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  • 1.
    Andrade, Pedro
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Pavlovic, Marko
    Faculty of Civil Engineering, University of Belgrade.
    Heistermann, Christine
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Heistermann, Tim
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Structural Behaviour of a Novel Column-Splice Joint: Finger Connection2015In: The 13th Nordic Steel Construction Conference: NSCC-2015 / [ed] Markku Heinisuo; Jari Mäkinen, Tampere: Tampere University of Technology, Department of Civil Engineering , 2015, p. 215-216Conference paper (Refereed)
    Abstract [en]

    The novel joint presented in this paper is a friction connection used for column-splice connections of modular buildings as part of the innovative construction method introduced in the research project Optimization of frames for effective assembling - FRAMEUP. This type of joint provides a quick assembly and can deal with misalignments by introducing a connection gap. A filler and finger plate are welded to the upper part of the column to this end.The gap between finger plates and lower column faces is closed during tightening of the bolts and, thus, establishes a slip-resistant connection. The efficiency of the joint resistance based on different connection gaps subjected to uniform compression is assessed.The column-splice is composed of four slip-resistant connections, one at each side of the tube. Each finger plate consists of three long slotted holes and is welded to the upper column face. Long slotted holes are used to accommodate vertical misalignments and, therefore, allow fitting the bolts which are pre-installed in the lower column. Filler plates with different thicknesses (4, 6 and 8 mm) welded between the finger plate and upper column face are used to create a connection gap which allows balancing horizontal misalignments. The lower column faces consist of each nine holes with no clearance in order to pre-fit the bolts in a workshop. Thus, the assembling process on the construction site can be speeded up as once the lowercolumns are in place all bolts can be tightened immediately.

  • 2.
    Heistermann, Christine
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Behaviour of pretensioned bolts in friction connections: towards the use of higher strength steels in wind towers2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    During recent years wind energy has established as an alternative to commonenergy sources. To advance its competitiveness, the costs for the constructionof a wind tower have to be reduced. One possible option is the use of frictiongrip joints instead of flange connections to join various tower segments in atubular steel tower. Additionally, the time necessary for installation andmaintenance of the bolts in these connections can be decreased, not only forimplementation in tubular towers but also in lattice towers.Four different bolt types have been investigated with respect to the ease ofinstallation and maintenance on the one hand and structural applicability on theother hand. The latter one is mainly defined by the behaviour of the pretensionforce in the bolts. Various influences on the reduction of clamping force areexperimentally checked, such as the type and thickness of coating, thethickness of the clamping package and external loading.The slip factor, which plays an important role in friction connections, isexperimentally achieved in a test on a double shear lap joint. The experiment isthoroughly examined by a finite element analysis, which models the interactionbetween bolts and plates.In various numerical analyses the influence of steel grade and possibleassembling tolerances on the resistance of a friction joint is investigated bothfor single and double shear lap joints.Shortages of EN 1993 parts 1-8 and 1-12 for the use of slip critical joints areidentified.

  • 3.
    Heistermann, Christine
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Resistance of Friction Connections with Open Slotted Holes in Towers for Wind Turbines2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The most common solutions for in-situ connections of steel tubular towersegments of onshore wind turbines are ring flange connections. These havecertain drawbacks, such as e.g. costly production, long delivery time and ratherlow fatigue endurance. Friction connections with long open slotted holes havepreviously been proven to be a competitive alternative. In this work, the newtype of connection is investigated in various scales: segment tests, down-scaledexperiments and full-scale models. The influence of tower cross-section shape,execution tolerance (horizontal gap between the tower segments) and length ofthe connection on the bending resistance is thoroughly studied. In addition,buckling behaviour of the shell in the vicinity of the friction connection intowers with circular and polygonal cross-sections is analysed in order to checkpossible advantages of either cross-section. The influence of two types of theexecution tolerances on the connection strength is investigated: inwards bent“fingers”, leading to inclined gaps, and a parallel gap created by differentdiameters of the tower segments. Based on validated finite element analysesrecommendations for execution tolerances are proposed.A closer look is taken at the level of bolt forces under load application for thenew friction connections as well as for the ring flange connection. For theformer case, the influence of slotted holes on the joint resistance is checked.For both types of connections, comparison is drawn to hand calculation modelsused in engineering practice. Additionally, the distribution of meridionalstresses in the shell in the vicinity of the connection is studied.Based on the findings from the above described investigations,recommendations for the design of friction connections with open slotted holesin steel tubular towers for onshore wind turbines are given.

  • 4.
    Heistermann, Christine
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Heistermann, Tim
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Limam, Marouene
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Finite element analysis of a single lap joint2012In: Nordic Steel Construction Conference 2012: September 5-7, 2012 Oslo, Norway : Proceedings, Oslo: Norwegian Steel Association , 2012, p. 673-682Conference paper (Refereed)
    Abstract [en]

    A single shear lap joint of steel grade S355 is modelled with finite elements to investigate the influence of externally applied tensile loading on the loss of pretension in the engaged bolts. Additionally, a parameter study is performed to understand the effect of various steel grades on the loss of pretension. It is found that the slip resistance of the specimen depends on the steel grade of the clamped plates. Besides, the final resistance of the single shear lap joint has been found to increase after a slip of 0,15 mm has occurred due to a secondary bending moment. However, the final resistance of the specimen has been found to depend on the size of assembling tolerances; the bigger the distance between the clamped plates, the lower the resistance.

  • 5. Heistermann, Christine
    et al.
    Heistermann, Tim
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Remaining pretension force in friction connections2010In: Proceedings of the 4th International Conference on Steel and Composite Structures: 21 - 23 July 2010, Sydney, Australia / [ed] Brian Uy, Singapore: Research Publishing Services, 2010, p. 275-278Conference paper (Refereed)
  • 6. Heistermann, Christine
    et al.
    Husson, Wylliam
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Flange connection vs. friction connection in towers for wind turbines2009In: Nordic Steel Construction Conference: Proceedings : September 2.-4., 2009, Malmö, Sweden, Stockholm: Stålbyggnadsinstitutet , 2009, p. 296-303Conference paper (Refereed)
    Abstract [en]

    The paper deals with connections used to assemble sections of tubular steel towers supporting wind turbines. The design of current ring flange connections is briefly presented. An alternative option for the assembling connection is to use single overlapping friction connection. This is introduced in on-going research project "HISTWIN- High-Strength Steel Tower for Wind Turbine, 2006-2009". The main characteristic of the friction connection is long open slotted holes. Design example for equivalent design load at ultimate load of the friction connection is compared to the flange solution on a particular example of REpower Tower MM92. The benefits of the new connection in terms of design simplicity, fatigue strength and material costs are discussed.

  • 7.
    Heistermann, Christine
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Pavlovic, Marko
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Andrade, Pedro
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Rebelo, Carlos
    ISISE, Department of Civil Engineering, University of Coimbra.
    Silva, Luís Simões da
    ISISE, Department of Civil Engineering, University of Coimbra.
    Finite Element Analysis of Lap Joints in Steel Tubular Towers2014In: Eurosteel 2014: 7th European Conference on Steel and Composite Structures / [ed] Raffaele Landolfo; Frederico M. Mazzolani, Brussels, Belgium: European Convention for Constructional Steelwork, ECCS , 2014, p. 291-292Conference paper (Refereed)
  • 8.
    Heistermann, Christine
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Tran, Anh Tuan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Rebelo, Carlos
    ISISE, Department of Civil Engineering, University of Coimbra.
    Flangeless Connections in Steel Tubular Wind Towers2014In: Proceedings of the METNET Seminar 2013 in Luleå: Metnet Annual Seminar in Luleå, Sweden, on 22 - 23 October 2013 / [ed] Kuldeep Virdi; Lauri Tenhunen, Hämeenlinna: HAMK University of Applied Science , 2014, p. 157-168Conference paper (Other academic)
    Abstract [en]

    Extensive research is conducted on the improvement of renewable energies. One field is the use of wind energy, where the tower construction is one of the main issues. This paper deals with new ideas and ongoing research in this area. To raise the height of steel tubular towers, fatigue as the design limit and constraints due to transportation issues have to be overcome. Changes in the cross-section are considered as one of possible solutions. This work presents an extensive finite element study dealing with different ways to improve shell stability, which become the limiting criteria if a friction connection substitutes the common flange connection between two tower segments. The use of circular and polygonal cross-sections is briefly described and will be investigated in an experimental program.

  • 9.
    Heistermann, Christine
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Bolts for slip resistant joints in towers for wind turbines2012In: Proceedings of the METNET Seminar 2012 in Izmir: Metnet Annual Seminar in Izmir, Turkey, on 10 - 11 October 2012 / [ed] Kuldeep Virdi; Lauri Tenhunen, Hämeenlinna, Finland: HAMK University of Applied Science , 2012, p. 31-39Conference paper (Other academic)
    Abstract [en]

    This paper deals with a new solution to connect various segments in a tubular steel tower for wind power plants. Tests are performed to determine appropriate bolts for such connections. They focus on checking the development of pretension forces in the bolts during a period of one week. The behaviour of four different types of bolts is described and evaluated. For one type of bolt the force reduction is monitored for two different clamping lengths. Finally, recommendations for further tests are given.

  • 10.
    Heistermann, Christine
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Loss of pretension in bolted connections: influence of loading2011In: Proceedings of the 6th European Conference on Steel and Composite Structures: Eurosteel 2011, August 31 - September 2, 2011, Budapest, Hungary, Budapest: European Convention for Constructional Steelwork, ECCS , 2011, p. 399-404Conference paper (Refereed)
    Abstract [en]

    A common problem in bolted connections is the self-loosening effect of bolts over time. Therefore the remaining strength in a slip resistant connection can only roughly be estimated for a certain point of time. A possible solution ot avoid self-loosening is the use of lockbolts, which have been studied in order to achieve recommendations for connections which are "free from maintenance". The pretension force in the bolt unavoidably reduces over time due to creep of primer, forces in bolts and in plates. These effects are experimentally studied. For all types of connections this effect is very important and in this paper the focus is brought on lap joints, where the influence of various types of loading is examined.

  • 11.
    Heistermann, Christine
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Simões, R.
    ISISE, Department of Civil Engineering, University of Coimbra.
    Rebelo, C.
    ISISE, Department of Civil Engineering, University of Coimbra.
    Silva, L. Simões da
    ISISE, Department of Civil Engineering, University of Coimbra.
    Design of slip resistant lap joints with long open slotted holes2013In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 82, p. 223-233Article in journal (Refereed)
    Abstract [en]

    Current design procedures for slip resistant connections according to Eurocodes and American specifications are reviewed. Although failure of a slip resistant connection is defined at different levels of slip, 0.15 mm and 0.5 mm respectively, the calculation of the resistance is similar. Most of the research is performed on bolts in normal clearance holes. A testing program was conceived to evaluate the influence of long open slotted holes on the behavior of slip resistant lap joints with tension control bolts because of possible use of such connections in towers for wind turbines. In comparison to specimens with normal clearance holes it is found that the friction coefficient is about 4% lower. This reduction is lower than suggested by the current correction factors. Since none of the design procedures takes the reduction in bolt forces by time into account, the loss of pretension force is experimentally studied and an approximation is proposed. A second testing program was carried out with friction standard specimens in order to determine the slip factor for different surface treatments and steel grades in range between S275 and S690. The achieved slip factors for different surface preparations are in accordance with the classification of friction surfaces in EN 1090-2:2008 and differences obtained are addressed to variations in exposure to weather conditions. The steel grade does not have a significant influence.

  • 12.
    Limam, Marouene
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Heistermann, Christine
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Finite element analysis of a single shear lap joint connection2012In: Nordic Steel Construction Conference 2012: September 5-7, 2012 Oslo, Norway : Proceedings, Oslo: Norwegian Steel Association , 2012Conference paper (Refereed)
    Abstract [en]

    In steel tubular towers flange connections are used to assemble two segments of the tower. As an alternative for the economical and technological barriers, a new type of friction connection is investigated.This connection consists of the upper tower segment, where normal clearance holes are made and where bolts are preinstalled and the lower tower segment where open slotted holes are prepared.This paper describes a method based on a three-dimensional finite element model of a single shear lap joint connection. A finite element (FE) model is developed using the non-linear code ABAQUS and a number of FE simulations are made by varying the most significant parameters which can affect the accuracy and efficiency of the model; boundary conditions, mesh density, fabrication tolerances etc.. The ability of the models to give a satisfactory representation of the assembling connection in a tower for wind turbines is evaluated. Secondary bending, which occurs because of geometric eccentricities when the element is loaded in tension, is studied by simplified analytical model and by ABAQUS.Results of FEA and resistance according to European codes, series EN1993-1-8 are considered.

  • 13.
    Pavlovic, Marko
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Heistermann, Christine
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Pak, Daniel
    Institut für Stahlbau, Institute for Steel Construction, RWTH Aachen, University.
    Feldmann, Markus
    Institut für Stahlbau, Institute for Steel Construction, RWTH Aachen, University.
    Rebelo, Carlos
    ISISE, Department of Civil Engineering, University of Coimbra.
    Silva, Luís Simões da
    ISISE, Department of Civil Engineering, University of Coimbra.
    Connections in towers for wind converters: part I: Evaluation of down-scaled experiments2015In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 115, p. 445-457Article in journal (Refereed)
    Abstract [en]

    The cost of a tubular steel tower supporting a wind converter becomes increasingly important in a competitive energy market. In-situ connection between tower segments is an important factor of the design. The tower segments are usually connected by welded ring flanges. An alternative solution based on a novel single lap friction connection is analysed. The purpose of the research presented in this paper is to thoroughly analyse the behaviour of both connections by an experimental testing programme and advanced finite element analysis (FEA). Down-scaled experiments of ring flange and friction connection in circular towers were performed using a 4-point bending test set-up. Altogether eight connections joining cylindrical shell, 1 m diameter, plate thickness 8 mm and total span of about 7 m were tested. A friction connection with long open slotted holes and two different cases of the ring flange connection are considered: with perfectly flat flanges and flanges with geometric imperfection. Results of advanced quasi-static FEA, using explicit dynamic solver and ductile damage material model for bolts, are compared to experiments. Failure modes, bolt forces and distribution of meridional membrane stresses in the shell in the vicinity of connections are analysed. Existing hand-calculation models, for the bolt force and normal stress distribution in the shell are validated by experiments and FEA.

  • 14.
    Pavlovic, Marko
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Heistermann, Christine
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Pak, Daniel
    Institut für Stahlbau, Institute for Steel Construction, RWTH Aachen, University.
    Feldmann, Markus
    Institut für Stahlbau, Institute for Steel Construction, RWTH Aachen, University.
    Rebelo, Carlos
    ISISE, Department of Civil Engineering, University of Coimbra.
    Silva, Luís Simões da
    ISISE, Department of Civil Engineering, University of Coimbra.
    Connections in towers for wind converters: Part II: The friction connection behaviour2015In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 115, p. 458-466Article in journal (Refereed)
    Abstract [en]

    A novel friction connection consisting of a single lap joint with long open slotted holes is proposed for use in tubular towers for wind converters for in-situ connections. This is a competitive alternative to the common ring flange connection as it has been shown in the European Project “HISTWIN”. Two sets of experiments are analysed: the down-scaled tubular steel tower 4-point bending experiments using high-strength bolts M20 and a single lap joint using plate thickness 25 mm and tension control bolts M30.The main motivation for this paper is a much higher bending resistance obtained in the 4-point bending experiments compared to predictions based on hand-calculation models.Results of experiments are used to validate finite element analysis (FEA). Explicit solver and the most realistic geometry of the bolts are the main characteristics of the FEA performed. Very good agreement between the experiments and FEA results is obtained, which provides credibility of the computational approach used to thoroughly examine experimental results. New evidences of the friction connection behaviour are provided: a short-term loss of preloading force due to external loading, transfer of shear force in the single lap joint and influence of the slotted hole on the joint resistance.Results obtained from hand-calculation models are used to predict the loss of preloading, the bending resistance of the connection and meridional stresses in the tower shell in the vicinity of the connection, which are compared to the experiments and the FEA. Recommendations related to use of the hand-calculation models in the design are provided.

  • 15.
    Pavlovic, Marko
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Heistermann, Christine
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Veljkovic, Milan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Pak, Daniel
    Institut für Stahlbau, Institute for Steel Construction, RWTH Aachen, University.
    Feldmann, Markus
    Institut für Stahlbau, Institute for Steel Construction, RWTH Aachen, University.
    Rebelo, Carlos
    ISISE, Department of Civil Engineering, University of Coimbra.
    Silva, Luís Simões da
    ISISE, Department of Civil Engineering, University of Coimbra.
    Friction connection vs. ring flange connection in steel towers for wind converters2015In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 98, p. 151-162Article in journal (Refereed)
    Abstract [en]

    Tubular steel towers are the most commonly used structures to support wind converters. Towers are fabricated in welded segments, complying with the traffic requirements for transportation, and in-situ assembled. Ring flange connections are used to connect two segments. Fatigue endurance of the ring flange to the shell weld, class 71, is often the design criterion and imposes a limit on the shell thickness. Recently studied friction connections with long opened slotted holes, in HISTWIN and HISTWIN2 projects, provides a remedy for this limitation. The main purpose of this paper is to compare performance of the ring flange connection and the novel friction considering connection of a real tubular tower segment 3.37 m in diameter and 24 mm shell thickness. This cross-section is designed for the ultimate load MEd = 45.8 MNm and the steel grade S355. Finite Element Method is used to investigate possible failure modes of the connection. Advanced FEA comprise the realistic geometry of the connection, ductile damage material model and element removal using explicit dynamic solver. This allows sophisticated analysis of the behaviour and direct comparison of the results for both connection alternatives. The FEA is validated by down-scaled experiments performed previously within the HISTWIN project. The friction connection is thoroughly examined: geometry of the connection, influence of the shell imperfection in the vicinity of the connection and possible use of higher resistance steel grades. By focusing on key issues of the friction connection recommendations for the design are provided together with a numerical example

  • 16.
    Veljkovic, Milan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Heistermann, Christine
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Husson, Wylliam
    Limam, Marouene
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Feldmann, M.
    Rheinisch-Westfälische Technische Hochschule Aachen (RWTH).
    Naumes, J.
    Rheinisch-Westfälische Technische Hochschule Aachen (RWTH).
    Pak, D.
    Rheinisch-Westfälische Technische Hochschule Aachen (RWTH).
    Faber, T.
    Germanischer Lloyd Industrial Services GmbH.
    Klose, M.
    Germanischer Lloyd Industrial Services GmbH.
    Fruhner, K-U
    Germanischer Lloyd Industrial Services GmbH.
    Krutschinna, L.
    Germanischer Lloyd Industrial Services GmbH.
    Baniotopoulos, C.
    Aristotle University of Thessaloniki.
    Lavasas, I.
    Aristotle University of Thessaloniki.
    Pontes, A.
    Martifer Energia — Equipamentos para energia, S.A..
    Ribeiro, E.
    Martifer Energia — Equipamentos para energia, S.A..
    Hadden, M.
    Martifer Energia — Equipamentos para energia, S.A..
    Sousa, R.
    Martifer Energia — Equipamentos para energia, S.A..
    Silva, L. da
    Faculdade de Ciências e Tecnologia da Universidade de Coimbra.
    Rebelo, C.
    Faculdade de Ciências e Tecnologia da Universidade de Coimbra.
    Simoes, R.
    Faculdade de Ciências e Tecnologia da Universidade de Coimbra.
    Henriques, J.
    Faculdade de Ciências e Tecnologia da Universidade de Coimbra.
    Matos, R.
    Faculdade de Ciências e Tecnologia da Universidade de Coimbra.
    Nuutinen, J.
    Rautaruukki Oy.
    Kinnunen, H.
    Rautaruukki Oy.
    High-strength tower in steel for wind turbines (Histwin): Final report2012Report (Refereed)
    Abstract [en]

    Innovative solutions for assembling joints of a tubular tower for wind turbines were studied and the project provides a background for design. This solution is simpler to produce and 80 % less expensive than traditional flange connection. Our feasibility study at the production plant indicates that the towers would be easy to assemble in situ. In addition to the direct cost savings due to the technical simplicity of the solution, the higher fatigue endurance than that of the flange connection is experimentally established. Further reduction of costs due to optimal use of higher-strength steel grades, especially in the bottom segments of the tower where the stiffening of the door opening is costly, is shown in the report. The total reduction of the costs for tower is estimated at about 10–15 % compared to the traditional tower. The project objectives are achieved in following sequences. • Experimental activities of the friction connection: small-scale tests to establish resistance of the friction connection for a variety of faying surfaces and bolt types, accompanying testing to ensure realistic input data for FEA, long-term testing to establish loss of pretension forces during the lifetime and fatigue tests.• Bending test of the friction and flange connection in a down-scaled tower. • Feasibility of production of the tower segments in the laboratory and at the production plant. • Monitoring of the existing tower to access a stress variation during the operation. • FEA analysis of experimental results and a complete case study of the monitored tower. Numerical examples for design of the friction connection are given for the sake of illustration and to encourage use of the new connection

  • 17.
    Veljkovic, Milan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Limam, Marouene
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Heistermann, Christine
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Rebelo, Carlos
    University of Coimbra.
    Simoes da Silva, Luis
    University of Coimbra.
    Feasibility study of friction connection in tubular towers for wind turbines2010In: Steel structures: culture & sustainability 2010: international symposium, Istanbul, 21 - 23 September 2010, Istanbul: Turkish Constructional Steelwork Association , 2010Conference paper (Refereed)
    Abstract [en]

    In steel tubular towers flange connections are used to assemble two segments of the tower. As an alternative for these fatigue-sensitive joints a new type of friction connection has been investigated both in laboratory and at a production plant where the feasibility study was performed. The specimen used in the feasibility test consists of two tower segments, each about 3m high and 2 m in diameter. The segments are connected by 222 M30 high-strength bolts. The production process and tolerances achieved are briefly explained. The assembling process is modeled using a realistic FEA model to predict the stress in the segments during pretensioning. A simplified FE analysis was performed to assess the influence of the compressive strength of the specimens. This paper presents results of a short parametric study on the influence of the gap between two tower segments exploring possibilities to use higher-strength steel in the towers. Keywords: Finite Element Model, Gap, High Strength Friction Grip Connection, Tubular Steel Tower, Wind Energy Converter

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