends on the types of bitumen used. Moreover, theoretical investigation based on the 3D X-ray computed tomography scan dataset of bubble merging showed that the disjoining pressure increased as the gap between the bubbles in the surface layer (foam film) decreased with time and finally was ruptured. 

     Examining the foam bitumen stream right at the nozzle revealed that foam bitumen at a very early stage contains fragmented pieces of irregular size rather resembling a liquid than foam. The result from thermogravimetric analysis demonstrated that residual water content depends on the initial water content, and was found to be between 38 wt% and 48 wt% of the initial water content of 4 wt% to 6 wt%.

    Moreover the influence of viscosity and surface tension on bubble shape and rise velocity of the bubbles using level-set method was implemented in finite element method. The modeling results were compared with bubble shape correlation map from literature. The results indicated that the bubble shapes are more dependent on the surface tension parameters than to the viscosity of the bitumen, whereas the bitumen viscosity is dominant for bubble rising velocity.

  • 37.
    Ahmad, Nawaz
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    REACTIVE TRANSPORT MODELLING OF DISSOLVED CO2 IN POROUS MEDIA: Injection into and leakage from geological reservoirs2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The geological sequestration of carbon dioxide (CO2) is one of the options of controlling the greenhouse gas emissions. However, leakage of CO2 from the storage reservoir is a risk associated with geological sequestration. Over longer times, large-scale groundwater motion may cause leakage of dissolved CO2 (CO2aq).

    The objectives of this thesis are twofold. First, the modelling study analyzes the leakage of CO2aq along the conducting pathways. Second, a relatively safer mode of geological storage is investigated wherein CO2aq is injected in a carbonate reservoir. A reactive transport model is developed that accounts for the coupled hydrological transport and the geochemical reactions of CO2aq in the porous media. The study provides a quantitative assessment of the impact of advection, dispersion, diffusion, sorption, geochemical reactions, temperature, and heat transport on the fate of leaking CO2aq.

    The mass exchange between the conducting pathway and the rock matrix plays an important role in retention and reactions of leaking CO2aq. A significant retention of leaking CO2aq is caused by its mass stored in aqueous and adsorbed states and its consumption in reactions in the rock matrix along the leakage pathway. Advection causes a significant leakage of CO2aq directly from the reservoir through the matrix in comparison to the diffusion alone in the rock matrix and advection in a highly conducting, but thin fracture. Heat transport by leaking brine also plays an important role in geochemical interactions of leaking CO2aq

    Injection of CO2aq is simulated for a carbonate reservoir. Injected CO2-saturated brine being reactive causes fast dissolution of carbonate minerals in the reservoir and fast conversion of CO2aq through considered geochemical reactions. Various parameters like dispersion, sorption, temperature, and minerals reaction kinetics are found to play important role in the consumption of CO2aq in reactions.

  • 38.
    Krounis, Alexandra
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Sliding stability re-assessment of concrete dams with bonded concrete-rock interfaces2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The shear strength of the concrete-rock interface is an important parameter in sliding stability analyses of concrete dams founded on rock and depends, in addition to the normal stress state, on the bonding conditions of the interface; concrete-rock interfaces can be either unbonded, partially bonded or fully bonded.

    In the Swedish guidelines for dam safety all dam-foundation contacts are treated as unbonded. This has the benefit of eliminating all uncertainties related to the cohesive strength of bonded contacts but it might also lead to unnecessary strengthening of dams. Other national guidelines deal with the uncertainties related to cohesion by applying higher safety factors, mainly determined based on previous experience, when both cohesion and friction are taken into account.

    The main objective of this project is to study if and how cohesion can be included when evaluating the shear strength of bonded or partially bonded interfaces. To accomplish this, uncertainties associated with cohesion are identified and their influence on the assessed stability is investigated.

    The results show that the influence on the assessed sliding stability is strongly dependent on the magnitude of the involved uncertainties that might vary significantly for different dams. It is thus questionable if one safety factor applicable for all dams can be established for use in deterministic analyses.

    Taking into account cohesion when reliability methods are used is somewhat less complicated because of the possibility of directly incorporating the uncertainties in the analysis. The main challenge in such cases is the quantification of the involved uncertainties due to lack of proper data and, in some cases, knowledge. In this thesis, a framework for quantification of parameter uncertainty is suggested and the model error due to brittle failure in combination with spatial variation in cohesion is analysed. Areas that require more research to further refine the analysis are also identified.

  • 39.
    Zhu, Jiqing
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Storage Stability and Phase Separation Behaviour of Polymer-Modified Bitumen: Characterization and Modelling2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Polymer-modified bitumen (PMB) is a high-performance material for road construction and maintenance. But its storage stability and phase separation behaviour are still not sufficiently understood and need to be studied toward a more successful and sustainable application of PMB. In this thesis, the equilibrium thermodynamics and phase separation dynamics of PMB are investigated with the aim at a fundamental understanding on PMB storage stability and phase separation behaviour. The development of polymer modifiers for paving bitumen is reviewed. The phase separation process in unstable PMBs is captured by fluorescence microscopy at the storage temperature (180 °C). A coupled phase-field model of diffusion and flow is developed to simulate and predict the PMB storage stability and phase separation behaviour. The temperature dependency of PMB phase separation behaviour is modelled by introducing temperature-dependent model parameters between 140 °C and 180 °C. This model is implemented in a finite element software package and calibrated with the experimental observations of real PMBs. The results indicate that storage stability and phase separation behaviour of PMB are strongly dependent on the specific combination of the base bitumen and polymer. An unstable PMB starts to separate into two phases by diffusion, because of the poor polymer-bitumen compatibility. Once the density difference between the two phases becomes sufficiently significant, gravity starts to drive the flow of the two phases and accelerates the separation in the vertical direction. The proposed model, based on the Cahn-Hilliard equation, Flory-Huggins theory and Navier-Stokes equations, is capable of capturing the stability differences among the investigated PMBs and their distinct microstructures at different temperatures. The various material parameters of the PMBs determine the differences in the phase separation behaviour in terms of stability and temperature dependency. The developed model is able to simulate and explain the resulting differences due to the material parameters. The outcome of this study may thus assist in future efforts of ensuring storage stability and sustainable application of PMB.

  • 40.
    Chen, Feng
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Sustainable Implementation of Electrified Roads: Structural and Material Analyses2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Given the promise of the Inductive Power Transfer (IPT) technology for eRoad applications, the potential challenges for a successful integration of dynamic IPT technology into the physical road structure are explored extensively in this research work. The Finite Element Method (FEM) is selected for studying the structural performance of an eRoad under operational conditions. In this, an energy-based finite strain constitutive model for asphalt materials is developed and calibrated, to enable the detailed investigation of the structural response and optimization of the considered eRoad. In the context of enabling both dynamic charging and autonomous driving for future electric vehicles, the influences to the pavement (rutting) performance by the changed vehicle behaviour are investigated as well. Moreover, to study the effect on the IPT system by the integration, the potential power loss caused within eRoad pavement materials is further examined by a combined analytic and experimental analysis. The direct research goal of this Thesis is therefore to enhance the possibility of a sustainable implementation of the eRoad solutions into the real society. At the same time, it aims to demonstrate that the road structure itself is an important part of smart infrastructure systems that can either become a bottleneck or a vessel of opportunities, supporting the successful integration of these complex systems.

  • 41.
    Spross, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Toward a reliability framework for the observational method2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Constructing sustainable structures in rock that satisfy all predefined technical specifications requires rational and effective construction methods. When the geotechnical behaviour is hard to predict, the Euro­pean design code, Eurocode 7, suggests application of the observational method to verify that the performance is acceptable. The basic principle of the method is to accept predefined changes in the design during con­struction to comply with the actual ground conditions, if the current de­sign is found unsuitable. Even though this in theory should ensure an effective design solution, formal application of the observational method is rare.

    Investigating the applicability of the observational method in rock en­gineering, the aim of this thesis is to identify, highlight, and solve the aspects of the method that limit its wider application. Furthermore, the thesis aims to improve the conceptual understanding of how design deci­sions should be made when large uncertainties are present.

    The main research contribution is a probabilistic framework for the observational method. The suggested methodology allows comparison of the merits of the observational method with that of conventional design. Among other things, the thesis also discusses (1) the apparent contradiction between the preference for advanced probabilistic calculation methods and sound, qualitative engineering judgement, (2) how the establishment of limit states and alarm limits must be carefully considered to ensure structural safety, and (3) the applicability of the Eurocode defini­tion of the observational method and the implications of deviations from its principles.

  • 42.
    Bergman, Niclas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Aspects of probabalistic serviceability limit state design of dry deep mixing2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    An expanding population and increased need for infrastructure increasingly necessitate construction on surfaces with poor soil conditions. To facilitate the construction of buildings, roads and railroads in areas with poor soil conditions, these areas are often improved by means of foundation engineering. Constructions that are fairly limited in scope are often founded on shallow or deep foundations. However, these methods are relatively expensive and thus not applicable for large-scale constructions like roads and railroads. A cost-effective way to deal with poor soil conditions is to use ground improvement. This thesis deals with a ground improvement method called deep mixing (DD)using lime-cement columns.

    Lime-cement columns are manufactured by pushing a mechanical mixing tool to the desired depth, with the tool then rotated and retracted while a lime-cement binder is distributed into soil, forming lime-cement columns. Because of the complex mixing process and inherent soil variability, soil improved by DD shows high variability with respect to strength and deformation properties. Due to this high variability, it is difficult to predict the properties in advance; it is therefore important to verify the properties after installation. In Sweden, this is normally done using the column penetration test (KKK) method.

    Current design praxis considers evaluated mean values in the design, and the effect of variability and uncertainties is dealt with by using a sufficiently high total factor of safety. A more rational approach for dealing with the effect of variability and uncertainties on the reliability of a mechanical system is to include them as parameters in the design model. This can be done by using reliability-based design (RRR). A major incentive for using 𝑅𝑅𝑅 is that lower variability in design properties produces higher design values. This is important since it encourages contractors to improve their manufacturing methodologies because 𝑅𝑅𝑅 allows more homogenous columns to be assigned higher design values. Reliability-based design is also in line with Eurocode 7, which states that the selection of the characteristic values for geotechnical parameters shall take the variability of the measured property values into account.

    The first part of this doctoral thesis deals with test methods and quantification of the strength variability of soil improved by lime-cement columns. Tip resistances from three different test sites using three different penetration test methods – the cone penetration test, the column penetration test and the total-sounding test – are analysed and quantified in terms of means, variances and scale of fluctuations. The second part introduces RRR in serviceability limit state (SSS) design, using First Order Reliability Methods (FFFF) and Monte-Carlo simulations.

    Summarizing the most important findings and conclusions from this study:

    •  The scale of fluctuation was estimated to be 0.2-0.7 m and 0-3 m in the vertical and horizontal direction, respectively.
    •  The relation between cone tip resistances measured using the cone penetration test and column penetration test does not correspond to the cone factors proposed in previous studies and in the Swedish Design Guidelines.
    •  The agreement between the column penetration test and total-sounding test was found to be “good enough”. It is therefore suggested that the total-sounding test be used as a complement to the column penetration test in evaluating the average strength properties of a group of medium- and high-strength lime-cement columns.
    • Reliability-based design is a rational approach to incorporate strength and deformation parameter variability with an SSS design.
  • 43.
    Lazzarotto, Alberto
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology.
    Developments in Ground Heat Storage Modeling2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Ground heat storage systems can play an important role for the reduction of green house gases emissions by increasing the exploitation of renewable energy sources and “waste heat” with a consequent diminution of the use of fossil fuels.

    A ground heat storage consists in an array of vertical boreholes placed in such a way that promotes the mutual thermal interaction between the ground heat exchangers creating the necessary conditions required to effectively store and retrieve heat. Suitable modeling tools for the estimation of the thermal behavior of these systems are very important to build installations yielding economical performance compatible with what expected during the design phase.

    This thesis aims at giving a contribution in the development of the thermal modeling of borehole heat storage systems. The main objective is introducing in the modeling process a few features that are not usually considered in state of the art models, with the goal of improving the representation of the physical phenomena. These features are the mathematical description of the topology of the borehole heat exchangers network, and the modeling of borehole fields with arbitrarily oriented boreholes.

    The detailed modeling of the topology of the borehole heat exchangers is approached with a network model. The overall geothermal system is discretized into smaller systems called components. These are linked between each other in a network fashion to establish the logical relations required to describe a given boreholes connections arrangement. The method showed that the combination of a sufficient level of discretization of the system and of a network representation yields respectively the granularity and the flexibility required to describe any borehole field connections configuration.

    The modeling of non-vertical borehole fields is approached by developing a method for the calculation of g-functions for these configurations. The method is an extension of a recent work done by Cimmino on the computation of g-functions for vertical borehole fields. This modeling technique is based on describing boreholes as sets of stacked finite line sources and on the superposition principle. This approach requires the computation of response factors relative to couples of finite lines. A procedure for the fast computation of these response factors for the case of arbitrarily oriented lines is given. This yields computational performance that guarantees the practical feasibility of the methodology.

    The last part of the thesis deals with the modeling of the storage system from a broader perspective. The borehole field is considered as part of a larger system constituted by several interacting components (i.e. heat pump, building, etc.). Interactions play a key role in the resulting overall performance of these systems. The analysis of the mutual relations between building envelope and borehole field design is utilized as an example to highlight advantages and challenges of strategies yielding a more integrated design.

  • 44.
    Sattari, Amir
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Service and Energy Systems.
    Investigations of Flow Patterns in Ventilated Rooms Using Particle Image Velocimetry: Applications in a Scaled Room with Rapidly Varying Inflow and over a Wall-Mounted Radiator2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis introduces and describes a new experimental setup for examining the effects of pulsating inflow to a ventilated enclosure. The study aimed to test the hypothesis that a pulsating inflow has potential to improve ventilation quality by reducing the stagnation zones through enhanced mixing. The experimental setup, which was a small-scale, two-dimensional (2D), water-filled room model, was successfully designed and manufactured to be able to capture two-dimensional velocity vectors of the entire field using Particle Image Velocimetry (PIV). Using in-house software, it was possible to conclude that for an increase in pulsation frequency or alternatively in the flow rate, the stagnation zones were reduced in size, the distribution of vortices became more homogeneous over the considered domain, and the number of vortices in all scales had increased. Considering the occupied region, the stagnation zones were moved away in a favorable direction from a mixing point of view. In addition, statistical analysis unveiled that in the far-field occupied region of the room model, stronger eddies were developed that we could expect to give rise to improved mixing. As a fundamental experimental study performed in a 2D, small-scale room model with water as operating fluid, we can logically conclude that the positive effect of enhanced mixing through increasing the flow rate could equally be accomplished through applying a pulsating inflow.

    In addition, this thesis introduces and describes an experimental setup for study of air flow over a wall-mounted radiator in a mockup of a real room, which has been successfully designed and manufactured. In this experimental study, the airflow over an electric radiator without forced convection, a common room-heating technique, was measured and visualized using the 2D PIV technique. Surface blackening due to particle deposition calls for monitoring in detail the local climate over a heating radiator. One mechanism causing particle deposition is turbophoresis, which occurs when the flow is turbulent. Because turbulence plays a role in particle deposition, it is important to identify where the laminar flow over radiator becomes turbulent. The results from several visualization techniques and PIV measurements indicated that for a room with typical radiator heating, the flow over the radiator became agitated after a dimensionless length, 5.0–6.25, based on the radiator thickness.

    Surface properties are among the influencing factors in particle deposition; therefore, the geometrical properties of different finishing techniques were investigated experimentally using a structured light 3D scanner that revealed differences in roughness among different surface finishing techniques. To investigate the resistance to airflow along the surface and the turbulence generated by the surfaces, we recorded the boundary layer flow over the surfaces in a special flow rig, which revealed that the types of surface finishing methods differed very little in their resistance and therefore their influence on the deposition velocity is probably small. 

  • 45.
    Du, Guangli
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Life cycle assessment of bridges, model development and case studies2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In recent decades, the environmental issues from the construction sector have attracted increasing attention from both the public and authorities. Notably, the bridge construction is responsible for considerable amount of energy and raw material consumptions. However, the current bridges are still mainly designed from the economic, technical, and safety perspective, while considerations of their environmental performance are rarely integrated into the decision making process. Life Cycle Assessment (LCA) is a comprehensive, standardized and internationally recognized approach for quantifying all emissions, resource consumption and related environmental and health impacts linked to a service, asset or product. LCA has the potential to provide reliable environmental profiles of the bridges, and thus help the decision-makers to select the most environmentally optimal designs. However, due to the complexity of the environmental problems and the diversity of bridge structures, robust environmental evaluation of bridges is far from straightforward. The LCA has rarely been studied on bridges till now.

    The overall aim of this research is to implement LCA on bridge, thus eventually integrate it into the decision-making process to mitigate the environmental burden at an early stage. Specific objectives are to: i) provide up-to-date knowledge to practitioners; ii) identify associated obstacles and clarify key operational issues; iii) establish a holistic framework and develop computational tool for bridge LCA; and iv) explore the feasibility of combining LCA with life cycle cost (LCC). The developed tool (called GreenBridge) enables the simultaneous comparison and analysis of 10 feasible bridges at any detail level, and the framework has been utilized on real cases in Sweden. The studied bridge types include: railway bridge with ballast or fix-slab track, road bridges of steel box-girder composite bridge, steel I-girder composite bridge, post tensioned concrete box-girder bridge, balanced cantilever concrete box-girder bridge, steel-soil composite bridge and concrete slab-frame bridge. The assessments are detailed from cradle to grave phases, covering thousands of types of substances in the output, diverse mid-point environmental indicators, the Cumulative Energy Demand (CED) and monetary value weighting. Some analyses also investigated the impact from on-site construction scenarios, which have been overlooked in the current state-of-the-art.

    The study identifies the major structural and life-cycle scenario contributors to the selected impact categories, and reveals the effects of varying the monetary weighting system, the steel recycling rate and the material types. The result shows that the environmental performance can be highly influenced by the choice of bridge design. The optimal solution is found to be governed by several variables. The analyses also imply that the selected indicators, structural components and life-cycle scenarios must be clearly specified to be applicable in a transparent procurement. This work may provide important references for evaluating similar bridge cases, and identification of the main sources of environmental burden. The outcome of this research may serve as recommendation for decision-makers to select the most LCA-feasible proposal and minimize environmental burdens. 

  • 46.
    Hesaraki, Arefeh
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology.
    Low-Temperature Heating and Ventilation for Sustainability in Energy Efficient Buildings2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In 2013, the building sector consumed approximately 39 % of the total final energy use in Sweden. Energy used for heating and hot water was responsible for approximately 60 % of the total energy consumption in the building sector. Therefore, energy-efficient and renewable-based heating and ventilation systems have high potential for energy savings. The potentials studied in this thesis include the combination of a low-temperature heat emitter (supply temperature below 45 °C) with heat pump and/or seasonal thermal energy storage, and variable air volume ventilation system. The main aim of this thesis was to evaluate energy savings and indoor air quality when those energy-efficient and sustainable heating and ventilation systems were implemented in buildings. For this purpose, on-site measurements, lab tests, analytical models, and building energy simulation tool IDA Indoor Climate and Energy 4 were used.

    Annual on-site measurements for five new two-family houses with low- and very-low-temperature heat emitters connected to an exhaust air heat pump showed  that  between  45–51 kWh∙m-2 energy was used  to  produce  and transport supply water for space heating and domestic hot water. Statistical data showed that these values are 39–46 % lower compared to the energy requirement for the same usage  which is, 84 kWh∙m-2)  in  an  average Swedish new single- and two-family house.

    Annual on-site measurements for five new two-family houses with low- and very-low-temperature heat emitters connected to an exhaust air heat pump showed that between 45–51 kWh∙m-2 energy was used to produce and transport supply water for space heating and domestic hot water. Statistical data showed that these values are 39–46 % lower compared to the energy requirement for the same usage (which is, 84 kWh∙m-2) in an average Swedish new single- and two-family house.

    In order to compare the energy performance of very-low- and low-temperature heat emitters with medium-temperature heat emitters under the same condition, lab tests were conducted in a climate chamber facility at Technical University of Denmark (DTU). To cover the heat demand of 20 W·m-2 by active heating, measurements showed that the required supply water temperatures were 45 ºC for the conventional radiator, 33 ºC in ventilation radiator and 30 ºC in floor heating. This 12–15 ºC temperature reduction with ventilation radiator and floor heating resulted in 17–22 % savings in energy consumption compared to a reference case with conventional radiator.

    Reducing the supply temperature to the building’s heating system allows using more renewable and low-quality heat sources. In this thesis, the application of seasonal thermal energy storage in combination with heat pump in a building with very-low-, low-, and medium-temperature heat emitters was investigated. Analytical model showed that using a 250 m3 hot water seasonal storage tank connected to a 50 m2 solar collector and a heat pump resulted in 85–92 % of the total heat demand being covered by solar energy.

    In addition to the heating system, this thesis also looked at ventilation system in terms of implementing variable (low) air volume ventilation instead of a constant (high) flow in new and retrofitted old buildings. The analytical model showed that, for new buildings with high volatile organic compound concentration during initial years of construction, decreasing the ventilation rate to 0.1 L·s-1·m-2 during the entire un-occupancy period (from 8:00–18:00) creates unacceptable indoor air quality when home is occupied at  18:00.  So,  in  order  to  create  acceptable  indoor  air  quality  when  the occupants come home, a return to the normal ventilation requirements was suggested to take place two hours before the home was occupied. This eight- hour ventilation reduction produced savings of 20 % for ventilation heating and 30 % for electricity consumption by ventilation fan.

    In addition, the influence of different ventilation levels on indoor air quality and energy savings was studied experimentally and analytically in a single- family house occupied by two adults and one infant. Carbon dioxide (CO2) concentration as an indicator of indoor air quality was considered in order to find  appropriate  ventilation  rates.  Measurements  showed  that,  with  an 0.20 L∙s-1∙m-2  ventilation rate, the CO2   level  was always below 950 ppm, which shows that this level is sufficient for the reference building (CO2 lower than 1000 ppm is acceptable). Calculations showed that low ventilation rates of 0.20 L∙s1∙m-2 caused 43 % savings of the combined energy consumption for  ventilation  fan  and  ventilation  heating  compared  to  the  cases  with 0.35 L∙s-1∙m-2  as a normal ventilation rate recommended by BBR (Swedish Building Regulations).

     

  • 47.
    Phdungsilp, Aumnad
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Service and Energy Systems.
    Modeling urban energy flows at macro and district levels: towards a sustainable urban metabolism2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The urban sustainability is a growing importance in the built environment research. Urban areas play a key role in planning for sustainable city development. Urbanization has implications for future energy systems and energy-related emissions. The new built environment requires systems that are cost-efficient and have more efficient utilization of energy with a low environmental impact. This can be analyzed and designed with efficient tools for current and future energy systems. The objectives of this dissertation are to examine and analyze the metabolic flows of urban areas, and to develop a methodology for optimization of energy systems and services for the urban district. The dissertation is comprised of two phases and eight appended publications.

    In the first phase of this dissertation, the research is emphasized on an in-depth understanding of the complex dynamics of energy utilization in large urban areas. An integrated approach applied in this phase includes the energetic urban metabolism, the long-term energy systems modeling using the Long-range Energy Alternative Planning (LEAP) system, and the Multi-Criteria Decision-Making (MCDM) approach. The urban metabolism approach has been employed to analyze the urban energy flows at macro level. The LEAP model and MCDM approach have been used to develop and evaluate energy scenarios in both demand and supply sides.

    In the second phase, the research recognizes the lack of tools that applicable for district energy systems analysis. This phase concentrates on the important role of the district level in urban energy systems. Research methods include the Multi-Objective Optimization using Genetic Algorithms, the carbon budget approach, and the case study method. Research in the second phase is mainly focused on the development of tool for energy systems and services at the district level.

  • 48.
    Gram, Annika
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Modelling of Bingham Suspensional Flow: Influence of Viscosity and Particle Properties Applicable to Cementitious Materials2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Simulation of fresh concrete flow has spurged with the advent of Self-Compacting Concrete, SCC. The fresh concrete rheology must be compatible with the reinforced formwork geometry to ensure complete and reliable form filling with smooth concrete surfaces. Predicting flow behavior in the formwork and linking the required rheological parameters to flow tests performed on the site will ensure an optimization of the casting process.

    In this thesis, numerical simulation of concrete flow and particle behaviour is investigated, using both discrete as well as a continuous approach. Good correspondence was achieved with a Bingham material model used to simulate concrete laboratory tests (e.g. slump flow).

    It is known that aggregate properties such as size, shape and surface roughness as well as its grading curve affect fresh concrete properties. An increased share of non-spherical particles in concrete increases the level of yield stress, τ0, and plastic viscosity, µpl. The yield stress level may be decreased by adding superplasticizers, however, the plastic viscosity may not. An explanation for the behaviour of particles is sought after experimentally, analytically and numerically. Bingham parameter plastic viscosity is experimentally linked to particle shape. It was found that large particles orient themselves aligning their major axis with the fluid flow, whereas small particles in the colloidal range may rotate between larger particles. The rotation of crushed, non-spherical fine particles as well as particles of a few microns that agglomorate leads to an increased viscosity of the fluid.

    Generally, numerical simulation of large scale quantitative analyses are performed rather smoothly with the continuous approach. Smaller scale details and phenomena are better captured qualitatively with the discrete particle approach. As computer speed and capacity constantly evolves, simulation detail and sample volume will be allowed to increase.

    A future merging of the homogeneous fluid model with the particle approach to form particles in the fluid will feature the flow of concrete as the physical suspension that it represents. One single ellipsoidal particle in fluid was studied as a first step.

     

     

  • 49.
    Ahmed, Lamis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Models for analysis of young cast and sprayed concrete subjected to impact-type loads2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The strive for a time-efficient construction process naturally put focus on the possibility of reducing the time of waiting between stages of construction, thereby minimizing the construction cost. If recently placed concrete, cast or sprayed, is exposed to impact vibrations at an early age while still in the process of hardening, damage that threatens the function of the hard concrete may occur. A waiting time when the concrete remains undisturbed, or a safe distance to the vibration source, is therefore needed. However, there is little, or no, fully proven knowledge of the length of this distance or time and there are no established guidelines for practical use. Therefore, conservative vibration limits are used for young and hardening concrete exposed to vibrations from e.g. blasting.

    As a first step in the dynamic analysis of a structure, the dynamic loads should always be identified and characterized. Here it is concluded that impact-type loads are the most dangerous of possible dynamic loads on young and hardening concrete. Shotcrete (sprayed concrete) on hard rock exposed to blasting and cast laboratory specimens subjected to direct mechanical impact loads have been investigated using finite element models based on the same analysis principles. Stress wave propagation is described in the same way whether it is through hard rock towards a shotcrete lining or through an element of young concrete. However, the failure modes differ for the two cases where shotcrete usually is damaged through loss of bond, partly or over larger sections that may result in shotcrete downfall. Cracking in shotcrete due to vibrations only is unusual and has not been observed during previous in situ tests. The study of shotcrete is included to demonstrate the need of specialized guidelines for cases other than for mass concrete, i.e. structural elements or concrete volumes with large dimensions in all directions.

    Within this project, work on evaluating and proposing analytical models are made in several steps, first with a focus on describing the behaviour of shotcrete on hard rock. It is demonstrated that wave propagation through rock towards shotcrete can be described using two-dimensional elastic finite element models in a dynamic analysis. The models must include the material properties of the rock and the accuracy of these parameters will greatly affect the results. It is possible to follow the propagation of stress waves through the rock mass, from the centre of blasting to the reflection at the shotcrete-rock interface. It is acceptable to use elastic material formulations until the strains are outside the elastic range, which thus indicates imminent material failure. The higher complexity of this type of model, compared with mechanical models using mass and spring elements, makes it possible to analyse more sophisticated geometries. Comparisons are made between numerical results and measurements from experiments in mining tunnels with ejected rock mass and shotcrete bond failure, and with measurements made during blasting for tunnel construction where rock and shotcrete remained intact. The calculated results are in good correspondence with the in situ observations and measurements, and with previous numerical modelling results. Examples of preliminary recommendations for practical use are given and it is demonstrated how the developed models and suggested analytical technique can be used for further detailed investigations.

    The modelling concept has also been used for analysis of impact loaded beams and concrete prisms modelled with 3D solid elements. As a first analysis step, an elastic material model was used to validate laboratory experiments with hammer-loaded concrete beams. The laboratory beam remained un-cracked during the experiments, and thus it was possible to achieve a good agreement using a linear elastic material model for fully hardened concrete. The model was further developed to enable modelling of cracked specimens. For verification of the numerical results, earlier laboratory experiments with hammer impacted smaller prisms of young concrete were chosen. A comparison between results showed that the laboratory tests can be reproduced numerically and those free vibration modes and natural frequencies of the test prisms contributed to the strain concentrations that gave cracking at high loads. Furthermore, it was investigated how a test prism modified with notches at the middle section would behave during laboratory testing. Calculated results showed that all cracking would be concentrated to one crack with a width equal to the sum of the multiple cracks that develop in un-notched prisms. In laboratory testing, the modified prism will provide a more reliable indication of when the critical load level is reached.

    This project has been interdisciplinary, combining structural dynamics, finite element modelling, concrete material technology, construction technology and rock support technology. It is a continuation from previous investigations of the effect on young shotcrete from blasting vibrations but this perspective has been widened to also include young, cast concrete. The outcome is a recommendation for how dynamic analysis of young concrete, cast and sprayed, can be carried out with an accurate description of the effect from impact-type loads. The type of numerical models presented and evaluated will provide an important tool for the work towards guidelines for practical use in civil engineering and concrete construction work. Some recommendations on safe distances and concrete ages are given, for newly cast concrete elements or mass concrete and for newly sprayed shotcrete on hard rock.

  • 50.
    Åkesson, Anna
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Peakflow response of stream networks: implications of physical descriptions of streams and temporal change2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Through distributed stream network routing, it has quantitatively been shown that the relationship between flow travel time and discharge varies strongly nonlinearly with stream stage and with catchment-specific properties.

    Physically derived distributions of water travel times through a stream network were successfully used to parameterise the streamflow response function of a compartmental hydrological model. Predictions were found to improve compared to conventional statistically based parameterisation schemes, for most of the modelled scenarios, particularly for peakflow conditions.

    A Fourier spectral analysis of 55-110 years of daily discharge time series from 79 unregulated catchments in Sweden revealed that the discharge power spectral slope has gradually increased over time, with significant increases for 58 catchments. The results indicated that the catchment scaling function power spectrum had steepened in most of the catchments for which historical precipitation series were available. These results suggest that (local) land-use changes within the catchments may affect the discharge power spectra more significantly than changes in precipitation (climate change).

    A case study from an agriculturally intense catchment using historical (from the 1880s) and modern stream network maps revealed that the average stream network flow distance as well as average water levels were substantially diminished over the past century, while average bottom slopes increased. The study verifies the hypothesis that anthropogenic changes (determined through scenario modelling using a 1D distributed routing model) of stream network properties can have a substantial influence on the travel times through the stream networks and thus on the discharge hydrographs.

    The findings stress the need for a more hydrodynamically based approach to adequately describe the variation of streamflow response, especially for predictions of higher discharges. An increased physical basis of response functions can be beneficial in improving discharge predictions during conditions in which conventional parameterisation based on historical flow patterns may not be possible - for example, for extreme peak flows and during periods of nonstationary conditions, such as during periods of climate and/or land use change.

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