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  • 1.
    Bennitz, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Externally unbonded post-tensioned CFRP tendons: a system solution2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The introduction of Fibre Reinforced Polymers (FRP) to the civil engineering market in the late 1980s resulted in the emergence of a range of new tools for rehabilitating and strengthening concrete structures. Strengthening using FRPs is typically accomplished using non-prestressed externally bonded FRPs. The technical and economic benefits of such strengthening could be further increased by prestressing the FRPs, especially when dealing with concrete structures. Prestressing concrete structures suppresses the appearance and growth of cracks in the serviceability limit state. This in turn increases the structure’s stiffness and resistance to degradation. Prestressing also increases the structure’s yield load but does not change its failure load relative to that of an analogous non-prestressed structure, provided that all other parameters are kept constant. In 2004, a pilot study was carried out at the Luleå University of Technology (LTU) to investigate the scope for using unbonded Carbon Fibre Reinforced Polymer (CFRP) strengthening systems, particularly those involving prestressing. In the early stages of this project, a number of difficulties were encountered in anchoring the CFRP rods to concrete structures: the conical wedge anchorages that were used tended to either cause premature failure of the rods or allowed the rod to slip out of the anchorage. It was therefore decided to study the mechanisms at work within these anchorages in more detail. The goal of the project was to develop a small, practical, reliable, and userfriendly anchorage for use in unbonded external CFRP strengthening systems. On the basis of a thorough literature review, which is described in Paper 1, it was concluded that despite the difficulties encountered, the conical wedge anchorages used with steel reinforcing rods were the most promising starting point for the design of a new anchorage for use with CFRPs. Importantly, the conical wedge anchorage can be made small in size and easy to mount while retaining a high degree of versatility; this is not true of bonded, sleeve, and clamping anchorages. Analytical and numerical models were used to investigate the distribution of radial stress within these highly pressurized anchorages. Paper 2 describes an evaluation of the capability of three types of models - an analytical axisymmetric model based on the thick-walled-cylinder-theory and two Finite Element (FE) models, one axisymmetric and one three-dimensional - to predict the behaviour of a conical wedge anchorage. It was concluded that the axisymmetric models were incapable of modelling the stress distribution within the anchorage with sufficient accuracy, and so 3D FE models were used exclusively in subsequent studies. Paper 3 describes the development of a new anchorage for CFRP rods. The design process involved conducting pull-out studies on a series of prototypes, in conjunction with computational studies using a basic FE model, to identify and understand the prototypes’ failure modes. Between the computational data and experimental results, a good understanding of the factors affecting the interaction between the CFRP rod and the anchorage was obtained. The new anchorage design employs a one-piece wedge which effectively incorporates the three wedges and the inner sleeve from more conventional wedge anchorages into a single unit. This increases the reliability and user-friendliness of the anchorage because it eliminates the need to check the alignment of individual wedges. The new design has been patented; the published Swedish patent is included in the thesis as Paper 6. The newly-developed anchorage was then incorporated into a prestressing system and its performance was evaluated using a series of test beams. In parallel with the planning of these tests, a series of pull-out tests was conducted using the new anchorage. The strain measurements obtained in these experiments were compared to predictions made using a new, more advanced FE model, and used to refine the design of the new anchorage. Paper 4 describes this new FE model, the most important parameters affecting anchorage behaviour, and the final anchorage design. Paper 5 focuses on the possibilities provided by the new anchorage. Tests were performed using seven three meter long concrete beams prestressed with external unbonded CFRP tendons. One beam was unstrengthened; the other six were strengthened in different ways, with different prestressing forces, initial tendon depths, and with or without the use of a midspan deviator for the tendons. The results of these tests were compared to those obtained using otherwise identical beams prestressed with steel tendons and to the predictions of an analytical beam model developed for use with steel tendons. These tests showed that the prestressing works as intended and that the behaviour of beams prestressed with external unbonded CFRP tendons is fully comparable to that of beams prestressed with steel tendons. It was also found that the predictions of the analytical model were in good agreement with experimental observations, although there were some differences between the measured and predicted tendon stresses. The development of a functional anchorage represents a fulfilment of the objectives laid out at the start of this project, and represents an important step towards the practical use of prestressed unbonded external CFRP tendons in strengthening concrete structures. However, a number of outstanding questions remain to be addressed. Little is known about the safety of this kind of system, and the benefits of using CFRP tendons should be quantified. Furthermore, there are a number of potential technical issues that must be addressed. These include the risk of creep-rupture in the CFRP, the effects of thermal contraction and expansion on the anchorage, and the scalability of the anchorage as the tendon diameter is increased. Finally, the long-term behaviour of the anchorage and prestressing system should be investigated.

  • 2.
    Bennitz, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Mechanical anchorage of prestressed CFRP tendons: theory and tests2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Fibre Reinforced Polymers (FRPs) are slowly becoming important materials to consider also for a structural engineer. They are light-weight, insensitive to corrosion and have highly modifiable mechanical properties. Strengths five times higher than that of ordinary reinforcing steel are common and that combined with the possibility to vary the modulus of elasticity makes them suitable to use in combination with concrete. Carbon fibre based polymers (CFRPs) especially serve as an excellent substitute for steel in the rehabilitation of structures. A case study on that subject is presented in this thesis while the focus lies on the use of CFRP as a material for use in prestressing tendons, and to be more precise, on the anchorage of prestressed CFRP tendons. FRPs orthotropic properties highly influence their behaviour in different directions. The best properties are reached through tension in the fibre direction, and as such CFRP is as good for prestressing tendons as any prestressing steel. It is also not sensitive to corrosion and easy to work with due to its light weight. Mechanical properties in the transverse direction are however not that advantageous and early attempts to anchor CFRP bars by traditional mechanical prestressing anchorages have consistently failed. A thorough program for the development of a successful anchorage has therefore been undertaken. In a first step a literature review was conducted to investigate CFRPs possibilities to replace steel in prestressing applications, internally and externally, as well as traditional anchorage techniques for steel tendons. From the literature study it was concluded that CFRP may very well serve as tendons but some doubts also arose concerning the environmental effect on the CFRPs long term behaviour and the materials ability to work under bent conditions in multispan applications. The traditional anchorages will however not work properly, all of them use mechanical grip to keep the steel stressed. This is possible through the steels capacity to yield but not suitable to anchor the brittle CFRP. A state-of-the-art survey on attempts made globally during the last 15 years to come up with a suitable frictional anchorage has also been performed. It can be seen that several ideas are discussed, often in one or two publications. One Canadian research team, Al-Mayah et al. (2001-2008), has taken the development further and focused on variations of the traditional wedge anchorage. Based on the knowledge gained from the literature it was decided to further concentrate on a conical anchorage with a barrel of steel and three smooth wedges in aluminium. Simple analytical approaches to the conical wedge anchorage with smooth interior surfaces prove the importance of the angle in the wedge-barrel interface. Also frictional behaviour in the rod-wedge and wedge-barrel interfaces proves to be important factors. Numerical studies of these and other geometrical and mechanical properties give further input into the development of a pilot anchorage to be tested in the laboratory. The optimum angle of the wedge towards the barrel seems to be between 2-3°. The thickness of the wedge should be kept as small as possible and it is favourable with high strength steel in the barrel. A small displacement of the wedges towards the unloaded end of the tendon in the design of the anchorage does also reduce the overall slip of the rod during tension. After overcoming initial problems not discovered in the analytical or numerical models the developed anchorage performed well during laboratory tests. In short term tests performed on an 8 mm thick circular rod 100 % of the rods ultimate capacity was reached. During the tests measurements of displacements and strains were performed. Fibre Optical Sensors (FOS - Bragg gratings) were for the first time included in the interior of the anchorage to give a complete picture of the load phase. These measurements were compared to a refined finite element model and show reasonable agreement. The largest source of error is assumed to be the complicated frictional behaviour in the material interfaces and the transverse material properties of the CFRP. Lastly a case study on the strengthening of a 50 year old trough bridge in Frövi is included. The bridge was successfully strengthened for bending in the transverse direction with 23 Near Surface Mounted Reinforcement (NSMR) bars in the lower part of the slab while 11 holes are drilled underneath the upper steel reinforcement to facilitate CFRP tubes with an outer diameter of 32 mm and a thickness of 4 mm. The lack of bending capacity was discovered by a consultant in 2005 and calculations with a new approach in this thesis show that the strengthening was necessary although on a minor scale. New calculations of the capacity show that the bridge's capacity after strengthening is well above the design load and measurements on site secure that the CFRP is utilized correctly as a load carrier.

  • 3.
    Bennitz, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Polymerbaserade kompositspännstag: litteratursammanställning2009Report (Other academic)
  • 4. Bennitz, Anders
    et al.
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Olofsson, Thomas
    Kronborg, A.
    Wahlberg, A.
    Dynamic behaviour of the Vindel River railway bridge2006In: Condition Monitoring and Diagnostic Engineering Management: COMADEM 2006: proceedings / [ed] Uday Kumar; Aditya Parida; Raj B. K. N. Rao, Luleå: Luleå tekniska universitet, 2006, p. 721-729Conference paper (Refereed)
    Abstract [en]

    The Swedish Railway administration has launched several projects aimed at increasing the accessibility of the railway lines in northern Sweden to meet future demands. One of these lines connects the southern and northern parts of Sweden and constitutes one of the major arteries for the transportation of heavy goods. Major investment are planned to upgrade the load bearing capacity of this railway line. The work is mainly focused on the larger structures and their dynamical properties. These properties can be used to assess existing infrastructure and to evaluate the performance. Advantages are obvious since the existing structural integrity form the base for investments in structural repair and upgrade of bridges. The Vindel River Railway Bridge situated 55 kilometers northwest of Umeå came into focus when large motion was discovered during train passages. The behaviour of the bridge crossing the river of Vindeln has been measured two times. Measurements of displacements and acceleration of the bridge during train passages has been conducted, the first measurements was done to give more experience on the motion of the bridge and to try out new sensors. The second measurement gave more information about the bridge's motion, results that could be used to calibrate a 3D FE-Model of the bridge used in the study. Based on the measurements, eigenfrequencies in the range of 0 to 8 Hz could be detected, modal shapes up to the ninth order could be extracted, deflections and transverse displacements for different sets of train and different train speeds were also found. However, new measurements are planned for this summer and will hopefully reinforce the already attained result and give answers to some of the unresolved questions.

  • 5.
    Bennitz, Anders
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Grip, Niklas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Schmidt, Jacob W.
    Technical University of Denmark.
    Thick-walled cylinder theory applied on a conical wedge anchorage2011In: Meccanica (Milano. Print), ISSN 0025-6455, E-ISSN 1572-9648, Vol. 46, no 5, p. 959-977Article in journal (Refereed)
    Abstract [en]

    In this paper, we derive and examine an analytical model for the internal stresses and strains within the anchorage for a prescribed presetting distance. This model is derived from the theory of thick walled cylinders under the assumptions regarding plane stress and axial symmetry. We simplify the resulting system of ten nonlinear equations and derive a method for solving them numerically. A comparison of plotted results for three different angles on the wedge's outer surface and six different presetting distances follows. These results are also compared to both axi-symmetric and 3D FE (Finite Element) models. Analytical and FE axi-symmetric models show good correspondence, though compared to the 3D FE model, they show a clear difference in the predicted radial stress distribution on the FRP. Thus, the derived analytical model can be a useful and faster alternative to FE modeling of axi-symmetric anchorages. However, the model is of more restricted value and should be complemented by, for example, 3D FE models for other designs.

  • 6.
    Bennitz, Anders
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Grip, Niklas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Schmidt, Jacob W.
    Department of Civil Engineering, Technical University of Denmark.
    Thick-walled cylinder theory applied on a conical wedge anchorage: Research report with Matlab implementation documentation2010Report (Other academic)
    Abstract [en]

    Conical wedge anchorages are frequently used to anchor steel tendons in prestressing applications within the construction industry. To replace the steel tendons with non-corrosive and low weight FRPs (Fiber Reinforced Polymers), the different mechanical interactions between the steel and FRPs call for further development of the anchorage.In this paper, we derive and examine an analytical model for the internal stresses and strains within the anchorage for a prescribed presetting distance. This model is derived from the theory of thick walled cylinders under the assumptions regarding plane stress and axial symmetry. We simplify the resulting system of ten nonlinear equations and derive a method for solving them numerically. A comparison of plotted results for three different angles on the wedge's outer surface and six different presetting distances follows.These results are also compared to both axi-symmetric and 3D FE (Finite Element) models. Analytical and FE axi-symmetric models show good correspondence, though compared to the 3D FE model, they show a clear difference in the predicted radial stress distribution on the FRP. Thus, the derived analytical model can be a useful and fasteralternative to FE modeling of axi-symmetric anchorages. However, the model is of more restricted value and should be complemented by, for example, 3D FE models for other designs.

  • 7.
    Bennitz, Anders
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Schmidt, Jacob W.
    Technical University of Denmark, Division of Structural Engineering.
    Nilimaa, Jonny
    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.
    Goltermann, Per
    Technical University of Denmark, Division of Structural Engineering.
    Ravn, Dorthe L.
    COWI A/S.
    Reinforced concrete T-beams externally prestressed with unbonded carbon fiber-reinforced polymer tendons2012In: ACI Structural Journal, ISSN 0889-3241, E-ISSN 1944-7361, Vol. 109, no 4, p. 521-530Article in journal (Refereed)
    Abstract [en]

    This study describes a series of experiments examining the behavior of seven beams prestressed with unbonded external carbon fiber-reinforced polymer (CFRP) tendons anchored using a newly developed anchorage and post-tensioning system. The effects of varying the initial tendon depth, prestressing force, and the presence of a deviator were investigated. The results were compared to those observed with analogous beams prestressed with steel tendons, common beam theory, and predictions made using an analytical model adapted from the literature. It was found that steel and CFRP tendons had very similar effects on the structural behavior of the strengthened beams; the minor differences that were observed are attributed to the difference between the modulus of elasticity of the CFRP and the steel used in the tests. The models predicted the beams’ load-bearing behavior accurately but were less effective at predicting the stress experienced by the tendons.

  • 8.
    Bennitz, Anders
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Schmidt, Jacob W.
    Technical University of Denmark.
    Täljsten, Björn
    Failure modes of prestressed CFRP rods in a wedge anchored set-up2009In: Advanced Composites in Construction (ACIC) 2009 Conference Proceedings / [ed] Sue Halliwell; Claire Whysall; Tim Stratford, ACIC , 2009, p. 104-114Conference paper (Refereed)
    Abstract [en]

    In the process of developing a new wedge anchorage to anchor prestressed CFRP rods, five different anchorage designs were manufactured. These designs have led to a constantly increased ultimate failure load of the prestressing system and an eventual load level above 95% of the ultimate failure load of the rod was achieved. If 100% efficiency is achieved the anchorage does not reduce the capacity of the system, but failure is then governed by the capacity of the rod itself, which is considered favourable and required by several guidelines. In the process seven different failure modes were identified: soft slip, power slip, cutting of fibres, crushing of rod, bending of fibres, frontal overload and intermediate rupture. In this paper the failure modes are discussed further. The failures are documented with explanatory figures and their backgrounds are found in the theory. Suggestions are given on how these failures can be avoided in theory and practice. From the experiences gained in the project, it is concluded that it is a challenging task to create a fully mechanical anchorage for CFRP tendons and that the failure margins are small between a successful and an unsuccesful anchorage system.

  • 9.
    Bennitz, Anders
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Täljsten, Björn
    Innovative strengthening of Swedish concrete trough bridges2008In: Proceedings, Nordic Concrete Research, Bålsta, Sweden: [ ... XXth Symposium on Nordic Concrete Research & Development ... The current proceedings contain 90 summaries of oral poster presentations] / [ed] Johan Silfwerbrand, Oslo: Norsk Betongforening , 2008, p. 92-93Conference paper (Refereed)
  • 10. Bennitz, Anders
    et al.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Undersökning av skjuvförband i trä: provning av bulttyper för Vasaskeppet2008Report (Other academic)
    Abstract [sv]

    Föreliggande rapport är resultatet av laboratorieförsök vilka utförts på avdelningen för byggkonstruktion vid Luleå tekniska universitet. Försöken har genomförts under slutet av 2007 och är en direkt fortsättning av tidigare försök från 2004 och 2005. De tidigare rapporterna pekade på ett behov av fortsatt provning. Föreliggande rapport är således en fortsättning av tidigare arbete, dock med vidareutveckling av möjliga bulltyper för Vasaskeppet. De testade bulltyperna har konstruerats och tillverkats i Statens Maritima Museer regi av Anders Ahlgren. Försöken har genomförts vid Luleå tekniska universitet och Complab, av Civ. Ing. Georg Danielsson samt forskarstuderande Anders Bennitz.

  • 11.
    Bennitz, Anders
    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.
    Danielsson, Georg
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    CFRP strengthening of a railway concrete trough bridge: a case study2012In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 8, no 9, p. 801-816Article in journal (Refereed)
    Abstract [en]

    This paper presents an upgrading and monitoring of a Swedish concrete railway bridge. The methods used for the upgrading as well as for the monitoring are innovative and new. Carbon fibre tubes are inserted in holes in the bridge deck, drilled in the transverse direction of the slab at a location ca. 40 mm from the top. Carbon fibre NSMR bars are bonded in transverse grooves in the soffit of the slab. Both methods are intended to increase the transverse bending moment capacity of the troughs' bottom slab in the ultimate limit state. Monitoring is performed to verify the effectiveness of the strengthening and to understand the behaviour of the bridge. However, for obvious reasons, monitoring is only carried out in the SLS (service limit state). Even though only marginal effects of strengthening could be recorded in the SLS, both the strengthening and monitoring were considered successful at a cost of approximately 8% of the total cost of a new bridge replacement.

  • 12. Bennitz, Anders
    et al.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Danielsson, Georg
    Strengthening of a railway bridge with NSMR and CFRP tubes2008In: FRP Composites in Civil Engineering: proceedings of the 4th International Conference on FRP Composites in Civil Engineering ; Zurich, Switzerland, 22 - 24 July 2008 / [ed] Masoud Motavalli, Dübendorf: EMPA-Akademie , 2008Conference paper (Refereed)
    Abstract [en]

    Strengthening of structures with CFRP is considered today as an accepted method in the upgrading of concrete structures. This paper presents the use of two different CFRP strengthening systems combined to extend the service life of a Swedish double-trough-doubletrack railway bridge, constructed in concrete with a 10 meter span. One system is the reliable NSMR (Near Surface Mounted Reinforcement) while the other is new. They were used with the intention to strengthen the interior of a concrete structure using integrated CFRP tubes. Both systems were used to increase the tensile flexural strength of the slab transverse to the tracks. NSMR bars were positioned in the bottom concrete cover of the trough's bottom-slabs, while the new system was inserted in holes drilled through the bridge in the cross direction and located in the upper part of the slab. In connection with the strengthening monitoring was conducted in order to obtain an understanding of the bridge behaviour before and after strengthening, and to demonstrate any effects of the extra CFRP reinforcement. Results from these measurements are presented together with how the strengthening work was carried out. Sensors on bars and tubes show evidence of utilization of the CFRP while displacement sensors and strain gauges on the steel reinforcement show minor effect due to the small loads in the service limit state.

  • 13.
    Bennitz, Anders
    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.
    Schmidt, Jacob W.
    Technical University of Denmark.
    External prestressing of RC T-beams with CFRP tendons2009In: Proceedings of the 9th International Symposium on Fiber-Reinforced Polymer Reinforcement for Concrete Structures / [ed] D. J. Oehlers; M.C. Griffith ; R. Seracino, Adeleide: University of Adelaide , 2009Conference paper (Refereed)
  • 14.
    Bennitz, Anders
    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.
    Schmidt, Jacob W.
    Technical University of Denmark, Division of Structural Engineering.
    Förankringsanordning för fiberkompositstängerPatent (Other (popular science, discussion, etc.))
  • 15.
    He, Goujing
    et al.
    CSUFT, Changsha, Hunan.
    Zou, Zhongquan
    CSUFT, Changsha, Hunan.
    Enochsson, Ola
    Bennitz, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Elfgren, Lennart
    Kronborg, Anders
    Banverket, Luleå.
    Töyrä, Björn
    Banverket, Luleå.
    Paulsson, Björn
    Banverket, Borlänge.
    Assessment of railway concrete arch bridge by numerical modelling and measurements2008In: 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: Taylor and Francis Group , 2008, p. 3733-3742Conference paper (Refereed)
  • 16.
    He, Guojing
    et al.
    Luleå tekniska universitet.
    Bennitz, Anders
    Enochsson, Ola
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    The Vindel river railway bridge: monitoring and numerical analysis of the dynamic behaviour2006Report (Other academic)
    Abstract [sv]

    Banverket (The Swedish Railway Administrator) wanted to increase the maximum allowed axle load from 225 to 250 kN along the Swedish main northern railway line. One of the bridges, Bridge over The Vindel River, needed to be studied more. The bridge crosses the Vindel River near Vindeln some 60 km NW of Umeå and was built in 1952. The structure consists of a concrete arch with a span of 110 m and a height of 22 m. The arch carries a concrete trough deck with concrete columns. This report summarizes the research work on monitoring and numerical analysis of dynamic behaviour for The Vindel Bridge.

  • 17.
    He, Guojing
    et al.
    Luleå tekniska universitet.
    Bennitz, Anders
    Enochsson, Ola
    Elfgren, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Paulsson, B.
    Banverket, Luleå.
    Töyrä, B.
    Banverket, Luleå.
    Olofsson, P.
    Banverket, Luleå.
    Kronborg, A.
    Banverket, Luleå.
    Numerical modeling and dynamic behavior of a railway concrete bridge over the Vindel River in 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 & Francis Group, 2006, p. 104-111Conference paper (Refereed)
    Abstract [en]

    The Vindel Railway Bridge in northern Sweden is composed of a concrete deck, columns and an arch with a span of 110 m and a height of 22 m. In order to check the possibility to increase the axle load from 225 kN to 250 kN, the properties of the bridge needed to be evaluated. Especially, the dynamic behavior of the bridge is an important factor as it is affecting the load bearing capacity and the serviceability. In this paper, two types of three-dimensional (3-D) finite element models have been developed. One uses shell elements and the other uses beam elements. Based on the 3-D FE models, the effects of nonstructural mass, side spans and connection between columns and deck on the dynamic behavior are discussed. Furthermore, field test data from passing through train are compared with the results calculated by the models. The numerical simulations of the dynamic response coincide reasonably well with the field test data

  • 18.
    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.

  • 19.
    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)
  • 20.
    Sas, Gabriel
    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.
    Nilimaa, Jonny
    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.
    Bennitz, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Carolin, Anders
    Trafikverket.
    Strengthening of concrete structures with carbon fibre reinforced polymers (CFRP): case studies2012In: 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. 423-426Conference paper (Refereed)
    Abstract [en]

    Carbon Fibre Reinforced Polymers (CFRP) has found an increased application in strengthening of concrete structures. Mostly the CFRP is used as externally bonded reinforcement. However, prestressing of it gives a possibility to increase the capacity and stiffness of existing concrete structures. A number of tests in the laboratory as well as field case studies have been carried out. The paper describes some of them.

  • 21.
    Schmidt, Jacob W.
    et al.
    Technical University of Denmark.
    Bennitz, Anders
    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.
    Goltermann, Per
    Technical University of Denmark.
    Pedersen, Henning
    COWI A/S.
    Mechanical anchorage of FRP tendons: a literature review2012In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 32, p. 110-121Article in journal (Refereed)
    Abstract [en]

    High tensile strength, good resistance to degradation and creep, low weight and, to some extent, the ability to change the modulus of elasticity are some of the advantages of using prestressed, unidirectional FRP (Fibre Reinforced Polymer) tendon systems. Bonded and non-bonded versions of these systems have been investigated over the last three decades with results showing that prestressing systems can be very efficient when the FRP properties are properly exploited. However, there are often concerns as to how to exploit those properties to the full and how to achieve reliable anchorage with such systems. This is especially important in external post-tensioned tendon systems, where the anchorage points are exposed to the full load throughout the life span of the structure. Consequently, there are large requirements related to the long-term capacity and fatigue resistance of such systems. Several anchorage systems for use with Aramid, Glass and Carbon FRP tendons have been proposed over the last two decades. Each system is usually tailored to a particular type of tendon. This paper presents a brief overview of bonded anchorage applications while the primary literature review discusses three methods of mechanical anchorage: spike, wedge and clamping. Some proposals for future research are suggested. In general, the systems investigated showed inconsistent results with a small difference between achieving either a successful or an unsuccessful anchorage. These inconsistencies seem to be due to the brittleness of the tendons, low strength perpendicular to the fibre direction and insufficient stress transfer in the anchorage/tendon interface. As a result, anchorage failure modes tend to be excessive principal stresses, local crushing and interfacial slippage (abrasive wear), all of which are difficult to predict.

  • 22.
    Schmidt, Jacob W.
    et al.
    Division of Structural Engineering, Technical University of Denmark.
    Bennitz, Anders
    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.
    Pedersen, Henning
    Operation Management and Systems, COWI A/S.
    Development of mechanical anchor for CFRP tendons using integrated sleeve2010In: Journal of composites for construction, ISSN 1090-0268, E-ISSN 1943-5614, Vol. 14, no 4, p. 397-405Article in journal (Refereed)
    Abstract [en]

    A durable and very efficient external strengthening system is achieved if steel tendons for posttensioning applications can be replaced with carbon fiber-reinforced polymer (CFRP) tendons, and if reliable anchorage systems are developed. This paper presents a newly developed and simple-to-use, two-piece wedge anchorage for CFRP tendons with an integrated sleeve and a differential angle between barrel and wedge sections. Three longitudinal slits are cut into the one-piece wedge, with one slit open and the other two stopping 1 mm from the inner wedge hole. The integrated sleeve holds the wedge's sections together during presetting and loading, resulting in a circumferential confined gripping of the CFRP tendon and optimized surface friction area. Therefore, the one-piece wedge differs from conventional wedge systems, where the wedges act separately with adjacent spaces, wedging the separate tendon sleeve in the longitudinal direction. Evaluation of the failure modes during testing was one of the main keys in achieving an increasingly better performance of the anchorage until the final anchorage was developed. The obtained failure modes are therefore described to enlighten the importance of addressing them when testing. The test setup used and measured behavior are described further together with the loading procedure. The anchorage reached the full capacity of the CFRP tendon and was seen to ensure a stable load of fracture

  • 23.
    Schmidt, Jacob W.
    et al.
    Technical University of Denmark, Division of Structural Engineering.
    Smith, Scott T.
    University of Hong Kong, Department of Civil Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Bennitz, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Goltermann, Per
    Technical University of Denmark, Division of Structural Engineering.
    Pedersen, Henning
    COWI A/S, Department 1704, Operation Management & Systems.
    Numerical simulation and experimental validation of an integrated sleeve-wedge anchorage for CFRP rods2011In: Journal of composites for construction, ISSN 1090-0268, E-ISSN 1943-5614, Vol. 15, no 3, p. 284-292Article in journal (Refereed)
    Abstract [en]

    The tensioning of carbon-fiber-reinforced polymer (CFRP) rods for prestressed concrete applications or posttensioning repair and strengthening has been met with mixed success. This is primarily because of limitations inherent in the use of traditional wedge anchors typically used for steel tendons. Recently, an integrated sleeve-wedge anchorage has been successfully developed specifically for CFRP rods. This paper presents a numerical simulation of the newly developed anchorage by using ABAQUS. The three-dimensional (3D) finite-element (FE) model, which considers material nonlinearity, uses hexagonal elements for the barrel, CFRP rod, and tetrahedral elements for the integrated sleeve wedge. The simulated barrel surface strains are shown to compare well with optically measured strains; however, the numerical results are shown to be sensitive to the mechanical properties of the anchorage and CFRP rod and especially the transverse elastic modulus of the CFRP rod. Finally, the simulated strain distributions throughout the anchorage as well as the distribution of CFRP rod confining pressure are presented. Such strain and pressure distributions enable insights into the inner workings of the anchorage to be achieved

  • 24.
    Schmidt, Jacob W.
    et al.
    Technical University of Denmark.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Bennitz, Anders
    Pedersen, Henning
    COWI A/S.
    FRP tendon anchorage in post-tensioned concrete structures2009In: Concrete Repair, Rehabilitation and Retrofitting: 2nd International Conference on Concrete Repair, Rehabilitation and Retrofitting, ICCRRR-2, 24-26 November 2008, Cape Town, South Africa / [ed] Mark G. Alexander; Hans-Dieter Beushausen; Frank Dehn; Pilate Moyo, Boca Raton, Fla: CRC Press, 2009, p. 419-420Conference paper (Refereed)
    Abstract [en]

    Strengthening of building structures by the use of various external post-tensioning steel tendon systems, is known to be a very efficient method. However, FRP as material in external post-tensioning projects has been investigated during the last decade. The advantages for this material are the high effective Young's modulus and the high stress capacity in the linear elastic range of the material. The use of external tendons increases the requirements on the anchorage systems. This is in particular important when using un-bonded tendon systems, where the anchorage and deviators are the only force transfer points. The demand for high capacity anchorage tendons is fulfilled for steel tendons, but no competitive mechanical anchor has yet been developed for FRP tendon. A new small, reliable and more user friendly anchor has to be developed, before FRP tendons can be utilized with all of its capacity. Thus, several attempts of developing a mechanical FRP anchor have been made worldwide with promising results. Some of these attempts are presented in this paper together wim an insight into a present research collaboration project at the Technical University of Denmark, Luleå University of Technology, Sweden, and COWI AS, Denmark

1 - 24 of 24
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