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Bennitz, Anders
Publications (10 of 24) Show all publications
Bennitz, A., Täljsten, B. & Danielsson, G. (2012). CFRP strengthening of a railway concrete trough bridge: a case study (ed.). Paper presented at . Structure and Infrastructure Engineering, 8(9), 801-816
Open this publication in new window or tab >>CFRP strengthening of a railway concrete trough bridge: a case study
2012 (English)In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 8, no 9, p. 801-816Article in journal (Refereed) Published
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.

National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-3183 (URN)10.1080/15732479.2010.489787 (DOI)000303612400001 ()2-s2.0-84861359940 (Scopus ID)0f93fcb2-85b6-473d-a567-59bdce0607aa (Local ID)0f93fcb2-85b6-473d-a567-59bdce0607aa (Archive number)0f93fcb2-85b6-473d-a567-59bdce0607aa (OAI)
Note
Validerad; 2012; 20110211 (benand)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Schmidt, J. W., Bennitz, A., Täljsten, B., Goltermann, P. & Pedersen, H. (2012). Mechanical anchorage of FRP tendons: a literature review (ed.). Paper presented at . Construction and Building Materials, 32, 110-121
Open this publication in new window or tab >>Mechanical anchorage of FRP tendons: a literature review
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2012 (English)In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 32, p. 110-121Article in journal (Refereed) Published
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.

National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-13789 (URN)10.1016/j.conbuildmat.2011.11.049 (DOI)000302762200010 ()2-s2.0-84858075949 (Scopus ID)d154f2bc-6d3e-434d-b0e6-d3b65bb4182b (Local ID)d154f2bc-6d3e-434d-b0e6-d3b65bb4182b (Archive number)d154f2bc-6d3e-434d-b0e6-d3b65bb4182b (OAI)
Note
Validerad; 2012; 20120203 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Bennitz, A., Schmidt, J. W., Nilimaa, J., Täljsten, B., Goltermann, P. & Ravn, D. L. (2012). Reinforced concrete T-beams externally prestressed with unbonded carbon fiber-reinforced polymer tendons (ed.). Paper presented at . ACI Structural Journal, 109(4), 521-530
Open this publication in new window or tab >>Reinforced concrete T-beams externally prestressed with unbonded carbon fiber-reinforced polymer tendons
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2012 (English)In: ACI Structural Journal, ISSN 0889-3241, E-ISSN 1944-7361, Vol. 109, no 4, p. 521-530Article in journal (Refereed) Published
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.

National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-3528 (URN)15b485ac-01f2-4558-bd32-2ded9750def0 (Local ID)15b485ac-01f2-4558-bd32-2ded9750def0 (Archive number)15b485ac-01f2-4558-bd32-2ded9750def0 (OAI)
Note
Validerad; 2012; 20110211 (benand)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-03-26Bibliographically approved
Sas, G., Blanksvärd, T., Nilimaa, J., Täljsten, B., Elfgren, L., Bennitz, A. & Carolin, A. (2012). Strengthening of concrete structures with carbon fibre reinforced polymers (CFRP): case studies (ed.). In: (Ed.), Dirch H. Bager; Johan Silfwerbrand (Ed.), Concrete Structures for Sustainable Community: proceedings of the International FIB Symposium 2012, Stockholm, Sweden, 11 - 14 June 2012. Paper presented at FIB Symposium : Concrete Structures for Sustainable Community 11/06/2012 - 14/06/2012 (pp. 423-426). Stockholm: Swedish Concrete Association
Open this publication in new window or tab >>Strengthening of concrete structures with carbon fibre reinforced polymers (CFRP): case studies
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2012 (English)In: 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, Published 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.

Place, publisher, year, edition, pages
Stockholm: Swedish Concrete Association, 2012
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-29762 (URN)35605e8c-0f23-4d04-8001-a28ec7443723 (Local ID)978-91-980098-1-1 (ISBN)35605e8c-0f23-4d04-8001-a28ec7443723 (Archive number)35605e8c-0f23-4d04-8001-a28ec7443723 (OAI)
Conference
FIB Symposium : Concrete Structures for Sustainable Community 11/06/2012 - 14/06/2012
Note

Godkänd; 2012; 20120614 (jonnil)

Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-03-26Bibliographically approved
Bennitz, A. (2011). Externally unbonded post-tensioned CFRP tendons: a system solution (ed.). (Doctoral dissertation). Paper presented at . Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Externally unbonded post-tensioned CFRP tendons: a system solution
2011 (English)Doctoral 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.

Abstract [sv]

I och med introduktionen av fiberkompositer i byggbranschen under slutet av 80-talet har en rad nya verktyg för förstärkning och underhåll av betongkonstruktioner utvecklats. Förstärkning har oftast utförts med pålimmade kompositer utan förspänning. För att ytterligare öka verkningsgraden, både den tekniska och ekonomiska, kan förspänning vara en möjlighet. Särskilt för betongkonstruktioner. Förspänning av en betongkonstruktion medför att man i bruksgränstillståndet begränsar uppkomsten av sprickor och deras storlek. Det ger i sin tur en ökad styvhet hos konstruktionen. Därutöver höjs lasten för när det slakarmerade stålet flyter. I jämförelse med ospända konstruktioner är dock brottlasten densamma, så länge övriga parametrar behålls. Under 2004 genomfördes en pilotstudie vid Luleå tekniska universitet (LTU) för att undersöka framtida möjligheter och utmaningar med förspända, icke vidhäftande kolfiberkompositkablar. I det läget upptäcktes svårigheter att förankra kompositkabeln mot betongen. De koniska killås som användes orsakade antingen brott på kabeln redan vid låga belastningar eller glidning hos kabeln, som omöjliggjorde fullgod kraftöverföring. Ett beslut togs då att tills vidare fokusera på förankringen och genomföra en mer ingående studie kring denna. Som mål sattes upp att arbetet skulle resultera i en liten, tillförlitlig och användarvänlig förankring. Den skulle sen i en förlängning kunna användas för att slutföra pilotstudien och därefter i större tillämpningar. Trots de förhållandevis nedslående resultaten från pilotförsöken visade den grundliga litteraturstudien som presenteras i Artikel 1 att koniska killås trots allt verkar vara den mest lovande typen av förankring för kolfiberkablar. Den bör därför användas som utgångspunkt för fortsatt utveckling. I motsats till vidhäftande, hyls och klämmande förankringar kan killåset göras litet, lätt att montera och också användas i många praktiska tillämpningar. För att undersöka hur de höga radiella tryckspänningarna i ett sådant killås fördelas är olika former av beräkningsmodeller nödvändiga verktyg. I Artikel 2 jämförs tre olika modeller med avseende på hur väl de kan beskriva komplexiteten hos ett koniskt killås. Det är dels en analytisk axisymmetrisk modell, som också härleds i artikeln, dels en axisymmetrisk Finita Element (FE) modell och dels en 3D FE modell. Undersökningen visade att ingen av de axisymmetriska modellerna har kapacitet nog att tillförlitligt modellera killåset. I fortsatta undersökningar har därför endast 3D FE använts. Resultaten från en enkel FE modell ligger också, tillsammans med tidiga laboratorieförsök, som grund för Artikel 3. Däri beskrivs hur ett nytt killås via prototyper och nya lösningar utvecklats, och hur arbetet för att få fram det nya låset också gett en bättre förståelse för interaktionen mellan kolfiberkompositkabel och lås. Som avslutning presenteras en innovativ design där de tre kilarna och den inre hylsan sammanfogats till en enhet. Med den nyutvecklade designen blir förankringen såväl mer tillförlitlig som användarvänlig. Alla kilar har då redan från början rätt position i förhållande till varandra. Den utvecklade förankringslösningen har också lett fram till ett beviljat svenskt patent, bifogat i avhandlingen som Artikel 6. Efter utvecklingen av den nya förankringen var nästa steg i de uppsatta målen implementering av densamma i ett förspänningssystem och nya balkförsök i konstruktionslabbet. Parallellt med planeringen för balkförsöken pågick ett arbete med att ytterligare förbättra låsdesignen. Bland annat användes en mer detaljerad FE modell som sedan jämfördes med mätningar från en ny serie med dragprov. Den nya FE modellen tillsammans med en utvärdering av viktiga parametrar och den slutliga förankringsdesignen presenteras i Artikel 4. Artikel 5 sammanfattar och avslutar forskningsstudien med en testserie om sju stycken, tre meter långa, betongbalkar förspända med utanpåliggande kolfiberkompositstavar. En av balkarna provades utan förstärkning. Förstärkningen hos de övriga varierades med avseende på förspänningsgrad, förspänningens effektiva höjd och användandet av deviator vid balkmitt. Resultaten har jämförts mellan de provade balkarna, med identiska balkar förspända med stålkablar samt med en analytisk modell utvecklad för förspänning med stålkablar. Från resultaten kan utläsas att förspänningen fungerar bra och att beteendet hos balkarna förspända med utanpåliggande kolfiberkablar är fullt jämförbart med det hos balkarna förspända med stålkablar. Likaså visar jämförelsen med de modellerade beteendena på god överensstämmelse, även om vissa skillnader finns mellan uppmätta och modellerade spänningar i kolfiberkabeln. Med målen för forskningen uppfyllda och en ny fungerande förankring framtagen så har vägen till praktiska tillämpningar kortats betydligt, ändå finns några frågetecken kvar att räta ut. Ett är säkerheten hos den här typen av system och nyttan av att använda kolfiberkomposit istället för stål. Innan systemet används i praktiken bör därför följande frågeställningar belysas: Risk för krypbrott i kolfiberarmeringen, inverkan av temperaturförändringar (och temperaturrörelser) i förankringen samt eventuella storlekseffekter vid förankring av kablar med större diametrar. De här frågorna tillsammans med långtidsförsök på förankringen och förspänningssystemet bör ses som viktiga framtida forskningsfrågor.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2011. p. 68
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords
CFRP, prestress, tendon, external, unbonded, anchorage, beams, Civil engineering and architecture - Building engineering, CFRP, förspänning, vajer, utanpåliggande, icke vidhäftande, förankring, Samhällsbyggnadsteknik och arkitektur - Byggnadsteknik
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-26606 (URN)f2ec06db-03e8-439f-ad12-94e73272c293 (Local ID)978-91-7439-206-7 (ISBN)f2ec06db-03e8-439f-ad12-94e73272c293 (Archive number)f2ec06db-03e8-439f-ad12-94e73272c293 (OAI)
Note
Godkänd; 2011; 20110128 (ysko); DISPUTATION Ämnesområde: Konstruktionsteknik/Structural Engineering Opponent: PhD Chris Burgoyne, Dep of Engineering, University of Cambridge, UK Ordförande: Professor Björn Täljsten, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Tid: Fredag den 18 februari 2011, kl 10.00 Plats: F1031, Luleå tekniska universitetAvailable from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-24Bibliographically approved
Schmidt, J. W., Smith, S. T., Täljsten, B., Bennitz, A., Goltermann, P. & Pedersen, H. (2011). Numerical simulation and experimental validation of an integrated sleeve-wedge anchorage for CFRP rods (ed.). Paper presented at . Journal of composites for construction, 15(3), 284-292
Open this publication in new window or tab >>Numerical simulation and experimental validation of an integrated sleeve-wedge anchorage for CFRP rods
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2011 (English)In: Journal of composites for construction, ISSN 1090-0268, E-ISSN 1943-5614, Vol. 15, no 3, p. 284-292Article in journal (Refereed) Published
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

National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-16065 (URN)10.1061/(ASCE)CC.1943-5614.0000171 (DOI)000291724300004 ()2-s2.0-79959346159 (Scopus ID)fa59dee8-5e7b-4349-982f-0ca9cd75a75e (Local ID)fa59dee8-5e7b-4349-982f-0ca9cd75a75e (Archive number)fa59dee8-5e7b-4349-982f-0ca9cd75a75e (OAI)
Note
Validerad; 2011; 20110211 (benand)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Bennitz, A., Grip, N. & Schmidt, J. W. (2011). Thick-walled cylinder theory applied on a conical wedge anchorage (ed.). Paper presented at . Meccanica (Milano. Print), 46(5), 959-977
Open this publication in new window or tab >>Thick-walled cylinder theory applied on a conical wedge anchorage
2011 (English)In: Meccanica (Milano. Print), ISSN 0025-6455, E-ISSN 1572-9648, Vol. 46, no 5, p. 959-977Article in journal (Refereed) Published
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.

Keywords
Mathematics, Matematik
National Category
Infrastructure Engineering Mathematical Analysis
Research subject
Structural Engineering; Mathematics
Identifiers
urn:nbn:se:ltu:diva-3473 (URN)10.1007/s11012-010-9352-6 (DOI)000292818600006 ()2-s2.0-79961022829 (Scopus ID)14d568a0-6d91-11df-ab16-000ea68e967b (Local ID)14d568a0-6d91-11df-ab16-000ea68e967b (Archive number)14d568a0-6d91-11df-ab16-000ea68e967b (OAI)
Note
Validerad; 2011; 20100601 (grip)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Schmidt, J. W., Bennitz, A., Täljsten, B. & Pedersen, H. (2010). Development of mechanical anchor for CFRP tendons using integrated sleeve (ed.). Paper presented at . Journal of composites for construction, 14(4), 397-405
Open this publication in new window or tab >>Development of mechanical anchor for CFRP tendons using integrated sleeve
2010 (English)In: Journal of composites for construction, ISSN 1090-0268, E-ISSN 1943-5614, Vol. 14, no 4, p. 397-405Article in journal (Refereed) Published
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

National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-3963 (URN)10.1061/(ASCE)CC.1943-5614.0000096 (DOI)000279991900006 ()2-s2.0-77955243924 (Scopus ID)1cf090e0-9bc3-11df-a707-000ea68e967b (Local ID)1cf090e0-9bc3-11df-a707-000ea68e967b (Archive number)1cf090e0-9bc3-11df-a707-000ea68e967b (OAI)
Note
Validerad; 2010; 20100730 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Bennitz, A., Grip, N. & Schmidt, J. W. (2010). Thick-walled cylinder theory applied on a conical wedge anchorage: Research report with Matlab implementation documentation (ed.). Paper presented at .
Open this publication in new window or tab >>Thick-walled cylinder theory applied on a conical wedge anchorage: Research report with Matlab implementation documentation
2010 (English)Report (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.

Publisher
p. 53
Keywords
Civil engineering and architecture - Building engineering, Samhällsbyggnadsteknik och arkitektur - Byggnadsteknik
National Category
Infrastructure Engineering Mathematical Analysis
Research subject
Structural Engineering; Mathematics
Identifiers
urn:nbn:se:ltu:diva-23287 (URN)65f1d400-6d76-11df-ab16-000ea68e967b (Local ID)65f1d400-6d76-11df-ab16-000ea68e967b (Archive number)65f1d400-6d76-11df-ab16-000ea68e967b (OAI)
Note
Godkänd; 2010; Bibliografisk uppgift: Förhandsexemplar av kommande artikel utökad med detaljerad dokumentation av Matlab-implementering av en algoritm som presenteras i artikeln; 20100601 (grip)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
Bennitz, A., Täljsten, B. & Schmidt, J. W. (2009). External prestressing of RC T-beams with CFRP tendons (ed.). In: (Ed.), D. J. Oehlers; M.C. Griffith ; R. Seracino (Ed.), Proceedings of the 9th International Symposium on Fiber-Reinforced Polymer Reinforcement for Concrete Structures: . Paper presented at International Symposium on Fiber-Reinforced Polymer Reinforcement for Concrete Structures : 13/07/2009 - 15/07/2009. Adeleide: University of Adelaide
Open this publication in new window or tab >>External prestressing of RC T-beams with CFRP tendons
2009 (English)In: 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, Published paper (Refereed)
Place, publisher, year, edition, pages
Adeleide: University of Adelaide, 2009
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-28448 (URN)2407b300-85b6-11de-8da0-000ea68e967b (Local ID)9780980675504 (ISBN)2407b300-85b6-11de-8da0-000ea68e967b (Archive number)2407b300-85b6-11de-8da0-000ea68e967b (OAI)
Conference
International Symposium on Fiber-Reinforced Polymer Reinforcement for Concrete Structures : 13/07/2009 - 15/07/2009
Note
Godkänd; 2009; 20090810 (benand)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-03-20Bibliographically approved
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