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  • 1301.
    Zirgulis, Giedrius
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Svec, Oldrih
    Risø, DTU, Division of Building and Construction, Danish Technological Institute (DTI), Taastrup.
    Geiger, Mette
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Cwirzen, Andrzej
    Aalto University School of Engineering, Department of Civil and Structural Engineering, Finland.
    Kanstadt, Terje
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Variation in fiber volume and orientation in walls: experimental and numerical investigations2016Inngår i: Structural Concrete, ISSN 1464-4177, E-ISSN 1751-7648, Vol. 17, nr 4, s. 576-587Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Previous research with fibre-reinforced slab elements has shown that the surface roughness of formwork and the presence of rebars affect fibre orientation and fibre volume distribution. This paper discusses the orientation and volume distribution of steel fibres in wall elements cast from a single point. In particular, the effect of formwork tie bars on fibre orientation and distribution was studied. To quantify the fibre orientation and distribution, numerical simulations and X-ray computed tomography were applied, and the mechanical performance was determined using three-point bending tests on sawn beams. The Thorenfeldt model (applied in the Norwegian proposal of the new fibre-reinforced concrete guideline) was used to estimate the residual flexural tensile strength based on fibre orientation and distribution. The simulation results show that the fibre orientation can be related to the flow pattern. The results indicate a large variation in fibre orientation, which was experimentally confirmed. The fibre volume distribution was mostly uniform, except for an area with fewer fibres at the casting point. The large variation in fibre orientation was reflected by a large variation in residual flexural tensile strengths. Weak zones due to anisotropic fibre orientation caused by formwork tie bars were observed.

  • 1302.
    Zou, Zhongquan
    et al.
    Central South University of Forestry and Technology, Changsha.
    Enochsson, Ola
    He, Guojing
    Central South University of Forestry and Technology, Changsha.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Finite element analysis of small span reinforced concrete trough railway bridge2009Inngår i: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 400-402, s. 645-650Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The static behavior of a reinforced concrete trough railway bridge is analyzed by finite element method. The influences of load distribution fashion, supporting width of the bearings and the additional support beneath the girder are investigated; and the spatial effect of the stress distribution is studied as well. To confirm the analysis accuracy, the results are calibrated with the field load test results. It is found that the influence of load distribution fashion is minor and negligible, while those of supporting width and additional support are not negligible; and the spatial effect is significant.

  • 1303.
    Öhult, Leif
    Luleå tekniska universitet.
    Hur bygga i kallt klimat1991Licentiatavhandling, monografi (Annet vitenskapelig)
  • 1304.
    Östlund, Per-Olov
    et al.
    Luleå tekniska universitet.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Inverkan av fleraxiell last och temperatur på betong1976Rapport (Annet vitenskapelig)
  • 1305.
    Žirgulis, Giedrius
    et al.
    Department of Structural Engineering, Norwegian University of Science & Technology (NTNU), Trondheim, Norway.
    Švec, Oldřich
    Division of Building & Construction, Danish Technological Institute (DTI), Taastrup, Denmark.
    Geiker, Mette Rica
    Department of Structural Engineering, Norwegian University of Science & Technology (NTNU), Trondheim, Norway.
    Cwirzen, Andrzej
    Department of Civil & Structural Engineering, Aalto University School of Engineering, Espoo, Finland.
    Kanstad, Terje
    Department of Structural Engineering, Norwegian University of Science & Technology (NTNU), Trondheim, Norway.
    Influence of reinforcing bar layout on fibre orientation and distribution in slabs cast from fibre-reinforced self-compacting concrete (FRSCC)2016Inngår i: Structural Concrete, ISSN 1464-4177, E-ISSN 1751-7648, Vol. 17, nr 2, s. 245-256Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fibre orientation and volume distribution affect the post-cracking tensile strength, which is one of the main design parameters of fibre-reinforced concrete (FRC). This paper discusses the influence of unidirectional and grid reinforcement on fibre orientation and distribution in FRC slabs. Slabs without conventional reinforcing bars were used as a reference. The slab size was 1200 × 1200 × 150 mm. Numerical simulations were used to predict the fibre orientation and X-ray computed tomography (CT) to determine the actual fibre orientation and distribution. Beams were sawn from each slab, CT-scanned and tested in three-point bending tests in accordance with EN 14651. Both the numerical simulations and the CT results show that the rebars caused a more isotropic fibre orientation in the lower halves of the slabs. This was confirmed in the bending tests, where the lowest variation and highest residual tensile strengths were documented for beams sawn from slabs with grid reinforcement. Fibre migration from the upper layer to middle and lower layers of the slabs due to gravity was observed in all slabs, and in the reinforced slabs, migration also depended on the distance from the casting point. The reinforcement led to an accumulation of fibres above the rebars in the middle layer of each reinforced slab. A set of mechanisms is proposed to explain the experimental results.

  • 1306.
    Žirgulis, Giedrius
    et al.
    Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim.
    Švec, Oldřich
    Division of Building and Construction, Danish Technological Institute (DTI), Taastrup.
    Sarmiento, Elena Vidal
    Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim.
    Geiker, Mette Rica
    Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim.
    Cwirzen, Andrzej
    Aalto University School of Engineering, Helsinki.
    Kanstad, Terje
    Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim.
    Importance of quantification of steel fibre orientation for residual flexural tensile strength in FRC2016Inngår i: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 49, nr 9, s. 3861-3877Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The orientation of steel fibres affects the flexural performance of fibre-reinforced concrete. In this paper, selected experimental methods for the characterization of fibre orientation are evaluated and the relationship between residual flexural tensile strength and fibre orientation is discussed. To illustrate the applicability of the methods, the impact of the formwork surface on fibre orientation in slabs cast with fibre-reinforced self-compacting concrete (slump-flow class SF1 according to EN206) was investigated for the cases of formwork surfaces with slip, semi-slip and rough condition. The comparison of fibre orientation quantification methods showed good agreement between X-ray computed tomography and image analysis of sections from sawn beams. The variation in fibre orientation over the slab thickness was strongly influenced by the flow and the roughness of the formwork surface. The Thorenfeldt model for the impact of the fibre orientation factor on residual flexural tensile strength (used in the Norwegian proposal for fibre concrete guidelines) was verified and showed good agreement.

  • 1307. Elfgren, Lennart ()
    Fracture mechanics of concrete structures: From theory to applications: Report of the Technical Committee 90-FMA Fracture Mechanics to Concrete/Applications, RILEM (the International Union of Testing and Research Laboratories for Materials and Structures)1989Rapport (Annet vitenskapelig)
    Abstract [en]

    Ductile and durable concrete structures are the goal of all designers. In order to achieve such goals it is necessarry to know the laws that govern the behaviour of materials and structures.This report explains how cracking, ductility and brittleness are influenced by dimensions (size effects) and material properties such as tensile strength, stiffness (modulus of elasticity) and fracture energy. This is done with the help of models of fracture mechanics. The different models that have emerged during the last ten years are first presented and accomodated inside a common frame. Practical applications are then presented in a variety of fields. The report should be of interest to persons engaged in design, development, research and teaching in the field of Concrete structures. It was prepared by RILEM Technical Committee 90-FMA 'Fracture Mechanics of Concrete - Applications' during 1986-1988.

  • 1308. Fransson, Lennart ()
    Ice mechanics and shipping in ice-infested waters2008Rapport (Annet vitenskapelig)
    Abstract [sv]

    Följande rapport ingår i projektet "Ismekanikk og havnedrift i islagte farvann" (delprogrammet Nordkalotten INTERREG III A Nord). Denna rapport är huvuddokumentet där alla delrapporter inom projektet sammanställts. Övriga rapporter som ingår är följande: - Nonlinear finite element simulations of ice forces on offshore structures - Mätning av islaster med isbrytare - Ice Induced Vibrations of Slender Structures - Isförhållanden längs svenska kusten, Bottenviken, Bottenhavet och Barents hav - Ice Control Measures in Swedish Harbours - Database Norströmsgrund

  • 1309. Collin, Peter ()
    Hällmark, Robert ()
    Nilsson, Martin ()
    International workshop on prefabricated composite bridges2009Rapport (Annet vitenskapelig)
  • 1310. Elfgren, Lennart ()
    Round Robin analyses and tests of anchor bolts in concrete structures: RILEM Technical Committee 90-FMA, Fracture Mechanics of Concrete - Applications1998Rapport (Annet vitenskapelig)
  • 1311. Enochsson, Ola ()
    Stål- och samverkansbroar: seminarieuppgifter i doktorandkurs 20042005Rapport (Annet (populærvitenskap, debatt, mm))
    Abstract [sv]

    Luleå tekniska universitet, LTU och Kungliga tekniska högskolan, KTH anordnade under 2004 en doktorandkurs i stål- och samverkansbroar. Kursen gavs inom det Vinnova stödda FOU-konsortiet Väg/Bro/Tunnel. Kursens syfte var att deltagarna skulle få en inblick i stål- och samverkansbroar genom föreläsningar och studiebesök, samt även få chansen att träna upp sina egna konstruktionsfärdigheter genom att själv välja och göra en konstruktionsuppgift. Kursen genomfördes med tre 2-dagars kurstillfällen antingen på KTH eller på LTU, samt med ett avslutande seminarium och studiebesök i Paris.

  • 1312. Elfgren, Lennart ()
    Noghabai, Keivan ()
    Luleå tekniska universitet.
    Tension of reinforced concrete prisms: round robin analysis and tests on bond : a report from an investigation arranged by RILEM technical committee 147-FMB fracture mechanics to anchorage and bond2001Rapport (Annet vitenskapelig)
    Abstract [en]

    Results are presented from a RILEM Round Robin Investigation. It deals with tension stiffening of reinforcement bars embedded in concrete tie elements. Seven groups of researches have performed some 50 tests and analyses. Parameters discussed are: cover thickness, crack spacing, bar size, tension stiffening of naked reinforcing bars, and influence of concrete strain softening. Similar trends were seen in the different tests and most of the applied theoretical models give reasonable results. The general behaviour is similar, although there seems to be some differences between the tested cracking loads. The models used are able to predict the bond behaviour in a correct way: analytical models based on the tension softening of concrete; bond-slip relations; as well as finite element methods with inner softening bands. The CEB-FIP Model Code can be used for design purposes and gives straight-forward predictions. The following new and/or refined insights were obtained from the tests: Cover thickness and crack spacing. - The number and spacing of visible cracks are more or less proportional to the thickness of the concrete cover. Bar diameter size effect. - There is a small tendency to a proportionally lower tension stiffening effect for larger bar sizes but the scatter is too large to secure definite conclusions. Longitudinal splitting and yielding of reinforcement. - Longitudinal splitting cracks occurred close to and after yielding of the reinforcement. Tension stiffening of naked reinforcing bars. - A new hypothesis of a tension stiffening of the bare reinforcing bar has been presented. Concrete strength and strain softening - The crack opening resistance is given by the tension softening curve of the concrete. By addition of fibres to the concrete matrix, the curve is changed, and the crack opening resistance is improved without necessarily changing other properties of the concrete. The chosen amount and type of fibers do not necessarily have much influence on the tensile strength, and the same crack patterns will be obtained on elements with the same geometry. The shape of the load-deformation curve, however, is considerably changed compared to that of the plain concrete. This is due to the enhanced crack-opening resistance, whereas the stiffening effect seems to depend on the crack spacing and consequently on the cover thickness and the degree of confinement it provides.

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