| 1. |
- Kehoe, Laura, et al.
(author)
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Make EU trade with Brazil sustainable
- 2019
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In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 364:6438, s. 341-
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Journal article (other academic/artistic)
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| 2. |
- Barredo, José I., et al.
(author)
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Mapping and assessment of forest ecosystems and their services : Applications and guidance for decision making in the framework of MAES
- 2015
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Reports (other academic/artistic)abstract
- The aim of this report is to illustrate by means of a series of case studies the implementation of mapping and assessment of forest ecosystem services in different contexts and geographical levels. Methodological aspects, data issues, approaches, limitations, gaps and further steps for improvement are analysed for providing good practices and decision making guidance. The EU initiative on Mappingand Assessment of Ecosystems and their Services (MAES), with the support of all Member States, contributes to improve the knowledge on ecosystem services. MAES is one of the building-block initiatives supporting the EU Biodiversity Strategy to 2020.
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| 3. |
- Eriksen, Jörgen, et al.
(author)
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Guidelines to perform life cycle analysis of bridges
- 2008
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In: Proceedings of Seminar on Sustainability of Constructions - Integrated approach to life-time structural engineering. - 9783867800945 ; , s. 5.27-5.51
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Conference paper (other academic/artistic)
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| 4. |
- Garzon, Olga
(author)
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Resistance of polygonal cross-sections : application on steel towers for wind turbines
- 2013
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Licentiate thesis (other academic/artistic)abstract
- Wind power is considered an efficient alternative for production of electrical energy. One advantage that wind power offers compared to conventional ways of producing energy such as fossil energy and nuclear energy is the low emission of carbon dioxide “CO2” during production of electrical energy. In the last two decades extensive research and huge resources have been focused on production of wind power around the world. In the European Union (EU) the installation of wind power has an annual growth rate of over 11% from 3.2 GW in 2000 to 11.9 GW in 2012 [1] A wind power station consists of a tower with a turbine at the top. In the tower equipment used for transforming kinetic energy in the wind and turbine to electrical energy is placed. The cost for the tower is up to 27% of the total building cost. Building higher towers increases the output of wind power as the wind becomes more constant and the wind speed increases with the increase of the tower height. To make the tower hollow to create space for equipment, decrease weight and increase bending stiffness the walls should be as thin as possible. For such thin walled structures stability is one of the most dangerous failure cases, it leads to brittle failure. The tower needs to be stiff enough to prevent instability. In addition to this, it is important to use connections with high fatigue endurance, which is no considered in this analysis.One solution to reduce transportation costs is to manufacture the tower in sections, at least for onshore towers where the access is difficult. These towers can be made from using a lattice (truss) tower or a tubular tower made from steel. By using sections of high strength steel the towers will have more structural strength with more stability and lower cost as less material is used. As many of the tubular and lattice (truss) towers are made from thin elements it is important to study buckling. Therefore, a study of optimization by geometrical analysis and comparison with the actual standards is performed. Thin plates are often made from cold-formed steel with higher yield strength. The focus of this thesis is in the evaluation and the use of thin folded plates that can be combined to form polygonal cross-sections in towers for wind turbines. An initial numerical study of a folded plate with three different polygonal cross-sections was done using the Finite Element software ABAQUS [2]. The results are compared with EN 1993 part 1-3 [3] and EN 1993 part 1-5 [4]. The FEA showed local buckling as failure mode in all cases of the folded plates. The folded plates are designed to be used as section members for tubular and lattice (truss) towers. In the design for lattice towers the thin folded plates may be connected with gusset plates at different distances over the length of the plate to form a semi-closed cross-section column. For tubular towers the plates were designed to be connected by longitudinal connections to form a tube with a polygonal cross-section. The validity of the design rules given in EN 1993 part 1-3[3], EN 1993 part 1-5 [4], EN 1993 part 3-2 [5]and EN 1993 part 1-6 [6] were used.
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| 5. |
- Gervásio, Helena, et al.
(author)
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Comparative life cycle assessment of tubular wind towers and foundations : Part 2: Life cycle analysis
- 2014
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In: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 74, s. 292-299
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Journal article (peer-reviewed)abstract
- In the first part of the paper the design of tubular towers and respective onshore foundations was addressed. The considered solutions were based on steel, concrete and hybrid steel-concrete tubular towers supporting multi-megawatt turbines of 2, 3.6 and 5 MW power with hub heights of 80, 100 and 150 m respectively. In this second part of the paper, the life cycle analysis of the designed case studies is performed and conclusions about their environmental impact are drawn. Two different scenarios concerning the lifetime of the towers were established. The first scenario considers 20 years lifetime and two different construction methods for the connection of the steel segments, the first based in current technology using flange connections and the second using newly developed friction connections. Assuming equal importance for all environmental categories in this scenario, it may be concluded that for heights up to 100 m hybrid towers with friction connections are the most efficient solution. For higher heights, the concrete tower becomes more efficient. The second scenario considers an increased total lifetime of 40 years, assuming the reuse of the tower after 20 years of operation. In this case, the use of friction connections in steel towers enhances the possibility of dismantling and reusing the tower potentiating much better performance in relation to the environmental category of global warming.
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| 6. |
- Heistermann, Christine
(author)
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Behaviour of pretensioned bolts in friction connections : towards the use of higher strength steels in wind towers
- 2011
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Licentiate thesis (other academic/artistic)abstract
- 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.
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| 7. |
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| 8. |
- Heistermann, Christine, et al.
(author)
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Flangeless Connections in Steel Tubular Wind Towers
- 2014
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In: Proceedings of the METNET Seminar 2013 in Luleå. - Hämeenlinna : HAMK University of Applied Science. - 9789517846417 - 9789517846424 ; , s. 157-168
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Conference paper (other academic/artistic)abstract
- 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.
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| 9. |
- Heistermann, Christine, et al.
(author)
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Influence of execution tolerances for friction connections in circular and polygonal towers for wind converters
- 2017
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In: Advanced steel construction. - : Hong Kong Institute of Steel Construction. - 1816-112X. ; 13:4, s. 343-360
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Journal article (peer-reviewed)abstract
- Friction connections with long open slotted holes have been proven to be a competitive alternative to the conventional flange connections in steel tubular towers for wind energy converters. As full-scale tests are not available, results of Finite Element Analysis (FEA) of the real-scale tower geometry are used in this paper to investigate the influence of tower cross section shape, execution tolerance (gap between the shells) and length of the connection on the bending resistance. Buckling behaviour of the shell in the vicinity of the friction connection in circular and polygonal towers is compared. The friction connection is thoroughly examined and recommendations for execution tolerances are given. The influence of two types of the execution tolerances on the connection strength is considered: inward bended "fingers", leading to inclined gaps, and a parallel gap created by different tower diameters.
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| 10. |
- Limam, Marouene, et al.
(author)
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Modeling three dimensional friction connection for wind towers using finite element methods
- 2011
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In: Proceedings of the 6th European Conference on Steel and Composite Structures. - Budapest : European Convention for Constructional Steelwork, ECCS. - 9789291471034
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Conference paper (peer-reviewed)abstract
- The tubular steel towers supporting wind turbines account for about 15 to 20% of the total installation costs and their optimization may lead to substantial savings with regard to costs and use of material. An innovative solution for assembling joints of a tubular tower for wind turbines has been studied in an European research project called HISTWIN (High-Strength Steel Tower for Wind Turbine). This solution is simpler to produce and 80% less expensive than the traditional flange connection.The paper deals with connections used to assemble sections of tubular steel towers supporting wind turbines. The starting point is a rather simple lap joint connection .This connection is chosen for the sake of simplicity but still having possibility of general conclusions. After that more realistic connection between two tower segments is presented, each section has about 3m high and 2 m in diameter and they are connected by 222 M30 high-strength bolts.Modeling such FE models, which consists of several parts in contact, requires knowledge in contact mechanics with friction, meshing techniques as well as stability and convergence algorithms.A short parametric study is made to evaluate influence of number of bolts and the pretension force on the tubular tower failure mode.Results of FEA and resistance according to European codes, series EN1993-1-8 is considered. Keywords: Finite Element Model, Gap, High Strength Friction Grip Connection, Tubular Steel Tower, contact.
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