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  • 1. Carolin, Anders
    et al.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Hejll, Arvid
    Concrete beams exposed to live loading during carbon fiber reinforced polymer strengthening2005In: Journal of composites for construction, ISSN 1090-0268, E-ISSN 1943-5614, Vol. 9, no 2, p. 178-186Article in journal (Refereed)
    Abstract [en]

    The need for structural rehabilitation of concrete structures all over the world is well known. Extensive amounts of research have been carried out and are ongoing in this field. Most of the laboratory research has been undertaken on structural elements without live load during the strengthening process. Normally owners of structures want to continue their activity or service during strengthening. Full-scale applications have shown that this is possible, but there is a lack of understanding as to how cyclic loads are distributed during strengthening; for example, traffic loads affect the final strengthening result. This paper presents laboratory tests on concrete beams strengthened with carbon fiber-reinforced polymer laminates and near-surface mounted reinforcement. The beams were subjected to a cyclic load during setting of the adhesive, and after additional hardening were then loaded by deformation control up to failure.

  • 2.
    Enochsson, Ola
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Hejll, Arvid
    Nilsson, Martin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Thun, Håkan
    Olofsson, Thomas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Bro över Luossajokk: beräkning med säkerhetsindexmetod, böjdragkapacitet i överkant i mittsnittet i korta spannet2002Report (Other academic)
    Abstract [sv]

    I samband med projektet "30 ton på Malmbanan", Paulson-Töyrä (1996), konstaterades att bron över Luossajokk i Kiruna inte klarade de nya förhöjda lasterna. Bron har två spann och en utkragande konsol 10,25 + 6,3 + 3,4 m. Överbyggnaden utgörs av ett slakarmerat betongtråg med ett nytt mellanstöd som uppfördes 1965 då en äldre överbyggnad byttes ut. En klassningsberäkning och en utredning av förstärkningsbehov utfördes. Efter en förnyad översyn av brons bärförmåga utfördes töjningsmätningar vintern och sommaren 2001. Töjningsmätningarna indikerade förvånansvärt små påkänningar i bron. En närmare utredning av brons säkerhet att bära uppträdande laster genomförs därför i denna rapport. Detta sker med hjälp av en nyanserad säkerhetsberäkning med säkerhetsindexmetod. Den nya genomgången visar att medelvärdet för bärförmågan för moment är 2,89 MNm med standardavvikelsen 0,19 MNm i det mest utsatta snittet med dragpåkänningar i överkant i korta spannet. Detta kan jämföras med det formella dimensioneringsvärdet 1,99 MNm som erhölls i klassningsberäkningen med beaktande av aktuella partialkoefficienter. I det nya medelvärdet har en lägre uppmätt effektiv höjd beaktats, att ett av tolv armeringsjärn borrats av samt att betong- och armeringshållfastheterna är högre än de nominella dimensioneringsvärdena. På lastsidan gav klassningsberäkningen i motsvarande snitt att det formella dimensioneringsvärdet för momentet är 2,79 MNm. En analys av verkliga uppträdande laster ger att medelvärdet maximalt uppgår till 2,05 MNm. Detta lastfall utgörs av ett lok placerat med tre axlar i längsta spannet och tre axlar placerade på konsolen, om såväl bromslast som ojämn temperaturlast och dynamiskt tillskott uppträder samtidigt. Enligt BV Bärighet (1996) behöver ojämn temperatur inte beaktas, vilket är rimligt med tanke på att detta är ett statiskt obestämt lastfall som försvinner vid uppsprickning i brottstadiet. Det har heller inte medräknats i tidigare klassningsberäkningar. I så fall fås att lasten har medelvärdet 1,66 MNm och att säkerhetsindex β varierar mellan 3,8 och 6,0 beroende på vilka antaganden som görs om lasternas statistiska fördelning. För en rimlig fördelning innehålls kravet i säkerhetsklass 3 att säkerhetsindex β 4,75. Bron visar sig därför, enligt vår bedömning och med beaktande av erhållna mätresultat, ha erforderlig bärförmåga om hastigheten begränsas på bron så att eventuella dynamiska tillskott blir låga och/eller inverkan av ojämn temperatur försummas. Brons fortsatta uppförande bör kontrolleras genom ett mätprogram. Detta bör förutom armeringstöjningar med befintliga givare även inkludera mätningar av nedböjningar för att säkerställa att använda beräkningsmodeller och randvillkor på ett korrekt sätt återger brons beteende. Storleken på den dynamiska förstoringsfaktorn D bör även mätas liksom inverkan av bromskrafter och ojämn temperaturfördelning. På så sätt kan ett säkrare underlag erhållas för bedömning av frekvensfunktionerna för dessa vanliga lasteffekter. Dessa värden borde även vara av intresse vid säkerhetsbedömning av likartade järnvägsbroar.

  • 3.
    Hejll, Arvid
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Civil structural health monitoring: strategies, methods and applications2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis describes a Civil Structural Health Monitoring (CSHM) method for assessment of civil structures by using a combination of advanced monitoring equipment with probabilistic based assessment. The numbers of civil structures such as bridges, tunnels, retaining walls, dams, etc. have increased dramatically the last 30 years since an increase in construction were present in the fifties and sixties. In the last decades new strategies in maintenance, inspection and assessment of out infrastructures have been developed to make it possible to continue to use the structures longer than the designed service life. Also the demands of the structures are different now compared to when they were erected, for example the loads are higher, fewer disturbances in traffic are accepted and higher traffic flows are present. Therefore new technologies for inspection, assessment, maintenance, strengthening are needed. Civil Structural Health Monitoring is defined as method for in-situ monitoring and performance evaluation of civil structures. Without CSHM it will not be possible to assess old structures in an effective way and the cost for rebuilding will have enormous impact of the society. Therefore it is motivated to use and continue to develop CSHM methods in the future. CSHM is also a very useful tool to evaluate the performance of constructions built with new materials and constructions which are strengthened with novel strengthening systems. In this thesis a new strategy to combine probabilistic evaluation of the structural performance with monitoring is described. Ideas how a strategic thinking can be done regarding inspections, investigations, monitoring and evaluation are also described in the presented CSHM method. Five cases have been used to develop, apply and validate my suggested CSHM method. The cases are testing different aspects of the model. - The first case shows a model application where the model is analysed in a recent performed strengthening and assessment project - The second case shows that it is possible to use CFRP strengthening without or with minor traffic disturbance. This is a important part of CSHM since proposed actions to continue use the structure as intended is the last step in the CSHM model - The third case is analysing tests, modelling, and verification of a composite hybrid bridge. - The forth case is testing of a new developed sensor type used to test the longterm effect of a strengthening system. The outcome of this paper is that the temperature effect was of major importance. - In the fifth case inspection, assessment and monitoring is used in a strengthening project where the goal was to evaluate the stiffness change of a bridge after it being strengthened. - The last case is an example of damage detection where the outcome point out the difficulties in global damage detection. Especially the first case shows the advantages of using probabilistic based evaluation in combination with monitoring.

  • 4. Hejll, Arvid
    Structural health of bridges: monitor, assess and retrofit2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The research presented in this Licentiate thesis is intended to cover minor areas of the wide research area Structural Health Monitoring (SHM) of Civil Engineering Structures. SHM is broadly the knowledge maintaining our infrastructure by assessing the condition, often by monitoring or measurements, diagnose damages, analyse risk levels, by using inputs from measurements and diagnoses, and in the end retrofit, if needed. In particular the methodology and the interaction between the different parts in SHM, ranging from assessment to upgrading, are explained. The thesis give also a brief introduction to sensor technology, mainly designed for monitoring, and to damage detection methods in Civil Engineering structures, such as bridges. The thesis is of the form "combination thesis" which is characterised by a relatively extensive literature study and a summary of the research presented at the beginning. Beyond this, it contains four papers, which are summarised below. Paper A: "Concrete beams exposed to Live Loading during CFRP strengthening", presents how strengthening of concrete beams can be done without stopping the traffic during execution. Results show that no significant decrease of the strengthening effect exists when carbon fibre laminates and quadratic rods (NSMR), is bonded with an epoxy adhesive, which had cured during the cyclic loading. If a cementitious bonding agent is used, cyclic loading decrease the strengthening effect dramatically. Paper B: "Large scale hybrid composite FRP girders for use in bridge structures - theory, test and field application". This paper presents the possibility to build a bridge in full scale using fiber reinforced polymers. Numerical analysis, full scale tests and theoretical investigations shows full composite action between the constituents. Paper C: "CFRP Strengthening and monitoring of the Gröndals Bridge in Sweden" discuss the retrofit of a large concrete box bridge using CFRP laminates and how the strengthening effect can be monitored and verified using fibre optical sensors (FOS). Due to shear cracks in the webs the Gröndals Bridge is strengthened with CFRP-laminates and post stressed with steel stays. Monitoring with FOS and conventional LVDT gauges shows that most of the measured strain is caused by natural temperature changes. The results also show that the CFRP laminates work as intended and that the crack propagation has stopped. Paper D: "Damage Detection of a Large-Scale 38-Years-Old Prestressed RC Bridge Girder using Natural Frequencies" gives and example how modal analysis can be used as a diagnostic tool to indicate damages. The results show very small changes of natural frequencies because no cracks during the whole tests occurred and the Young's modulus of the concrete was increasing after unloading.

  • 5. 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.

  • 6. 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)
  • 7. 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.

  • 8. 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.

  • 9.
    Täljsten, Björn
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Hejll, Arvid
    Structural health monitoring of two railway bridges in Sweden2003In: Structural Health Monitoring and Intelligent Infrastructure: Proceedings of the 1st International Conference on Structural Health Monitoring and Intelligent Infrastructure / [ed] Z.S. Wu; M. Abe, Lisse: Balkema Publishers, A.A. / Taylor & Francis The Netherlands , 2003, Vol. 2, p. 1047-1055Conference paper (Refereed)
    Abstract [en]

    Upgrading, assessment and maintenance of our ageing infrastructure like bridges, dams and buildings has grown in importance. Recently the Swedish and Norwegian Railway Association decided to upgrade the iron ore railway transport system going from Luleå to Narvik from 25 to 30 ton of axle load to increase the iron ore transport capacity. This paper describes a part of the upgrade procedure for two concrete bridges. In the first case, the Kallkällan Bridge, the moment capacity in the bridge cross direction was to low and it was decided to strengthen the bridge with CFRP sheets. Since, at that time, the strengthen method never been used on railway bridges in Sweden before it was decided to launch a comprehensive testing program to monitor the performance of the bridge before and after strengthening. In addition a long-term periodic monitoring program was launched. In the second case, the Loussajokk Bridge, calculations showed that the increased axle loads would exceed the yield limit in the top steel reinforcement. However, since field strain measurement indicated much lower levels than expected, refined calculations methods using First Order of Reliability Method, FORM, were conducted. The application of the SHM system to the Luossajokk Bridge, located in the very north of Sweden, was successful, and in spite of minor problems, it was decided to undertake a long term monitoring scheme of the bridge instead of strengthening it. Based on the experience from the two cases a SHM system is suggested where live data from health monitoring can be used with probabilistic methods to evaluate the current state in form of a safety index. This system will include; Prognosis, Sensor system, Acquisition system, Communication system, Storage system and a Diagnostic system. In this paper a brief description of the parts in the SHM system will be given together with real data from field measurements.

  • 10.
    Täljsten, Björn
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Hejll, Arvid
    Tvärbanebroarna - Gröndal och Alviksbron: mätning av rörelser med hjälp av fiberoptiska sensorer (FOS)2005Report (Other academic)
    Abstract [sv]

    Under våren 2003 utfördes mätningar på Gröndal- och Alviksbron med en för Sverige relativt okänd mätteknik, åtminstone för bygg- och anläggningskonstruktioner, nämligen genom användandet av fiberoptiska sensorer. Det som föranledde den aktuella mätningen var att båda lådbroarnas liv hade spruckit i flera snitt och sprickorna karaktäriserades som skjuvsprickor. Broarna förstärktes först temporärt med utanpåliggande stålstag och därefter permanent med stag som efterspändes i hål borrade genom flänsarna och livet. Denna teknik användes i tvärsnitt som var mest uppspruckna. I tvärsnitt som hade högre dragpåkänningar än tillåtet, men med fina eller inga sprickor, användes pålimmade kolfiberlaminat för förstärkning. För att kartlägga effekter av kolfiberförstärkningen samt för att undersöka om sprickorna fortsatte att propagera efter förstärkning togs beslut om mätning. Mätning har utförts såväl med traditionell teknik där LVDT (Linear Voltage Displacement Transducers) användes samt med teknik där FOS-givare (Fibre Optic Sensors) användes. I denna rapport redovisas endast från mätningarna med FOS-givare, för de traditionella mätningarna hänvisas till (James, 2004). Den genomförda mätningen med FOS-sensorer måste anses som lyckad. Med en relativt blygsam insats var det möjligt att mäta påkänningen i ett stort antal punkter och totalt har 50 sensorer använts på de båda broarna, dessa täcker då in mätning på betong, i sprickor och på kolfiberlaminat såväl som kompensering av temperatur. Det var tyvärr inte möjligt att genomföra någon mätning innan förstärkning, vilket gör utvärderingen något bristfällig och medför att det endast går att undersöka om de existerande sprickorna propagerar under last samt vilken rörlig last som har störst inverkan på påkänningarna. På grund av en relativt begränsad budget för mätningen har det inte varit möjligt att genomföra en kontinuerlig mätning med FOS tekniken över en längre tid utan mätningen har varit periodisk och hittills endast under ett tillfälle under tre dagar. Den genomförda mätningen visar tydligt att påkänningarna är små, som störst uppmättes en rörelse av 0.0625 mm i en spricka (Gröndalsbron). Mätningen visar att kolfiberlaminaten är verksamma. Därutöver framgår det att temperaturvariationen ger största påkänningen och överstiger påkänningen av spårvagnstrafiken med en faktor 10. Slutligen bör nämnas att tekniken med FOS-sensorer är både smidig ur utförandesynpunkt och ekonomiskt konkurrenskraftig i jämförelse med traditionell mätteknik och därav är en ytterligare utveckling av tekniken önskvärd.

  • 11.
    Täljsten, Björn
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Hejll, Arvid
    Olofsson, Thomas
    Strengthening and civil structural health monitoring of the Panken road bridge in Sweden2007In: Recent Developments in Structural Engineering, Mechanics and Computation: SEMC 2007 / [ed] Alphose Zigoni, Rotterdam: Millpress , 2007, Vol. 1, p. 699-700Conference paper (Refereed)
1 - 11 of 11
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