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  • 1.
    Bonath, Victoria
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Kurkinen, Eva-Lotta
    SP Sveriges Tekniska Forskningsinstitut.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    A comparison between a commercial energy calculation tool for buildings with calculations using a response model2014In: NSB 2014 10th Nordic Symposium on Building Physics 15-19 June 2014 Lund, Sweden, Malmö, 2014, p. 863-870, article id 107Conference paper (Refereed)
    Download full text (pdf)
    FULLTEXT01
  • 2.
    Cao, Da-fu
    et al.
    School of Civil Science and Engineering, Yangzhou University, No.198 HuaYang XiLu, HanJiang District, Yangzhou 225127, P.R. China.
    Qin, Xiao-Chuan
    School of Civil Engineering, Southeast University, No.2 SiPaiLou, XuanWu District, Nanjing 210096, P.R. China.
    Meng, Shao-Ping
    School of Civil Engineering, Southeast University, No.2 SiPaiLou, XuanWu District, Nanjing 210096, P.R. China.
    Tu, Yong-Ming
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering. School of Civil Engineering, Southeast University, No.2 SiPaiLou, XuanWu District, Nanjing 210096, P.R. China.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sabourova, Natalia
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Grip, Niklas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Evaluation of prestress losses in prestressed concrete specimens subjected to freeze–thaw cycles2016In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 12, no 2, p. 159-170Article in journal (Refereed)
    Abstract [en]

    Prestressed concrete structures are considered to be reliable and durable. However, their long-term performance when subjected to frost attack is still unclear. In this work, experiments were carried out to evaluate the prestress losses in post-tensioned prestressed concrete specimens subjected to freeze–thaw cycles (FTCs). Two cases were considered: in one case, a series of specimens were prepared and tested in a freeze–thaw chamber; in the second case, the same series of specimens were tested in an indoor environment (outside the chamber). The difference between the prestress losses of the specimens inside the freeze–thaw chamber and those outside the chamber equalled the prestress losses due to FTCs. When using mathematical models to predict the prestress losses due to the FTCs, it was found that they were relatively small when the concrete was slightly damaged. However, they increased rapidly when the FTCs were repeated. The eccentricity of the prestress wires led to larger prestress losses when subjected to FTCs. Moreover, the same cross section and eccentricity resulted in similar prestress losses due to the FTCs, and the relatively high-strength concrete could withstand more FTCs.

  • 3.
    Coric, Ibrahim
    et al.
    Trafikverket, Luleå, Sweden .
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Skanska Sverige.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Norut, Norge.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Railway Bridges on the Iron Ore Line in Northern Sweden: From Axle Loads of 14 to 32,5 ton2018In: IABSE Conference Copenhagen 2018: Engineering the Past, to Meet the Needs of the Future, International Association for Bridge and Structural Engineering (IABSE) , 2018, p. 55-62Conference paper (Refereed)
    Abstract [en]

    The Iron Ore Railway Line was built around 1900 and has more than 100 bridges. It has a length of ca 500 km and runs from Kiruna and Malmberget in northern Sweden to the ice-free harbour in Narvik in Norway on the Atlantic and to Luleå in Sweden on the Baltic. The original axle load was 14 ton. The axle load has gradually been increased to 25 ton in 1955, to 30 ton in 1998 and to 32,5 ton in 2017.

    The increases in axle loads have been preceded by monitoring and assessment studies of the bridges. The capacity and need for strengthening or replacement of the bridges have been evaluated. Many of the bridges could carry a higher load than what it was designed for. Experiences from studies before the axle load was increased in 1998 and 2017 are presented and discussed.

    Download full text (pdf)
    fulltext
  • 4.
    Cyron, Wojciech
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Nilsson, Martin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Emborg, Mats
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Head of R&D department, BetongIndustri AB, Luleå, Sweden.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Bonded Concrete Overlays: A Brief Discussion on Restrained Shrinkage Deformations and Their Prediction Models2019In: Nordic Concrete Research, ISSN 0800-6377, Vol. 61, no 2, p. 107-129Article in journal (Refereed)
    Abstract [en]

    Bonded concrete overlays (BCO) on bridge decks are beneficial solutions due to their superior properties as compared to the typical asphalt pavement. A significant number of overlays suffer however, from occurrence of cracks and delamination due to poor bond, and restrained shrinkage and thermal dilation. Over the past years different appraisals for estimation of the restrained deformations have been developed, from micro-scale models, based on poromechanics, to empirical equations as given in B3 or B4 models suggested by Baiant. This paper provides a short overview of calculation models along with a brief theoretical explanation of shrinkage mechanism.

  • 5.
    Daerga, Per-Anders
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Behaviour of concrete at low temperatures1989In: POAC '89: 10th International conference on port and ocean engineering under arctic conditions / [ed] Kenneth B.E. Axelsson; Lennart Å. Fransson, Luleå: Luleå tekniska universitet, 1989, Vol. 2, p. 808-819Conference paper (Other academic)
  • 6.
    Duvnjak, Ivan
    et al.
    University of Zagreb, Croatia.
    Damjanović, Domagoj
    University of Zagreb, Croatia.
    Sabourova, Natalia
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Grip, Niklas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Tu, Yongming
    School of Civil Engineering, Southeast University, Nanjing, China.
    Damage Detection in Structures – Examples2019In: IABSE Symposium 2019: Towards a Resilent Built Environment - Risk and Asset Management, nternational Association for Bridge and Structural Engineering (IABSE) , 2019, p. 471-478Conference paper (Refereed)
    Abstract [en]

    Damage assessment of structures includes estimation of location and severity of damage. Quite often it is done by using changes of dynamic properties, such as natural frequencies, mode shapes and damping ratios, determined on undamaged and damaged structures. The basic principle is to use dynamic properties of a structure as indicators of any change of its stiffness and/or mass. In this paper, two new methods for damage detection are presented and compared. The first method is based on comparison of normalised modal shape vectors determined before and after damage. The second method uses so-called 𝑙1-norm regularized finite element model updating. Some important properties of these methods are demonstrated using simulations on a Kirchhoff plate. The pros and cons of the two methods are discussed. Unique aspects of the methods are highlighted.

    Download full text (pdf)
    Preprint
  • 7.
    Elfgren, Lennart
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Grip, Niklas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sabourova, Natalia
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Signal processing in modal analysis of bridges2009Conference paper (Other academic)
    Download full text (pdf)
    FULLTEXT01
  • 8.
    Elfgren, Lennart
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Nilforoush, Rasoul
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Nilsson, Martin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Assessment of Fasteners to Concrete: A Tribute to Rolf Eligehausen2017In: Connections between Steel and Concrete: 3rd International Symposium / [ed] Akanshu Sharma and Jan Hofmann, Stuttgart, 2017, p. 1294-1302Conference paper (Refereed)
    Abstract [en]

    Some examples are given of assessment of fastenings to concrete structures and the work started by Rolf Eligehausen in fib Task Group 2.9 “Fastenings to structural concrete and masonry”. Studies have been made on e.g. the influence of creep on adhesive anchors and of surface reinforcement and size effects on headed anchors.

    Download full text (pdf)
    fulltext
  • 9.
    Elfgren, Lennart
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Noghabai, Keivan
    Ohlsson, Ulf
    Olofsson, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Applications of fracture mechanics to anchors and bond1995In: Fracture mechanics of concrete structures: proceedings / [ed] Folker H. Wittmann, AEDIFICATIO Publishers , 1995, p. 1685-1694Conference paper (Refereed)
  • 10.
    Elfgren, Lennart
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ohlsson, Ulf
    Anchor bolts modelled with fracture mechanics1992In: Applications of fracture mechanics to reinforced concrete: based on the papers presented at the International Workshop on the Applications of Fracture Mechanics to Reinforced Concrete, held in Turin, Italy, 6 October 1990, London: Elsevier, 1992, p. 267-283Chapter in book (Other academic)
  • 11.
    Elfgren, Lennart
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Danielsson, Georg
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Åström, Lars
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Johansson, Håkan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Paulsson, Björn
    Trafikverket.
    Töyrä, Björn
    Trafikverket.
    30 ton på Malmbanan. Rapport 3.3 Infrastruktur.: Forsknings- och utvecklingsprojekt avseende betongbroars bärighet1996Report (Refereed)
    Abstract [sv]

    I rapporten redovisas fältmätningar på fyra broar och provbelastning I laboratoriet av en bro

    Download full text (pdf)
    FULLTEXT01
  • 12.
    Elfgren, Lennart
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ohlsson, Ulf
    Paulsson, Björn
    Töyrä, Björn
    Utmattningshållfasthet hos järnvägsbroar1997In: Bygg och Teknik, ISSN 0281-658X, E-ISSN 2002-8350, p. 48-Article in journal (Other (popular science, discussion, etc.))
  • 13.
    Ge, Yuanfei
    et al.
    Southeast University, Nanjing.
    Yu, Shaojun
    Southeast University, Nanjing.
    Yu, Zhang
    Southeast University, Nanjing.
    Tu, Yongming
    Southeast University, Nanjing.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    A refined model of concrete carbonation by coupling of multi-factors2016In: IABSE CONGRESS, STOCKHOLM, 2016: Challenges in Design and Construction of an Innovativeand Sustainable Built Environment / [ed] ennart Elfgren, Johan Jonsson, Mats Karlsson, Lahja Rydberg-Forssbeck and Britt Sigfrid, H - 8093 Zürich, Switzerland, 2016, p. 1198-1206Conference paper (Refereed)
    Abstract [en]

    Studies on carbonation of concrete play an important role in accurately predicting the service life. However, most research work on carbonation of concrete was carried out in qualitative ways and seldom in quantitative ways. In this paper, based on conservation of mass of C3S(s), C2S(s), CSH(s), CH(s), CH(aq), CO2(aq) and CO2(g) and one-dimensional diffusion and reaction equation, a refined mathematical model of concrete carbonation composed of a series of partial differential equations (PDEs) was built. Corresponding MATLAB codes were developed with calculus of differences to solve the mathematical model of concrete carbonation. The results of the mathematical models in this paper agree very well with measurements, which show that this model can be used to accurately predict concrete carbonation as well as remaining service life of concrete bridges and other concrete structures

  • 14.
    Huang, Zheng
    et al.
    Southeast University, Nanjing, China.
    Tu, Yong-Ming
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Grip, Niklas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Sabourova, Natalia
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Bagge, Niklas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Modelling of Damage and its use in Assessment of a Prestressed Concrete Bridge2016In: IABSE CONGRESS, STOCKHOLM, 2016: Challenges in Design and Construction of an Innovativeand Sustainable Built Environment / [ed] Lennart Elfgren, Johan Jonsson, Mats Karlsson, Lahja Rydberg-Forssbeck and Britt Sigfrid, CH - 8093 Zürich, Switzerland, 2016, p. 2093-2108Conference paper (Refereed)
    Abstract [en]

    A five-span prestressed concrete bridge has been subjected to a loading test up to failure in Kiruna, Sweden. The bridge was 55 years old and had a length of 121.5 m. The test has been used to validate and calibrate existing nonlinear finite element programs for predicting the shear behavior of reinforced and prestressed concrete structures. Two 3D finite element (FE) models of the Kiruna Bridge are built in commercial software Abaqus, one using shell-elements and one using a combination of shell and beam elements. Predictions obtained from these two models are well consistent with mode shapes and eigenfrequencies computed from acceleration measurements on the bridge before and after loading it to failure.The shear failure of the bridge is also simulated using the built-in concrete damage plasticity (CDP)model in Abaqus. The predicted load-displacement curve is in good agreement with the measurements. Verification of the CDP model is conducted at element and member level with two different damage parameter evolutions. The verification indicates that the damage parameter will affect the predicted shear behavior. It does not seem to be reliable to adopt the CDP model to simulate the shear behavior in the present research. A long term goal is to use use the measured mode shapes, eigenfrequencies and FE models for evaluating methods for damage identification. Such methods are important for maintenance of different structures, for extending their life span and for better knowledge of their load carrying capacity. The use is described of so-called sparse regularized finite element method updating (FEMU) methods. Some important properties of such methods are demonstrated using simulations on a Kirchhoff plate. For instance, the simulations suggest that both eigenfrequencies and mode shapes should be used for precise localization of the damage.

    Download full text (pdf)
    fulltext
  • 15.
    Huang, Zheng
    et al.
    School of Civil Engineering, Southeast University,Nanjing, China.
    Tu, Yongming
    School of Civil Engineering, Southeast University,Nanjing, China.
    Meng, Shaoping
    School of Civil Engineering, Southeast University,Nanjing, China.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    A practical method for predicting shear deformation of reinforced concrete beams2020In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 206, article id 110116Article in journal (Refereed)
    Abstract [en]

    This paper presents a practical method for predicting the deflections, including both the flexure and shear contributions, of reinforced concrete (RC) beams. The shear force - shear strain (V-γ) curve of a section in the shear span of RC beams is represented by a piecewise model and the tangent shear stiffness after shear cracking, Kt,cr, is assumed to be constant. A 2D finite element model, which has been validated for predicting shear deformation of RC beams, was used to identify factors that may affect the shear reduction factor (the ratio of Kt,cr to the elastic shear stiffness) and establish methodology for predicting the V-γ curve. Two types of methods, integration-form and closed-form, for predicting the total deflection were developed, in which the flexure-induced deflection (FD) was predicted using the Bischoff model while the shear-induced deflection (SD) was predicted using the method proposed in this paper. Comparison of the predictions with experimental results confirms that the Bischoff model provides reliable predictions of FDs of RC beams with and without shrinkage. It also shows that the proposed method can provide accurate predictions for SD after shear cracking, provided the effect of shrinkage on the shear cracking load is adequately quantified.

    Support from: National Natural Science Foundation of China (No. 51378104) and A Project Funded by the Priority Academic Program Development ofJiangsu Higher Education Institutions. The Development Fund of the Swedish Construction Industry (SBUF), the Swedish Research Council Formas and Elsa and Sven Thysell Foundation

  • 16.
    Nilforoush, Rasoul
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Nilimaa, Jonny
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Bagge, Niklas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Wsp Bridges and Tunnels, Göteborg, Sweden.
    Puurula, A
    Savonia University of Applied Sciences, Kuopio, Finland.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Nilsson, Martin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Fracture energy of concrete for bridge assessment2020In: 1st IABSE Online Symposium 2020: Synergy of Culture and Civil Engineering - History and Challenges / [ed] Jan Bien; Jan Biliszczuk; Pawel Hawryszkow; Maciej Hildebrand; Marta Knawa-Hawryszkow; Krzysztof Sadowski, International Association for Bridge and Structural Engineering (IABSE) , 2020, p. 692-699Conference paper (Refereed)
    Abstract [en]

    In numerical assessments of concrete bridges, the value of the concrete fracture energy GF plays an important role. However, mostly the fracture energy is only estimated based on the concrete compressive strength using empirical formulae. In order to study methods to determine the concrete fracture energy for existing bridges, tests were carried out on 55-year-old concrete from a bridge tested to failure in Kiruna in northern Sweden. Uniaxial tensile tests are performed on notched cylindrical concrete cores drilled out from this and other bridges. In the paper, different methods to determine the concrete fracture energy are discussed and recommendations are given for assessment procedures.

  • 17.
    Nilimaa, Jonny
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Häggström, Jens
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Bagge, Niklas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Bernspång, Lars
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Carolin, Anders
    Trafikverket, Borlänge, Sweden.
    Paulsson, Björn
    Trafikverket, Borlänge, Sweden.
    Maintenance and Renewal of Concrete Rail Bridges - Results from EC project MAINLINE2014In: Nordic Concrete Research, ISSN 0800-6377, Vol. 50, p. 25-28Article in journal (Refereed)
    Abstract [en]

    There is a need to extend the life and capacity of many existing railway bridges. One of the objects of the EC-FP7-Project MAINLINE, 2011-2014, is to facilitate this. Guidelines for assessment and strengthening methods are presented as well as case studies in which existing bridges are being studied in order to extend their life length. Case studies on bridges tested to failure in order to calibrate assessment methods are also presented. Fatigue is often a vital question. A Life Cycle Assessment Tool (LCAT) is being prepared to enable Infrastructure Managers to choose optimal maintenance strategies.

  • 18.
    Nilsson, Martin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Effects of surface reinforcement on bearing capacity of concrete with anchor bolts2011In: Nordic Concrete Research, ISSN 0800-6377, Vol. 2011, no 44, p. 161-174Article in journal (Refereed)
    Abstract [en]

    66 tests of the influence of surface reinforcement on the tensile load capacity of cast-in fasteners have been carried through. In the tests threaded rods ∅30 mm with a ∅45 mm nut at the end were cast-in centrically in concrete slabs (1.2 m × 1.2 m × 0.3 m up to 2.2 m × 2.2 m × 0.6 m). The amount of surface reinforcement was varied from 0% up to about 1.2%. There is a considerable increase in the load capacity with surface reinforcement present. The increase depends on the geometry and the amount and placement of the reinforcement.

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    fulltext
  • 19. Nilsson, Martin
    et al.
    Ohlsson, Ulf
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Partialkoefficienter för hållfasthet i betongbroar längs Malmbanan1999Report (Other academic)
    Abstract [sv]

    Denna rapport redovisar två metoder att bestämma nyanserade värden på betonghållfasthetens partialkoefficienter för befintliga betongbroar längs Malmbanan. Rapporten presenterar därefter dimensionerande drag- och tryck-hållfasthetsvärden för sju broar mellan Luleå och Boden. Hållfasthetsvärden är baserade dels på de nya partialkoefficienterna, dels på provresultat, Thun et al (1999). Provresultaten ligger till grund för karakteristiska hållfasthetsvärden som bestämts enligt BBK94 (1995). Partialkoefficienter för hållfasthetsvärdena har bestämts med vad som i rapporten benämns tabellmetoden och sannolikhetsteoretisk metod. Tabellmetoden är hämtad från NKB (1978) och NKB (1987). Metoden bygger, som namnet indikerar, på tabeller varur fyra delfaktorer till partialkoefficienten bestäms. Faktorerna behandlar (1) osäkerheter i karakteristiska värden och i förhållandet mellan hållfasthet i konstruktion och i provkropp etc.; (2) osäkerheter i beräk-ningsmodeller; (3) brottkaraktär (segt eller sprött) och (4) omfattningen av kontroll vid uppförandet av broarna. Den sannolikhetsteoretiska metoden för att bestämma partialkoefficienter tar i sin tur också hänsyn till osäkerheter i karakteristiska värden, i förhållandet mellan hållfasthet i konstruktion och i provkropp och osäkerheter i beräkningsmodeller. Metoden tar även med partialkoefficienter för laster, vilka här har satts till normenliga värden förutom tåglastens partialkoefficient som satts till 1,1 enligt en utredning av Östlund (1997) i bilaga A och används här endast vid statistiska beräkningar och godtas därför inte av Banverket. Inverkan av tåglast och last av betong och ballast ingår. Även broarnas individuella längder beaktas då tåglasternas dynamiska förstoringsfaktorer bestäms. Resultaten av bestämning av partialkoefficienten med tabellmetoden och den sannolikhetsteoretiska metoden ger för de sju broarna mellan Luleå och Boden något skilda resultat. Tabellmetoden ger generellt högre värden än den sannolikhetsteoretiska metoden. Tabellmetodens värden varierar mellan 1,44 och 1,95 för draghållfastheten och mellan 1,44 och 1,48 för tryckhållfastheten. Värdena från den sannolikhetsteoretiska metoden ligger ca 15% lägre. Vi förordar i första hand, på grund av sin enkelhet, att tabellmetoden används vid bestämning av partialkoefficienten. Den sannolikhetsteoretiska metoden är något mer komplicerad och måste ofta kompletteras med kvalificerade bedömningar. De dimensionerande hållfasthetsvärdena som bestäms i rapporten är betydligt högre än de värden som föreskrivna hållfasthetsklasser ger. Den största inverkan på detta har de provade hållfasthetsvärdena, som ligger väsentligt över de föreskrivna värdena. Partialkoefficienternas inverkan är mindre. Rapporten avslutas med en diskussion om inverkan av hållfasthetens variation inom konstruktionsdelar, vilken kan ha stor inverkan på bärförmågan. Likaså har läget för uttagna provkroppar i förhållande till aktuellt beräkningssnitt betydelse. Båda dessa faktorer bör ingå vid en bestämning av hållfastheters partialkoefficienter i befintliga konstruktioner.

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  • 20.
    Nilsson, Martin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Emborg, Mats
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Fastenings (anchor bolts) in concrete structures: influence of surface reinforcement2012In: Concrete Structures for Sustainable Community: proceedings of the International FIB Symposium 2012, Stockholm, Sweden, 11 - 14 June 2012 / [ed] Dirch H. Bager; Johan Silfwerbrand, Stockholm: Swedish Concrete Association , 2012, p. 419-422Conference paper (Refereed)
    Abstract [en]

    Tests have been carried out to study the influence of surface reinforcement on the load bearing capacity of cast-in headed bars. In 66 tests, rods with a diameter of Φ30 mm and a Φ45 mm nut at the end, were cast-in place centrically in concrete slabs. Width, length and thickness of the slabs varied from 1.2 m × 1.2 m × 0.3 m up to 2.2 m × 2.2 m × 0.6 m. The top reinforcement varied from 0% to about 1.2% (Φ 16 #100). A considerable increase in the load-bearing capacity was noted. The increase depends on the geometry and the amount and placement of the reinforcement. A numerical model to evaluate the influence is proposed.

  • 21.
    Noghabai, Keivan
    et al.
    Luleå University of Technology.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Olofsson, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Bond properties of high-strength concrete1993In: Utilization of High Strength Concrete : Proceedings: Symposium in Lillehammer, Norway / [ed] Ivar Holand, Oslo: Norsk Betongforening , 1993, p. 1169-1176Conference paper (Refereed)
  • 22.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Beställarens kostnadsökningar under byggskedet: analys av 9 st väg- och gatuentrepren1982Report (Other academic)
  • 23.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Fracture mechanics analysis of concrete structures1995Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents results from numerical and analytical analyses of concrete structures as well as results from laboratory tests. Numerical methods based on the finite element method and fracture mechanics are used. The thesis comprises five papers and a general introductory part. The five papers deal with the following topics: Material properties for concrete at low temperatures, Paper A: This paper presents results from an investigation of the fatigue strength and the fracture energy of water saturated unreinforced concrete. The tests were carried out both at room temperature and under cold conditions. The experiments show that the load bearing capacity of water saturated specimens is strongly affected of low temperatures. The water in the pores freezes and generates a load bearing ice skeleton. The compressive and splitting strength of the concrete will as a result increase. Also the fracture energy increases at low temperatures. Both the absolute and the relative fatigue strength increase for water saturated concrete. Bond properties of concrete, Paper B: The paper discusses the influence of splitting failure on the bond properties of deformed reinforcement bars. Laboratory tests with normal and high strength concrete are presented. The tests were designed to obtain a high degree of confinement with the intention to establish the upper limit of the bond strength. The bond strength has been normalized with regard to the concrete splitting strength. The high strength concrete has a higher normalized bond strength than the normal strength concrete for bar diameters of 8 and 16 mm. A theoretical model, based on fracture mechanics, is presented. The model gives relationships between the pressure generated by the mechanical interaction and the length of the splitting cracks. Modelling of concrete shaft in a gravity based offshore structure. Influence of hydraulic pressure on fracture mechanics parameters, Paper C: The paper describes an analysis carried out in order to predict the risk of concrete delamination in the shaft of the Draugen Gravity Based Structure (GBS) platform situated in the northern Atlantic. The analysis formed part of an independent verification of the platform by VERITEC in Norway and was performed using a nonlinear finite element program (DIANA) with a material model based on fracture mechanics. The analysis shows that there was no risk of progressive cracking or delamination in the shaft of the studied gravity based offshore structure. Modelling of mixed mode fracture, Paper E: This paper describes numerical modelling of fracture formation under combined tensile and shear loading. The numerical model used is based on the Inner Softening Band Approach, see Klisinski et al. (1991). The results are compared with test results presented in Hassanzadeh (1992) and Nooru-Mohamed (1992). The model reproduces crack pattern and nominal stress displacement curves. The compressive stresses due to dilation can also be modelled. The stress rotations are generally small. In the final stage of the test, the stress rotation increases in some elements, especially in the smallest elements, so that more cracks should be introduced in each element in order to avoid interlocking effects. Anchor bolts in concrete, Papers D and E: The first paper [D] presents results from anchor bolt tests, comprising both plane and axisymmetric specimens. Different design formulas are discussed. Results from finite element analyses are presented. The second paper [E] presents analyses and tests on a plane anchor bolt specimen. The analyses are based on the Inner Softening Band Approach, see Klisinski et al. (1991). The analysis reproduces deformations at maximum load and crack pattern at an early stage of the test. Peak loads are overestimated. The post peak behaviour is not properly captured due to stress interlocking even before the peak load is reached. The possibility to introduce more then one crack in an element seems to be an essential step for further development of the analysis.

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  • 24.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Fracture mechanics studies of concrete structures1990Licentiate thesis, comprehensive summary (Other academic)
  • 25.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Funktionsentreprenad för drift och underhåll av vägar och gator1993Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Contracts for the operation and maintenance of roads and streets are today characterized by short-term perspectives and a low rate of development. One reason for this is that the client placing an order, within the framework of traditional contract procedures, specifies in detail what shall be done and sometimes even orders a certain type of machinery and equipment. The contractors are not made aware of the longterm quality ambitions of the client with respect to traffic safety and ease of flow. A performance contract means that the client, instead of presenting technical solutions, makes measurable functional demands with regard to the finished product. The demand is for example made that the road surface shall have a certain smoothness and a certain friction The functional requirements are formulated so that they have a direct relevance for the safety and flow of traffic. The functional requirements should be divided into an absolutely lowest permissible level (acute level) and a target level. The target level shall be maintained both as an average functional level during the contract period and when the contract is completed. Functionally directed road maintenance should include measures to reduce traffic disturbances to a minimum. It should also be required of the contractor that he reports planned measures to the relevant road-user information centres. Performance contracts radically change the roles of both the client and the contractor. The client's efforts are concentrated on controlling the quality of the final product from a user point of view, while the contractor takes over many of the traditional roles of the client such as planning, projecting, choice of technical solutions, choice of material and duty activities. Direct contact with road-users and residents will also be included in the tasks of the contractor. The advantages of a performance contract are the functional expectations of the users become the guiding star for the contractor it stimulates the development of creative solutions by the contractor the responsibility boundary between client and contractor becomes "sharp" Trials with performance contracts for operation and maintenance have been carried out in both Sweden and the USA.

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  • 26.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Funktionsentreprenad för drift och underhåll av vägar och gator1992Report (Other academic)
  • 27. Ohlsson, Ulf
    et al.
    Daerga, Per-Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Fracture energy and fatigue strength of unreinforced concrete beams at normal and low temperatures1990In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 35, no 1-3, p. 195-203Article in journal (Refereed)
    Abstract [en]

    Results are presented from tests where the fracture energy and the fatigue strength have been determined for unreinforced concrete beams. The tests were performed at temperatures between +20 and −35°C with concrete with compressive strength varying between 25 and 100 MPa.

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  • 28. Ohlsson, Ulf
    et al.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Anchor bolts analyzed with fracture mechanics1991In: Fracture Processes in Concrete, Rock and Ceramics: Proceedings of the International RILEM/ESIS Conference / [ed] J.G.M. van Mier; J.G. Rots; A. Bakker, London: Taylor and Francis Group , 1991, p. 887-897Conference paper (Refereed)
  • 29.
    Ohlsson, Ulf
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Anchor bolts modelled with fracture mechanics1990In: Proceedings: Nordic Concrete Research Meeting : Trondheim 1990 / [ed] Jens Jacob Jensen, Oslo: Norsk Betongforening , 1990, p. 270-271Conference paper (Refereed)
  • 30.
    Ohlsson, Ulf
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Infästningar i betongkonstruktioner analyserade med brottmekanik1990In: Bygg och Teknik, ISSN 0281-658X, E-ISSN 2002-8350, no 7, p. 57-59Article in journal (Other (popular science, discussion, etc.))
  • 31.
    Ohlsson, Ulf
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Tests of the load-bearing capacity of anchor bolts1993In: Fracture and damage of concrete and rock : FDCR-2: proceedings of the second International Conference on Fracture and Damage of Concrete and Rock, Vienna, Austria, 9-13 November 1992 / [ed] H.P. Rossmanith, London: E & F N Spon (An imprint of Routledge) , 1993, p. 579-587Conference paper (Refereed)
  • 32.
    Ohlsson, Ulf
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ghasemlou, Farough
    Anchor bolt tests: plane and axisymmetric stresses1993Report (Other academic)
  • 33.
    Ohlsson, Ulf
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Nyström, Mikael
    Olofsson, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Waagaard, Knut
    Influence of hydraulic pressure in fracture mechanics modelling of crack propagation in concrete1998In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 31, no 3, p. 203-208Article in journal (Refereed)
    Abstract [en]

    This paper presents a nonlinear fracture mechanics analysis of a part of an offshore concrete structure. The analysis focuses on the risk of cracking between the prestressing ducts in the shaft of the submerged platform. The influences of water and grout pressure in prestressing ducts have been taken into consideration. The analysis has been performed using both discrete and smeared crack analysis.

  • 34. Ohlsson, Ulf
    et al.
    Olofsson, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Anchor bolts in concrete structures: finite element calculations based on inner softening bands1995In: Fracture mechanics of concrete structures: proceedings of the Second International Conference on Fracture Mechanics of Concrete Structures (FRAMCOS 2) held at ETH Zurich, Switzerland, July 25 - 28, 1995 / [ed] Folker H. Wittmann, AEDIFICATIO Publishers , 1995, Vol. 2, p. 1545-1554Conference paper (Refereed)
  • 35.
    Ohlsson, Ulf
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Olofsson, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Mixed-mode fracture and anchor bolts in concrete analysis with inner softening bands1997In: Journal of engineering mechanics, ISSN 0733-9399, E-ISSN 1943-7889, Vol. 123, no 10, p. 1027-1033Article in journal (Refereed)
    Abstract [en]

    The paper presents a nonlinear fracture mechanics analysis of mixed-mode fracture and anchor pullout in concrete. The analysis is based on elements with inner softening bands (ISB). A major advantage of the ISB approach is that discrete cracks can be introduced anywhere and in any direction within the finite-element mesh. Calculated loads, deformations, and crack patterns are compared to experimental results. A good correspondence is achieved.

  • 36.
    Olofsson, Thomas
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Noghabai, Keivan
    Ohlsson, Ulf
    Elfgren, Lennart
    Anchorage and bond properties in concrete1995In: Fracture of brittle, disordered materials: concrete, rock and ceramics : proceedings of the International Union of Theoretical and Applied Mechanics (IUTAM) Symposium on Fracture of Brittle, Disordered Materials: Concrete, Rock and Ceramics / [ed] G. Baker; B.L. Karihaloo, London: Taylor and Francis Group , 1995, p. 525-543Conference paper (Refereed)
  • 37.
    Olofsson, Thomas
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ohlsson, Ulf
    A simple fracture mechanics model for mixed-mode failure in concrete1995In: Fracture mechanics of concrete structures: proceedings of the Second International Conference on Fracture Mechanics of Concrete Structures (FRAMCOS 2) held at ETH Zurich, Switzerland, July 25 - 28, 1995 / [ed] Folker H. Wittmann, AEDIFICATIO Publishers , 1995, Vol. 1, p. 473-482Conference paper (Refereed)
  • 38. Paulsson, Björn
    et al.
    Töyrä, Björn
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ohlsson, Ulf
    Danielsson, Georg
    Increased loads on railway bridges of concrete1997In: Advanced design of concrete structures: [papers presented at the Symposium on Advanced Design of Concrete Structures, held in Chalmers University of Technology in Göteborg, Sweden on June 12 - 14, 1997] / [ed] Kent Gylltoft, Barcelona: International Center for Numerical Methods in Engineering (CIMNE), 1997, p. 201-206Conference paper (Refereed)
  • 39.
    Persson, Martin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Emborg, Mats
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Bridge deck concrete overlays: full scale studies2014In: Nordic Concrete Research, ISSN 0800-6377, Vol. 49, p. 163-180Article in journal (Refereed)
    Abstract [en]

    Concrete overlays on bridge decks are thought to be more durable when comparing with the more common solution with asphalt. Of interest is to evaluate the concrete overlay regarding traffic and shrinkage/temperature induced stresses. In a pilot study nondestructive test systems were evaluated with focus on detecting hidden defects, (e.g. debonding), that may have induced identified surface cracks. Furthermore, calibration of material parameters for a similar composite slab was done using finite element technique and compared with experimental studies in laboratory. Good agreement was found between numerical and experimental results. This will serve as an input for future bridge FE-models.

  • 40.
    Persson, Martin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Emborg, Mats
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Bridge deck concrete overlays: full scale studies and theoretical analysis2014In: Nordic Concrete Research, ISSN 0800-6377, Vol. 50, p. 509-512Article in journal (Refereed)
    Abstract [en]

    Concrete overlays on bridge decks are thought to be more durable when comparing with the more common solution with asphalt. Of interest is to evaluate the concrete overlay regarding traffic and shrinkage/temperature induced stresses. In a pilot study nondestructive test systems were evaluated with focus on detecting hidden defects, (e.g. debonding), that may have induced identified surface cracks. Furthermore, calibration of material parameters for a similar composite slab was done using finite element technique and compared with experimental studies in laboratory. Good agreement was found between numerical and experimental results. This will serve as an input for future bridge FE-models.

  • 41.
    Persson, Martin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Silfwerbrand, Johan
    Department of Civil and Architectural Engineering Department of Structural and Architectual Engineering Division, Royal Institute of Technology.
    Emborg, Mats
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Interface stresses in concrete bridge deck overlays subjected to differentialshrinkage2017In: Proceedings of the 23rd Nordic Concrete Research Symposium, Oslo, Norway: Nordic Concrete Federation , 2017Conference paper (Refereed)
    Abstract [en]

    Concrete overlays on bridge decks are expected to be more durable as compared with the more common asphalt solution. Besides stresses due to traffic load and temperature variations at service, the overlays are exposed to stresses due to long term shrinkage. Of interest is to evaluate the concrete overlay due to the shrinkage induced stresses at the composite interface. Three strategies have been employed to gain knowledge on the stresses; 1) use of non-destructive test systems via field observations, 2) a numerical study on a concrete composite slab tested in laboratory, 3) recordings of realistic shrinkage and climate data on a reference bridge using vibrating strain gauges and humidity probes in the newly cast concrete overlay. The data were used as input data for a linear elastic finite element model. This article demonstrates this last phase of the work.

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  • 42.
    Popescu, Cosmin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Mirzazade, Ali
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Häggström, Jens
    Trafikverket.
    Bridge inspections using unmanned aerial vehicles – A case study in Sweden2021Report (Other academic)
    Abstract [en]

    The aim of the current project is to digitalize inspections and monitoring of structures’ health using drones in order to identify and allow for easier inspection of damages in transport infrastructure. The objectives set are to perform aerial photogrammetry to recreate the as-is condition to enable off-site inspection of difficult to reach areas in structures and identify damages – e.g. cracks, spalling, corrosion. The drone is controlled either autonomously or with the use of a remote control by a pilot from the ground. The drone can carry a wide range of imaging technologies including still, video and infrared sensors. The high flexibility and accessibility of drones in hard-to-reach or risk exposed areas makes the airborne photogrammetry a better alternative to the ground-based method. Given the potential of UAVs to help bridge inspectors performing inspections off-site, the Swedish Transport Administration developed a demonstration project to evaluate the effectiveness and future opportunities within inspection field. Five bridges of varying sizes and types were selected as demonstrators. Data collection including the 3D model creation has been performed by three different contractors while the model-based inspection for all bridges was performed by the same team. It has been shown that the 3D models could serve as a tool for bridge inspectors from which measurements could be extracted and certain damages identified. A full off-site inspection is currently not feasible as some areas of the bridges were difficult to capture. The models are only providing near-surface information, and therefore, in-depth inspection should not be overlooked. The difficulty to capture local defects such as delaminations and narrow cracks also reduces versatility. The main conclusion from the study is that drones cannot be used independently to conduct inspections. Currently, they can only be used as a complement to traditional inspections. The added value of a 3D model derives from the possibility of using it as tool to better plan large inspections in the field and/or future maintenance work.

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  • 43.
    Puurula, Arto
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Enochsson, Ola
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sas, Gabriel
    NORUT, Narvik, NO 8517, Norway.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Bernspång, Lars
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Carolin, Anders
    Trafikverket, SE 97 125 Luleå, Sweden.
    Paulsson, Björn
    Trafikverket, SE 78 189 Borlänge, Sweden.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Assessment of the Strengthening of an RC Railway Bridge with CFRP utilizing a Full-Scale Failure Test and Finite-Element Analysis2015In: Journal of Structural Engineering, ISSN 0733-9445, E-ISSN 1943-541X, Vol. 141, no 1, article id D4014008Article in journal (Refereed)
    Abstract [en]

    A finite element (FE) model was calibrated using the data obtained from a full-scale test to failure of a 50 year old reinforced concrete (RC) railway bridge. The model was then used to assess the effectiveness of various strengthening schemes to increase the loadcarrying capacity of the bridge. The bridge was a two-span continuous single-track trough bridge with a total length of 30 m, situated in Örnsköldsvik in northern Sweden. It was tested in situ as the bridge had been closed following the construction of a new section of the Railway line. The test was planned to evaluate and calibrate models to predict the load-carrying capacity of the bridge and assess the strengthening schemes originally developed by the European research project called Sustainable bridges. The objective of the test was to investigate shear failure, rather than bending failure for which good calibrated models are already available. To that end, the bridge was strengthened in flexure before the test using near-surface mounted square section carbon fiber reinforced polymer (CFRP) bars. The ultimate failure mechanism turned into an interesting combination of bending, shear, torsion, and bond failures at an applied load of 11.7 MN (2,630 kips). A computer model was developed using specialized software to represent the response of the bridge during the test. It was calibrated using data from the test and was then used to calculate the actual capacity of the bridge in terms of train loading using the current Swedish load model which specifies a 330 kN (74 kips) axle weight. These calculations show that the unstrengthened bridge could sustain a load 4.7 times greater than the current load requirements (which is over six times the original design loading), whilst the strengthened bridge could sustain a load 6.5 times greater than currently required. Comparisons are also made with calculations using codes from Canada, Europe, and the United States.

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  • 44.
    Puurula, Arto
    et al.
    Savonia University of Applied Sciences, Kuopia, Finland.
    Enochsson, Ola
    Bodens kommun, Sverige.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Bernspång, Lars
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    3D non-linear FE analysis of a full scale test to failure of a RC Railway Bridge strengthened with carbon fibre bars2016In: IABSE CONGRESS, STOCKHOLM, 2016: Challenges in Design and Construction of an Innovativeand Sustainable Built Environment / [ed] Lennart Elfgren, Johan Jonsson, Mats Karlsson, Lahja Rydberg-Forssbeck and Britt Sigfrid, CH - 8093 Zürich, Switzerland: International Association for Bridge and Structural Engineering, 2016, p. 2527-2535Conference paper (Refereed)
    Abstract [en]

    At a full scale loading test to failure a 50 year old concrete railway trough bridge in Örnsköldsvik, in northern Sweden was tested to failure. The test was a part of the European Research Project “Sustainable Bridges” regarding assessment and strengthening of existing bridges. In the projectnew calculation methods were developed to capture the behaviour of the bridge during increasing load. The bridge was strengthened in bending with rods of Carbon Fiber Reinforced Polymer (CFRP) before the loading test. Failure was reached for an applied load of 11.7 MN by pulling a steel beam placed in the middle of one of the two spans downwards. The achieved failure was a combination of bond, shear, torsion and bending. The developed model, a 3D -non-linear finiteelement (FE) model with discrete reinforcement, gave accurate accounts of the response of thebridge. The FE calculations show the effect of the strengthening with CFRP and even the effect of the epoxy when using the Near Surface Mounted Reinforcement (NSMR) strengthening method.

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    fulltext
  • 45.
    Puurula, Arto M.
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering. Structural Engineering, Savonia University of Applied Sciences, P.O. Box 88 (Opistotie 2), FI-70101 Kuopio, Finland.
    Enochsson, Ola
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sas, Gabriel
    Department of Infrastructure Structures and Materials, NORUT Narvik, Lodve Langes gt. 2, P.O. Box 250, N-8504 Narvik, Norway.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Bernspång, Lars
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Loading to failure and 3D nonlinear FE modelling of a strengthened RC bridge2014In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 10, no 12, p. 1606-1619Article in journal (Refereed)
    Abstract [en]

    A reinforced concrete railway trough bridge in Örnsköldsvik, Sweden, was strengthened in bending with rods of carbon-fibre-reinforced polymer and loaded to failure. The aim was to test and calibrate methods developed in the European Research Project ‘Sustainable Bridges’ regarding assessment and strengthening of existing bridges. A steel beam was placed in the middle of one of the two spans and was pulled downwards. Failure was reached at an applied load of 11.7 MN. It was initiated by a bond failure caused by a combined action of shear, torsion as well as bending after yielding in the longitudinal steel reinforcement and the stirrups. The bond failure led to a redistribution of the internal forces from the tensile reinforcement to the stirrups, causing the final failure. The computer models developed to simulate the loading process were improved step by step from linear shell models to more detailed models. The most developed model, a three-dimensional nonlinear finite element model with discrete reinforcement, gave accurate accounts of the response of the bridge.

  • 46.
    Qin, Xiao-Chuan
    et al.
    School of Civil Engineering, Southeast University.
    Meng, Shao-Ping
    School of Civil Engineering, Southeast University.
    Cao, Da-Fu
    School of Civil Science and Engineering, Yangzhou University.
    Tu, Yong-Ming
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Sabourova, Natalia
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Grip, Niklas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Sas, Gabriel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Evaluation of freeze-thaw damage on concrete material and prestressed concrete specimens2016In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 125, p. 892-904Article in journal (Refereed)
    Abstract [en]

    The pore structure of the hardened concrete and the microscopic changes of a few selected pores throughout the freeze-thaw test were investigated by a method combining RapidAir and digital metalloscope. Traditional tests were also performed to evaluate the macroscopic change caused by freeze-thaw cycles (FTCs). The investigation shows that the concrete material, of which the spacing factor is 0.405 mm and the air content is 2.38%, can still withstand more than 300 FTCs. Severe microscopic damages occurred after approximately 200 FTCs and the freeze-thaw damage were gradually aggravated afterwards. Prestress forces have a remarkable impact on the failure pattern under FTCs. It was further found that the compressive strength as an indicator is more reliable than the relative dynamic modulus of elasticity in evaluating the freeze-thaw damage on concrete material. In addition, the test and analysis show that the measured prestress losses of bonded specimen are larger than that of unbounded specimen under the attack of FTCs due to the duct grouting effect. The ultimate freeze-thaw prestress loss is about 5% of σconσcon for both the bonded and unbonded specimens because the grouting cement paste will eventually be completely destroyed.

  • 47.
    Sabourova, Natalia
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Duvnjak, I.
    University of Zagreb, Zagreb, Croatia..
    Grip, Niklas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Damjanovic, D.
    University of Zagreb, Zagreb, Croatia..
    Tu, Yongming
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. School of Civil Engineering, Southeast University, Nanjing, China.
    Popescu, Cosmin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Detection of sparse damages in plates2020In: IABSE Symposium, Wroclaw 2020: Synergy of Culture and Civil Engineering – History and Challenges / [ed] Jan Bień, Jan Biliszczuk, Paweł Hawryszków, Maciej Hildebrand, Marta Knawa-Hawryszków, Krzysztof Sadowski, Zürich: International Association For Bridge And Structural Engineering (IABSE) , 2020, p. 1141-1148Conference paper (Refereed)
    Abstract [en]

    Structural damage is often a spatially sparse phenomenon, i.e. it occurs only in a small part of the structure. This property of damage has not been utilized in the field of structural damage identification until quite recently, when the sparsity-based regularization developed in compressed sensing problems found its application in this field. In this paper we consider classical sensitivity-based finite element model updating combined with a regularization technique appropriate for the expected type of sparse damage. The validity of the proposed methods is demonstrated using simulations on a bridge. The pros and cons of these methods are discussed.

    Download full text (pdf)
    Sabourova
  • 48.
    Sabourova, Natalia
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Grip, Niklas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Tu, Yongming
    School of Civil Engineering, Southeast University, Nanjing, China.
    Duvnjak, Ivan
    University of Zagreb, Croatia.
    Damjanović, Domagoj
    University of Zagreb, Croatia.
    Detection of Sparse Damages in Structures2019In: IABSE Symposium 2019: Towards a Resilent Built Environment - Risk and Asset Management, International Association for Bridge and Structural Engineering (IABSE) , 2019, p. 515-522Conference paper (Refereed)
    Abstract [en]

    Structural damage is often a spatially sparse phenomenon, i.e. it occurs only in a small part of the structure. This property of damage has not been utilized in the field of structural damage identification until quite recently, when the sparsity-based regularization developed in the compressed sensing found its application in this field.

    In this paper we consider classical sensitivity-based finite element model updating combined with a regularization technique appropriate for the expected type of sparse damage. Traditionally (1) 𝑙2-norm regularization was used to solve the ill-posed inverse problems, such as damage identification. However, using (2) already well established 𝑙1-norm regularization or (3) our proposed 𝑙1-norm total variation regularization and (4) general dictionary-based regularization allows us to find damages with special spatial properties quite precisely using much fewer measurement locations than the number of possibly damaged elements of the structure. The validity of the proposed methods is demonstrated using simulations on a Kirchhoff plate model. The pros and cons of these methods are discussed.

    Download full text (pdf)
    Preprint
  • 49.
    Sabourova, Natalia
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Grip, Niklas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Puurula, Arto
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Enochsson, Ola
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Tu, Yongming
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Nilsson, Martin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Carolin, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Thun, Håkan
    The railway concrete arch bridge over Kalix river: dynamic properties and load carrying capacity2012In: Concrete Structures for Sustainable Community: proceedings of the International FIB Symposium 2012, Stockholm, Sweden, 11 - 14 June 2012 / [ed] Dirch H Bager; Johan Silfwerbrand, Stockholm: Swedish Concrete Association , 2012, p. 609-612Conference paper (Refereed)
    Download full text (pdf)
    FULLTEXT01
  • 50.
    Sabourova, Natalia
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Grip, Niklas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Tu, Yongming
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Southeast University, Nanjing, China.
    Wang, Chao
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Southeast University, Nanjing, China.
    Enochsson, Ola
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Boden Kommun.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Nilsson, Martin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Railway Concrete Arch Bridge over Kalix River at Långforsen: Dynamic Properties and Load-Carrying Capacity2019Report (Refereed)
    Abstract [en]

    The concrete arch bridge over Kalix River at Långforsen was built in 1960 and has a mid-span of 89,5 m and a height of 13,7 m. The bridge owner, Trafikverket, wanted to increase its allowable axle load from 225 to 300 kN. Field tests were carried out under service condition and with ambient vibrations. The test results were used to update and validate Finite Element Models. At last, the refined models were used to check the possibility to increase the axle load.

    According to earlier assessments, most parts of the bridge is capable of carrying an axle load of 330 kN. The only critical sections are located in the beams carrying the rail on top of the arch in the section where the beams are united with the arch. Here the stresses in the longitudinal bottom reinforcement are slightly too high.

    These sections have been studied in a FEM model for different loads and results show maximum strains of about 50·10-6 corresponding to stresses of only about 10 MPa in the reinforcement in the critical sections. Live load vertical deflections of the crown of the arch is of the order of only ± 6 mm. Dynamic studies have also been made showing that fatigue is no issue. Altogether the studies show that the bridge is able to carry an increased axle load of 300 kN without problems.

    Download full text (pdf)
    fulltext
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    App A Drawings
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    App B Design calculations
    Download full text (pdf)
    App C Photos construction
    Download full text (pdf)
    App D Assessment 2002-04
    Download full text (pdf)
    App E Measurements
    Download full text (pdf)
    App F FEM
12 1 - 50 of 58
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