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Lundqvist, Joakim
Publications (7 of 7) Show all publications
Lundqvist, J., Bernspång, L., Täljsten, B. & Olofsson, T. (2007). A probability study of finite element analysis of near surface mounted carbon fiber reinforced polymer bonded to reinforced concrete (ed.). In: (Ed.), T.C. Triantafillou (Ed.), Fiber-Reinforced Polymer Reinforcement for Concrete Structures: Proceedings of the 8th International Symposium on Fiber Reinforced Polymer Reinforcement for Concrete Structures, FRPRCS-8. Paper presented at International Symposium on Fiber Reinforced Polymer Reinforcement for Concrete Structures : 16/07/2007 - 18/07/2007. Patras: FRPRCS-8 Symposium Secretariat
Open this publication in new window or tab >>A probability study of finite element analysis of near surface mounted carbon fiber reinforced polymer bonded to reinforced concrete
2007 (English)In: Fiber-Reinforced Polymer Reinforcement for Concrete Structures: Proceedings of the 8th International Symposium on Fiber Reinforced Polymer Reinforcement for Concrete Structures, FRPRCS-8 / [ed] T.C. Triantafillou, Patras: FRPRCS-8 Symposium Secretariat , 2007Conference paper, Published paper (Refereed)
Abstract [en]

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

Place, publisher, year, edition, pages
Patras: FRPRCS-8 Symposium Secretariat, 2007
National Category
Infrastructure Engineering Construction Management
Research subject
Structural Engineering; Construction Engineering and Management
Identifiers
urn:nbn:se:ltu:diva-31661 (URN)5e8d53b0-7733-11dc-80da-000ea68e967b (Local ID)978-960-8969-0-0 (ISBN)5e8d53b0-7733-11dc-80da-000ea68e967b (Archive number)5e8d53b0-7733-11dc-80da-000ea68e967b (OAI)
Conference
International Symposium on Fiber Reinforced Polymer Reinforcement for Concrete Structures : 16/07/2007 - 18/07/2007
Note
Godkänd; 2007; Bibliografisk uppgift: CD-ROM; 20071010 (lber)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-03-20Bibliographically approved
Enochsson, O., Lundqvist, J., Täljsten, B., Rusinowski, P. & Olofsson, T. (2007). CFRP strengthened openings in two-way concrete slabs: an experimental and numerical study (ed.). Paper presented at . Construction and Building Materials, 21(4), 810-826
Open this publication in new window or tab >>CFRP strengthened openings in two-way concrete slabs: an experimental and numerical study
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2007 (English)In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 21, no 4, p. 810-826Article in journal (Refereed) Published
Abstract [en]

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

National Category
Infrastructure Engineering Construction Management
Research subject
Structural Engineering; Construction Engineering and Management
Identifiers
urn:nbn:se:ltu:diva-9815 (URN)10.1016/j.conbuildmat.2006.06.009 (DOI)000244502000012 ()2-s2.0-33845354214 (Scopus ID)88022d20-b05e-11db-840a-000ea68e967b (Local ID)88022d20-b05e-11db-840a-000ea68e967b (Archive number)88022d20-b05e-11db-840a-000ea68e967b (OAI)
Note
Validerad; 2007; 20061212 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Lundqvist, J. (2007). Numerical analysis of concrete elements strengthened with carbon fiber reinforced polymers (ed.). (Doctoral dissertation). Paper presented at . Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Numerical analysis of concrete elements strengthened with carbon fiber reinforced polymers
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Due to the growing number of ageing reinforced concrete structures such as buildings and bridges, there is an increasing interest in condition assessment and strengthening methods. Deterioration processes and demands for higher loads contribute to this interest. If the service life of a structure can be extended by repair and/or strengthening instead of building a new structure, much money can be saved. A strengthening method that has gained increasing acceptance and popularity in recent years is strengthening with fiber reinforced polymer (FRP) composites. One common type of FRP material is carbon FRP (CFRP). The FRP strengthening system consists of the strengthening material, a FRP, and the bonding material, usually an epoxy adhesive. Strengthening with FRP can generally be divided in two types of techniques: externally bonded sheets/plates and near surface mounted reinforcement (NSMR). The technique of bonding FRP sheets/plates externally encompass of bonding the FRP onto a prepared surface on a structural member. In the NSMR technique, a longitudinal groove is cut in the surface of a structural element, followed by applying the bonding material into the groove and inserting a FRP bar. The most important characteristic of a FRP strengthening system is the ability to transfer loads acting on a deficient structural member to the strengthening material. A detrimental event for a strengthened member is failure in the bond region, denoted as debonding. This means failure is occurring prior to the designed or predicted capacity of the strengthened member and must be avoided. The behavior of the complete composite system with concrete, adhesive, FRP, and internal reinforcement is quite complex. A sophisticated alternative when studying the performance of concrete structural members strengthened with FRP is the finite element (FE) method. To properly model the problem at hand, several considerations must be made in a FE analysis: solution procedures, material models, boundary conditions, etc. This thesis aims to contribute to the understanding of the behavior of FRP strengthened structures in general and NSMR CFRP strengthened concrete members in particular. Nonlinear 3D FE analysis is utilized to investigate the behavior of FRP strengthened slabs, with and without openings, and two different kinds of bond testing methods: a beam bending test and a NSMR anchorage test. The results from the slab tests show that slabs with openings can be strengthened with externally bonded CFRP sheets and the performance is even better than for traditionally steel reinforced slabs. The numerical evaluations show good agreement with the experimental results. The results from the beam bending tests indicate that the externally bonded sheet and plate have an effective bond length and that NSMR have an anchorage length larger than tested bond lengths. The numerical results are sensitive to the values of the fracture energy, the tensile strength, and the shape of the softening response for the concrete. The results in the NSMR anchorage test show that the failure behavior could be captured and explained only by combining the experimental observations and the FE analysis. The failure mode is a combined failure in the concrete and the adhesive; however, the maximum transferable load is obtained when a major crack at the very end of the bond length is developing in the concrete.

Abstract [sv]

Idag finns det ett växande intresse för tillståndsbedömning och förstärkningsmetoder eftersom många betongkonstruktioner i vårt samhälle, som t.ex. broar och byggnader, blir allt äldre. Under sin livslängd kan en konstruktion vara utsatt för nedbrytningsangrepp eller ökade belastningar och mycket pengar kan sparas om konstruktionen kan repareras och/eller förstärkas istället för att bytas ut. Inom detta område har förstärkning med fiberkompositer blivit en allt mer accepterad och populär metod. Särskilt kolfiberkompositer används mycket.De ingående delarna i ett fiberförstärkningssystem är förstärkningsmaterialet, fiberkompositen, och limmet vilket vanligtvis är ett epoxilim. Det finns två typer av fiberförstärkningssystem: utanpåliggande och ytmonterad förstärkning (near surface mounted reinforcement; NSMR). En utanpåliggande fiberförstärkning utförs genom att limma fiberkompositen på betongytan. I NSMR-metoden sågas först ett spår upp i betongytan därefter fylls spåret med epoxi och avslutas med att en fiberstav trycks in i limmet. Den viktigaste uppgiften för ett fiberförstärkningssystem är dess förmåga att föra över laster från en svag konstruktionsdel till förstärkningsmaterialet. En mycket olycklig händelse för ett fiberförstärkt betongelement vore om det sker ett brott i limmet eller området kring limmet vilket gör att konstruktionen inte kan bära den last den är konstruerad för. Ett fiberförstärkt betongelement består av flera material: betong, stålarmering, lim och fiberkomposit. Detta gör att elementets uppträdande är mycket komplicerat och avancerade analysmetoder måste tillämpas för att undersöka det. Finita element (FE) metoden är ett bra val för sådana undersökningar. I FE-analyser finns det många faktorer att ta hänsyn till t.ex. typ av lösningsalgoritm, materialmodell, randvillkor, mm.Målet för denna avhandling är att tillföra kunskap om hur fiberförstärkta betongkonstruktioner beter sig och speciellt beteendet hos NSMR-förstärkta betongelement. Med hjälp av FE-metoden analyseras beteendet hos dels kolfiberförstärkta plattor, med och utan hål, dels metoder för att prova förankringsbeteendet för fiberförstärkningar nämligen balkböjningstest och förankringstest för NSMR. Resultaten visar att det är möjligt att kolfiberförstärka plattor med uppsågade hål och att kapaciteten blir högre än för plattor utan hål. Resultatet från FE-analyser överensstämmer väl med de experimentella resultaten. Balkböjningstesterna tyder på att den utanpåliggande förstärkningen har en effektiv förankringslängd och att NSMR har en förankringslängd som är längre än de prövade. FE-analyserna visade sig känsliga för vilka värden som valts på brottenergi, draghållfasthet och utseende på mjuknandekurva. Endast genom att kombinera resultaten från experimenten och FE-analysen kunde brottbeteendet hos NSMR-förankringstestet identifieras och förklaras. Brottmoden är ett kombinerat brott i både betongen och limmet. Brottlasten erhålls emellertid när en större spricka uppstår i slutet av den limmade längden.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2007. p. 50
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544 ; 2007:07
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-18415 (URN)883b26c0-d2f5-11db-b6e3-000ea68e967b (Local ID)883b26c0-d2f5-11db-b6e3-000ea68e967b (Archive number)883b26c0-d2f5-11db-b6e3-000ea68e967b (OAI)
Note
Godkänd; 2007; 20070315 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
Jonasson, J.-E. & Lundqvist, J. (2007). Planering av sprickbegränsning för parkeringsgaraget Davidshalls torg i Malmö (ed.). Paper presented at . Bygg & Teknik, 99(7), 21-24
Open this publication in new window or tab >>Planering av sprickbegränsning för parkeringsgaraget Davidshalls torg i Malmö
2007 (Swedish)In: Bygg & Teknik, ISSN 0281-658X, Vol. 99, no 7, p. 21-24Article in journal (Other (popular science, discussion, etc.)) Published
Abstract [sv]

Parkeringsgaraget Davidshalls torg i Malmö planeras att utföras med stomme i armerad betong. Då en stor del av garaget kommer att ligga under grundvattenytan kommer stommen att utsättas för ensidigt horisontellt och vertikalt vattentryck. Byggandet startar med gjutning av en omslutande slitsmur, som efter urschaktning sammanfogas med grundplattan via gjutfog och ingjutning av slitsmuren utstickande armering. Aktuell studie är genomförd på uppdrag av Tyréns AB och visar hur man kan genomföra gjutningen av bottenplattan samt vilka åtgärder som behövs för att bottenplattan ska bli "sprickfri" och därmed vattentät.

National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-10665 (URN)98086740-91e8-11dc-9a81-000ea68e967b (Local ID)98086740-91e8-11dc-9a81-000ea68e967b (Archive number)98086740-91e8-11dc-9a81-000ea68e967b (OAI)
Note
Godkänd; 2007; 20071113 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
Rusinowski, P., Täljsten, B., Enochsson, O., Olofsson, T. & Lundqvist, J. (2006). Numerical analysis of two-way concrete slabs with openings strengthened with CFRP (ed.). In: (Ed.), Paulo J. S. Cruz; Dan M. Frangopol (Ed.), Bridge maintenance, safety, management, life-cycle performance and cost: proceedings of the Third International Conference on Bridge Maintenance, Safety and Management, Porto, Portugal, 16 - 19 July 2006. Paper presented at International Conference on Bridge Maintenance, Safety and Management : 16/07/2006 - 19/07/2006 (pp. 1045-1046). London: Taylor & Francis Group
Open this publication in new window or tab >>Numerical analysis of two-way concrete slabs with openings strengthened with CFRP
Show others...
2006 (English)In: Bridge maintenance, safety, management, life-cycle performance and cost: proceedings of the Third International Conference on Bridge Maintenance, Safety and Management, Porto, Portugal, 16 - 19 July 2006 / [ed] Paulo J. S. Cruz; Dan M. Frangopol, London: Taylor & Francis Group, 2006, p. 1045-1046Conference paper, Meeting abstract (Other academic)
Abstract [en]

Carbon Fibre Reinforced Polymers, CFRP, offer excellent corrosion resistance to environmental agents as well as the advantages of high stiffness-to-weight and strength-to-weight ratios when compared to conventional construction materials. Perhaps the biggest advantage of CFRP is its tailorability. One common application for CFRP sheets is to strengthen slabs and walls when openings are to be made. In spite of this, there have not been many studies reported on slabs with openings strengthened with CFRP and especially, not with distributed loading. This paper presents numerical analyses of simply supported two-way concrete slabs with openings strengthened with CFRP sheets. The finite element program ABAQUS is utilized for the analyses. The analyses are compared with full-scale laboratory tests and show a good agreement

Place, publisher, year, edition, pages
London: Taylor & Francis Group, 2006
National Category
Infrastructure Engineering Construction Management
Research subject
Structural Engineering; Construction Engineering and Management
Identifiers
urn:nbn:se:ltu:diva-38912 (URN)d76e28b0-7d0a-11df-ab16-000ea68e967b (Local ID)0-415-40315-4 (ISBN)978-0-415-40315-3 (ISBN)d76e28b0-7d0a-11df-ab16-000ea68e967b (Archive number)d76e28b0-7d0a-11df-ab16-000ea68e967b (OAI)
Conference
International Conference on Bridge Maintenance, Safety and Management : 16/07/2006 - 19/07/2006
Note
Godkänd; 2006; 20100621 (andbra)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2018-03-20Bibliographically approved
Lundqvist, J., Nordin, H., Täljsten, B. & Olofsson, T. (2005). Numerical analysis of concrete beams strengthened with CFRP: a study of anchorage lengths (ed.). In: (Ed.), J.F. Chen; J.G. Teng (Ed.), Proceedings of the International Symposium on Bond Behaviour of FRP in Structures: BBFS 2005. Paper presented at International Symposium on Bond Behaviour of FRP in Structures : 07/12/2005 - 09/12/2005 (pp. 239-246). : International Institute for FRP in Construction
Open this publication in new window or tab >>Numerical analysis of concrete beams strengthened with CFRP: a study of anchorage lengths
2005 (English)In: Proceedings of the International Symposium on Bond Behaviour of FRP in Structures: BBFS 2005 / [ed] J.F. Chen; J.G. Teng, International Institute for FRP in Construction , 2005, p. 239-246Conference paper, Published paper (Refereed)
Abstract [en]

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

Place, publisher, year, edition, pages
International Institute for FRP in Construction, 2005
National Category
Infrastructure Engineering Construction Management
Research subject
Structural Engineering; Construction Engineering and Management
Identifiers
urn:nbn:se:ltu:diva-31715 (URN)5f866830-09ef-11dc-9854-000ea68e967b (Local ID)5f866830-09ef-11dc-9854-000ea68e967b (Archive number)5f866830-09ef-11dc-9854-000ea68e967b (OAI)
Conference
International Symposium on Bond Behaviour of FRP in Structures : 07/12/2005 - 09/12/2005
Note
Godkänd; 2005; 20070524 (ysko)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-03-20Bibliographically approved
Lundqvist, J. (2004). Numerical simulation of tube hydroforming: adaptive loading paths (ed.). (Licentiate dissertation). Paper presented at . Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Numerical simulation of tube hydroforming: adaptive loading paths
2004 (English)Licentiate thesis, monograph (Other academic)
Abstract [en]

The tube hydroforming process is still to be considered a new and advanced technique. The process has been adopted into several industries, e.g. automotive and aero. A tube that has been cut to appropriate length, and by bending or crushing often been preformed, is placed in a die. The tube is filled with a hydraulic liquid and the ends are closed by side cylinders that press against the ends, creating an axial force in the tube. Simultaneously, the liquid is pressurized and the material of the tube yields and flows into the die cavities. The part is formed. In simulations of forming processes, users prescribe the fluid pressure in the work piece and the axial load exerted by the cylinders. Nowadays, many simulations must be performed, trial-and-error, to find appropriate loading paths for the pressure and the axial load. A more effective technique would be that the simulation program itself generates the pressure and the axial load. Depending on the magnitude and the proportionality between the pressure and the axial load, the tube fails either by rupture or wrinkling. In between these two failure boundaries there is a safe area, a process window, where the simulation yields useful results. An adaptive loading procedure would react to the boundaries and change the pressure and axial load accordingly to avoid failure. Today, the preferable virtual verification tool for tube hydroforming processes is the explicit finite element method. The economical cost of simulations by explicit time integration methods is directly proportional to the computational time. It is desirable to prescribe the simulation time to be as short as possible. Till now, program users have set a very high simulation time to avoid the problem with shorter simulation times - unreliable results due to dynamic effects. An easy way of defining the limit of the simulation time when it goes from reliable results to unreliable would be desirable. A part of the process window is established for different simulation times. It is shown that the simulation results changes abruptly at a certain value of the simulation time. Also, adaptive loading algorithms, the process window and the simulation time problem are investigated. A thorough literature survey is carried out in the tube hydroforming area.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2004. p. 88
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757 ; 2004:26
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-17759 (URN)50911c80-aee6-11db-803d-000ea68e967b (Local ID)50911c80-aee6-11db-803d-000ea68e967b (Archive number)50911c80-aee6-11db-803d-000ea68e967b (OAI)
Note

Godkänd; 2004; 20070128 (ysko)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved

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