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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)
  • 2.
    Coric, Ibrahim
    et al.
    Trafikverket.
    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 2018 – Engineering the Past, to Meet the Needs of the FutureJune 25-27 2018, Copenhagen, Denmark: IABSE Reports, Vol 111, 2018, Vol. 111Conference 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.

  • 3.
    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)
  • 4.
    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, 2019Conference 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.

  • 5.
    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)
  • 6.
    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)
  • 7.
    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)
  • 8.
    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

  • 9.
    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 & Teknik, ISSN 0281-658X, p. 48-Article in journal (Other (popular science, discussion, etc.))
  • 10.
    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

  • 11.
    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 PrestressedConcrete 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.

  • 12.
    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
    Paulsson, Björn
    UIC, Trafikverket.
    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.

  • 13.
    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.

  • 14. 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.

  • 15.
    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.

  • 16.
    Noghabai, Keivan
    et al.
    Luleå tekniska universitet.
    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)
  • 17.
    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)
  • 18.
    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.

  • 19.
    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)
  • 20.
    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.

  • 21.
    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)
  • 22. 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.

  • 23. 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)
  • 24.
    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)
  • 25.
    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 & Teknik, ISSN 0281-658X, no 7, p. 57-59Article in journal (Other (popular science, discussion, etc.))
  • 26.
    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)
  • 27.
    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)
  • 28.
    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.

  • 29. 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)
  • 30.
    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.

  • 31.
    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)
  • 32.
    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)
  • 33. 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)
  • 34.
    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.

  • 35.
    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.

  • 36.
    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.

  • 37.
    Puurula, Arto
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering. Savonia University of Applied Scinces, Kuopia, Finland.
    Enochsson, Ola
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering. Bodens kommun.
    Sas, Gabriel
    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.
    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
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering. Trafikverket.
    Paulsson, Björn
    Trafikverket.
    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 (Special Issue), p. D4014008-1-D4014008-11, 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.

  • 38.
    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.

  • 39.
    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
    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.
    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 bridge.2014In: 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.

  • 40.
    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.

  • 41.
    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, 2019Conference 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.

  • 42.
    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)
  • 43. Thun, Håkan
    et al.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ohlsson, Ulf
    Utmattningskapacitet: en studie av deformationer under cyklisk dragbelasning2001In: Bygg & Teknik, ISSN 0281-658X, no 7, p. 56-58Article in journal (Other (popular science, discussion, etc.))
  • 44. Thun, Håkan
    et al.
    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.
    A deformation criterion for fatigue of concrete in tension2011In: Structural Concrete, ISSN 1464-4177, E-ISSN 1751-7648, Vol. 12, no 3, p. 187-197Article in journal (Refereed)
    Abstract [en]

    A deformation criterion is proposed for the fatigue failure of concrete in tension. According to the criterion, a fatigue failure is imminent when the total deformation approaches the deformation at maximum stress in a corresponding static test. This criterion was originally proposed for bond slip by Balázs in 1991. It is tested on two series of new and old concrete cylinders loaded in cyclic tension. How the criterion may be used to predict the number of load cycles to failure for existing structures under cyclic tensile loading is also shown

  • 45. Thun, Håkan
    et al.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Betonghållfasthet i järnvägsbroar på Malmbanan: karakteristisk tryck- och draghållfasthet för 20 broar mellan Luleå och Gällivare1999Report (Other academic)
    Abstract [sv]

    Denna rapport redovisar provningsresultat från en utökad provning med hjälp av Capo-test och studsmätningar (Schmidthammare) för en bro över Lautajokki som tidigare har utmattningsprovats i LTUs testlaboratorium. Förutom resultaten från denna provning redovisas även provningsresultat som erhållits med hjälp av enaxiella dragförsök och provning av tryckhållfasthet i cylindrar, för broar (vägportar) på Malmbanan längs bansträckningen Luleå-Gällivare. Med hjälp av provningsresultaten har tryck- och draghållfasthetsklass samt karaktäristisk tryck- och draghållfasthet bestämts för aktuella broar. Studien visar att tryckhållfastheten i de studerade äldre konstruktionerna har ökat kraftigt jämfört med fordrad hållfasthet (aktuella objekt K40-45) men att de varierar från bro till bro. Resultaten visar att draghållfastheten varierar kraftigt mellan broarna (eg. deras sidobalkar) och att det inte på basis av enbart dessa försök går att säkerställa att draghållfastheten ökat i samma takt som tryckhållfastheten. Resultaten från de olika testmetoderna som använts på Lautajokki-bron antyder att det är olika hållfasthet i sidobalk respektive platta. Av denna orsak har en reduktion av hållfastheten föreslagits om provning skett i sidobalkarna och det är plattan som ska analyseras. I rapporten redovisas även metoder att ur provningsresultaten bestämma karaktäristisk hållfasthet.

  • 46. Thun, Håkan
    et al.
    Ohlsson, Ulf
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Concrete strength in old Swedish concrete bridges2006In: Nordic Concrete Research, ISSN 0800-6377, Vol. 35, no 1-2, p. 47-60Article in journal (Refereed)
    Abstract [en]

    In this paper the development and variation of compressive and tensile strength of concrete are presented for old reinforced concrete bridges in Sweden. The mean increase in concrete compressive strength was about 70% for twenty bridges built during 1931-1962 (a rather high dispersion must be taken into consideration). The increase is related to the original 28-day concrete compressive strength which varied between 18 and 51 MPa. The compressive strength within a typical reinforced railway concrete trough bridge was approximately 15% higher in the longitudinal beams than in the bottom slab (measured on drilled cores). The tensile strength showed a similar variation as the compressive strength, but the difference could not be statistically verified. Different equations to convert compressive strength into tensile strength have also been studied. The investigation shows that it is important which conversion equation that is used in an assessment situation.

  • 47. Thun, Håkan
    et al.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Determination of concrete compressive strength with pullout tests2009In: Structural Concrete, ISSN 1464-4177, E-ISSN 1751-7648, Vol. 10, no 4, p. 173-180Article in journal (Refereed)
    Abstract [en]

    A pullout test using post-installed inserts has been examined as an alternative to drilled cores to determine the in-place concrete compressive strength. Tests have been carried out on eight railway bridges from 1965 to 1980 and on a one year old concrete slab. An empirical strength relationship is proposed between the compressive strength of a drilled core with the diameter and height of 100 mm and the pullout force from the pullout test. It is a power function and the relationship is valid for concrete compressive strengths up to 105 MPa; it gives higher concrete strengths than earlier proposed functions.

  • 48. Thun, Håkan
    et al.
    Ohlsson, Ulf
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Fatigue Capacity of Small Railway Concrete Bridges: Prevision of the Results of Swedish Full-scale Tests. Comparison and Analyses2000Report (Other academic)
    Abstract [en]

    In this report results and analyses are presented from a full-scale fatigue test on a typical Swedish railway concrete bridge. The tests were performed at Luleå University of Technology in 1996. The purpose of the test was to study static and fatigue behaviour of the bridge under increased load in order to check its remaining life length. The bridge was originally situated in Lautajokk about 200 km northwest of Luleå along the iron ore line between Luleå and Narvik in Norway. The bridge had a length of 6,1 m and a width of 4,1 m and had the shape of a trough. It was built in 1967 and had been in service for 20 years. In the tests, the bridge was exposed to 6 million load cycles between 50 and 360 kN. No failure occurred even though the Swedish Concrete code BBK 94 indicated that. Especially the connection between the slab and the longitudinal beams was in a critical state according to the code.A study regarding the fatigue shear capacity with the Swedish code and the present Eurocode EC2 (1991) has shown that the codes are conservative and that further studies are needed in this area.Methods are proposed that can be used to estimate the remaining life length (Strain/deflection criterion and Wöhler curves). An analysis using a fracture mechanics approach is presented as well as studies regarding concrete strength development for Swedish Railway concrete bridges.Measurements of deflections and strains have also been carried out on four railway bridges during passing of trains

  • 49. Thun, Håkan
    et al.
    Ohlsson, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Tensile fatigue capacity of concrete2007In: Nordic Concrete Research, ISSN 0800-6377, Vol. 36, no 1-2, p. 48-64Article in journal (Refereed)
    Abstract [en]

    Results and analyses are presented from cyclic uniaxial tensile tests on plain cylindrical concrete cores. The influence of the load amplitude and the mean load level were studied with so called factorial design. It was found that both factors were important but that neither of them could be established to be more important than the other. Further, the deformation rate was studied. It appears that a certain fatigue limit exists below which a clearly greater number of load cycles is required for failure. From this research the exact limit cannot be predicted, but for tests with a mean load level of 40% of fpeak and an amplitude of 40% of fpeak, a very low deformation rate has been obtained. Finally, the test results have been compared with other Wöhler curves proposed for cyclic load in tension.

  • 50.
    Wang, Chao
    et al.
    Southeast University, Nanjing.
    Wang, Zhilan
    Southeast University, Nanjing.
    Zhang, Jiwen
    Southeast University, Nanjing.
    Tu, Yong-Ming
    Southeast University, Nanjing.
    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.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    FEM based research on the dynamic response of a concrete railway arch bridge2016In: IABSE CONGRESS, STOCKHOLM, 2016: Challenges in Design and Construction of an Innovative and Sustainable Built Environment / [ed] Elfgren, Lennart; Jonsson, Johan; Karlsson, Mats; Rydberg-Forssbeck, Lahja; Sigfid, Britt2016, CH - 8093 Zürich, Switzerland, 2016, p. 2472-2479Conference paper (Refereed)
    Abstract [en]

    The dynamic response of a concrete railway arch bridge is studied through a case study of the bridge over Kalix River, situated at Långforsen on the railway line between Kalix and Morjärv in northern Sweden. A simplified beam-element model, a spatial grillage-beam model and a refined shell-element model were built to analyze the bridge structure. A methodology was applied where measured static and dynamic responses were used to update finite element models of Långforsen Bridge. A multi-response objective function was presented, and the finite element method was proved feasible by comparison of predicted and measured response. In the paper comparative analyses were made of the time history displacement of three finite element models under three measured load cases. A standard train model from EUROCODE, HSLM-A 1, was applied and the dynamic responses under different speeds were studied. The results showed that a refined shell element model could accurately analyze dynamic responses of the concrete railway arch bridge in a better way than beam element and spatial grillage models. The dynamic analysis based on this type of shell model can give an optimized suggestion for the railway operation as well as for the design of high-speed railway bridges.

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