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  • 1.
    Högdahl, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport planning.
    Bohlin, Markus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport planning.
    Fröidh, Oskar
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport planning.
    A combined simulation-optimization approach for minimizing travel time and delays in railway timetables2019In: Transportation Research Part B: Methodological, ISSN 0191-2615, E-ISSN 1879-2367, Vol. 126, p. 192-212Article in journal (Refereed)
    Abstract [en]

    Minimal travel time and maximal reliability are two of the most important properties of a railway transportation service. This paper considers the problem of finding a timetable for a given set of departures that minimizes the weighted sum of scheduled travel time and expected delay, thereby capturing these two important socio-economic properties of a timetable. To accurately represent the complex secondary delays in operational railway traffic, an approach combining microscopic simulation and macroscopic timetable optimization is proposed. To predict the expected delay in the macroscopic timetable, a surrogate function is formulated, as well as a subproblem to calibrate the parameters in the model. In a set of computational experiments, the approach increased the socio-economic benefit by 2-5% and improved the punctuality by 8-25%.

  • 2.
    Lei, Lei
    et al.
    Gui Lin Univ Elect Technol, Sch Architecture & Transportat Engn, 1 Jinji Rd, Guilin 541004, Peoples R China..
    Chen, Wei
    Gui Lin Univ Elect Technol, Sch Architecture & Transportat Engn, 1 Jinji Rd, Guilin 541004, Peoples R China..
    Xue, Yu
    Dalian Univ Technol, Sch Civil Engn, 2 Linggong Rd, Dalian 116024, Peoples R China..
    Liu, Wei
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Sustainable Buildings.
    A comprehensive evaluation method for indoor air quality of buildings based on rough sets and a wavelet neural network2019In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 162, article id UNSP 106296Article in journal (Refereed)
    Abstract [en]

    Understanding the level of indoor air quality is very important to improve the quality of air that people breathe indoors. In this paper, a comprehensive evaluation method combining rough sets and a wavelet neural network is proposed to evaluate the indoor air quality of buildings. Through on-site inspections of the indoor air in six large shopping malls in Beijing, Wuhan and Guangzhou, raw data of the environmental parameters affecting the indoor air quality of large shopping malls are obtained. First, rough sets are used to reduce the dimension of features that affect indoor air quality by removing unimportant features, and important environmental parameters that affect indoor air quality are obtained. These important environmental parameters are used as input parameters of the wavelet neural network. Then, the structure of the wavelet neural network is determined, and an evaluation model of the indoor air quality of buildings based on rough sets and the wavelet neural network is established. Finally, the model is applied to the evaluation of indoor air quality in large shopping malls, and the back propagation neural network, fuzzy neural network and Elman neural network are introduced for comparison of the testing accuracy of the wavelet neural network in the sample testing stage. The results show that the structure of the wavelet neural network is optimized by using a rough set to reduce the redundant attributes of the data, and that the comprehensive evaluation method based on rough sets and a wavelet neural network can accurately evaluate the indoor air quality level of buildings. The results of this study have significance for and can guide the evaluation of the indoor air quality of buildings.

  • 3.
    Olsson, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    A contact model for the normal force between viscoelastic particles in discrete element simulations2019In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 342, p. 985-991Article in journal (Refereed)
    Abstract [en]

    DEM modeling of granular materials composed of viscoelastic particles can provide valuable insights into the mechanical behavior of a wide range of engineering materials. In this paper, a new model for calculating the normal contact force between visoelastic spheres is presented based on contact mechanics that takes the mechanical behavior of the DEM particles into account. The model relies on an application of the viscoelastic correspondence principle to elastic Hertz contact. A viscoelastic relaxation function for the contact is defined and a generalized Maxwell material is used for describing this function. An analytical expression for the increment in contact force given an increment in overlap is derived leading to a computationally efficient model. The proposed model provides the analytical small deformation solution upon loading but provides an approximate solution at unloading. Comparisons are made with FEM simulations of contact between spheres of different sizes of equal and dissimilar materials. An excellent agreement is found between the model and the FEM simulations for almost all cases except at cyclic loading where the characteristic times of the viscoelastic behavior and the loading are similar.

  • 4.
    Ploskic, Adnan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Wang, Qian
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Sadrizadeh, Sasan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    A holistic performance evaluation of ventilation radiators – An assessment according to EN 442-2 using numerical simulations2019In: Journal of Building Engineering, E-ISSN 2352-7102, Vol. 25, article id 100818Article in journal (Refereed)
    Abstract [en]

    This research explored the importance of airflow rate and convector plate design on the operational performance of heating radiators equipped with an air device (ventilation radiators). The radiator was analyzed according to European Norm EN 442-2 using numerical simulations. The largest benefit of using staggered convector plates was the more efficient preheating of the incoming outdoor air supply. With this plate design, the evaluated radiator increased the temperature of the incoming airflow of 10 l/s from -5 °C to 26 °C with water supply/return temperatures of 45 °C/35 °C. With these water temperatures, the radiator was able to cover a room heat loss of 34 W/m2 floor area. However, the design of the convector plate alone was found to have a limited impact on the heat output from the radiator. Neither did the plate design significantly affect the uniformity of heat distribution nor the vertical temperature stratification inside the room. The results also showed that ventilation radiators might cover a building heating load (kW) with a lower supply water temperature but not necessarily give a lower annual energy use (kWh) for the space heating of a building.

  • 5.
    Eriksson, Daniel
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Gasch, Tobias
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    A Hygro-Thermo-Mechanical Multiphase Model for Long-Term Water Absorption into Air-Entrained Concrete2019In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 127, no 1, p. 113-141Article in journal (Refereed)
    Abstract [en]

    Many concrete structures located in cold climates and in contact with free water are cast with air-entrained concrete. The presence of air pores significantly affects the absorption of water into the concrete, and it may take decades before these are fully saturated. This generally improves the long-term performance of such structures and in particular their frost resistance. To study the long-term moisture conditions in air-entrained concrete, a hygro-thermo-mechanical multiphase model is presented, where the rate of filling of air pores with water is described as a separate diffusion process. The driving potential is the concentration of dissolved air, obtained using an averaging procedure with the air pore size distribution as the weighting function. The model is derived using the thermodynamically constrained averaging theory as a starting point. Two examples are presented to demonstrate the capabilities and performance of the proposed model. These show that the model is capable of describing the complete absorption process of water in air-entrained concrete and yields results that comply with laboratory and in situ measurements.

  • 6. Misiek, T.
    et al.
    Norlin, Bert
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Höglund, Torsten
    KTH.
    A look at European buckling curves for aluminium members2019In: Steel ConstructionArticle in journal (Refereed)
    Abstract [en]

    Numerical investigations of compression members made of aluminium are presented and recommendations for reorganizing the buckling classes and curves are derived from these. Finally, the curves are compared with test results

  • 7.
    Lövqvist, Lisa
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Balieu, Romain
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    A micromechanical model of freeze-thaw damage in asphalt mixtures2019In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268XArticle in journal (Refereed)
    Abstract [en]

    Freeze-thaw damage in asphalt pavements is a complex phenomenon dependent on many parameters such as moisture infiltration, temperature and mechanical properties of the asphalt constituents as well as the interface between them. As a first step in creating a comprehensive multiscale model including all of these parameters, a micromechanical model has been developed. This model couples the infiltration of moisture and the associated damage, the expansion caused by the water inside the air voids freezing, and the mechanical damage. The expansion of the air voids is implemented by applying a volumetric expansion in the air voids dependent on the temperature. The cohesive damage in the mastic and adhesive damage in the mastic-aggregate interface are included by implementing an energy-based damage model and the cohesive zone model, respectively. To show the capabilities of the model, the effect of different parameters (the number of freeze-thaw cycles, the gradation of the microstructure, and the freezing time) was investigated through simulations. From the analyses it was concluded that the model was capable of capturing the deteriorating effect of an increasing number of freeze-thaw cycles, and was sensitive to the freezing time in the freeze-thaw cycles.

  • 8.
    Jin, Junchen
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport planning. Enjoyor Co Ltd, Hangzhou 310030, Zhejiang, Peoples R China.
    Ma, Xiaoliang
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport planning.
    A non-parametric Bayesian framework for traffic-state estimation at signalized intersections2019In: Information Sciences, ISSN 0020-0255, E-ISSN 1872-6291, Vol. 498, p. 21-40Article in journal (Refereed)
    Abstract [en]

    An accurate and practical traffic-state estimation (TSE) method for signalized intersections plays an important role in real-time operations to facilitate efficient traffic management. This paper presents a generalized modeling framework for estimating traffic states at signalized intersections. The framework is non-parametric and data-driven, without any requirement on explicit modeling of traffic flow. The Bayesian filter (BF) approach is the core of the framework and introduces a recursive state estimation process. The required transition and measurement models of the BFs are trained using Gaussian process (GP) regression models with respect to a historical dataset. In addition to the detailed derivation of the integration of BFs and GP regression models, an algorithm based on the extended Kalman filter is presented for real-time traffic estimation. The effectiveness of the proposed framework is demonstrated through several numerical experiments using data generated in microscopic traffic simulations. Both fixed-location data (i.e., loop detector) and mobile data (i.e., connected vehicle) are examined with the framework. As a result, the method shows good performance under the different traffic conditions in the experiment. In particular, the approach is suitable for short-term estimation, a challenging task in traffic control and operations.

  • 9.
    Stigsson, Martin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering. SKB, Swedish Nuclear Fuel and Waste Management Co, Solna, Sweden.
    Ivars, Diego Mas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    A Novel Conceptual Approach to Objectively Determine JRC Using Fractal Dimension and Asperity Distribution of Mapped Fracture Traces2019In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 52, no 4, p. 1041-1054Article in journal (Refereed)
    Abstract [en]

    The understanding of fractures in hard rock is important for topics such as geomechanics, rock mechanics and groundwater flow and solute transport. One key aspect is the roughness of the fracture, often described as the joint roughness coefficient, JRC. JRC is often subjectively interpreted by one geologist comparing a fracture trace with different type traces. It has been shown that several geologists are needed to get reliable interpretations of JRC. There are numerous attempts in the literature to develop objective methods to estimate JRC from digital traces. Some methods are not applicable to fractures, which give arbitrary results while other methods are sensitive to the resolution of the digitalisation and hence need a new relationship for each resolution. Another way of describing the roughness is by the two parameters fractal dimension and magnitude distribution of the asperities. These parameters can be objectively inferred using algorithms and act as input for a model to estimate JRC. Using several evaluation methods, the uncertainty can be decreased and, hence, more robust results achieved. A multilinear model is developed, JRC = − 4.3 + 54.6σδh(1mm) + 4.3H, that estimates JRC, of the classic ten type curves by Barton and Choubey, with standard deviation ± 1 unit. Despite the simplicity of the model it explains 96.5% of the variance in JRC. The developed model is benchmarked against an ensemble of geologists, using nine synthetic fracture traces. The median difference of JRC is 0.2 units and the model shows 40% smaller spread compared to the geologists.

  • 10.
    Vieira, Tiago
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. VTI.
    Sandberg, Ulf
    VTI.
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering. VTI.
    Acoustical performance of winter tyres on in-service road surfaces2019In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 153, p. 30-47Article in journal (Refereed)
    Abstract [en]

    Exposure to excessively high noise levels is a relevant health problem in Europe and road traffic noise is the most widespread noise source. When considering cold climate countries, the available scientific literature on noise emission properties of winter tyres is still very limited. In order to contribute into filling this knowledge gap, this paper investigates the acoustical performance of different types of tyres, with focus on winter tyres, on different road surfaces, at different speeds, and with different states of wear. The results indicate that studded winter tyres have, indeed, an increased noise level at frequencies between 315 Hz and 10 kHz, having a significantly different response especially at frequencies higher than 4 kHz. The acoustical response also depends on the tyre type when comparing different road surfaces, as a result of conflicting vibrational and aerodynamic noise generation mechanisms. Additionally, the relationship between labelled and measured values was explored, however, no statistically significant relationship was found between them (and labelling is not applied for studded tyres). A frequency spectrum correction was attempted based on previous measurements on an ISO track, which reduced the difference between measured and labelled values, however, further investigation is still required to properly understand differences between label and road measurements, where the label is determined on a test track with a special, smooth surface.

  • 11.
    Neves, Ana C.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Gonzalez, Ignacio
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    An approach to decision-making analysis for implementation of structural health monitoring in bridges2019In: Structural Control and Health Monitoring: The Bulletin of ACS, ISSN 1545-2255, E-ISSN 1545-2263, Vol. 26, no 6, article id e2352Article in journal (Refereed)
    Abstract [en]

    Adverse situations such as prolonged downtime of a structure, unnecessary inspections, expensive allocation of personal and equipment, deficient structural performance, or failure can be avoided by using structural health monitoring (SHM). Enhanced structural safety is the leading reason for its implementation, but one of the remaining obstacles to fully implement SHM systems deals with justifying their economic benefit. At any point in time, the preference towards one particular action depends on factors such as the probability of the triggered events and their consequences. All the possible decisions and relevant information can be illustrated by decision tree models, and the optimal decision corresponds to the one with the highest utility. Applying the Bayesian Theorem, the assumed prior probabilities of the structural state are updated in the light of new information provided by a system and the optimal decision is revised. This paper proposes a dynamic decision-making framework to manage civil engineering structures, where the ultimate goal is to achieve greater overall economy without jeopardizing safety. This paper covers a case study of a bridge where the optimal SHM and maintenance decisions are determined in the context of different scenarios in which the event probabilities and associated costs are made-up.

  • 12.
    Ghaderi, Abdolvahed
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Abbaszadeh Shahri, Abbas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. Islamic Azad Univ, Roudehen Branch, Fac Civil Engn, Tehran, Iran..
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    An artificial neural network based model to predict spatial soil type distribution using piezocone penetration test data (CPTu)2019In: Bulletin of Engineering Geology and the Environment, ISSN 1435-9529, E-ISSN 1435-9537, Vol. 78, no 6, p. 4579-4588Article in journal (Refereed)
    Abstract [en]

    Soil types mapping and the spatial variation of soil classes are essential concerns in both geotechnical and geoenvironmental engineering. Because conventional soil mapping systems are time-consuming and costly, alternative quick and cheap but accurate methods need to be developed. In this paper, a new optimized multi-output generalized feed forward neural network (GFNN) structure using 58 piezocone penetration test points (CPTu) for producing a digital soil types map in the southwest of Sweden is developed. The introduced GFNN architecture is supported by a generalized shunting neuron (GSN) model computing unit to increase the capability of nonlinear boundaries of classified patterns. The comparison conducted between known soil type classification charts, CPTu interpreting procedures, and the outcomes of the GFNN model indicates acceptable accuracy in estimating complex soil types. The results show that the predictability of the GFNN system offers a valuable tool for the purpose of soil type pattern classifications and providing soil profiles.

  • 13.
    Tympakianaki, Athina
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport Planning, Economics and Engineering.
    Koutsopoulos, Haris N.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport Planning, Economics and Engineering.
    Jenelius, Erik
    KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Transport Studies, CTS.
    Anatomy of tunnel congestion: Causes and implications for tunnel traffic management2019In: Tunnelling and Underground Space Technology, ISSN 0886-7798, E-ISSN 1878-4364, Vol. 83, p. 498-508Article in journal (Refereed)
    Abstract [en]

    Tunnel congestion is an important safety problem and is often dealt with using disruptive traffic management strategies, such as closures. The paper proposes an approach to identify the underlying causes of recurrent congestion in tunnels and tests the hypothesis that the cause may vary from day to day. It also suggests that the appropriate tunnel management strategy to deploy depends on the cause. Utilizing traffic sensor data the approach consists of: (i) cluster analysis of historical traffic data to identify distinct congestion patterns; (ii) in-depth analysis of the underlying demand patterns and associated bottlenecks; (iii) simulation to evaluate alternative strategies for each demand pattern; (iv) on-line classification analysis which is able to identify, in real time, the emerging congestion pattern, and inform the type of mitigation strategy to be implemented. The methodology is demonstrated for a congested tunnel in Stockholm, Sweden revealing two different spatio-temporal congestion patterns. The results show that, if the current strategy of closures is to be used, the timing should depend on the congestion pattern. However, metering is the most promising strategy. The on-line classification of the emerging congestion pattern is effective and can inform appropriate strategy proactively. The analysis emphasizes that the effectiveness of tunnel traffic management can be increased by identifying the causes of congestion on a given day.

  • 14.
    Bekele, Abiy
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Rydén, Nils
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Gudmarsson, Anders
    Peab Asfalt AB, Drivhjulsvagen 11, S-12630 Hagersten, Sweden..
    Birgisson, Bjorn
    Texas A&M Univ, Dept Civil Engn, College Stn, TX 77843 USA..
    Automated Non-contact Resonance Excitation Method to Assess Low Temperature Dynamic Modulus of Asphalt Concrete2019In: Journal of nondestructive evaluation, ISSN 0195-9298, E-ISSN 1573-4862, Vol. 38, no 2, article id 43Article in journal (Refereed)
    Abstract [en]

    This paper studies the applicability of an automated non-destructive testing method to monitor the stiffness of asphalt concrete at low temperatures. A loudspeaker is used as a source of non-contact excitation of the axially symmetric fundamental resonant frequencies of a disc-shaped asphalt concrete specimen positioned inside an environmental chamber. Measured resonant frequencies are used to calculate the dynamic moduli of the specimen at different temperatures. The repeatability of the method as well as the effect of loudspeaker height above the sample are studied. Results show that the main advantage of the non-contact excitation method, compared to manually applied impact hammer excitation, is that repeatable automated measurements can be performed while the specimen is placed inside an environmental temperature chamber. This methodology enables to study the effect of only low temperature conditioning on the dynamic modulus of asphalt concrete without interference from mechanical loading.

  • 15.
    Silfwerbrand, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Mohaghegh, Ali Mohammadi
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Basaltfiberbetong för marina miljöer2019In: Betong, ISSN 1101-9190, no 3, p. 56-58Article in journal (Other (popular science, discussion, etc.))
  • 16. Hellström, Arne
    et al.
    Silfwerbrand, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Beräkna stommars livslängd till 400 år2019In: Betong, ISSN 1101-9190, no 1, p. 57-58Article in journal (Other (popular science, discussion, etc.))
  • 17.
    Possidente, Luca
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Tondini, Nicola
    Univ Trento, Dept Civil Environm & Mech Engn, Via Mesiano 77, I-38123 Trento, Italy..
    Battini, Jean-Marc
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering. Royal Inst Technol, KTH, Dept Civil & Architectural Engn, SE-10044 Stockholm, Sweden..
    Branch-switching procedure for post-buckling analysis of thin-walled steel members at elevated temperature2019In: Thin-walled structures, ISSN 0263-8231, E-ISSN 1879-3223, Vol. 136, p. 90-98Article in journal (Refereed)
    Abstract [en]

    The paper investigates the effects of the geometrical imperfections in buckling analyses of plated steel elements at elevated temperatures and provides an alternative branch-switching procedure to perform post-buckling analyses without introducing initial imperfections into the model. This procedure is appealing since the choice of appropriate imperfections in classical analyses is not straightforward, above all at elevated temperature. Several numerical analyses show that the choice of the imperfections is not trivial and that the buckling mode may vary with temperature. They also show that the proposed branch-switching procedure is an interesting preliminary tool to understand the instability behaviour of steel structural members.

  • 18.
    Zou, Liangchao
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Håkansson, Ulf
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Cement grout propagation in two-dimensional fracture networks: Impact of structure and hydraulic variability2019In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 115, p. 1-10Article in journal (Refereed)
    Abstract [en]

    Analysis of cement grout propagation in water-saturated two-dimensional discrete fracture networks is presented in this study. A two-phase flow model for Bingham fluids flow in a single saturated fracture is extended to simulate cement grouts propagation in saturated networks. Using this extended model, the impacts of network structure and hydraulic variability, i.e., network geometry and aperture distribution, on the propagation process are investigated through numerical simulations. Cement grout propagation in 50 realizations of a two-dimensional discrete fracture network (2D DFN) are simulated with different cases of aperture variability, i.e. constant aperture, uncorrelated and length-correlated heterogeneous apertures following a truncated lognormal distribution. The results indicate that network structure and hydraulic variability significantly affect the grout propagation in 2D DFN systems. The randomized network structure and uncorrelated heterogeneous apertures significantly delay the propagation rate and largely increase the variability range of the propagation volume fraction. In contrast, in the case with length-correlated heterogeneous apertures, the propagation rate increases, while the variability range and rate of change of the propagation volume fraction decreases. The extended two-phase flow model for fracture networks and the simulation results presented in this work are useful for basic understanding of the processes relevant for design, monitoring and execution of rock grouting.

  • 19.
    Prästings, Anders
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Spross, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Characteristic values of geotechnical parameters in Eurocode 72019In: Proceedings of the Institution of Civil Engeneers: Geotechnical Engineering, ISSN 1353-2618, E-ISSN 1751-8563, Vol. 172, no 4, p. 301-311Article in journal (Refereed)
    Abstract [en]

    Lack of harmonisation between reliability-based design and the partial factor method in Eurocode 7 (EN 1997-1:2004) is preventing the widespread introduction of a risk-based concept in geotechnical design. This paper discusses how uncertainties are managed according to EN 1997-1:2004 and possible implications of not harmonising the current safety format with reliability-based design. One of several challenges highlighted is how EN 1997-1:2004 defines the characteristic value and design value. The characteristic value is therein defined based on a classical frequentist approach through a confidence interval. From a Bayesian point of view, the current definition does not treat the characteristic value as an uncertain variable. Consequently, the definitions of the characteristic value and design value in EN 1997-1:2004 feature weak connections between uncertainties in the geotechnical properties and the consequences of failure, as regulated by the target reliability index.

  • 20.
    Olsson, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Forquin, P. A.
    Computational framework for analysis of contact-induced damage in brittle rocks2019In: International Journal of Solids and StructuresArticle in journal (Refereed)
    Abstract [en]

    This paper presents a numerical approach for predicting damage in rock materials caused by contact loading. The rock material is modelled using a constitutive description that combines pressure dependent plasticity, for capturing shear deformation under high confining pressure, with an anisotropic damage model for capturing mode I cracking in tension. Material parameters for the model are taken from a recently performed investigation on a granite material. The model has been used to simulate two types of contact loading experiments from the literature, cyclic loading and monotonic loading up to fracture. In order to achieve accurate predictions, the model has been extended to account for small loaded volumes which occur at contact loading. The results show that the main damage mechanism at cyclic loading is crack propagation due to Hertzian stresses whereas in the monotonic experiments sub-surface cracks could initiate. All features measured in the contact loading experiments are captured by the model and hence, the modelling framework is judged to be able to capture contact damage if real stone geometries are studied in FEM.

  • 21.
    Heng, Piseth
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering. Univ Europeenne Bretagne, INSA Rennes, LGCGM Struct Engn Res Grp, 20 Ave Buttes de Coesmes,CS 70839, F-35708 Rennes 7, France.
    Alhasawi, Anas
    Univ Europeenne Bretagne, INSA Rennes, LGCGM Struct Engn Res Grp, 20 Ave Buttes de Coesmes,CS 70839, F-35708 Rennes 7, France..
    Battini, Jean-Marc
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Hjiaj, Mohammed
    Univ Europeenne Bretagne, INSA Rennes, LGCGM Struct Engn Res Grp, 20 Ave Buttes de Coesmes,CS 70839, F-35708 Rennes 7, France..
    Co-rotating rigid beam with generalized plastic hinges for the nonlinear dynamic analysis of planar framed structures subjected to impact loading2019In: Finite elements in analysis and design (Print), ISSN 0168-874X, E-ISSN 1872-6925, Vol. 157, p. 38-49Article in journal (Refereed)
    Abstract [en]

    The purpose of this paper is to model the nonlinear dynamical response of steel frame structures subjected to impact loading. A 2D co-rotational rigid beam element with generalized elasto-plastic hinges is presented. The main idea is to integrate the concept of the generalized elasto-plastic hinge into the standard co-rotational framework by performing a static condensation procedure in order to remove extra internal nodes and their corresponding degrees of freedom. In addition, impact loading is applied through a contact model that is described in the rigorous framework of non-smooth dynamics. In this framework, equations of motion are derived using a set of differential measures and convex analysis tools, whereas Newton's impact law is imposed by means of a restitution coefficient in order to accommodate energy losses. An energy and momentum conserving scheme is adopted to solve the dynamical equations. The main interest of the current model is the ability to evaluate the geometrically nonlinear inelastic behaviour of steel structures with semi-rigid connections subjected to impact in a simple and efficient way, using only a few number of elements. The accuracy of the proposed formulation is assessed in three numerical applications.

  • 22.
    Jenelius, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport planning.
    Data-driven metro train crowding prediction based on real-time load data2019In: IEEE transactions on intelligent transportation systems (Print), ISSN 1524-9050, E-ISSN 1558-0016Article in journal (Refereed)
  • 23.
    Ivar, Björnsson
    et al.
    Lund University.
    Larsson Ivanov, Oskar
    Lund University.
    Honfi, Dániel
    RISE.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Decision support framework for bridge condition assessments2019In: Structural Safety, ISSN 0167-4730, E-ISSN 1879-3355, Vol. 81Article in journal (Refereed)
    Abstract [en]

    An essential aspect in the maintenance of existing bridges is the ability to adequately and accurately assess and evaluate the condition of the structure. Condition assessments, which can be carried out in any number of ways, provide valuable information concerning the actual state of a bridge, including the severity of potential damages, and form the basis for further maintenance decisions. Any decision support concerning the management of existing structures thus requires attention towards the uncertainties associated with the assessment methods when applied in practice as well as the maintenance actions these support. These uncertainties cannot be solely described as model uncertainties but are also a result of the variation in engineering performance observed in practice. In the current paper a rational and systematic framework is presented which provides practical decision support concerning whether condition assessments are necessary, what assessment methods are recommended, if invasive actions are needed, or if some other non-invasive option may be more appropriate. The framework takes into account three main attributes of an enhanced condition assessment, namely, modelling sophistication, considerations of uncertainties and risks, and knowledge/information content. Increasing the level of one or more of these attributes may be advantageous only if the expected benefits or added value of information is considered appropriate in relation to the cost of implementation in practice. A decision making model, based on Bayesian decision theory, is adopted to evaluate this problem. Two case studies, in which the framework is applied, are provided for illustrative purposes; the first is a generic numerical example and the second a decision scenario related to the fatigue assessment of an existing railway bridge.

  • 24.
    Cats, Oded
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport Planning, Economics and Engineering. Delft Univ Technol, Dept Transport & Planning, NL-2600 GA Delft, Netherlands..
    Determinants of Bus Riding Time Deviations: Relationship between Driving Patterns and Transit Performance2019In: JOURNAL OF TRANSPORTATION ENGINEERING PART A-SYSTEMS, ISSN 2473-2907, Vol. 145, no 1, article id 04018078Article in journal (Refereed)
    Abstract [en]

    Urban bus services e subject to high levels of uncertainty and disturbances. Methods to determine the timetable are designed to absorb variations in riding times between stops by allocating additional travel time. The propagation of service unreliability along the route could be restrained by drivers' adjustment at stops and between stops. This paper analyzes the main determinants of bus riding times deviations based on automatic vehicle location (AVL) data from four trunk lines in Stockholm, Sweden. The analysis indicates that drivers can and do adjust their speeds in response to instantaneous real-time schedule adherence information, although these adjustments depend on the underlying control scheme: locations where the performance is measured. A model for bus riding time deviations was estimated with autoregressive effects, performance indicators, link characteristics, and trip attributes as the explanatory factors. The results can support the development of travel time prediction and real-time control strategies that take drivers' response to operations into account. This highlights the importance of the human factor in designing control schemes and the corresponding transit performance evaluation.

  • 25.
    Xue, Yu
    et al.
    Dalian Univ Technol, Sch Civil Engn, Dalian 116024, Peoples R China..
    Liu, Wei
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Sustainable Buildings.
    Wang, Qian
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Sustainable Buildings. Uponor AB, Hackstavagen 1, S-72132 Vasteras, Sweden..
    Bu, Fang
    Beijing Aerosp Inst Metrol & Measurement Technol, Beijing 10000, Peoples R China..
    Development of an integrated approach for the inverse design of built environment by a fast fluid dynamics-based generic algorithm2019In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 160, article id 106205Article in journal (Refereed)
    Abstract [en]

    It is essential to further design built environments with improved thermal comfort level, air quality, and reduced energy consumption of the HVAC system. The CFD-based GA was able to identify the global optimal design, but this method requires numbers of CFD simulations which is time consuming. Besides, there is no general rule in determining the critical parameters of GA, such as population size, mutation rate, and crossover rate. Therefore, this study adopted the FFD instead of CFD and developed the FFD-based GA in OpenFOAM. By testing the FFD-based GA in designing the thermal environment in an office with displacement ventilation, it was found that the FFD-based GA had the similar performance with that of the CFD-based GA and saved more than 75% computational effect. Making use of the efficiency of the FFD-based GA, this investigation tested the effect of population size, mutation rate, and crossover rate on the inverse design by GA. In the same design case, the appropriate population size was and mutation rate was m = 0.1, while the crossover rate had no general effect on the inverse design.

  • 26.
    Zhang, Wei
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Jenelius, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Badia, Hugo
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Efficiency of semi-autonomous and fully autonomous bus services in trunk-and-branches networks2019In: Journal of Advanced Transportation, ISSN 0197-6729, E-ISSN 2042-3195, article id 7648735Article in journal (Refereed)
    Abstract [en]

    Automation technology is expected to change the public transport sector radically in the future. One rising issue is whether to embrace the intermediate stage of semi-autonomous buses or to wait until fully autonomous buses are available. This paper proposes a cost model of bus operations considering automation technology. The generalized cost, which is the sum of waiting, riding, operating, and capital cost, is modeled for conventional, semi-autonomous, and fully autonomous bus services on a generic trunk-and-branches network. Semi-autonomous buses achieve reduced unit operating cost through automated platooning on the corridor. The relative efficiency of the different services is studied under a range of scenarios for commercial speed, network structure, and demand distribution. Analytical and numerical results show that fully autonomous buses exhibit great potential through reduced operating and waiting costs even if the additional capital cost is high. The advantages of semi-autonomous buses are weaker and most prominent in networks with low demand along a long corridor such as interurban networks. For both automation levels a commercial speed comparable to conventional vehicles is crucial. The established criteria provide input to planners and operators for understanding the potential of automated bus services.

  • 27.
    Langbroek, Joram H. M.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment. KTH, School of Industrial Engineering and Management (ITM), Centres, Integrated Transport Research Lab, ITRL.
    Cebecauer, Matej
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport planning.
    Malmsten, Jon
    Franklin, Joel P.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment.
    Susilo, Yusak O.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment.
    Georén, Peter
    KTH, School of Industrial Engineering and Management (ITM), Centres, Integrated Transport Research Lab, ITRL. Solkompaniet Sverige AB, Vastbergavagen 4, S-12630 Hagersten, Sweden..
    Electric vehicle rental and electric vehicle adoption2019In: Research in Transportation Economics, ISSN 0739-8859, E-ISSN 1875-7979, Vol. 73, p. 72-82Article in journal (Refereed)
    Abstract [en]

    This case study describes the project Elbilsiandet (The Electric Vehicle Country) in Gotland, Sweden, where the island Gotland is made "ready for electric vehicles" by providing a network of charging infrastructure and electric vehicle rental during several summer seasons. The influence of the electric vehicle (EV) rental scheme on the process towards electric vehicle adoption is investigated using the Protection Motivation Theory (PMT) and the Transtheoretical Model of Change (TTM). Moreover, the travel patterns of electric rental cars are compared with those of conventional rental cars. The main results of this study are the following: Firstly, people renting an EV are on average closer to electric vehicle adoption than people renting a conventional vehicle. Secondly, people who rent an EV are at the time of rental associated with more positive attitudes towards EVs, have more knowledge about EVs and would feel more secure driving an EV. Thirdly, EV-rental does not seem to have a large additional effect on the stage-of-change towards EV-adoption of the participants. Lastly, the driving patterns of EVs do not seem to indicate serious limitations regarding driving distance, parking time and the destinations that have been visited, as compared to the driving patterns of conventional rental cars.

  • 28.
    Wang, Dongxing
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering. Wuhan Univ, Sch Civil Engn, Key Lab Geotechn & Struct Engn Safety Hubei Prov, Wuhan, Peoples R China.;Wuhan Univ, Sch Civil Engn, Key Lab Geotech & Struct Engn Safety Hubei Prov, 8 Dong Hu South Rd, Wuhan 430072, Hubei, Peoples R China.
    Gao, Xiangyun
    Wuhan Univ, Sch Civil Engn, Key Lab Geotechn & Struct Engn Safety Hubei Prov, Wuhan, Peoples R China.;Wuhan Univ, Sch Civil Engn, Key Lab Geotech & Struct Engn Safety Hubei Prov, 8 Dong Hu South Rd, Wuhan 430072, Hubei, Peoples R China..
    Wang, Ruihong
    China Three Gorges Univ, Minist Educ, Key Lab Geol Hazards Three Gorges Reservoir Area, Yichang, Hubei, Peoples R China..
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Benzerzour, Mahfoud
    LGCgE GCE, Inst Mines Telecom Lille Douai, Douai, France..
    Elevated curing temperature-associated strength and mechanisms of reactive MgO-activated industrial by-products solidified soils2019In: Marine georesources & geotechnology, ISSN 1064-119X, E-ISSN 1521-0618Article in journal (Refereed)
    Abstract [en]

    Alkali-activated industrial by-products (granulated blast furnace slag, Class F fly ash) by traditional alkali activator (such as NaOH and Na2SiO3) serves as a partial replacement for Portland cement in soil stabilization projects and suffers from environmental and technical problems. Reactive MgO - a greener and more practical alternative has recently emerged as a potential activator for slag and fly ash, but its micromechanisms of alkaline activation still need to be deeply investigated for strength improvement of soils. Hence, this study focuses on the strength and hydration properties of reactive MgO-slag and MgO-fly ash solidified soils, especially incorporating the impact of elevated curing temperature. Reactive MgO is proved to be excellent as a novel activator for activation of slag and fly ash, and their activating efficiency increases with elevated curing temperature that helps to remarkably enhance the compressive strength of soils. The major hydration products for reactive MgO-slag solidified soils, detected jointly by X-ray diffraction, scanning electron microscopy and thermogravimetric/differential thermogravimetric tests, are calcium silicate hydrate gels and hydrotalcite-like phases. The primary hydration products for MgO-fly ash solidified soils are magnesium silicate hydrate gels and Mg(OH)(2). That is just the intrinsic reason why the microstructure of solidified soils becomes much denser and the mechanical behavior is significantly improved. The minor carbonate phases such as magnesium carbonate and/or calcite are also observed in reactive MgO-slag and MgO-fly ash solidified soils, depending on the period of exposure to air. The curing temperature and binder amount are proved to be the two major factors governing the hydration process of reactive MgO-slag and MgO-fly ash blends. A higher curing temperature and binder amount can generate more hydration products, but their chemical compositions such as accurate element ratios need to be investigated in the future study.

  • 29.
    Babicheva, Tatiana
    et al.
    VEDECOM, 77 Rue Chantiers, F-78000 Versailles, France..
    Burghout, Wilco
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport planning. VEDECOM, 77 Rue Chantiers, F-78000 Versailles, France..
    Andreasson, Ingmar
    LogistikCtr Goteborg AB, Osbergsgatan 4 A, S-42677 Vastra Frolunda, Sweden..
    Faul, Nadege
    VEDECOM, 77 Rue Chantiers, F-78000 Versailles, France..
    Empty vehicle redistribution and fleet size in autonomous taxi systems2019In: IET Intelligent Transport Systems, ISSN 1751-956X, E-ISSN 1751-9578, Vol. 13, no 4, p. 677-682Article in journal (Refereed)
    Abstract [en]

    This study investigates empty vehicle redistribution algorithms for personal rapid transit and autonomous taxi services. The focus is on passenger service and operator cost. A new redistribution algorithm is presented in this study: index-based redistribution (IBR). IBR is a proactive method, meaning it takes into account both current demand and anticipated future demand, in contrast to reactive methods, which act based on current demand only. From information on currently waiting for passengers, predicted near-future demand and projected arrival of vehicles, IBR calculates an index for each vehicle station, and redistribution is done based on this index. Seven different algorithm combinations are evaluated using a test case in Paris Saclay, France (20 stations and 100 vehicles). A combination of simple nearest neighbours and IBR is shown to be promising. Its results outperform the other methods tested in peak and off-peak demand, in terms of average and maximum passenger waiting times as well as station queue length. The effect of vehicle fleet size on generalised cost is analysed. Waiting times, mileage and fleet size are taken into account while assessing this generalised cost.

  • 30.
    Nourozi, Behrouz
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology.
    Wang, Qian
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology. Uponor AB, Hackstavägen 1, S-72132 Västerås, Sweden..
    Ploskic, Adnan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology. Bravida Holding AB, Mikrofonvägen 28, S-12637 Hägersten, Sweden..
    Energy and defrosting contributions of preheating cold supply air in buildings with balanced ventilation2019In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 146, p. 180-189Article in journal (Refereed)
    Abstract [en]

    Residential wastewater is a constant and available source for saving energy. This paper mainly investigated the possibility of utilizing wastewater heat to reduce ventilation heat load. Swedish residential buildings are to a significant extent served by mechanical ventilation with heat recovery (MVHR) systems. MVHR in airtight buildings has greatly reduced ventilation heat loads, especially in cold climate countries such as Sweden. However, cold outdoor air might lead to frost formation in heat recovery exchangers which increases the energy use. Therefore, this study focused on reducing the defrosting need by preheating the incoming cold outdoor air to MVHR during the coldest days. The effects of preheating the incoming air to MVHR on ventilation heat load and annual ventilation heating demand were also studied. It was found that the heat recovery efficiency of MVHR is the most decisive factor in rating the performance of the combined system with an air preheater. Contributions of the studied air preheater to annual energy savings were negligible. On the other hand, the reduction of the initial defrosting need was significant. The obtained results showed that the defrosting need in a building located in central Sweden in two cases of an MVHR system equipped with a rotary heat exchanger/plate heat exchanger was eliminated/reduced to one-third. The defrosting need was reduced by 50% in northern Sweden for both cases.

  • 31.
    Liu, Fangzhou
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Battini, Jean-Marc
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Pacoste, Costin
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Experimental and numerical analyses of single pedestrian walking on a hollow core concrete floor2019In: International Journal of Civil Engineering, ISSN 1735-0522, Vol. 17, no 7A, p. 1201-1209Article in journal (Refereed)
    Abstract [en]

    The purpose of this paper is to study experimentally and numerically the dynamic response of a hollow core concrete slab due to a single pedestrian. To achieve this aim, a test structure consisting of six hollow core concrete elements of dimension 10mx1.2m has been built. A finite element model of the structure based on orthotropic shell elements has been implemented. The accuracy of the finite element model has been assessed by reproducing numerically hammer-impact tests. For that, the experimental impact load has been imported to the finite element model. Very good agreements between experimental and numerical results have been obtained. Then, three different single pedestrian walking paths have been tested experimentally. Each of these paths has been reproduced numerically using four numerical load models taken from the literature. The results show that the four pedestrian loads give rather different numerical results regarding the amplitudes of the acceleration for each mode. In addition, a small change in the numerical parameters of the slab can give large differences in the numerical results. This shows that an accurate numerical modelling of a single pedestrian loading is not an easy task. The results show also that during transversal and diagonal walking paths, the vibrations due to the torsional mode of the slab can be higher than the ones due to the lowest bending mode.

  • 32.
    Chen, Feng
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. EMPA–Swiss Federal Laboratories for Materials Science and Technology, Duebendorf, Switzerland.
    Experimental and numerical analysis of asphalt flow in a slump test2019In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 20, p. S446-S461Article in journal (Refereed)
    Abstract [en]

    The mechanical behaviour of uncompacted asphalt mixtures is still not well understood,threatening directly to the pavement practices such as control of mixture’s workability andsegregation. This situation may become even worse due to the gradually increasing complexityand advances in paving materials and technologies. This study adopts a slump flow testbased on concrete technology and a Discrete Element (DE)-based numerical tool to investigatethe mechanical behaviour of uncompacted asphalt mixture from a microstructural point ofview, particularly focusing on the bituminous binder effects. The combined experimental andnumerical analysis indicates that bitumen distinctly influences the contact interactions withinthe mixture and thus its macroscopic flow, which can be physically interpreted as a combinedeffect of lubricated friction and bonding force. Additional case studies demonstrate that the DEmodel is capable of simulating the flow response of asphalt mixtures under changed particlecontact conditions and driven force.

  • 33.
    Liu, Fangzhou
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Battini, Jean-Marc
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Pacoste, Costin
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Finite-shell-element models for the dynamic analysis of hollow-core concrete floor2019In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 71, no 10, p. 519-532Article in journal (Refereed)
    Abstract [en]

    Precast and prestressed hollow-core concrete slabs are widely used in construction. The combination of low self-weight and high strength of such slabs makes it possible to design floors with long spans. However, this also implies that the slabs are sensitive to human-induced vibrations. The purpose of this work was to develop a methodology to implement finite-shell-element models that can be used to analyse the dynamic behaviour of hollow-core concrete slabs. Three different shell models with different material properties (orthotropic material, isotropic material with strips and isotropic material) were designed and tested. The models were calibrated and assessed using experimental results obtained on a test structure of dimensions 10 m × 7·2 m consisting of six hollow-core elements.

  • 34.
    Zangeneh, Abbas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges. ELU Konsult AB.
    Battini, Jean-Marc
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Pacoste, Costin
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Karoumi, Raid
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Fundamental Modal Properties of Simply Supported Railway Bridges Considering Soil-Structure Interaction Effects2019In: Soil Dynamics and Earthquake Engineering, ISSN 0267-7261, E-ISSN 1879-341X, Vol. 121, p. 212-218Article in journal (Refereed)
    Abstract [en]

    In this paper, a simplified discrete model for calculating the modal parameters of the fundamental vertical mode of a simple beam on viscoelastic supports is proposed. Exact closed-form expressions for the fundamental natural frequency and modal damping ratio of the aforementioned coupled system are derived, as a function of the beam geometry and the foundation impedances. Using this model, the effect of the dynamic stiffness and dissipation capacity of the foundation-soil system on the modal characteristics of the fundamental vertical mode of the railway beam bridges is investigated and discussed. The proposed closed-form expressions, in combination with the impedance functions of different foundation-soil systems, can clarify the main features of dynamic SSI analysis of the railway beam bridges and lead to review the recommended modal damping ratios in the code provisions and design manuals.

  • 35.
    Lin, Chang
    et al.
    Natl Chung Hsing Univ, Dept Civil Engn, Taichung 40227, Taiwan..
    Wong, Wei-Ying
    Natl Chung Hsing Univ, Dept Civil Engn, Taichung 40227, Taiwan..
    Kao, Ming-Jer
    Natl Chung Hsing Univ, Dept Civil Engn, Taichung 40227, Taiwan..
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Älvkarleby Lab, Vattenfall AB Res & Dev, SE-81426 Älvkarleby, Sweden..
    Raikar, Rajkumar V.
    KLE Dr MS Sheshgiri Coll Engn & Technol, Dept Civil Engn, Angol Main Rd, Belgaum 590008, Karnataka, India..
    Yuan, Juan-Ming
    Providence Univ, Dept Data Sci & Big Data Analyt, Taichung 43301, Taiwan..
    Hydrodynamic Features of an Undular Bore Traveling on a 1:20 Sloping Beach2019In: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 11, no 8, article id 1556Article in journal (Refereed)
    Abstract [en]

    The hydrodynamic characteristics, including local and convective accelerations as well as pressure gradient in the horizontal direction, of the external stream of an undular bore propagating on a 1:20 sloping beach are experimentally studied. A bore with the water depth ratio of 1.70 was generated downstream of a suddenly lifted gate. A high-speed particle image velocimetry was employed to measure the velocity fields during the run-up and run-down motions. The time series of free surface elevation and velocity field/profile of the generated bore, comprising a pure bore accompanied by a series of dispersive leading waves, are first demonstrated. Based on the fast Fourier transform (FFT) and inverse FFT (IFFT) techniques, the free surface elevation of leading waves and the counterpart of pure bore are acquired separately at a specified measuring section (SMS), together with the uniform horizontal velocity of the pure bore. The effect of leading-wave-induced velocity shift on the velocity profiles of the generated bore are then evaluated at the SMS. To understand the calculation procedure of accelerations and pressure gradient, three tabulated forms are provided as illustrative examples. Accordingly, the relationships among the partially depth-averaged values of the non-dimensional local acceleration, convective acceleration, total acceleration and pressure gradient of the generated/pure bore acquired at the SMS versus the non-dimensional time are elucidated. The trends in the non-dimensional accelerations and pressure gradient of the external stream of generated bore are compared with those of the pure bore. During the run-up motion from the instant of arrival of the bore front to the moment of the peak level at the SMS, continuous decrease in the onshore uniform horizontal velocity, and successive deceleration of the pure bore in the onshore direction are evidenced, exhibiting the pure bore under the adverse pressure gradient with decreasing magnitude. However, the pure bore once ridden by the leading waves is decelerated/accelerated spatially and accelerated/decelerated temporally in the onshore direction during the rising/descending free surface of each leading wave. This fact highlights the effect of pre-passing/post-passing of the leading wave crest on the velocity distribution of generated bore. It is also found that, although the leading waves have minor contribution on the power spectrum of the free surface elevation as compared with that of the pure bore, the leading waves do play an important role on the magnitudes of both accelerations and pressure gradient. The largest magnitude of the acceleration contributed by the leading waves is around 26 times the counterpart contributed by the pure bore. Further, during the run-down motion right after the moment for the peak level of the bore, a linear increase in the magnitude of the offshore uniform horizontal velocity and a constant local acceleration with increasing time are both identified. The partially depth-averaged value of the non-dimensional pressure gradient is equal to a small negative constant (-0.0115) in the offshore direction, indicating that the bore is subject to a constant favorable pressure gradient.

  • 36.
    Polak, Joanna
    et al.
    Aalborg Univ, Danish Bldg Res Inst, AC Meyers Vaenge 15, DK-2450 Copenhagen SV, Denmark..
    Afshari, Alireza
    Aalborg Univ, Danish Bldg Res Inst, AC Meyers Vaenge 15, DK-2450 Copenhagen SV, Denmark..
    Sadeghian, Parastoo
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Sustainable Buildings.
    Wang, Cong
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Sustainable Buildings.
    Sadrizadeh, Sasan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Sustainable Buildings.
    Improving the performance of heat valve ventilation system: A study on the provided thermal environment2019In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 164, article id UNSP 106338Article in journal (Refereed)
    Abstract [en]

    The current study presents and evaluates the performance of two types of supply air terminal devices applied in a heat valve ventilation (HVV) system with regard to the provided thermal environment in a room heated and ventilated by the HVV system. To that end, air temperature and air velocity patterns and local thermal discomfort due to draught were studied both experimentally and numerically. Using numerical simulations, parametric analysis was carried out for investigating the provided indoor thermal environment for a wider range of boundary conditions. The considered parameters included the influence of cold vertical surfaces, supply airflow rate and temperature, and room heating energy demand. The results showed that both of the applied air terminal devices could avoid temperature stratification within the occupied zone. The maximum air temperature difference between 0.1 and 1.8 m above the floor was 2.1 degrees C when using a circular valve placed in the external wall below the window and 2.6 degrees C in the case when the air was supplied through three nozzles located in the wall opposite to the window in the upper part of the room. In general, placing the air terminal device below the window provided more uniform air temperature distribution and contributed to the prevention of downdraught caused by a cold window surface. The outcomes of this study are relevant to selecting and designing ventilation and air heating systems for low-energy buildings.

  • 37.
    Wei, Yun
    et al.
    DUT, Sch Civil Engn, 2 Linggong Rd, Dalian 116024, Peoples R China..
    Liu, Wei
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Sustainable Buildings.
    Xue, Yu
    DUT, Sch Civil Engn, 2 Linggong Rd, Dalian 116024, Peoples R China..
    Zhai, Zhiqiang (John)
    DUT, Sch Civil Engn, 2 Linggong Rd, Dalian 116024, Peoples R China.;Univ Colorado, Civil Environm & Architectural Engn, Boulder, CO 80309 USA..
    Chen, Qingyan (Yan)
    Purdue Univ, Sch Mech Engn, W Lafayette, IN 47907 USA..
    Zhang, Tengfei (Tim)
    DUT, Sch Civil Engn, 2 Linggong Rd, Dalian 116024, Peoples R China.;Tianjin Univ, Sch Environm Sci & Engn, Tianjin Key Lab Indoor Air Environm Qual Control, 92 Weijin Rd, Tianjin 300072, Peoples R China.;DUT, Key Lab Ocean Energy Utilizat & Energy Conservat, Minist Educ, 2 Linggong Rd, Dalian 116024, Peoples R China..
    Inverse design of aircraft cabin ventilation by integrating three methods2019In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 150, p. 33-43Article in journal (Refereed)
    Abstract [en]

    To create a healthy and comfortable aircraft cabin, air-supply parameters of the cabin ventilation system must be designed appropriately. Several methods, such as the computational fluid dynamics (CFD)-based genetic algorithm, CFD-based adjoint method and CFD-based proper orthogonal decomposition (POD), have been developed in recent years for conducing an inverse design. The target environmental performance is specified first, and then the corresponding air-supply parameters are inversely solved with the use of a particular method. However, each method has its pros and cons in terms of efficiency and accuracy. To expedite the inverse design process, this study proposed to integrate the above three methods. The genetic algorithm was adopted first to circumscribe ranges of the air-supply parameters. Next, POD was applied to further narrow the ranges and estimate the optimal air-supply parameters for each design criterion. Finally, the estimated optimal design from POD was supplied to the adjoint method for fine tuning. The above strategy was applied to a five-row aircraft cabin to determine the air-supply opening sizes, directions and temperatures. Criteria that had been proposed specifically for aircraft cabins were used as design targets. Results show that the proposed integration was able to provide the optimal design for each design target. The integrated optimal design was superior to the design provided by each individual method. The bottleneck in further acceleration of the integrated design was the hundreds of design cases resolved by full CFD simulation.

  • 38.
    Ghafoori Roozbahany, Ehsan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Investigation of asphalt joint compaction using discrete element simulation2019In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402Article in journal (Refereed)
    Abstract [en]

    Constructing high quality asphalt joints plays a vital role in preventing premature failures of pavements. Previous studies suggested that many construction parameters directly and indirectly influence the quality of asphalt joints. Due to uncertainties about the influence of each parameter on the quality of the finalised joints, closer and more detailed studies are still needed for achieving further improvements in this field. This study investigates the possible impacts of thickness, bottom layer roughness, joint interface geometries and compaction techniques on the particle flow of a coarse structured mixture during compaction. Therefore, discrete element method (DEM) was utilised to evaluate the influence of each construction parameter on the interlock between the cold and the hot side of an asphalt pavement joint. The results helped to explain earlier experimental findings about the joints and revealed potential for further laboratory and field investigations.

  • 39.
    Nourozi, Behrouz
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Sustainable Buildings.
    Härer, Simon
    Wang, Qian
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Sustainable Buildings. Uponor AB.
    Ploskic, Adnan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Sustainable Buildings. Bravida AB.
    Life cycle cost analysis of air preheating systems using wastewater and geothermal energy2019In: The REHVA European HVAC Journal, ISSN 1307-3729, Vol. 56, no 1, p. 47-51Article in journal (Other (popular science, discussion, etc.))
    Abstract [en]

    Frosting is a common problem in air handling units in buildings in cold climates. Tacklingthis problem is so far achieved by using considerable amount of energy while during thisprocess, the indoor air quality is compromised. This article presents the Life Cycle Cost(LCC) assessment of a preventive solution for frosting using two renewable heat sources.

  • 40.
    Balieu, Romain
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Architecture, Architectural Technologies. KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Chen, Feng
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Life Cycle Sustainability Assessment of Electrified Road Systems2019In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402Article in journal (Refereed)
    Abstract [en]

    The widespread use of Electric Vehicles (EVs) has been one of the main directionsfor pursuing a sustainable future of road transport in which, the deployment ofthe associated charging infrastructures, static or dynamic, has been included as oneof the main cornerstones for its success. Different electrified road (eRoad) systemswhich allow for dynamic charging of EVs by transferring electrical power from theroad to the vehicle in-motion, either in a conductive or contactless way, are underactive investigation. One of the important tasks in feasibility analysis of suchinfrastructure is to quantitatively assess its environmental performance and, thus,the consequential influences to the sustainability of road electrification as a whole.Having this concern in mind, in this study, a systematic LCA study is carried out in which the environmental impacts from the different life cycle stages have beencalculated and compared among several promising eRoad systems. In a next step,suitable strategies can be accordingly made to minimize these impacts in a most effectiveway; and more importantly, the LCA results of this study can serve as one ofthe important bases for conducting a more comprehensive and objective evaluationof the potential environmental benefits EVs could bring.

  • 41.
    Fadil, Hassan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Measurement of the viscoelastic properties of asphalt mortar and its components with indentation tests2019In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402Article in journal (Refereed)
    Abstract [en]

    Reliable determination of material properties is a key component for modelling and performance prediction of asphalt pavements. This paper deals with the potential use of instrumented indentation tests for viscoelastic characterisation of asphalt mortar as a new alternative to existing techniques. The main focus lies on the potential of indentation tests for multi-scale measurement of the shear relaxation modulus. A three-dimensional finite element model of a rigid spherical indenter penetrating an asphalt mortar sample is developed and used to model indentation tests performed at different material scales. The asphalt mortar is modelled as an idealised fine aggregate composite with elastic spheres, suspended within a viscoelastic bitumen mastic matrix. Based on the obtained numerical results the scale-dependency of the shear relaxation modulus measured with the indentation test is investigated. It is shown that the measurement scale is effectively controlled by the size of the indenter-specimen contact area, while the effect of indentation depth is minimal. The minimum contact area size required for obtaining representative properties, measured at the mortar scale, is determined. The viscoelastic parameters obtained from the indentation model are compared to those obtained using a representative volume element (RVE) for the asphalt mortar. In this way, the paper provides a new impulse for linking the mortar and asphalt scales in the multiscale modelling of asphalt mixtures. Feasibility of the proposed testing technique is further evaluated experimentally. Viscoelastic indentation tests are performed on asphalt mastics and mortar at two different sizes of contact areas. Experimental results indicate that indentation tests allow reliable characterisation of mortars relaxation modulus on both macro-scale as well as on individual component level.

  • 42.
    Liu, Wei
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Sustainable Buildings. School of Civil Engineering, ZJU-UIUC, Zhejiang University, Haining 314400, China.
    You, Ruoyu
    Department of Building Services Engineering, The Hong Kong Polytechnic University, Kowloon, 999077, Hong Kong, China.
    Chen, Chun
    Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong, Shatin, N.T. 999077, Hong Kong, China ; Shenzhen Research Institute, The Chinese University of Hong Kong, Shenzhen 518057, China.
    Modeling transient particle transport by fast fluid dynamics with the Markov chain method2019In: Building Simulation, ISSN 1996-3599, E-ISSN 1996-8744, p. 1-9Article in journal (Refereed)
    Abstract [en]

    Fast simulation tools for the prediction of transient particle transport are critical in designing the air distribution indoors to reduce the exposure to indoor particles and associated health risks. This investigation proposed a combined fast fluid dynamics (FFD) and Markov chain model for fast predicting transient particle transport indoors. The solver for FFD-Markov-chain model was programmed in OpenFOAM, an open-source CFD toolbox. This study used two cases from the literature to validate the developed model and found well agreement between the transient particle concentrations predicted by the FFD-Markov-chain model and the experimental data. This investigation further compared the FFD-Markov-chain model with the CFD-Eulerian model and CFD-Lagrangian model in terms of accuracy and efficiency. The accuracy of the FFD-Markov-chain model was similar to that of the other two models. For the two studied cases, the FFD-Markovchain model was 4.7 and 6.8 times faster, respectively, than the CFD-Eulerian model, and it was 137.4 and 53.3 times faster than the CFD-Lagrangian model in predicting the steady-state airflow and transient particle transport. Therefore, the FFD-Markov-chain model is able to greatly reduce the computing cost for predicting transient particle transport in indoor environments.

  • 43.
    Massarsch, K. R.
    et al.
    Geo Risk & Vibrat Scandinavia AB, Stockholm, Sweden..
    Wersäll, Carl
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Monitoring and Process Control of Vibratory Driving2019In: Geotechnical Engineering, ISSN 0046-5828, Vol. 50, no 3, p. 1-10Article in journal (Refereed)
    Abstract [en]

    Vibrators are used increasingly in the foundation industry, primarily for installation of piles and sheet piles, but also for deep vibratory compaction. Fundamentals of vibratory driving are described that make it possible to choose vibrator performance parameters based on field monitoring and performance control. Variable frequency and amplitude vibrators have become available that make it possible to adapt the driving process to project-specific requirements. The components of modern electronic measuring systems are detailed that can be used to monitor, control, and document different aspects of vibratory driving. Two examples are presented-vibratory driving of sheet piles and resonance compaction-which show how the performance of vibrators and sheet piles can be analysed and adapted to meet specific requirements. By using the advanced monitoring and process control systems, the efficiency of vibratory driving is enhanced. From the retrieved parameters, a better understanding of the vibratory driving process is gained, which can be used to develop a valuable database.

  • 44.
    Kharazmi, Parastou
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Sustainable Buildings.
    Monitoring the quality of sewer renewal using polymeric systems in Sweden2019In: Water practice and technology, E-ISSN 1751-231XArticle in journal (Refereed)
    Abstract [en]

    Water and wastewater pipes require some of the highest levels of infrastructure investment; they also deteriorate faster than they can be repaired. The use of alternative rehabilitation technologies, which are quicker and less expensive than pipe replacement, has therefore increased significantly in recent years, worldwide. Field studies on relined wastewater pipes removed from buildings in different parts of Sweden revealed the existence of a variety of common defects, most of which could have been prevented by better installation. Increased quality-focused monitoring could help to ensure that relined pipes reach their expected service life, while comprehensive documentation could assist in providing sufficient information to facilitate progress in the field. This paper includes a brief overview of the technologies used in Sweden, current quality control practices, repeated observed defects related to installation, crucial steps that affect final quality, and recommendations to be considered in the contexts of detailed quality control and quality assurance procedures.

  • 45. Laskaris, Georgios
    et al.
    Cats, Oded
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Jenelius, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Rinaldi, Marco
    Viti, Francesco
    Multiline holding based control for lines merging to a shared transit corridor2019In: Transportmetrica B: Transport Dynamics, ISSN 2168-0566, Vol. 7, no 1, p. 1062-1095Article in journal (Refereed)
    Abstract [en]

    In transit corridors, multiple lines share a sequence of consecutive stops to provide higher joint frequency in higher demand areas. A key challenge is to coordinate the transition from single line to joint operation. A holding control strategy aimed at minimizing passenger travel times is introduced for lines merging into a shared corridor, accounting for the coordination of vehicle arrivals from the merging lines as well as the regularity of each line. The criterion is tested using an artificial network and a real-world network to analyze the impact of demand distribution and compare cooperative versus single line control. We illustrate how the real-time strategy yields overall passenger gains, depending on the composition of different user groups. Results are assessed based on operation and passenger performance indicators and show that coordination is achieved. When combined with joint control in the common part, the proposed approach achieves consistent network-wide travel time benefits.

  • 46.
    Vieira, Tiago
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. VTI.
    Sandberg, Ulf
    VTI.
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering. VTI.
    Negative texture, positive for the environment: effects of horizontal grinding of asphalt pavements2019In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, p. 1-22Article in journal (Refereed)
    Abstract [en]

    A pavement surface having deflections from a plane mostly directed downwards in valleys is said to have a “negative texture”, in contrast to a “positive texture” dominated by peaks. Negative textures are typical of porous asphalt pavements, but another way to achieve this feature is to grind off the peaks of the surface. This paper explores the effects of grinding off texture peaks in the horizontal plane on a number of Swedish asphalt pavements in order to reduce noise and rolling resistance. Noise measurements were made to evaluate the ground-off surfaces versus the original surfaces, and, in most cases, also rolling resistance, texture and friction were also evaluated. It was found that grinding led to a more negative texture, tyre/road noise reductions up to 3 dB and tyre/road rolling resistance reductions up to 15%. It is concluded that horizontal grinding provides a maintenance operation with a significant potential for reduction of noise and rolling resistance, without sacrificing friction, though with limited longevity.

  • 47.
    Olsson, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Jelagin, Denis
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    New discrete element framework for modelling asphalt compaction2019In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402Article in journal (Refereed)
    Abstract [en]

    During asphalt mixture compaction, loads in the material are mainly transferred through contact between the stones and the interaction between the stones and the binder. The behaviour of such materials is suitable to model using the Discrete Element Method (DEM). In this study, a new DEM modelling approach has been developed for studying the asphalt compaction process, incorporating contact and damage laws based on granular mechanics. In the simulations, aggregate fracture is handled by a recently developed method of incorporating particle fracture in DEM, based on previously performed fracture experiments on granite specimens. The binder phase is modelled by adding a viscoelastic film around each DEM particle. This surface layer has a thickness that obtains the correct volume of the binder phase and has mechanical properties representative for the binder at different temperatures. The ability of the model to capture the influence of mixture parameters on the compactability and the eventual stone damage during compaction is examined for the cases of compaction flow test and gyratory compaction. Explicitly, the influence of different aggregate gradations, mixture temperatures and binder properties are studied. The results show that the proposed DEM approach is able to capture qualitatively and quantitatively responses in both cases and also provide predictions of aggregate damage. One large benefit with the developed modelling approach is that the influence of different asphalt mixture parameters could be studied without re-calibration of model parameters. Furthermore, based on comparative DEM simulations, it is shown that the proposed approach provides more realistic force distribution networks in the material.

  • 48.
    Bjurström, Henrik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Rydén, Nils
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Non-contact rolling surface wave measurements on asphalt concrete2019In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 20, no 2, p. 334-346Article in journal (Refereed)
    Abstract [en]

    Rolling surface wave measurements on a single, thin asphalt concrete (AC) layer are presented to investigate their use in rapid nondestructive field tests. An array of 47 micro-electro-mechanical sensor (MEMS) microphones is mounted on a trailer together with an automated impact source. Multichannel recordings from single impacts are obtained at 80 equally spaced array positions as the trailer moves at a constant speed. The complete battery-powered data acquisition system enables large-scale testing of newly built pavements. Multiple sets of test results show good repeatability for the assessed shear wave velocity and demonstrate the strong temperature dependency of AC. The presented results indicate a possible application for quality assurance of AC using rolling surface wave measurements.

  • 49.
    Magnusson, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hallgren, Mikael
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. Tyréns.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Ansell, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Numerical analyses of shear in concrete structures subjected to distributed blast loads2019In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323Article in journal (Refereed)
  • 50.
    Hov, Sölve
    et al.
    GeoMind/LabMind.
    Prästings, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Persson, Erik
    Bjerking.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    On empirical correlations for normalised shear strengths from fall cone and direct simple shear tests in soft Swedish clays2019In: Geotechnical and Geological Engineering, ISSN 0960-3182, E-ISSN 1573-1529Article in journal (Refereed)
1234567 1 - 50 of 958
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