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  • 1. Shi, Can
    et al.
    Zhao, Chunfa
    Zhang, Xu
    Andersson, Andreas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Analysis on dynamic performance of different track transition forms using the discrete element/finite difference hybrid method2020In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 230, article id 106187Article in journal (Refereed)
    Abstract [en]

    To analyze the mesodynamic and macrodynamic performance of the track transitions more precisely, a bridge-embankment transition model has been established by combining the discrete element method (DEM) with the finite difference method (FDM). In this model, the DEM is utilized to model sleepers and ballast particles with complex shape, and the FDM is applied to simulate the abutment, transition section and embankment. The DEM/FDM coupled model is then achieved by exchanging displacements, velocities, and contact forces at the interface. Afterwards, the influence of the transition section parameters and transition forms on dynamic behaviour of the track-substructure system is studied under measured rail seat load. The numerical simulations indicate that the increase of the transition section elastic modulus, decrease of the backfill slope values and the transition form of trapezoid backfill following by inverted trapezoid backfill can provide a better displacement gradient between the abutment and the embankment. Additionally, the results show that the inverted trapezoid transition form can provide a better transition of the track dynamic performance than the trapezoid transition form and the embankment soil over the wedge-shape backfill has the tendency to propagate along the slope toward the embankment section under the moving train load for the trapezoid transition form.

  • 2.
    Lindblad, Hannes
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Guerrero, J. R.
    Client’s role in promoting BIM implementation and innovation in construction2020In: Construction Management and Economics, ISSN 0144-6193, E-ISSN 1466-433XArticle in journal (Refereed)
    Abstract [en]

    Innovation is often viewed as vital in addressing future demands on the construction industry, but innovation implementation is also considered challenging in this fragmented, project-based industry. In order to address the challenges, client organisations are commonly acknowledged as key actors in driving construction innovation. However, the details of what the client role constitutes is less clear, and the question of whether innovation should be mainly client-led or supplier-led is debated. The purpose in this paper is to explore different roles public client organisations can enact to promote innovation. To fulfil this purpose, an explorative case study has been conducted at the largest transport infrastructure client in Sweden; exploring two initiatives which have simultaneously been deployed to promote innovation. The studied organisation is on the one hand trying to influence the industry to implement Building Information Modelling (BIM), adopting a BIM policy and actively influencing the supply chain, while on the other hand promoting innovation through policies aimed at providing more flexibility in projects, enabling suppliers to propose new solutions and emphasising market competition. Even though the overarching goals are similar, promote innovation, the research finds that the simultaneous use of the policies create intra-organisational tension within the client organisation. The findings provide insights into the different roles clients can enact in promoting innovation, and contribute to the understanding of clients as a key actor for promoting innovation in the construction industry.

  • 3.
    Peftitsi, Soumela
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport planning.
    Jenelius, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport planning.
    Cats, Oded
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport planning.
    Determinants of passengers' metro car choice revealed through automated data sources: a Stockholm case study2020In: Transportmetrica A: Transport Science, ISSN 2324-9935, Vol. 16, no 3, p. 529-549Article in journal (Refereed)
    Abstract [en]

    We propose a methodology based on multiple automated data sources for evaluating the effects of station layout, arriving traveler flows, and platform and on-board crowding on the distribution of boarding passengers among individual cars of metro trains. The methodology is applied to a case study for a sequence of stations in the Stockholm metro network. The findings suggest that passengers opt for less crowded train cars in crowded situations, trading-off walking and in-vehicle crowding while waiting and riding. We find that the boarding car distribution is also affected by the locations of platform access points and the distribution of entering traveler flows. These insights may be used by transit planners and operators to increase the understanding of how passengers behave under varying crowding conditions, identify the factors that affect travelers' choice of metro car and eventually reduce experienced on-board crowding and increase the capacity utilization of the trains through investments in infrastructure or operational interventions.

  • 4.
    Wang, Dongxing
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering. Key Laboratory of Geotechnical and Structural Engineering Safety of Hubei Province, School of Civil Engineering, Wuhan University, Wuhan, 430072, China.
    Wang, H.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Benzerzour, M.
    Maherzi, W.
    Amar, M.
    Effect of basalt fiber inclusion on the mechanical properties and microstructure of cement-solidified kaolinite2020In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 241, article id 118085Article in journal (Refereed)
    Abstract [en]

    The polypropylene fibers, which are currently attracting enormous attention in various geotechnical applications, carry a risk of aging under an integrated effect of heat, oxygen, light and other environmental factors, causing potentially infrastructure failure. An eco-friendly and biologically inactive material – basalt fiber, which has excellent natural resistance to aging and can eliminate aging-associated disasters, deserves more attention in geotechnical field. However, quite few studies are available on the beneficial reuse of basalt fibers to improve the engineering performance of soils. Therefore, this study aims to incorporate the sustainable basalt fiber and clarify how its inclusion impacts the mechanical properties and microstructure of cemented kaolinite. The experimental programs are comprised of three types of tests, i.e. two to examine the compressive strength and triaxial shear behavior and one to evaluate the microstructure properties. The results indicate that the basalt fiber reinforcement plays an essential role in enhancing the compressive strength and peak deviatoric stress of cemented and uncemented kaolinite. The inclusion of basalt fibers improves the ductility and weakens the brittleness of cemented kaolinite. The compressive strength increases with basalt fiber content and curing time, and reaches the peak at the fiber content of 0.2%, followed by a reduction due to the formation of weak zone at higher fiber content. The peak deviatoric stress is elevated until reaching the maximum at the basalt fiber content of 0.4%, after which further addition of basalt fiber tends to reduce its reinforcing effect. The peak deviatoric stress increases as the basalt fiber length is shortened and the confining pressure is raised. The strength gain of cement-basalt fiber inclusion is much more than the sum of strength increase induced by them individually. The combination of basalt fiber and cement has the virtues of both cement-stabilized and basalt fiber-reinforced kaolinite. The SEM analysis reveals that the mechanical interaction in the form of interface bonding and friction between kaolinite particle, cement hydration product and basalt fiber is the dominant mechanism controlling the reinforcement-cementation benefits. The bridging effect (reinforcement) of basalt fibers and binding effect (cementation) of hydration products make a major contribution to the formation of stable and interconnected microstructure, which results in an evident improvement in the mechanical behaviour of cemented kaolinite. The combination of basalt fiber and cement stabilization would be an innovative and effective method for geotechnical engineering works such as soft ground improvement.

  • 5.
    Zade, Sagar
    et al.
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Mechanics.
    Shamu, Tafadzwa John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Finite-size spherical particles in a square duct flow of an elastoviscoplastic fluid: an experimental study2020In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 883, article id A6Article in journal (Refereed)
    Abstract [en]

    The present experimental study addresses the flow of a yield stress fluid with some elasticity (Carbopol gel) in a square duct. The behaviour of two fluids with lower and higher yield stress is investigated in terms of the friction factor and flow velocities at multiple Reynolds numbers Re* is an element of (1, 200) and, hence, Bingham numbers Bi is an element of (0.01, 0.35). Taking advantage of the symmetry planes in a square duct, we reconstruct the entire 3-component velocity field from two-dimensional particle image velocimetry (PIV). A secondary flow consisting of eight vortices is observed to recirculate the fluid from the core towards the wall centre and from the corners back to the core. The extent and intensity of these vortices grows with increasing Re* or, alternately, as the plug size decreases. The second objective of this study is to explore the change in flow in the presence of particles. To this end, almost neutrally buoyant finite-size spherical particles with a duct height, 2H, to particle diameter, d(p), ratio of 12 are used at two volume fractions phi = 5 and 10 %. Particle tracking velocimetry is used to measure the velocity of these refractive-index-matched spheres in the clear Carbopol gel, and PIV to extract the fluid velocity. Additionally, simple shadowgraphy is also used to qualitatively visualise the development of the particle distribution along the streamwise direction. The particle distribution pattern changes from being concentrated at the four corners, at low flow rates, to being focussed along a diffused ring between the centre and the corners, at high flow rates. The presence of particles induces streamwise and wall-normal velocity fluctuations in the fluid phase; however, the primary Reynolds shear stress is still very small compared to turbulent flows. The size of the plug in the particle-laden cases appears to be smaller than the corresponding single-phase cases. Similar to Newtonian fluids, the friction factor increases due to the presence of particles, almost independently of the suspending fluid matrix. Interestingly, predictions based on an increased effective suspension viscosity agrees quite well with the experimental friction factor for the concentrations used in this study.

  • 6.
    Chen, Yuejun
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures. College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing, 210098, China.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Yu, J.
    Fu, Z.
    Chen, Q.
    Flow Expansion and Deflection Downstream of a Symmetric Multi-gate Sluice Structure2020In: KSCE Journal of Civil Engineering, ISSN 1226-7988, E-ISSN 1976-3808, Vol. 24, no 2, p. 471-482Article in journal (Refereed)
    Abstract [en]

    A sluice structure with multiple gates is often followed by an enlarging channel downstream. Experiments are conducted for different enlargement ratios in cross-section and Froude numbers at the gates. A large-scale PIV system is adopted to capture the surface flow field for examination of the flow features. The study shows that, despite the centrally placed sluice structure with symmetric outflow, a hydraulic jump occurs and the main flow downstream exhibits, in terms of expansion and deflection, a high degree of asymmetry and formation of large circulation zones. The degree of deflection increases significantly along the longitudinal direction for all the enlargement ratios except the smallest. The toe of the hydraulic jump is controlled at the upper edge of the sloping surface downstream of the gates. In light of outflow width, Froude number and enlargement ratio, the flow is classified into three regions. Immediately downstream, the effect of outflow width gradually decreases with increasing Froude number. Further downstream, the degree of deflection augments with increasing enlargement ratio, with circulation zones. At a given cross-section, the degree of expansion is positively related to the enlargement ratio. The study is expected to provide guidance for examination of similar issues of flow pattern and erosion protection design.

  • 7.
    Malm, Richard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Hellgren, Rikard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Enzell, Jonas
    Lessons Learned Regarding Cracking of a Concrete Arch Dam Due to Seasonal Temperature Variations2020In: Infrastructures, Vol. 5, no 2, article id 19Article in journal (Refereed)
    Abstract [en]

    Dams located in cold areas are subjected to large seasonal temperature variations and many concrete dams have cracked as a result. In the 14th International Commission on Large Dams (ICOLD) Benchmark Workshop, a case study was presented where contributors should predict the cracking and displacements due to seasonal variations. In this paper, the conclusions from this case study are presented. Overall, the results from the contributors are well in line with the observations that can be made on the dam and the measurements performed. This shows that using non-linear numerical models is a suitable tool to accurately predict cracking and estimate the displacements of cracked dams. This case study also highlighted important aspects that need special consideration in order to obtain realistic results that can be used to predict the crack pattern, these being: (1) the importance of performing transient thermal analyses based on robin boundary conditions; (2) the influence of contact formulation between the concrete dam and the foundation; and (3) the use of realistic non-linear material properties. The results and conclusions presented in this paper constitute one important step in achieving best practices to estimate dam safety and better understand the potential failure modes and ageing of concrete dams.

  • 8.
    Hellgren, Rikard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Malm, Richard
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Luleå, Sweden.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Westberg Wilde, Marie
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Measurement of ice pressure on a concrete dam with a prototype ice load panel2020In: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 170, article id 102923Article in journal (Refereed)
    Abstract [en]

    This paper presents the development and installation of a prototype ice load panel and measurements of ice load from February 2016 to February 2018 at the Rätan hydropower dam in Sweden. The design of the 1 × 3 m2 panel enables direct measurement of ice pressure on the concrete surface is based on previous experience from similar measurements with sea ice. Important features of the design are sufficient height and width to reduce scale effects and to cover the ice thickness and variations in water level. The Rätan dam was chosen based on several criteria so that the ice load is considered to be reasonably idealized against the dam structure.

    For the three winters 2016, 2016/2017, 2017/2018, the maximum ice load recorded was 161 kN/m, 164 kN/m and 61 kN/m respectively. There were significant daily fluctuations during the cold winter months, and the daily peak ice loads showed a visual correlation with the daily average temperature and with the daily pattern of operation of the power station with its corresponding water level variations.

  • 9.
    Ignat, Razvan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Baker, Sadek
    Skanska Sweden AB, Stockholm, Sweden..
    Karstunen, Minna
    Chalmers Univ Technol, Dept Architecture & Civil Engn, Gothenburg, Sweden..
    Liedberg, Sven
    Skanska Sweden AB, Stockholm, Sweden..
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Numerical analyses of an experimental excavation supported by panels of lime-cement columns2020In: Computers and geotechnics, ISSN 0266-352X, E-ISSN 1873-7633, Vol. 118, article id 103296Article in journal (Refereed)
    Abstract [en]

    The influence of ground improvement with panels of overlapping lime-cement columns on the behavior of a braced excavation loaded to failure has been investigated using 3D numerical analyses and the results are compared with an experimental full-scale failure test. The analyses reveal that stress-induced strength anisotropy of lime-cement improved clay needs to be considered when the stress path for the actual field conditions differs from that in conventional laboratory testing. In addition to strength parameters, the modulus of deformation that is consistent with the actual encountered stress path is also needed for reasonable predictions.

  • 10.
    Li, Shicheng
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Li, Qiulin
    Chongqing Jiaotong Univ, Southwest Sci Res Inst Water Transport Engn, Chongqing 400016, Peoples R China..
    Numerical Modelling of Air-Water Flows over a Stepped Spillway with Chamfers and Cavity Blockages2020In: KSCE Journal of Civil Engineering, ISSN 1226-7988, E-ISSN 1976-3808, Vol. 24, no 1, p. 99-109Article in journal (Refereed)
    Abstract [en]

    Owing to effective aeration and energy dissipation, a stepped spillway is commonly used in a roller-compacted concrete (RCC) dam. However, its complex air-water flow features are far from being fully understood. Roughness density, step and cavity shapes are essential parameters. Numerical simulations are carried out to investigate their effects on hydraulic properties. In combination with the realizable k-epsilon turbulence model, the two-phase Mixture Model is used. The results indicate higher air concentrations for the spillway with rounded steps than the ones with trapezoidal steps; the roughness density and cavity shape show no observable effects on the aeration performance with cavity blockages. The characteristic air-water velocity for the trapezoidal steps layout is larger than that for the rounded steps. However, neither layout is sensitive to the roughness density; the velocity results for trapezoidal cavity and rounded cavity cases are almost independent of the roughness density. The velocity for all cases exclusive of trapezoidal steps increase with an increase in roughness density. The min. and max. pressures on the trapezoidal steps are slightly larger than those on the rounded steps; they increase with an increasing roughness density. The cavity shape and roughness density do not evidently influence the extreme pressures. Compared with the conventional step layout, chamfering the step edges slightly enhance the energy dissipation; partially blocking the cavities do not lead to any substantial change. In addition, the energy loss is not clearly related to the roughness density and step edge/cavity shape.

  • 11. Ait Ali, A.
    et al.
    Warg, Jennifer
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport planning.
    Eliasson, J.
    Pricing commercial train path requests based on societal costs2020In: Transportation Research Part A: Policy and Practice, ISSN 0965-8564, E-ISSN 1879-2375, Vol. 132, p. 452-464Article in journal (Refereed)
    Abstract [en]

    On deregulated railway markets, efficient capacity allocation is important. We study the case where commercial trains and publicly controlled traffic (“commuter trains”) use the same railway infrastructure and hence compete for capacity. We develop a method that can be used by an infrastructure manager trying to allocate capacity in a socially efficient way. The method calculates the loss of societal benefits incurred by changing the commuter train timetable to accommodate a commercial train path request, and based on this calculates a reservation price for the train path request. If the commercial operator's willingness-to-pay for the train path exceeds the loss of societal benefits, its request is approved. The calculation of these benefits takes into account changes in commuter train passengers’ travel times, waiting times, transfers and crowding, and changes in operating costs for the commuter train operator(s). The method is implemented in a microscopic simulation program, which makes it possible to test the robustness and feasibility of timetable alternatives. We show that the method is possible to apply in practice by demonstrating it in a case study from Stockholm, illustrating the magnitudes of the resulting commercial train path prices. We conclude that marginal societal costs of railway capacity in Stockholm are considerably higher than the current track access charges.

  • 12.
    Spross, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Stille, Håkan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Palmstrøm, Arild
    Rock Mass Consulting Company.
    Principles of risk‑based rock engineering design2020In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 53, p. 1129-1143Article in journal (Refereed)
    Abstract [en]

    In comparison with other types of construction, the development of rock engineering design codes has been slow. Codesmust, however, be developed with relevant discipline-specific characteristics in mind. This paper, therefore, presents ageneric design framework for rock engineering. The framework is based on the presumption that rock engineering designmust be viewed as decision-making under uncertainty, which makes the design process subject to general risk managementprinciples, as risk is defined as “effect of uncertainties on objectives” (ISO 31000). Thus, rock engineering design codesultimately need to facilitate design processes that target the risk, to enable design of structures that not only are sufficientlysafe and durable and cost-effectively constructed, but also imply safe and healthy work conditions during construction andan acceptably low environmental impact. The presented framework satisfies this fundamental requirement and the authorsfind codification of its principles to be rather straightforward, as long as the level of detail in the code is governed by a strictapplication of ISO’s general risk management principles. Further details on methods and practical recommendations caninstead be supplemented in separate handbooks and application guidelines.

  • 13.
    Shamu, John
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Zou, Liangchao
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Kotzé, Reinhardt
    Incipientus Ultrasound Flow Technologies AB, Sweden.
    Wiklund, Johan
    Incipientus Ultrasound Flow Technologies AB, Sweden.
    Håkansson, Ulf
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. Skanska Sweden AB, Sweden.
    Radial Flow Velocity Profiles of a Yield Stress Fluid between Smooth Parallel Disks2020In: Rheologica Acta, ISSN 0035-4511, E-ISSN 1435-1528Article in journal (Refereed)
  • 14. Shi, B.
    et al.
    Yang, H.
    Liu, J.
    Crocetti, Roberto
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Liu, W.
    Short- and long-term performance of bonding steel-plate joints for timber structures2020In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 240, article id 117945Article in journal (Refereed)
    Abstract [en]

    The long-term performance of bonding steel-plate joints in controlled environmental conditions in this work. The bonding steel-plate joint consists of a steel plate with a vulcanized rubber layer and six wood screws. The vulcanized rubber layer is intended to improve the ductility of bonding steel-plate joints. Six pull-pull specimens were tested in order to determine the short-term load bearing capacity of bonding steel-plate joints, and the dimension of the shear plane of each bond line was 80 mm × 80 mm. A total of 12 specimens were employed in long-term tests. Two stress levels, including the 30% and 60% of ultimate bearing capacity, were adopted. All specimens were monitored over 800 days except that one series of specimens with 0.6 stress level which failed during the long-term tests. At the end of 858-day loading, the average slip at the connection for the specimens with 30% and 60% stress level were 0.623 mm and 0.939 mm, respectively. The creep coefficients were calculated according to the measured experimental data. The Burger's model, two term and six term Kelvin's model were adopted to fit the curves of creep coefficients, and then predict the creep slip of joints in the duration of service. The long-term slip stiffness and the ratio of stiffness loss are calculated according to experimental curves, and are predicted on the basis of the prediction results of creep coefficients through by six term Kelvin's model.

  • 15.
    Chen, Feng
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering. KTH Royal Institute of Technology.
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Vibration-induced aggregate segregation in asphalt mixtures2020In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 53, no 27Article in journal (Refereed)
    Abstract [en]

    Aggregate segregation in asphalt mixture is a bothersome engineering issue during pavement construction. The practitioners have some measures to mitigate the segregation potential based on experiences which, however, can only reduce the risk to a certain extent. In this research, the authors aim to contribute to the discussion in a rational non-empirical way, by using novel experimental and numerical techniques. A case study is carried out to investigate the vibration-induced segregation in asphalt mixtures, corresponding to the circumstance arising during material transportation to the construction site. A novel experimental test is conducted for evaluating the segregation characteristics of asphalt mixtures under vertical vibration in laboratory conditions. A numerical investigation based on discrete element method is further performed to study the phenomenon from a micromechanical point of view. The obtained experimental and numerical results indicate that vibratory loading induces aggregate size segregation in asphalt mixtures, and the degree of segregation is influenced profoundly by the adhesive properties of bituminous binders and the aggregate gradation.

  • 16.
    Chen, Feng
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Elaguine, Denis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Partl, Manfred N.
    EMPA, Uberlandstr 129, CH-8600 Dubendorf, Switzerland..
    Vibration-induced aggregate segregation in asphalt mixtures2020In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 53, no 2, article id 27Article in journal (Refereed)
    Abstract [en]

    Aggregate segregation in asphalt mixture is a bothersome engineering issue during pavement construction. The practitioners have some measures to mitigate the segregation potential based on experiences which, however, can only reduce the risk to a certain extent. In this research, the authors aim to contribute to the discussion in a rational non-empirical way, by using novel experimental and numerical techniques. A case study is carried out to investigate the vibration-induced segregation in asphalt mixtures, corresponding to the circumstance arising during material transportation to the construction site. A novel experimental test is conducted for evaluating the segregation characteristics of asphalt mixtures under vertical vibration in laboratory conditions. A numerical investigation based on discrete element method is further performed to study the phenomenon from a micromechanical point of view. The obtained experimental and numerical results indicate that vibratory loading induces aggregate size segregation in asphalt mixtures, and the degree of segregation is influenced profoundly by the adhesive properties of bituminous binders and the aggregate gradation.

  • 17.
    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, Soil and Rock Mechanics.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Yield-power-law fluid propagation in water-saturated fracture networks with application to rock grouting2020In: Tunnelling and Underground Space Technology, ISSN 0886-7798, E-ISSN 1878-4364, Vol. 95, article id 103170Article in journal (Refereed)
    Abstract [en]

    Cement grouting is widely applied in rock tunneling and underground construction to reduce groundwater inflow and increase the tightness of rock masses. The rock grouting process involves complex non-Newtonian grouts propagation in fracture networks. In this study, a two-phase flow model extended for yield-power-law fluid (e.g., cement grout) propagation in water-saturated fracture networks is presented. The effective transmissivity is scaled from analytical solutions for single-phase yield-power-law fluids flow between a pair of smooth parallel plates. This extended two-phase flow model for fracture networks is verified based on a unique set of experimental data. The full experiment dataset is presented in this work for the first time. Impacts of rheological parameters and time-dependent rheological properties of injected yield-power-law fluids on propagation processes are investigated through numerical simulations. A measure referred to as the propagation volume fraction is defined as an indicator of the propagation process. The results generally show that the rheological properties significantly affect the evolution of the propagation volume fraction. The propagation rate reduces with increased yield stress, consistency index and flow index. The two-phase flow of yield-power-law fluid propagation in a heterogeneous fracture network is also simulated, showing that the heterogeneity of fracture apertures may significantly affect the propagation process. For the heterogeneous case, with two-point distribution of apertures, the propagation volume fraction can be represented by using the harmonic mean aperture. Since the yield-power-law constitutive model covers a wide range of non-Newtonian fluids, the results presented in this work can be used for studying non-Newtonian fluid propagation in a variety of homogeneous or heterogeneous fracture networks, which can be used for rock grouting design.

  • 18.
    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%.

  • 19.
    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.

  • 20.
    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.

  • 21.
    de Frias Lopez, Ricardo
    et al.
    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.
    Silfwerbrand, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    A discrete element material model including particle degradation suitable for rockfill embankments2019In: Computers and geotechnics, ISSN 0266-352X, E-ISSN 1873-7633, Vol. 115, article id 103166Article in journal (Refereed)
    Abstract [en]

    A material model for future implementation in high rockfill embankments has been developed using discrete elements. Compared to previous modelling of railway ballast representing particles as clumps of spheres with bonded asperities, much simpler breakable clumps are used. This allows considering not only corner breakage but also particle splitting without a prohibitive computational time, something unique when modelling three-dimensional assemblies of particles. Moreover, breakage is controlled by values of contact forces and particle loading configuration, resulting in significantly fewer parameters and with a much clearer physical meaning. All in all, it results in a more computationally efficient and robust model suitable for implementation in rockfill embankments. Numerical monotonic and cyclic triaxial tests are performed under a range of low deviatoric to confinement stress ratios, as anticipated for railway embankments. A comparable degree of resemblance to empirical results as the previous modelling efforts with bonded asperities is observed when including degradation. Results at particle level proved useful to partially explain the observed macroscopic responses; however, these were substantially affected by breakage and none of the studied variables could, on its own, satisfactorily fully explain the observed behaviour. As a matter of fact, a complex interdependency of different factors, both at particle and macroscopic level, was identified that ultimately explained the macroscopic response. The key contribution is thus presenting an efficient and realistic material model specifically aimed at modelling high rockfill embankments including degradation, something not attempted to date.

  • 22.
    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.

  • 23.
    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.

  • 24. 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

  • 25.
    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.

  • 26.
    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 Multi-Objective Agent-Based Control Approach With Application in Intelligent Traffic Signal System2019In: IEEE transactions on intelligent transportation systems (Print), ISSN 1524-9050, E-ISSN 1558-0016, Vol. 20, no 10, p. 3900-3912Article in journal (Refereed)
    Abstract [en]

    Agent-based approaches have gained popularity in engineering applications, but its potential for advanced traffic controls has not been sufficiently explored. This paper presents a multi-agent framework that models traffic control instruments and their interactions with road traffic. A constrained Markov decision process (CMDP) model is used to represent agent decision making in the context of multi-objective policy goals, where the policy goal with the highest priority becomes the single optimization objective and the other goals are transformed as constraints. A reinforcement learning-based computational framework is developed for control applications. To implement the multi-objective decision model, a threshold lexicographic ordering method is introduced and integrated with the learning-based algorithm. Moreover, a two-stage hybrid framework is established to improve the learning efficiency of the model. While the proposed approach is potentially applicable for different road traffic operations, this paper applies the framework for traffic signal control in a network of Stockholm based on traffic simulation. The computational results show that the proposed control approach can handle a complex case of multiple policy requirements. Meanwhile, the agent-based intelligent control has shown superior performance when compared to other optimized signal control methods.

  • 27.
    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.

  • 28.
    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.

  • 29.
    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.

  • 30.
    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.

  • 31.
    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.

  • 32.
    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.

  • 33.
    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.

  • 34.
    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.))
  • 35. 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.))
  • 36.
    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.

  • 37.
    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.

  • 38.
    Li, Shicheng
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Li, Qiulin
    Chongqing Jiaotong Univ, Southwest Sci Res Inst Water Transport Engn, Chongqing 400016, Peoples R China..
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    CFD Modelling of a Stepped Spillway with Various Step Layouts2019In: Mathematical problems in engineering (Print), ISSN 1024-123X, E-ISSN 1563-5147, Vol. 2019, article id 6215739Article in journal (Refereed)
    Abstract [en]

    A traditional stepped spillway is prone to cavitation risks. To improve its hydraulic behaviors, distorted step faces and pool weirs are devised. By numerical modelling, comparative studies are conducted to look into the flow features. The pressures on step surfaces of the unconventional layouts exhibit 3D distributions. Pool weirs are essential in increasing both the min. and max. pressure loads. Pressures on the downstream bed show a unique pattern for V- and inverted V-shaped models, with the extreme pressures at the sidewalls for the former and at the central plane for the latter. Symmetrical secondary flows are formed in V- and inverted V-shaped cases with different patterns. Distributions of turbulent kinetic energy suggest differences in flow motions in all cases. Furthermore, the relative energy loss of flat setups is similar to 5.4% lower than that of the pooled ones with the same step face angle; inverting the face angle does not give rise to noticeable change. The results provide reference for relevant projects.

  • 39.
    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.

  • 40.
    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.

  • 41.
    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.

  • 42.
    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)
  • 43.
    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.

  • 44.
    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.

  • 45.
    Abenoza, Roberto
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment.
    Cats, Oded
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport planning. Department of Transport and Planning, Delft University of Technology, P.O. Box 5048, GA Delft, 2600, Netherlands.
    Susilo, Yusak
    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.
    Determinants of traveler satisfaction: Evidence for non-linear and asymmetric effects2019In: Transportation Research Part F: Traffic Psychology and Behaviour, ISSN 1369-8478, E-ISSN 1873-5517, Vol. 66, p. 339-356Article in journal (Refereed)
    Abstract [en]

    Classifying public transport service attributes based on their influence on overall traveler satisfaction can assist stakeholders and practitioners in introducing cost-efficient measures. To date most studies employed methods that were based on the assumption that the impact of service attributes on traveler satisfaction is entirely linear and symmetric. This study examines whether service attributes have a non-linear and asymmetric influence on the overall travel experience by employing the Three-factor theory (basic, performance and exciting factors). The analysis is conducted for different traveler segments depending on their level of captivity, travel frequency by public transport and travel mode used, and is based on a relatively large sample size collected for Stockholm County. Moreover, the estimated models control for important socio-demographic and travel characteristics that have been insofar overlooked. Results are presented in the form of a series of multi-level cubes that represent different essentiality of traveler needs which provide a useful methodological framework to further design quality service improvements that can be applied to various geographical contexts. Our findings highlight that a “one size fits all” approach is not adequate for identifying the needs of distinct traveler segments and of travelers using different travel modes. Furthermore, two-thirds of the attributes are consistently classified into the same factor category which entails important policy implications. This research deepens and expands the very limited knowledge of the application of the three-factor theory in the transport field.

  • 46.
    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.

  • 47.
    Kharazmi, Parastou
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Björk, Folke
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Durability study of reinforced polyester composite used as pipe lining under artificial aging conditions2019In: Cogent Engineering, E-ISSN 2331-1916, Vol. 6, no 1, article id UNSP 1693719Article in journal (Refereed)
    Abstract [en]

    The aging of sewer infrastructure is an ongoing problem. As a result, different materials and methods are being used in alternative sewer rehabilitation approaches. This work was conducted to study one pipe lining, namely the reinforced polyester composite, under artificial aging; this was done to provide a better understanding of the material’s performance under operating conditions, where it is regularly exposed to degrading factors such as heat and water. Aging of the material was monitored by means of several tests, including thermal and mechanical analyses, water absorption and microscopy. The results showed that the combination of aging in water and at high temperatures resulted in greater effects on the material compared to aging at high temperatures in dry conditions. Although the measured properties were affected significantly when immersed in water at high temperatures, the material showed acceptable properties at lower exposure temperatures close to the expected temperature inside sewer systems.

  • 48.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Editorial2019In: Proceedings of the Institution of Civil Engeneers: Geotechnical Engineering, ISSN 1353-2618, E-ISSN 1751-8563, Vol. 172, no 2, p. 111-112Article in journal (Refereed)
  • 49.
    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..
    Effect of cyclic low temperature conditioning on stiffness modulus of asphalt concrete based on non-contact resonance testing method2019In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 225, p. 502-509Article in journal (Refereed)
    Abstract [en]

    The stiffness modulus behaviors of three different asphalt concrete specimens that are subjected to cyclic cooling and heating are monitored. In an attempt to identify the sole effect of temperature cycles and to avoid any other biasing effects such as thermal contamination that can possibly corrupt measurements, resonance frequency measurements of the specimens are taken using an automated non-contact resonance method. The resonance frequency measurements are based on the fundamental axially symmetric mode of vibration. A hysteretic effect is observed on the measured resonance frequencies of the specimens with an application of cyclic cooling and heating. Lower stiffness moduli are obtained during the heating phase of a complete cooling and heating cycle. The stiffness moduli are calculated from measured resonance frequencies of the specimens in order to show their relative reductions due to the hysteretic effect. This finding is particularly important since it enables us to observe and understand the effect of the thermal history of asphalt concrete with regards to the reversibility behavior of its stiffness modulus. The damping of the specimens is also calculated from the measured resonance frequencies at the temperatures within the applied cyclic cooling and heating. Their observed behavior is also discussed with respect to a presence of potential micro damage.

  • 50.
    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.

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