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  • 51.
    Elfgren, Lennart
    et al.
    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.
    Strengthening of conrete structures by externally bonded reinforcement steel plates1990In: Proceedings: Nordic Concrete Research Meeting : Trondheim 1990 / [ed] Jens Jacob Jensen, Oslo: Norsk Betongforening , 1990, p. 200-201Conference paper (Refereed)
  • 52.
    Elfgren, Lennart
    et al.
    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.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Load Testing as Part of Bridge Management in Sweden.: Chapter 112019In: Load Testing of Bridges: Proof load Testing and the Future of Load Testing, Volume Editor Eva O. L. Landsoght: Series: Structures and Infrastructures, Vol. 13, Series Editor Dan M. Frangopol, / [ed] Eva O.L. Landsoght (Vol 13), Dan M. Frangopol (Series Editor), London/Leiden: Taylor and Francis Group , 2019, 1, p. 333-346Chapter in book (Refereed)
    Abstract [en]

    Load testing of new and existing bridges was performed regularly in Sweden up to the 1960ies. It was then abandoned due to high costs versus little extra information obtained. Most bridges behaved well in the serviceability limit range and no knowledge of the ultimate limit stage could be obtained without destroying the bridge. At the same time the methods for calculating the capacity developed and new numerical methods were introduced. Detailed rules were given on how these methods should be used. Some decommissioned bridges were tested to their maximum capacity to be able to study their failure mechanisms and to calibrate the numerical methods. In this paper some examples are given on how allowable loads have increased over the years and of tests being performed. Nowadays, load testing may be on its way back, especially to test existing rural prestressed concrete bridges, where no design calculations have been retained

  • 53.
    Elfgren, Lennart
    et al.
    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.
    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.
    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, Luleå, Sweden.
    Tu, Yongming
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Puurula, Arto
    Savonia University of Applied Sciences, Kuopio.
    Häggström, Jens
    Trafikverket, Luleå, Sweden.
    Paulsson, Björn
    Charmec, Chalmers University of Technology.
    Load-testing used for qulity control of bridges2018In: Quality Specifications for Roadway Bridges: Workshop of COST TU 1406 / [ed] José Matos, 2018, p. 1-6Conference paper (Refereed)
    Abstract [en]

    Load testing is a way to control the capacity and function of a bridge. Methods and recommendations for load testing are described and examples are given form tests carried out. In order not to damage the bridge being tested, the load must be limited, often to be within the serviceability limit state (SLS). Numerical models can be calibrated by load tests and then be used to check the carrying capacity for higher loads than what has been tested. Need for further work and recommendations are discussed. By effective planning costs can be saved and a more sustainable use of bridges can be obtained.

  • 54. Elfgren, Lennart
    et al.
    Täljsten, Björn
    Carolin, Anders
    Eriksen, Jörgen
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Guidelines for strengthening of railway bridges2009In: Proceedings of Workshop: COST Action C25 : Sustainability of Constructions - Integrated Approach to Life-time Structural Engineering / [ed] Luís Bragança, 2009, p. 141-145Conference paper (Refereed)
    Abstract [en]

    In the international project "Sustainable Bridges", one of the deliverables is a design guide for strengthening of bridges. This paper gives the reader a first look into this guidelinewhich can be found at the projects website: www.sustainablebridges.net

  • 55. Enochsson, Ola
    et al.
    Elfgren, Lennart
    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.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Töyrä, Björn
    Banverket, Luleå.
    Kronborg, Anders
    Banverket, Luleå.
    Paulsson, Björn
    Banverket, Luleå.
    Assessment and condition monitoring of a concrete railway bridge in Kiruna, Sweden2006In: Bridge maintenance, safety, management, life-cycle performance and cost: Proceedings of the third International Conference on Bridge Maintenance, Safety and Management. IABMAS'06 / [ed] Paulo J. da Sousa Cruz; Dan M Frangopol; Luis C Canhoto Neves, London: Taylor and Francis Group , 2006Conference paper (Refereed)
    Abstract [en]

    A two-span railway concrete trough bridge over Luossajokk in Kiruna in northern Sweden has been studied. The owner wanted to increase the axle loads from 250 to 300 kN in order to reduce freight costs for iron ore. Examples are given of methods used and results obtained from the assessment where bending, shear and fatigue were studied. Material properties, loads and load carrying capacity were evaluated using deterministic and probabilistic methods. It was shown that the bridge could carry the higher loads with a safety index β > 4.7 for reasonable assumptions of the load distributions. A measurement system was installed to check the actual level of critical strains and the worst positions of the train. Results are also given from a condition monitoring program 2001-2006, launched to periodically check the development of strains with time

  • 56.
    Enochsson, Ola
    et al.
    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.
    Täljsten, Björn
    Paulsson, B.
    Sustainable railway bridges with higher axle loads: monitoring examples from northern Sweden2009In: International Journal of COMADEM, ISSN 1363-7681, Vol. 12, no 2, p. 39-45Article in journal (Refereed)
    Abstract [en]

    Monitoring of several railway bridges has been carried out in northern Sweden in order to increase the allowable axle load. The work is part of a European Integrated Project "Sustainable Bridges - Assessment for Future Traffic Demands and Longer Lives", 2003 - 2008. This paper describes the project and gives some examples of applications.

  • 57.
    Enochsson, Ola
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Lundqvist, Joakim
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Rusinowski, Piotr
    Technical University of Denmark.
    Olofsson, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    CFRP strengthened openings in two-way concrete slabs: an experimental and numerical study2007In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 21, no 4, p. 810-826Article in journal (Refereed)
    Abstract [en]

    Rehabilitation and strengthening of concrete structures with externally bonded fibre reinforced polymers (FRPs) has been a viable technique for at least a decade. An interesting and useful application is strengthening of slabs or walls where openings are introduced. In these situations, FRP sheets are very suitable; not only because of their strength, but also due to that they are easy to apply in comparison to traditional steel girders or other lintel systems. Even though many benefits have been shown by strengthening openings with FRPs not much research have been presented in the literature. In this paper, laboratory tests on 11 slabs with openings, loaded with a distributed load are presented together with analytical and numerical evaluations. Six slabs with openings have been strengthened with carbon fibre reinforced polymers (CFRPs) sheets. These slabs are compared with traditionally steel reinforced slabs, both with (four slabs) and without openings (one slab). The slabs are quadratic with a side length of 2.6 m and a thickness of 100 mm. Two different sizes of openings are used, 0.85 × 0.85 m and 1.2 × 1.2 m. The results from the tests show that slabs with openings can be strengthened with externally bonded CFRP sheets. The performance is even better than for traditionally steel reinforced slabs. The numerical and analytical evaluations show good agreement with the experimental results.

  • 58. Enochsson, Ola
    et al.
    Olofsson, Thomas
    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.
    CFRP Strengthened openings in two-way concrete slabs2005In: FRP composites in civil engineering - CICE 2004: Proceedings of the Second International Conference on FRP Composites in Civil Engineering / [ed] Rudolf Seracino, Leiden: Balkema Publishers, A.A. / Taylor & Francis The Netherlands , 2005Conference paper (Refereed)
  • 59. Enochsson, Ola
    et al.
    Puurula, Arto
    Stenlund, Anders
    Thun, Håkan
    Nilsson, Martin
    Täljsten, Björn
    Olofsson, Thomas
    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.
    Condition assessment of concrete bridges in Sweden2005In: Concrete repair, rehabilitation and retrofitting / [ed] Mark G. Alexander; Hans-Dieter Beushausen; Frank Dehn; Pilate Moyo, London: Taylor and Francis Group , 2005, p. 257-259Conference paper (Refereed)
    Abstract [en]

    Examples are given of methods used and results obtained from two bridges assessed in Sweden. The following sectional forces were critical: (a) Bending, shear and fatigue in a two-span railway trough bridge and (b) Shear and torsion in a three-span prestressed cantilever box girder road bridge. In the assessments we evaluated material properties, loads and load carrying capacity using deterministic and probabilistic methods

  • 60. Enochsson, Ola
    et al.
    Puurula, Arto
    Thun, Håkan
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Täljsten, Björn
    Olofsson, Jan
    Skanska Teknik, Göteborg.
    Paulsson, Björn
    Banverket.
    Test of a concrete bridge in Sweden: III. Ultimate capacity2008In: Bridge Maintenance, Safety Management, Health Monitoring and Informatics: Proceedings of the Fourth International Conference on Bridge Maintenance, Safety and Management, July 13-17 2008, Seoul, Korea - IABMAS '08 / [ed] Hyun-Moo Koh; Dan G Frangopol, Boca Raton, Fla: Taylor and Francis Group , 2008, p. 3601-3608Conference paper (Refereed)
  • 61.
    Enochsson, Ola
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Täljsten, Björn
    Kolfiberförstärkning av betongplattor - med och utan öppningar2006In: Bygg & Teknik, ISSN 0281-658X, no 7, p. 12-Article in journal (Other (popular science, discussion, etc.))
    Abstract [sv]

    Förstärkning med kolfiberkompositer har visat sig var ett effektivt förstärkningsalternativ vid så kalladet ROT-projekt, det vill säga vid reparation, ombyggnad och tillbyggnad av anläggningar och byggnader. Ett användningsområde där behovet ökat markant är förstärkning av plattor och väggar vid ombyggnader, och särskilt då nya öppningar tas upp. Exempel på sådana öppningar kan vara hiss- och ventilationsschakt, trappöppningar samt fönster- och dörröppningar. Anledningen till att behovet inom detta område expanderar är en ökad vilja av fastighetsägarna och byggsektorn att effektivisera och spara på samhällets resurser.

  • 62. Enochsson, Ola
    et al.
    Täljsten, Björn
    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.
    Structural health monitoring of a concrete bridge in Sweden2006In: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, Vol. 6176, no 18Article in journal (Refereed)
    Abstract [en]

    Over the past decade the interests in upgrading, assessment and maintenance of our ageing infrastructure has grown avalanche-like. The main reason is economical aspects but also reasons due to accessibility environmental consideration play a vital role. Recently the Swedish and Norwegian Railway Association decided to upgrade the Iron Ore Line "Malmbanan", a railway line for transportation of iron from northern Sweden to the coasts of Norway and Sweden. Here the owner wanted to increase the axle loads from 25 to 30 tons to reduce the transportation costs. In one of the cases, the Luossajokk Bridge, a recalculation according to design codes showed that the increased axle loads would exceed the yield limit in the reinforcement. Before any decision was taken regarding strengthening or replacing the bridge an assessment with probabilistic methods was used. It appeared that the bridge could carry the higher load with a safety index β ≥ 4.7 for reasonable assumptions of the load distributions. A measurement system was installed to check the real worst placement of the new iron ore locomotive (IORE), and the actually level of strains in the reinforcement for the worst load case1. It was shown that the strain level was far from critical and that the evaluated worst placement of the locomotive was almost correct2. To assure a reliable transportation a long term monitoring program was arranged to check the development of strains with time. Examples from the probabilistic evaluation and the monitoring of the bridge are given and discussed.

  • 63.
    Guadagnini, M.
    et al.
    University of Sheffield.
    Serbescu, A.
    University of Sheffield.
    Ceroni, F.
    University of Sannio.
    Palmieri, A.
    Ghent University.
    Matthvs, S.
    Ghent University.
    Czaderski, C.
    Laboratory EMPA, Dubendorf.
    Olia, S.
    Laboratory EMPA, Dubendorf.
    Bilotta, A.
    University of Naples.
    Niaro, E.
    University of Naples.
    Szabo, Z.
    University of Budapest.
    Balazs, G.
    University of Budapest.
    Mazzotti, C.
    University of Bologna.
    Barros, J.
    University of Minho.
    Costa, I.
    University of Minho.
    Sas, Gabriel
    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.
    Tamuzs, V.
    University of Latvia.
    Bond of FRP strengthening systems for concrete structures: A Round Robin Test2012In: Proceedings of the Sixth International Conference on Bridge Maintenance, Safety and Management / [ed] Fabio Biondini; Dan M. Frangopol, Boca Raton: CRC Press, 2012, p. 1179-1186Conference paper (Refereed)
    Abstract [en]

    Although various test methods to examine the local bond behaviour of FRP strengthening systems to concrete have been proposed thus far, their implementation can lead to a wide range of results and a standard methodology has yet to be generally accepted. With these issues in mind, a Round Robin Testing (RRT) programme was carried out to assess the performance and reliability of small scale testing on various FRP strengthening systems, including both externally bonded laminates and near surface mounted reinforcement. Ten laboratories and eight manufacturers and suppliers participated in this extensive international exercise, which was initiated within the framework of the European funded Marie Curie Research Training Network, EN-CORE, with the support of Task Group 9.3 of the International Federation for Structural Concrete (fib). This paper describes the proposed testing programme and summarized some of the results obtained by the participating laboratories.

  • 64. Hejll, Arvid
    et al.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Civil Structural Health Monitoring (CSHM): tillståndsbedömning genom mätning anpassad för anläggningskonstruktioner2005Report (Other academic)
    Abstract [sv]

    Tillståndsbedömning genom mätning sk SHM (Structural Health Monitoring) ibland CSHM (Civil Structural Health Monitoring) har stora möjligheter att bli ett effektivt instrument för att förbättra underhållsprocessen för anläggningskonstruktioner. Tillståndsbedömning och mätningen måste dock alltid kopplas till beräkningsmodeller och anläggningens tillstånd och den bör också pågå under en längre tidsperiod. Användandet att avancerad mätutrustning för att undersöka tillståndet hos befintliga anläggningar eller för att kartlägga beteendet t ex i samband med överlast har under de senaste 10 åren ökat väsentligt - inte lika mycket i Sverige som i omvärlden, men vi har också ett flertal exempel där mätning har gett mycket värdefull information. Ett problem har dock visat sig vara den bristande kunskap som de flesta inom byggnadsindustrin besitter när det gäller möjligheter med SHM och hur de olika teknikerna kan och bör tillämpas. Ett större samarbete med andra discipliner är nödvändigt. I denna rapport ges en översiktlig generell beskrivning av SHM. Dessutom presenteras ett stort antal olika mättekniker och hur de används, speciellt fokuseras här på fiberoptiska sensorer. I tillägg redovisas kort några tillämpningar med SHM.

  • 65. Hejll, Arvid
    et al.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Structural health monitoring of two large railway bridges strengthened with CFRP2005In: FRP composites in civil engineering - CICE 2004: Proceedings of the Second International Conference on FRP Composites in Civil Engineering / [ed] Rudolf Seracino, Leiden: Balkema Publishers, A.A. / Taylor & Francis The Netherlands , 2005Conference paper (Refereed)
  • 66. Hejll, Arvid
    et al.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Carolin, Anders
    Structural health monitoring of the Gröndals bridge in Sweden: the behaviour of CFRP strengthening in cold temperature2006In: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, Vol. 6176, no 17Article in journal (Refereed)
    Abstract [en]

    To obtain a better knowledge of existing structures behaviour monitoring can be used. The use of monitoring in bridge structures by the use of instruments to assess the integrity of structures is not new and there are reports from structures tested as early as in the 19th century according to ISIS Canada1 However, the term SHM (Structural Health Monitoring) is relatively new to civil engineering and the driving force to implement SHM comes from recognising the limitations of conventional visual inspections and evaluations using conservative codes of practice. The possibilities to monitor existing structures with help of the rapidly evolving Information Technology are to day carried out. The objective of SHM is to monitor the in-situ behaviour of a structure accurately and efficiently, to assess its performance under various service conditions, to detect damage or deterioration, and to determine the health or condition of the structure1. In Sweden strengthening and periodic monitoring of a large freivorbau bridge (pre-stresed concrete box girder bridge) has been carried out, the Gröndals Bridge. The bridge is located in Stockholm and is approximately 400 m in length with a free span of 120 m. It was opened to tram traffic in year 2000. Just after opening cracks were noticed in the webs, these cracks have then increased, the size of the largest cracks exceeded 0.5 mm, and at the end of year 2001 the bridge was temporarily strengthened. This was carried out with externally placed prestressed steel stays. The reason for cracking is quite clear but the responsibility is still debated. Nevertheless, it was evidently that the bridge needed to be strengthened. The strengthening methods used were CFRP plates in the Service Limit State (SLS) and prestressed dywidag stays in the Ultimate Limit State (ULS). The strengthening was carried out during year 2002. At the same time monitoring of the bridge commenced, using LVDT crack gauges as well as optical fibre sensors. This monitoring was carried out during the summer period. In addition to this a winter monitoring was carried out in the beginning of 2005. This paper presents the background to strengthening and a comparison between summer and winter monitoring where the strengthening behaviour between the two seasons is enlightened. The result from the monitoring is very interesting; it would have been preferable to strengthen the bridge during the winter.

  • 67. Hejll, Arvid
    et al.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Motavalli, Masoud
    Technical University of Denmark.
    Large scale hybrid FRP composite girders for use in bridge structures: theory, test and field application2005In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 36, no 8, p. 573-585Article in journal (Refereed)
    Abstract [en]

    This paper presents the manufacturing process and testing of large scale hybrid composite girders. The evaluation of the girders was a part of the European funded ASSET project. The bridge project, started in 1998 and finished in the autumn of 2002. The ASSET project has in brief covered the design, manufacture and construction of a fully polymer composite traffic bridge. The longitudinal girders are the most important part for the load carrying system of the bridge. Different types of girders were discussed, i.e. steel, concrete or FRP girders. Due to the advantages of FRP girders, for example; light weight, easy installation, superb durability and less maintenance compared to traditional materials it was decided to use FRP in the girders. However, before this could be carried out, tests were needed to verify theoretical calculations. Also a FE-analysis has been carried out, and this analysis is compared with an engineering analytical solution and tests. Both the numerical and the analytical theory correspond quite well with obtained test results.

  • 68.
    Häggström, Jens
    et al.
    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.
    Nilimaa, Jonny
    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.
    Blanksvärd, Thomas
    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.
    Puurula, Arto
    Savonia University of applied Sciences, Kuopia, Finland.
    Rydberg-Forssbeck, Lahja
    Trafikverket, Stockholm.
    Carolin, Anders
    Trafikverket, Luleå.
    Testing Bridges to Failure: Experiences2017In: IABSE Symposium, Vancouver, 2017: Engineering the Future, Zürich, Switzerland: IABSE - International Association for Bridges and Structural Engineering , 2017, p. 2832-2839Conference paper (Refereed)
    Abstract [en]

    Four bridges of different types have been tested to failure and the results have been compared to the load-carrying capacity calculated using standard code models and advanced numerical methods. The results may help to make accurate assessments of similar existing bridges. Here it is necessary to know the real behaviour, weak points, and to be able to model the load-carrying capacity in a correct way.

    The four bridges were: (1) a one span steel truss railway bridge; (2) a two span strengthened concrete trough railway bridge; (3) a one span concrete trough bridge tested in fatigue; and (4) a five span prestressed concrete road bridge.

    The unique results in the paper are the experiences of the real failure types, the robustness/weakness of the bridges, and the accuracy of different codes and models.

  • 69.
    Häggström, Jens
    et al.
    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. Skanska Teknik, Göteborg.
    Collin, Peter
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering. Ramböll Sverige AB, Luleå.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Assessment and full scale failure test of a steel truss bridge2015In: IABSE symposium Madrid 2014: Engineering for progress, nature and people, Zürich: International Association for Bridge and Structural Engineering, 2015, p. 2757-2764Conference paper (Refereed)
    Abstract [en]

    Large amount of resources has been invested in maintaining existing infrastructure. Several of these structures are now becoming old and do not meet the requirements of today or are reaching the end of their lifecycle. It is not possible to replace all of these structures that are deemed or are about to be deemed obsolete, due to high cost and environmental impacts.One way to keep these structures in use for a longer time is innovative and intelligent assessment of the actual state of stress and behaviour. In such cases, using structural health monitoring to assess the structure might be an efficient way to extend the life of the structure.This paper will describe a unique monitoring program over two similar 33 m long steel truss bridges situated in Sweden. One of these bridges, Aby River, has a regulated axle load of 25 tons and is deemed to have reached is end of life due to fatigue. The other bridge, Rautasjokk, has a regulated axle load of 30 tons but will be in use for the coming years.The monitoring program has the following outline; monitoring of the bridge over Aby river when it is in service, after replacement this bridge will be moved and tested under static loads to assess boundary conditions and state of stress, then parts of this bridge will be disassembled and these parts will be tested in laboratory environment for fatigue life assessment, all of these results will then be controlled by monitoring of the bridge over Rautasjokk in service limit state.The outline of this project will give input for the fatigue life models that are used today and probably upgrade the fatigue life of the bridge over Rautasjokk.

  • 70.
    Häggström, Jens
    et al.
    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 Fire Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Bridge over Åby River: Evaluation of full scale testing2017Report (Other academic)
  • 71.
    Johansson, Thomas
    et al.
    Luleå tekniska universitet.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    End peeling of mineral based CFRP strengthened concrete structures: a parametric study2005In: Proceedings of the International Symposium on Bond Behaviour of FRP in Structures: BBFS 2005 / [ed] J.F. Chen; J.G. Teng, International Institute for FRP in Construction , 2005, p. 197-204Conference paper (Refereed)
    Abstract [en]

    The advantages of FRP-strengthening have been shown time and again during the last decade. All over the world several thousand structures retrofitted with FRPs exist. The most common way to bond the FRP composite to the structure is by the use of epoxy. Epoxy has many advantages; adhere well to concrete and to the FRP material, it has low shrinkage and has in comparison low moisture uptake when set. It is also easy to apply on surfaces of the adherents. However, it also contain some drawbacks; do not adhere well to wet surfaces, are sensitive to low temperature, in particular during curing and it cannot stand high temperatures after curing. It is normally not diffusion open and it might be harmful to men if not handled properly during the application phase. It would therefore be advantageously if the epoxy could be replaced with a more environmental friendly bonding material, which is diffusion open and has the possibility to be applied in wet areas and at low temperature and still function as a shear transfer medium. Here mineral based bonding agents might be a solution. A test program at Luleå University of Technology (LTU) shows that this might be possible and preformed tests have shown very promising results. To increase the understanding of the bonding properties a theoretical study to investigate the shear stress at the cut-off end of concrete beams strengthened for flexure has been carried out. The theoretical study will later be followed by laboratory tests - unfortunately no laboratory tests with MBC (Mineral Based Composite) was ready at time for this paper. In this theoretical study the shear stress at the cut off-end of a concrete beam strengthen in flexural with traditional CFRP plate bonding is calculated and compared with a beam strengthened with MBC (Mineral Based Composite) bonding. The parametric study reveals that the shear stress is considerably smaller for the MBC system used compared to a CFRP epoxy based system at the same load level and loading conditions.

  • 72.
    Kerrouche, A.
    et al.
    School of Engineering and Mathematical Sciences, City University London.
    Boyle, W.O.J.
    School of Engineering and Mathematical Sciences, City University London.
    Gebremichael, Y.
    School of Engineering and Mathematical Sciences, City University London.
    Sun, T.
    School of Engineering and Mathematical Sciences, City University London.
    Grattan, K.T.V.
    School of Engineering and Mathematical Sciences, City University London.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Bennitz, Anders
    Field tests of fibre Bragg grating sensors incorporated into CFRP for railway bridge strengthening condition monitoring2008In: Sensors and Actuators A-Physical, ISSN 0924-4247, E-ISSN 1873-3069, Vol. 148, no 1, p. 68-74Article in journal (Refereed)
    Abstract [en]

    The EU is in the process of upgrading the national railway networks to meet the demands from high-speed passenger trains and heavy Freight traffic. This upgrade necessitates a review of the development and implementation of novel technologies to repair and strengthen the existing bridge structures and to improve their performance.This paper presents the evaluation results of the use of FBG strains sensors incorporated in CFRP (carbon fibre reinforcement polymer) rods and tubes as part of the methodology for monitoring the performance of the NSMR (near surface mounted reinforcement) which is an essential part of the repair and strengthening of bridges. In addition, a new method has been tested for the first time using CFRP tubes which calls for the drilling of holes instead of sawing grooves in the installation process.The paper discusses in some detail the strengthening mechanism, FBG sensor implementation and the electronic system used to interrogate the FBG sensors. The results obtained from the monitoring show that FBG sensors can be integrated into CFRP and that reliable measurements can be made. However, in this particular project, the strain loading is very moderate so consequently the strain levels are in the elastic regime.

  • 73.
    Kerrouche, Abdel
    et al.
    City University, London.
    Boyle, W J O
    City University, London.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Bennitz, Anders
    Field test - strengthening and monitoring of the Frövi Bridge2008In: Bridge Maintenance, Safety Management, Health Monitoring and Informatics: Proceedings of the Fourth International Conference on Bridge Maintenance, Safety and Management, July 13-17 2008, Seoul, Korea - IABMAS '08 / [ed] Hyun-Moo Koh; Dan G Frangopol, Boca Raton, Fla: CRC Press, Taylor & Francis Group , 2008, p. 3743-3750Conference paper (Refereed)
  • 74. Lundqvist, Joakim
    et al.
    Bernspång, Lars
    Täljsten, Björn
    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.
    A probability study of finite element analysis of near surface mounted carbon fiber reinforced polymer bonded to reinforced concrete2007In: Fiber-Reinforced Polymer Reinforcement for Concrete Structures: Proceedings of the 8th International Symposium on Fiber Reinforced Polymer Reinforcement for Concrete Structures, FRPRCS-8 / [ed] T.C. Triantafillou, Patras: FRPRCS-8 Symposium Secretariat , 2007Conference paper (Refereed)
    Abstract [en]

    A structure is typically designed for a long life and it is probable that the demands on it change over time, e.g. carry larger loads or fulfill new standards. The structure might also have been exposed to a harsh environment leading to a degradation of its structural capacity. These reasons, and more, may lead to a need for strengthening the structure. Strengthening of reinforced concrete structures with carbon fiber reinforced polymers (CFRP) has been shown to be a very effective and advantageous retrofitting technique. The weight-to-strength ratio and resistance to corrosion are some of the advantages. Several different strengthening systems are available with CFRP and a relatively new technique is the near surface mounted reinforcement (NSMR) method. As opposed to externally mounted strengthening systems, NSMR is composed of sawing a groove in a concrete member, applying an adhesive in the groove and inserting a CFRP bar. Although the idea of embedding reinforcing tendons in existing structures has been present for several decades [1], acceptance of the method has only been possible with the emergence of the FRP material. As NSMR comprise of the properties and advantages of an ordinary FRP strengthening system, e.g. plates, it also has the benefit of being embedded in the concrete. This means better protection against impact, fire, abrasion and a natural resistance to peeling stresses. Strengthening of concrete members with NSMR have been reported by e.g. [2], [3], [4], and [5]. For NSMR, or indeed for most FRP strengthening techniques, the bond between the concrete and the strengthening material is the most important issue. This is where the transfer of stresses takes place to realize full composite action. The behavior of strengthened reinforced concrete is quite complex and an approach to investigate this is to utilize the finite element (FE) method. Many numerical analyses of reinforced concrete strengthened with CFRP using the FE method have been carried out in recent years. These concern primarily studies of plate bonding though there are a few studies of bonding of NSMR. In [6], concrete beams are strengthened with plates and the analytical shear and peeling stresses are compared with a linear finite element (FE) analysis. Several authors, e.g. [7], have emphasized that sufficiently small elements must be used in a FE analysis to accurately describe stress distributions, particularly at the end of a bonded plate. Teng et al, [8], make further refinement of the FE mesh and examine the interfacial stresses in reinforced concrete beams bonded with a soffit plate. A concern for the element size where stress singularities occur was also raised. Nonlinear FE analyses of reinforced concrete strengthened with NSMR are performed in [3], [4], [5], and [9]. The common failure mode of a strengthening system with plates is in the outermost concrete layer close to the adhesive. This has been reported in many papers, e.g. [9]. The failure mode for NSMR is more complex. It spans from being a failure in the adhesive close to the FRP bar, i.e. pure pullout, to the concrete layer close to the adhesive, as for FRP plates but with the difference that more concrete is dislodged. In between, a mixed mode of failure is present with cracks in both the adhesive and the concrete. Where the failure occurs is determined by geometrical and material parameters. The thickness of the adhesive, the position of the bar in the adhesive, and the bonding length are possible geometrical parameters. Material parameters are the modulus of elasticity and Poisson's ratio of the concrete, adhesive and the FRP, and of course the tensile strength of the concrete and adhesive. Also, the configuration and the properties of the internal reinforcement may determine the failure mode. To study the bond behavior of reinforced concrete strengthened with NSMR, a test for CFRP bar pullout was devised. This is illustrated in Figure 1 and is reported in [10]. The concrete beam has a minimum amount of reinforcing steel not shown in the drawing. In this paper, the pullout of a rectangular NSMR CFRP bar bonded to reinforced concrete is studied by a finite element analysis in the linear elastic domain. Also, a Monte Carlo simulation, with the FE model incorporated, is carried out with the purpose of determining which geometrical and material parameters that are the most important for where the tensile strength is attained; in the adhesive or the concrete. The following simplifications have been made in this study; all materials are considered as isotropic and linear elastic, and the FE model utilizes symmetry.

  • 75. Lundqvist, Joakim
    et al.
    Nordin, Håkan
    Täljsten, Björn
    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.
    Numerical analysis of concrete beams strengthened with CFRP: a study of anchorage lengths2005In: Proceedings of the International Symposium on Bond Behaviour of FRP in Structures: BBFS 2005 / [ed] J.F. Chen; J.G. Teng, International Institute for FRP in Construction , 2005, p. 239-246Conference paper (Refereed)
    Abstract [en]

    The advantages of Fibre Reinforced Polymer (FRP) strengthening have been shown time and again during the last decade. All over the world several thousand structures have been retrofitted using FRP. Buildings and civil structures usually have a very long life and it is not uncommon that the demands on the structure change with time. The structures may have to carry larger loads at a later date or fulfil new standards. In extreme cases, a structure may need repair due to an accident, or due to errors made during the design or construction phase. To guarantee the function of the strengthening properties, anchorage of the FRP is essential. Without sufficient anchorage lengths, full utilization of the strengthening material cannot be achieved, leading to possible premature failure. In this paper, experimental work and numerical analyses of three different Carbon Fibre Reinforced Polymer (CFRP) strengthening techniques have been carried out. The techniques are externally bonded plates, sheets and the use of Near Surface Mounted Reinforcement (NSMR). The aim is to find a critical anchorage length, where a longer anchorage length does not contribute to the load bearing capacity. Three different anchorage lengths have been investigated; 100, 200 and 500 mm. The finite element program ABAQUS has been used for the numerical study. The results show that a critical anchorage length exists for plates and sheets as well as for NSMR. However, the present study also shows that an exact critical anchorage length may be difficult to estimate, at least with the present test set-up. Further tests and investigations of the constitutive model for the concrete are needed.

  • 76.
    Mahal, Mohammed
    et al.
    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.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    A two-scale damage model for high-cycle fatigue at the fiber-reinforced polymer-concrete interface2016In: Computers and Concrete, ISSN 1598-8198, Vol. 116, p. 12-20Article in journal (Refereed)
    Abstract [en]

    This paper presents a new two-scale damage model of the fiber-reinforced polymer (FRP)-concrete bond under high-cycle fatigue. The material behavior is modeled as elastic-plastic coupled with damage for the microscale analysis and as elastic for the mesoscale analysis. A new damage law for the interface joint is described. The two-scale damage model has been implemented as a material model for a three dimensional an eight-node interface element of zero thickness and used to simulate a double shear joint specimen under high cycle fatigue. The numerical calculations were performed with a full incremental cycle solution and a new cycle jump approach. Comparing the results from the finite element method (FEM) model with experimental data shows that the model is capable of accurately predicting the cyclic fatigue loading slip response of the joint interface.

  • 77.
    Mahal, Mohammed
    et al.
    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.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Examination at a material and structural level of the fatigue life of beams strengthened with mineral or epoxy bonded FRPs: the state of the art2013In: Advances in Structural Engineering, ISSN 1369-4332, E-ISSN 2048-4011, Vol. 16, no 7, p. 1329-1345Article in journal (Refereed)
    Abstract [en]

    This paper presents a state of the art review of different material combinations and applications of mineral-based and epoxy-based bonded Fiber Reinforced Polymers (FRP), used for the strengthening of concrete structures subjected to fatigue loading. In this review, models of the fatigue life at the material and structural level are presented. This study examines the mechanical behavior of the FRP-material, surface bonding behavior and concrete beams strengthened under fatigue loading with different types of FRP-systems. The parameters that are investigated are applied load value, time dependent effects, type of strengthened structures (shear, flexural or combined) and the configuration of sheets or plates. The building codes and researchers' recommendations are also discussed. As a result of this review, the reader will obtains an overview of suitable materials and methods for strengthening structures subjected to fatigue loading by referring to the estimated fatigue life of material and strengthening structures at various applied stress levels.

  • 78.
    Mahal, Mohammed
    et al.
    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.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    FE modeling of FRP-concrete interface for very high cycle fatigue behavior2014In: Advances in fracture and damage mechanics XII: selected, peer reviewed papers from the 12th International Conference on Fracture and Damage Mechanics (FDM 2013), September 17 - 19, 2013, Sardinia, Italy / [ed] A. Milazzo; M.H. Aliabadi, Durnten-Zurich: Trans Tech Publications Inc., 2014, p. 165-168Conference paper (Refereed)
    Abstract [en]

    The fatigue damage of FRP-concrete interface is a major problem in strengthened structures subjected to fatigue loading. The available FRP-concrete interface models published in the literature usually deal with fracture mechanism approach, which is unsuitable for high cycle fatigue damage. In this study, a constitutive micro model is developed for FRP-concrete interface for high cycle fatigue and incorporated into a three dimensional finite-element program. Numerical analysis of a double lap joint is carried out, and the results show that the proposed model is reasonably accurate

  • 79.
    Mahal, Mohammed
    et al.
    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.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sas, Gabriel
    Northern Research Institute.
    Using digital image correlation to evaluate fatigue behavior of strengthened reinforced concrete beams2015In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 105, p. 277-288Article in journal (Refereed)
    Abstract [en]

    The fatigue behavior of reinforced concrete beams externally strengthened with carbon fiber reinforced polymer plates and near-surface mounted bars has been investigated using a digital image correlation (DIC) technique. Displacement fields obtained from digital images recorded during specific load cycles in fatigue tests are analyzed to provide information on crack width, beam deflection and curvature, and major principal strains to enable crack detection. The results obtained in this way were compared to data gathered using conventional sensors, revealing that the DIC technique provided very accurate and detailed information. The experimental results for plate-strengthened, bar-strengthened, and unstrengthened beams are discussed.

  • 80.
    Mahal, Mohammed
    et al.
    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.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Experimental performance of RC beams strengthened with FRP materials under monotonic and fatigue loads2016In: Journal of composites for construction, ISSN 1090-0268, E-ISSN 1943-5614, Vol. 122, p. 126-139Article in journal (Refereed)
    Abstract [en]

    Carbon fiber-reinforced polymers (CFRPs) are increasingly being used to repair and strengthen reinforced concrete (RC) bridge members. CFRP strengthening may be applied by bonding polymeric plates to the exterior of the member’s tension surface or by placing CFRP bars inside the concrete member cover to provide near-surface mounted reinforcement. It is not clear which of these approaches is most effective at resisting fatigue loads. To compare their efficacy, four-point bending tests with reinforced concrete beams were conducted under monotonic and fatigue loading using both strengthened and unstrengthened RC beams having steel reinforcements with identical stress levels. The influence of the strengthening material’s properties and prior cracking of the member are investigated and discussed by analyzing failure mechanisms, load-deflection curves, and strain measurements for steel bars and CFRP materials observed during loading experiments. The results obtained indicate that the efficiency of strengthening is primarily determined by the relief of local stress in the member’s reinforcing steel bars before they rupture, and the fatigue life of the reinforcing steel after its initial fracturing. The latter of these quantities is related to the strengthened member’s ability to absorb the energy released at the moment the reinforcing bar fractures.

  • 81.
    Mahal, Mohammed
    et al.
    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.
    Blanksvärd, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Fatigue analysis of RC beams strengthened in flexure using CFRP2016In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085Article in journal (Refereed)
    Abstract [en]

    The increasing use of Fiber Reinforced Polymers (FRP) to repair, strengthen or upgrade reinforced concrete (RC) structural elements means that there is a need to develop analytical methods for analyzing the behavior of strengthened members under fatigue loading. This paper describes an analytical model for simulating the fatigue behavior of RC beams strengthened with Carbon Fiber Reinforced Polymer (CFRP). Fatigue calculations are performed using a lamellar model that considers the fatigue behavior of the RC and CFRP strengthening materials during loading. The model’s output is compared to experimental data for four CFRP-strengthened beams, showing that the new model accurately predicted the deflection and strain of each one. In addition, various models for predicting the fatigue life of CFRP-strengthened RC beams were tested and a model capable of providing conservative fatigue life estimates was identified.

  • 82.
    Mufti, A.A.
    et al.
    University of Manitoba, Winnipeg.
    Bakht, B.
    JMBT Structures Research Inc., Scarborough.
    Banthia, N.
    University of British Columbia, Vancouver.
    Benmokrane, B.
    University of Sherbrooke.
    Desgagne, G.
    Ministere des Transports du Quebec.
    Eden, R.
    Manitoba Floodway Authority, Winnipeg.
    Erki, M.A.
    Royal Military College of Canada, Kingston.
    Karbhari, V.
    University of California San Diego, La Jolla.
    Kroman, J.
    City of Calgary.
    Lai, D.
    Ontario Ministry of Transportation, St. Catharines.
    Machida, A.
    Saitama University.
    Neale, K.
    University of Sherbrooke.
    Tadros, G.
    SPECO Engineering Ltd, Calgary.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Reply to the discussion by A.K. El-Sayed on "New Canadian Highway Bridge Design Code design provisions for fibre-reinforced structures"2007In: Canadian journal of civil engineering (Print), ISSN 0315-1468, E-ISSN 1208-6029, Vol. 34, no 10, p. 1378-Article in journal (Other academic)
  • 83.
    Mufti, A.A.
    et al.
    ISIS Canada Research Network, University of Manitoba, Winnipeg.
    Bakht, B.
    JMBT Structures Research Inc., Scarborough.
    Banthia, N.
    University of British Columbia, Vancouver.
    Benmokrane, B.
    Department of Civil Engineering, University of Sherbrooke.
    Desgagné, G.
    Structural Department, Ministère des Transports du Québec.
    Eden, R.
    Design and Contracts, Bridges and Roads, Manitoba Floodway Authority, Winnipeg.
    Erki, M.A.
    Royal Military College of Canada, Kingston.
    Karbhari, V.
    Department of Structural Engineering, University of California San Diego.
    Kroman, J.
    Structural Design, Calgary.
    Lai, D.
    Ontario Ministry of Transportation.
    Machida, A.
    Saitama University.
    Neale, K.
    Department of Civil Engineering, University of Sherbrooke.
    Tadros, G.
    SPECO Engineering Ltd.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Erratum: New Canadian Highway Bridge Design Code design provisions for fibre-reinforced structures (Canadian Journal of Civil Engineering (2007) vol.34 (3) (267-283))2007In: Canadian journal of civil engineering (Print), ISSN 0315-1468, E-ISSN 1208-6029, Vol. 34, no 10, p. 1379-Article in journal (Other academic)
  • 84.
    Mufti, A.A.
    et al.
    ISIS Canada Research Network, University of Manitoba, Winnipeg.
    Bakht, B.
    JMBT Structures Research Inc., Scarborough.
    Banthia, N.
    Department of Civil Engineering, The University of British Columbia, Vancouver.
    Benmokrane, B.
    Department of Civil Engineering, University of Sherbrooke.
    Desgagné, G.
    Structural Department, Ministère des Transports du Québec.
    Eden, R.
    Design and Contracts, Bridges and Roads, Manitoba Floodway Authority, Winnipeg.
    Erki,, M.-A.
    Royal Military College of Canada, Kingston.
    Karbhari, V.
    Department of Structural Engineering, University of California San Diego, La Jolla.
    Kroman, J.
    Structural Design, Calgary.
    Lai, D.
    Ontario Ministry of Transportation, St. Catharines.
    Machida, A.
    Saitama University.
    Neale, K.
    Department of Civil Engineering, University of Sherbrooke.
    Tadros, G.
    SPECO Engineering Ltd, Calgary.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    New Canadian highway bridge design code design provisions for fibre-reinforced structures2007In: Canadian journal of civil engineering (Print), ISSN 0315-1468, E-ISSN 1208-6029, Vol. 34, no 3, p. 267-283Article in journal (Refereed)
    Abstract [en]

    This paper presents a synthesis of the design provisions of the second edition of the Canadian Highway Bridge Design Code (CHBDC) for fibre-reinforced structures. New design provisions for applications not covered by the first edition of the CHBDC and the rationale for those that remain unchanged from the first edition are given. Among the new design provisions are those for glass-fibre-reinforced polymer as both primary reinforcement and tendons in concrete; and for the rehabilitation of concrete and timber structures with externally bonded fibre-reinforced-polymer (FRP) systems or near-surface-mounted reinforcement. The provisions for fibre-reinforced concrete deck slabs in the first edition have been reorganized in the second edition to explicitly include deck slabs of both cast-in-place and precast construction and are now referred to as externally restrained deck slabs, whereas deck slabs containing internal FRP reinforcement are referred to as internally restrained deck slabs. Resistance factors in the second edition have been recast from those in the first edition and depend on the condition of use, with a further distinction made between factory- and field-produced FRP. In the second edition, the deformability requirements for FRP-reinforced and FRP-prestressed concrete beams and slabs of the first edition have been split into three subclauses covering the design for deformability, minimum flexural resistance, and crack-control reinforcement. The effect of sustained loads on the strength of FRPs is accounted for in the second edition by limits on stresses in FRP at the serviceability limit state.

  • 85.
    Nilimaa, Jonny
    et al.
    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.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    NSM CFRP Strengthening and Failure Loading of a Posttensioned Concrete Bridge2016In: Journal of composites for construction, ISSN 1090-0268, E-ISSN 1943-5614, Vol. 20, no 3, article id 04015076.Article in journal (Refereed)
    Abstract [en]

    Two carbon-fiber-reinforced polymer (CFRP) systems developed as possible means to strengthen existing concrete structures have been applied to a bridge at Kiruna (Sweden). The bridge was no longer in service and was thus used in extensive tests to failure. It was a posttensioned five-span bridge consisting of three longitudinal main girders topped with a concrete slab. The program reported here consisted of a series of three tests of the girders in the second span: loading each girder up to 2.0 MN before strengthening, loading each girder up to 2.0 MN after strengthening, and loading to failure after strengthening. One of the girders was strengthened by installing three 10×10  mm 2 near-surface mounted (NSM) CFRP bars on the soffits, and another by installing three prestressed 1.4×80  mm 2 CFRP laminates. This paper focuses on the NSM-strengthened girder, which failed at a maximum load of 6.1 MN, with a corresponding midspan deflection of 159 mm. The failure was a combination of flexure and shear, and the strain in the NSM bars at the ULS was 1.2%.

  • 86.
    Nilimaa, Jonny
    et al.
    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.
    Häggström, Jens
    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.
    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.
    More Realistic Codes for Existing Bridges2016In: IABSE CONGRESS, STOCKHOLM, 2016: Challenges in Design and Construction of an Innovativeand Sustainable Built Environment / [ed] Elfgren, Lennart; Jonsson, Johan; Karlsson, Mats; Rydberg-Forssbeck, Laja; Sigfrid, Britt, CH - 8093 Zürich, Switzerland, 2016, p. 399-407Conference paper (Refereed)
    Abstract [en]

    Examples are given from comparisons of analyses based on (1) code models, (2) finite element models and (3) full scale tests to failure of three bridges. The analyses based on the code models gave very conservative results, while the finite element models could better predict the real behaviour.

  • 87.
    Nilimaa, Jonny
    et al.
    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.
    Elfgren, Lennart
    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.
    Transversal post tensioning of RC trough bridges: laboratory tests2012In: Nordic Concrete Research, ISSN 0800-6377, Vol. 46, no 2, p. 57-74Article in journal (Refereed)
  • 88.
    Nilimaa, Jonny
    et al.
    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.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Assessment of concrete double-trough bridges2015In: Journal of Civil Structural Health Monitoring, ISSN 2190-5479, Vol. 5, no 1, p. 29-36Article in journal (Refereed)
    Abstract [en]

    The behaviour of reinforced concrete double-trough bridges has been assessed regarding the stress distribution in the transverse direction of the slab. Two bridges were studied and the curvature, as well as the tensile steel reinforcement strain, was monitored. One bridge was loaded with a reference train, producing a distributed load of 17.1 kN/m on a theoretical 1-m-wide slab strip, while the load on the other bridge was not specified. Each bridge consisted of two parallel troughs, presumably cast on different occasions, and connected by continuous reinforcement and a concrete shear stud. Previous assessment calculations regarded these two troughs acting as two separate structures, with the slab simply supported by the main beams. This paper, however, shows that there is a composite action between the troughs, and the bridge deck should instead be regarded as continuous in the transverse direction. By using this approach, the load capacity of the bridge can be increased without strengthening. Structural health monitoring using curvature- or tensile strain monitoring, is finally recommended for double-trough bridges and an assessment chart is proposed for the Haparanda Bridge.

  • 89.
    Nilimaa, Jonny
    et al.
    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.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Post-tensioning of reinforced concrete trough bridge decks2012In: 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. 415-418Conference paper (Refereed)
    Abstract [en]

    All aging structures are affected by different deterioration processes, which might cause a performance decrease, and eventually lack of safety, in the structures. In addition to this the changing infrastructural demands pose the Swedish Transport Administration to increase the load capacity of the railway system which then also includes the bridges. This might be carried out by many different methods where strengthening is one. A particular interesting bridge type to strengthen is the concrete trough bridge and in particular in shear between the transition of the beam and the slab. Methods for flexural strengthening of trough bridges have been tested and documented, but there is a lack of methods for strengthening the bottom slab in shear. This paper presents promising laboratory test results for transversal post tensioning of the bottom slab of a concrete trough bridge specimen, and measurements reveal a vast decrease in reinforcement strains.

  • 90.
    Nilimaa, Jonny
    et al.
    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.
    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.
    Unbonded Transverse Posttensioning of a Railway Bridge in Haparanda, Sweden2014In: Journal of Bridge Engineering, ISSN 1084-0702, E-ISSN 1943-5592, Vol. 19, no 3, article id 4013001Article in journal (Refereed)
    Abstract [en]

    The majority of railway lines in Sweden are designed to support axle loads of up to 250 kN. Because of increased transport needs on some lines, an axle load limit of at least 300 kN would be beneficial. To upgrade the Haparanda line in northern Sweden to 300 kN, the slabs in existing concrete trough bridges require a higher transverse shear resistance. Methods for in situ strengthening of bridge slabs in this way have not been fully developed, and this paper discusses the possibility of increasing the load capacity by horizontal prestressing. Internal, unbonded posttensioning was performed on one bridge on the Haparanda line, and the strengthening effects were investigated. The strengthening was designed according to the European Eurocode design regulations, and testing was conducted before and after the implementation. Strains in the main transverse reinforcement, caused by a train with an axle load of 215 kN, were completely counteracted by eight prestressing bars, stressed with 430 kN/bar. The results indicate that the actual strengthening effect is larger than what is predicted by the design equations. The Haparanda project showed that unbonded posttensioning can be implemented relatively fast and does not obstruct the ongoing railway traffic during installation

  • 91.
    Nilimaa, Jonny
    et al.
    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.
    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
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Paulsson, Björn
    Trafikverket.
    Extended Life of Railway Bridges. Results from EC-FP7-project MAINLINE2013In: Assessment, Upgrading and Refurbishment of Infrastructures: IABSE Conference Rotterdan 2013 / [ed] Philippe Van Bogaert, Zürich: International Association for Bridge and Structural Engineering, 2013, p. 314-315Conference paper (Refereed)
    Abstract [en]

    There is a need to extend the life of many existing railway bridges. To facilitate this is one of the objects of the EC-FP7-Project MAINLINE, covering a period from 2011 to 2014. Three case studies are presented in which existing bridges are being studied in order to extend their life length: First a concrete trough bridge strengthened with post stressed bars in drilled holes through the slab is considered; followed by another concrete trough bridge strengthened with sawn in Near Surface Mounted Reinforcement (NSMR) of Carbon Fibre Reinforce Polymers (CFRP); and finally a steel truss bridge which will be loaded to failure to calibrate the assessment methods.

  • 92.
    Nilimaa, Jonny
    et al.
    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.
    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.
    Extending the life of elderly rail bridges by strengthening2014In: Bridge Maintenance, Safety, Management and Life Extension: proceedings of the Seventh International Conference of Bridge Maintenance, Safety and Management, 7-11 July 2014, Shanghai, China / [ed] Airong Chen; Dan M. Frangopol; Xin Ruan, London: CRC Press, Taylor & Francis Group , 2014, p. 1082-1088Conference paper (Refereed)
    Abstract [en]

    There is a need to extend the life of many existing railway bridges. To facilitate this is one of the objects of the EC-FP7-Project MAINLINE, covering a period from 2011 to 2014. New or improved technologies are investigated to help with this. For bridges, the most promising techniques are enhanced inspection, assessment and strengthening methods. Case studies are presented where three different strengthening techniques have been applied to existing concrete trough bridges. First, sawn in Near Surface Mounted Reinforcement (NSMR) of Carbon Fibre Reinforce Polymers (CFRP) are used; followed by a bridge where carbon fibre cables were drilled through the bridge and finally a bridge was strengthened with post tensioned bars in drilled holes through the slab in the transverse direction. All three methods proved to be very successful.

  • 93.
    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.

  • 94.
    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.
    Blanksvärd, Thomas
    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.
    Tu, Yongming
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Carolin, Anders
    Trafikverket, Trafikverket, Luleå.
    Paulsson, Björn
    Trafikverket, UIC, Banverket.
    Extend the life of existing railway bridges: Results from EU FP7 project MAINLINE2015In: IABSE Conference Geneva 2015: Structural Engineering: Providing Solutions to Global Challenges, Geneva: International Association for Bridge and Structural Engineering, 2015, p. 1219-1226Conference paper (Other academic)
    Abstract [en]

    There is a need to extend the life and capacity of many existing bridges. One of the objects of the EU FP7 Project MAINLINE, 2011-2014, was to facilitate this. Guidelines for assessment and strengthening methods are presented as well as case studies in which existing bridges are studied in order to extend their life length. One example is the prestressing of the slab in a one-span concrete trough bridge in order to increase its load-carrying capacity. Horizontal holes were drilled trough the slab and in them steel bars were placed and post-tensioned. In this way a compressive stress was introduced into the concrete section so that it’s bending and shear capacity was increased.In another study a metal truss bridge was monitored in order to check strain and stress ranges in critical connections to enable an enhanced evaluation of the remaining fatigue resistance. The studied bridge was then replaced and loaded to failure to study its robustness and the reliability of applied assessment methods. The results could then be applied to prolong the life of an identical twin bridge located in the northern part of Sweden. A Life Cycle Assessment Tool (LCAT) has been developed to enable Infrastructure Managers to choose optimal maintenance strategies.

  • 95.
    Nilimaa, Jonny
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Sabau, Cristian
    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.
    Puurula, Arto
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Savonia University.
    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. Skanska.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Carolin, Anders
    Trafikverket.
    Paulsson, Björn
    Charmec Railway Center.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Assessment and Loading to Failure of Three Swedish RC Bridges2018In: Evaluation of Concrete Bridge Behavior through Load Testing: International Perspectives / [ed] Eva Lantsoght and Pinar Okumus, Faarmington Hills, MI: American Concrete Institute, 2018, Vol. 323, p. 8.1-8.18, article id SP-323-8Chapter in book (Refereed)
    Abstract [en]

    Current codes often underestimate the capacity of existing bridges. The purpose of the tests presented here has been to assess the real behaviour and capacity of three types of bridges in order to be able to utilize them in a more efficient way.

    The three studied bridges are: (1) Lautajokk – A one-span trough bridge tested in fatigue to check the shear capacity of the section between the slab and the girders; (2) Övik – A two span trough bridge strengthened with Near Surface Mounted Reinforcement (NSMR) of Carbon Fibre Reinforced Polymers (CFRP) tested in bending, shear and torsion; and (3) Kiruna – A five-span prestressed three girder bridge tested to shear-bending failures in the girders and in the slab.

    The failure capacities were considerably higher than what the code methods indicated. With calibrated and stepwise refined finite element models, it was possible to capture the real behaviour of the bridges. The experiences and methods may be useful in assessment and better use of other bridges.

  • 96. Nordin, Håkan
    et al.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Concrete beams strengthened with prestressed near surface mounted CFRP2006In: Journal of composites for construction, ISSN 1090-0268, E-ISSN 1943-5614, Vol. 10, no 1, p. 60-68Article in journal (Refereed)
    Abstract [en]

    Retrofitting concrete structures with fiber reinforced polymer (FRP) has today grown to be a widely used method throughout most parts of the world. The main reason for this is that it is possible to obtain a good strengthening effect with a relatively small work effort. It is also possible to carry out strengthening work without changing the appearance or dimensions of the structure. Nevertheless, when strengthening a structure with external FRP, it is often not possible to make full use of the FRP. The reason for this depends mainly on the fact that a strain distribution exists over the section due to dead load or other loads that cannot be removed during strengthening. This implies that steel yielding in the reinforcement may already be occurring in the service limit state or that compressive failure in the concrete is occurring. By prestressing, a higher utilization of the FRP material is made possible. It is extremely important to ensure that, if external prestressing is used, the force is properly transferred to the structure. Most of the research conducted with prestressing carbon fiber reinforced polymer (CFRP) for strengthening has been on surface bonded laminates. However, this paper presents research on prestressed CFRP quadratic rods bonded in sawed grooves in the concrete cover. This method has proven to be an advantageous means of bonding CFRP to concrete, and in comparison to surface bonded laminates, the shear and normal stress between the CFRP and the concrete are more efficiently transferred to the structure. In the presented test, no mechanical device has been used to maintain the prestress during testing, which means that the adhesive must transfer all shear stresses to the concrete. Fifteen beams with a length of 4 m have been tested. The tests show that the prestressed beams exhibited a higher first-crack load as well as a higher steel-yielding load as compared to nonprestressed strengthened beams. The ultimate load at failure was also higher, as compared to nonprestressed beams, but in relation not as large as for the cracking and yielding. In addition, the beams strengthened with prestressed FRP had a smaller midpoint deflection. All strengthened beams failed due to fiber rupture of the FRP.

  • 97. Nordin, Håkan
    et al.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Strengthening of concrete structures by external prestressing2006In: Bridge maintenance, safety, management, life-cycle performance and cost: proceedings of the Third International Conference on Bridge Maintenance, Safety and Management, Porto, Portugal, 16 - 19 July 2006 / [ed] Paulo J. S. Cruz; Dan M. Frangopol, London: Taylor & Francis Group, 2006, p. 1047-1048Conference paper (Other academic)
    Abstract [en]

    Rehabilitation and strengthening of existing concrete structures has become more and more in focus during the last decade. All over the world there are structures intended for living and transportation. The structures are of varying quality and function, but they are all ageing and deteriorating over time. Some of these structures will need to be replaced since they are in such a bad condition. However, it is not only the deterioration processes that make upgrading necessary, errors can have been made during the design or construction phase so that the structure needs to be strengthened before it can be used. The causes for repair and/or strengthening can be many, but normally deteriorated concrete, steel corrosion, change of use, increased demands on the structure, errors in the design or/and construction phase or accidents are governing factors. Many methods to repair or/and strengthen concrete structures exists such as concrete overlays, shotcrete, use of external prestressed tendons, just to mention a few. Prestressing is in particular interesting with several comparable advantages to other methods. In this paper the use of prestressing for repair and strengthening are briefly discussed and tests on concrete T-beams with external Prestressed tendons of steel or CFRP (Carbon Fibre Reinforced Polymer) are presented. The tests shown that prestressing is a very effective way to increase the existing load carrying capacity of existing concrete members. The presented project is a small part of a larger European funded project, the "Sustainable Bridges", where the aim is to evaluate the load carrying capacity and life of existing railway bridges with the purpose to increase existing load carrying capacity with 25% and the train speed to 350 km/h. The tests were carried out at Luleå University ofTechnology (LTU). The test specimens were concrete T-beams with a length of 6 meters, see figure 1. The beams were loaded under four-point bending, the load was applied with deformation control at 0.2 mm/s until failure or to a point where the beam no longer could carry any more load. A total of eight beams were tested during the series. The strengthening techniques used were externally prestressed steel rods, externally prestressed CFRP rods and Near Surface Mounted Reinforcement (NSMR) CFRP rods with and without prestress. For the steel tendons a traditional steel wedge anchor was used, but that was not possible for the CFRP tendons, as normal steel wedge anchors would crush the FRP tendons. For the tests an anchor was developed using a nylon wedge. To get better effect of the anchor, the tendons had quarts sand glued on them in the zone for anchoring. As those anchors would not be able to take as high forces as a steel anchor on a steel tendon six tendons were used instead of two. However, as the prestressing was applied it became clear that it would not be possible to achieve the same prestressing force as with the steel tendons. With the exception of the beam with external CFRP tendons all the tested beams behaved as expected. The strengthening effects for the prestressed beams were over 100% bom for concrete cracking and steel yielding. When looking at the post-steel yielding behaviour it is interesting to compare the beams strengthened with unbonded tendons and those with bonded tendons (Steel 3 and NSMR PS). The beams with bonded tendons and rods showed a better behaviour after steel yielding than those with (Graph Presented) unbonded tendons. The problems with the CFRP anchor during prestress continued during loading and the loads were much lower for that beam then predicted. In figure 2 the loads and displacements are shown. The tests show a large increase in crack and steel yielding loads. The increase in load for steel yielding can be very important for a constructions life, the fatigue behaviour will improve and as a consequence the crack widths will be smaller which can result in increased durability. Together with higher crack loads the cracks also go smaller, this should also indicate a more advantageous behaviour in the service limit state (SLS).

  • 98. Nordin, Håkan
    et al.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Testing of hybrid FRP composite beams in bending2004In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 35, no 1, p. 27-33Article in journal (Refereed)
    Abstract [en]

    This paper presents tests where hybrid composite beams have been investigated. The hybrid beam consists of a glass fibre I-beam with carbon fibre strengthened bottom flange and a rectangular concrete block in the compressive zone. The interaction between the concrete and composite beam were obtained in two ways; casting in shear connectors of steel and bonding by epoxy adhesive. As a reference, a beam without concrete in the compressive zone was also tested. The idea of combining carbon, glass and concrete was to utilize the stiffness contribution from the carbon and the compressive strength from the concrete. The glass fibre I-beam would then take up the main part of the shear force. The results from the test showed that a good composite action could be achieved between carbon, glass and concrete. However, it could also be noticed, as expected, that an I-beam is not the ultimate form due to stability problems. In the tests, problems arose due to lateral instability, but this was solved by placing stiffeners manufactured from wood between the flanges of the Fibre Reinforced Polymer beam over the supports. With a few modifications of the hybrid beam it is believed, that it would be possible to create both a technical and economical hybrid profile that benefits from carbon, glass and concrete.

  • 99. Nordin, Håkan
    et al.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Carolin, Anders
    Concrete beams strengthened with prestressed near surface mounted reinforcement (NSFR)2001In: FRP Composites in Civil Engineering: Proceedings of the International Conference on FRP Composites in Civil Engineering, Amsterdam: Elsevier, 2001, p. 1067-1075Conference paper (Refereed)
    Abstract [en]

    The need for repair and strengthening of concrete structures has increased considerably over the last decade. A number of methods for repair and/or strengthening of concrete structures have been used over the years, but very recently the use of carbon fiber reinforced polymer (CFRP) plate bonding has gained acceptance. The technique was originally developed with steel plates being bonded with an epoxy adhesive to a concrete structure, but lately advances have been made in use of more suitable plate materials such as CFRP composites. This paper presents a pilot study of lab tests for concrete beams strengthened with prestressed near surface mounted CFRP laminates. Primary results indicate an increased strengthening effect when the steel reinforcement yielded and an increased cracking load, but the ultimate load is the same as a beam strengthened without prestress. Failure modes were the same with or without prestress, failure in the fiber, but the prestressed beams had smaller deflections at failure.

  • 100.
    Olofsson, Ingvar
    et al.
    Skanska Teknik, Göteborg.
    Elfgren, Lennart
    Bell, Brian
    Network Rail, London.
    Paulsson, Björn
    Banverket, Borlänge.
    Niederleithinger, Ernst
    BAM, Berlin.
    Jensen, Jens Sandager
    COWI A/S, Lyngby.
    Feltrin, Glauco
    EMPA, Zurich.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Cremona, Christian
    LCPC, Paris.
    Kiviluoma, Risto
    North Finnish Building Cluster, Helsinki.
    Bien, Jan
    Wroclaw University of Technology.
    Assessment of European railway bridges for future traffic demands and longer lives: EC project "sustainable bridges"2005In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 1, no 2, p. 93-100Article in journal (Refereed)
    Abstract [en]

    A European Integrated Research Project has recently been started within the 6th Framework Program of the European Commission. The project aims at improved methods for the upgrading of existing railway bridges within the European railway network. The main objectives of the project are to increase the transport capacity by allowing higher axle loads and by increasing the maximum speeds. Other objectives are to increase the residual lifetime of existing bridges and to enhance management, strengthening and repair systems. The overall goal is to enable the delivery of improved capacity without compromising the safety and economy of the working railway. A consortium consisting of railway bridge owners, consultants, contractors, research institutes and universities carry out the project, having a gross budget of more than 10 million Euros. Funding from the European Commission covers a major portion of the four-year project costs

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