Optimization of a hybrid tower for onshore wind turbines by ......RESEARCH Open Access Optimization of a hybrid tower for onshore wind turbines by Building Information Modeling and

Alvarez-Anton et al. Visualization in Engineering 2016, 3:http://www.viejournal.com/content/3/1/

RESEARCH Open Access

Optimization of a hybrid tower for onshorewind turbines by Building InformationModeling and prefabrication techniques

Abstract

Background: Nowadays wind energy is becoming increasingly significant in the planning, development andgrowth of new electricity supply systems. Special attention has been given to land-based turbines for ensuring theefficient economical operation of massive hubs rising 100m above the ground, based on the idea that the biggerthe turbine, the more complicated are the transportation and assembly processes.

Methods: A new design of a wind turbine has several advantages compared to conventional designs; one of theseadvantages lies in the use of prefabricated elements, which increases efficiency. The implementation of informationtechnology as a complement to prefabrication techniques is a further aim of this research, which seeks to improvethe overall performance of the project. Consequently, Building Information Modelling is suggested as the mostsuitable methodology for complementing off-site techniques and reaching higher efficiency by improving design,manufacture, transportation and assembly processes.

Results: This paper will present the research project “hybrid² tower for wind turbines” funded by the State of Hesse,Germany, which focuses on a new, efficient and economical design for high wind turbine towers. The new hybrid²tower is composed of a concrete tower containing prefabricated concrete quarter-circle elements, steel beams anda steel tube tower on the top. The combination of concrete and steel beams improves the static and dynamicperformance of the main supporting structure. With this new design, the weight of the concrete tower is estimatedto decrease by 40 % compared to a traditional full-concrete tower and, as a positive consequence, the cost ofassembly (including assembly on site) is reduced.

Conclusions: Due to the energy revolution, a special focus is put on the development of renewable energies,especially wind power. The steadily increasing hub heights of wind turbines means that tower structures have tobe more massive. The development of the hybrid² tower by using Building Information Modeling andprefabrication techniques leads to an optimized performance and reduces transport and assembly costs.

BackgroundShortly after the nuclear disaster in Fukushima in 2011,the German Federal Government decided to phase outall nuclear power plants and now plans to achieve thisby 2022. The aim is to shut down the plants gradually.For this reason, Germany puts special focus on the de-velopment of renewable energies like wind power, solarenergy, hydroelectricity, biomass energy, etc. Of theserenewable forms of energy, wind power has the greatest

* Correspondence: [email protected] of Civil Engineering, Technische Hochschule Mittelhessen,Gießen, Germany

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potential for expansion. Countries like China, the U.S.,Germany, Spain and India have a worldwide share of72 % of wind power production. Consequently, they arethe most important markets. In relation to the other top20 countries which have installed wind power systems,Germany is in second place in terms of surface area(right behind Denmark) with 99 kW/km2. The firstnon-European country is China (ranked 16th) with10 kW/km2, followed by Japan and the U.S., each with7 kW/km2 (Fraunhofer IWES, 2013). In 2013, 24.7 % ofGermany’s gross power consumption came from renew-able energies. Wind power had the largest share with33 % onshore and 1 % offshore wind turbines. Thus

article is distributed under the terms of the Creative Commons Attribution 4.0rg/licenses/by/4.0/), which permits unrestricted use, distribution, ande appropriate credit to the original author(s) and the source, provide a link tochanges were made.

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onshore wind turbines made the largest contribution tothe overall power yield.This paper briefly describes the development of exist-

ing onshore wind turbines. The Technische HochschuleMittelhessen (University of Applied Sciences) in theState of Hesse in Germany has been doing research on anew tower for turbines of this type. The design of thenew tower aims at reducing the requirement of con-struction materials and optimizing the time and cost oftransportation and assembly. A visualization of the hy-brid2 tower is shown in Fig. 1. Moreover, the researchgoes a step further and looks for ways of generatingsynergies with existing methodologies. One such meth-odology is Building Information Modelling (BIM), whichhas several performance-enhancing features during theentire life cycle. Therefore this methodology has beentaken into account regarding the development of thenew hybrid2 tower.

Research problem: Inefficient constructionprocessesIt is well known that the bigger the wind turbine is, themore complicated are the transportation and assemblyprocesses. Moreover, another important concern of theiron-site construction is the quality control and the effi-ciency of the construction processes. Therefore, the re-search problem definition will be focused on how toimprove this situation, trying to combine a new designwith the implementation of existing methodologies inthe construction industry.

General inefficiency problems in constructionThe rate of productivity improvement in the constructionsector is significantly lower than in other industries. Thisis mainly due to certain inherent features, such as low rateof innovation, general inefficiency, lack of communication,

Fig. 1 Design of hybrid2 towers

and overall fragmentation (McGraw Hill Construction,2011).Fragmentation in the construction sector between pro-

ject phases and among stakeholders causes numerousconflicts, waste of resources, legal claims and overruns,all of which severely affect efficiency (Dawood et al.2002). Construction projects involve a wide variety ofstakeholders with different backgrounds and interests,and therefore fragmentation is often closely connectedwith inefficient communication and loss of information(Nawi et al. 2014), culminating in “Information silos”(Hu and Zhou, 2009). It is evident that there is a needfor closer collaboration and improved communicationbetween stakeholders throughout the different projectphases (Mohd Nawi et al. 2014). This can be achieved byimplementing information technology systems and en-hancing interoperability to reduce information loss.Moreover, the fact that each construction project is

unique also means a loss in productivity compared tomore industrialized sectors (Organisation for EconomicCo-operation and Development, 2002). As a result, it isnecessary today, especially in the face of increased com-petition and greater environment demands, that theconstruction sector develops a more industrialized ap-proach whereby prefabrication practices enhance effi-ciency (Nawari, 2012).

Inefficiency in the construction process of onshore windturbinesFor the efficient operation of a wind turbine, an averagewind speed of 5 to 6 m/s is required. The energy of thewind flow thereby changes with the third power of windvelocity. Accordingly, the tower height of a wind turbineis dependent on location and its hub height ultimatelydetermines economic efficiency. Therefore a number ofwind turbine manufacturers create different combina-tions of rotor diameters and hub heights to offer the op-timal solution for each location. For non-coastal regions,the following proportionality can be applied as a rule ofthumb: the yield increases by up to 1 percent per meterof hub height of the wind turbine. For that reason, hubheights of over 100 m are often suitable for inland sites.Increasing hub height is an essential factor in the futureof wind power production. This can already be seen inthe case of newly installed wind turbines in Germany. Inorder to reach the desired hub height, the structure ofthe tower is of particular importance. Furthermore, thetower is the largest and heaviest component of a windturbine and makes up 20 to 25 % of the total costs, in-cluding assembly and transportation (Gasch and Twele,2007).The structure of new wind turbines continues to de-

velop in the direction of prefabrication of individual

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components as well as complete tower sections. Therapid development of such wind turbines in recent yearshas received political support. For higher wind turbines,self-supporting towers are mainly used. They can bebuilt in various forms of structures. In addition to thehub height, natural frequency is also an important cri-terion regarding the efficiency of a wind turbine. Thecrucial objective for the manufacturer is to achieve therequired tower height and the corresponding stiffnesswith low construction costs. The most popular towertypes according to (Hau, 2014) are lattice towers, steeltube towers, concrete towers and hybrid towers.Lattice towers are used for greater hub heights. Be-

cause of their effective transmittance, lattice towers caneasily be integrated into the surroundings. In addition,they are more economical in terms of material andweight. However, the manufacture and maintenance ofthese towers is very labor-intensive. Due to the highlabor costs in Germany, lattice towers are becoming lesscommon.Steel tube towers have a total height of 60 to 100 m

and are used for a large number of wind turbines. Suchtowers usually consist of an upwards conically taperingcross-section. One can say: the higher the tower, thewider its base. Due to problems regarding transportabil-ity and the limited thickness of the plates, the towerheight is limited to 100 m. German road bridges have avertical clearance of 4.0 m and thus limit the diameter ofthe lower tower sections when it is delivered in onepiece. Composite in-situ steel towers did not becomepopular because of the high welding and assembly costs.There are different forms of concrete towers (Hau,

2014). Centrifugal concrete towers can be produced morecheaply, but have high transportation and assemblycosts. In-situ concrete towers are easier to transport andassemble. They can be constructed directly on site bymeans of sliding or climbing formwork. However, themain problem with in-situ construction is to control thequality of the concrete casting. In bad weather condi-tions, such as cold temperatures and strong winds, theassembly is time-consuming and becomes more costlywith increasing altitude.In order to overcome these difficulties, a production

method based on precast concrete elements was intro-duced. It is possible to prefabricate the individual seg-ments cost-effectively and with a high level of quality. Theprefabricated structure optimizes transport and assemblyand the tower can be adapted to the local conditions. Theaim is to manufacture the components as far as possiblein serial production without alterations. This leads to asignificant reduction in formwork and lowers the costsper segment. After the precast concrete parts have beenassembled on site, they are suppressed by means of verti-cal prestressing bars across the entire height to protect the

concrete from tensile stress. Towers with bigger contactareas can be built more efficiently with the help of thisconstruction method. An important advantage comparedto the in-situ concrete towers is the easier deconstructionof prefabricated components after the wind turbine hasreached the end of its service life.A combination of concrete towers and steel tube towers

has been used increasingly during the last few years. Theso-called hybrid towers consist of a concrete tower withprecast elements in the lower part and an attached steeltube tower in the upper part. Larger hub heights of over100 m can be manufactured at comparably low cost usingthis variant. Furthermore, by varying the height of theconcrete and steel tube tower, it is possible to influencethe natural frequency, thus improving operating efficiency.

Methods and innovative solutionThe research problem aim of this paper consists in ad-dressing the complex processes involved in the trans-portation and assembly of wind turbine towers. A newand more efficient and economical design supported byindustrialized and computerized processes could be anappropriate solution.

Development of tower designStructural designPrefabricated hybrid towers consisting of a prestressedreinforced concrete tower and an attached steel tubetower offer considerable potential for improvement. Thedevelopment of hybrid towers is quite recent, which iswhy there is still a great need for further advancementin this field. The lower part of the concrete has consider-able self-weight. This has to be optimized with regard tomaterial requirements and assembly. Furthermore, thecomposite precast concrete towers are built of verticaland horizontal joints, which are prone to damage underdynamic loads. One idea is to minimize these problemswith the development of a new structure for hybridtowers made of precast reinforced concrete. A frame-work would replace part of the concrete section, thuscreating an open tower construction. With the combin-ation of precast concrete and framework, the concretetower itself becomes a hybrid which is completed by anattached steel tube tower. The result is a hybrid tower ina double sense, the so-called hybrid2 tower.The new hybrid2 towers consist of four prefabricated

quarter-circle-shaped concrete elements in the cross-section which are connected by a framework. A side-view of the concrete tower as well as a lower and uppercross-section are shown in Fig. 2. The quarter-circle-shaped elements are 10 m high and have an identicalconstruction at every level. Thus it is possible to pro-duce these elements in series with the same formworkin precasting factories. The weight of one single

Fig. 2 Side-view of the tower (left); lower and upper cross-sections of the tower (right)

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element is less than 20 t. This means that they can bedelivered to the building site without the need for spe-cial transports, which are inevitably expensive.The desired hub height determines the horizontal dis-

tance between each concrete element. It should beborne in mind that the higher the tower, the greater thebase needs to be. The framework connects the concreteelements, thus the distances between the elements arevariable. Moreover, the concrete elements are constructedwith a slight inclination which means that the respectivedistance and the framework taper upwards. For example,a hub height of 145 m, which is common in hybrid towersin Germany, requires a base of 10x10 m. Towers of thisdimension are made up of a concrete tower includingfoundations, an adapter ring with a height of 85 m andthe attached steel tube tower with a height of 60 m. Dueto the modular construction concept of the hybrid2 towerand the fact that each level has a height of 10 m, it is not aproblem to vary individual heights. Because of the taper,the conventional steel tower, which has a diameter ofabout 4 m, can be attached flush to the concrete towerwith the help of the adapter ring.Different materials have been tested with regard to the

framework construction. The best option is to employcommercial steel profiles, whereby trussed steel beamsare used to connect the precast elements. This

framework gives the hybrid2 tower a lower weight andan open structure. In addition, the trussed beams have astrutting function. All in all, the beams are an essentialcomponent of the tower. They absorb tensile and com-pressive forces and transmit them to the next precastconcrete corner element. The steel framework and theprecast concrete elements are connected by grouting,which is a well-established procedure in precast andcomposite constructions. For this purpose, there aregaps in the precast elements where the trussed beamscan be put in position, adjusted and grouted during theconstruction progress.Inside the tower there are vertical external prestressing

steel tendons, which set the concrete elements undercompressive stress and thus counter the occurring ten-sile forces. The prestressing tendons are anchored in thefoundations and the adapter ring. The adapter ring is animportant link between the concrete tower and the steeltube tower.The open structure of the framework offers further

creative possibilities. In the standard version of the openframework, the tower is transmittance and can be easilyintegrated into the landscape. The open areas betweenthe concrete elements may be used to enhance the over-all appearance of the tower, e.g. illuminated billboardscould provide space for advertising. Alternatively, the

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intermediate gaps can be filled with various materials(e.g. film, trapezoidal sheet metal) to create a uniformsurface.

Joints of the precast concrete elementsPre-constructed hybrid towers consist of a completeconcrete cross-section in the lower part. Especially inthe case of precast constructions, horizontal and verticaljoints cannot be avoided. A concrete butt joint withoutmortar can only be made with complex and expensiveequipment. Grouting the joints is considered to be a bet-ter alternative. However, post-grouting the vertical jointsbecomes difficult in bad weather conditions and at highaltitudes, and often faults appear if the joint is not filledcorrectly. At a later stage, serious problems may arisewith respect to durability and density, and efficient forcetransmission cannot be guaranteed, a situation which iscritical regarding dynamic loads. The hybrid2 tower hasno vertical joints if a framework is used, a fact which im-proves the structure as a whole.Horizontal joints are less problematic than vertical

joints. The vertical prestressed tendons are adapted toavoid tensile stress in the horizontal joint under dynamicload, and a gap only appears in the joint between twooverlapping concrete elements in the ultimate limit state.The prestressed steel tendons absorb the resulting tensileforces. Depending on the weather, huge problems mayoccur when using grout. Especially in colder regions, groutcannot be used without first applying special measures.Alternative connections (e.g. elastomer supports) stillneed to be researched.

Foundations and adapter ringThe foundations of prestressed concrete towers forwind turbines have a circular ring shape and are builtwith in-situ concrete. In the middle opening of thefoundations there is a place where the prestressed steeltendons are anchored. The prestressing jack has to beset in this so-called cellar to apply vertical prestressingto the concrete tower. The required working space isquite large and the tendons must be anchored in thefoundations. For this reason, foundations for wind tur-bines with a height of 4 m are not uncommon. Theelaborate formwork and time-consuming concretingmake the foundations a significant cost factor. There-fore it is necessary to reduce the material requirementfor the foundations so as to build them as economicallyas possible.In order to absorb the prestressed steel tendons on the

upper side of the concrete tower, an adapter ring is used.This ring also has the function to transfer the forcesfrom the steel tube tower to the concrete tower. It ismade of reinforced concrete and often has a weight of

more than 50 t. However, there is room for improve-ment in this area.

Assembling the hybrid2 towerThe first step in assembling the tower is to build thefoundations, including the cellar and the anchor for theprestressing steel tendons. To speed up the process, theconcrete corner elements and the trussed beams shouldbe delivered to the building site in good time. As men-tioned above, the formwork used in the precast factoriesis usually the same each time, a factor which optimizespre-production and guarantees punctual delivery. Thefirst corner elements are placed on the foundations andaligned on grout. In the next step, the trussed beams areput in place and secured in the right position. Duringassembly, a steel ring stabilizes the quarter-circle-shapedconcrete corner elements and ensures accurate installa-tion of the trussed beams. The gaps in the precast ele-ments are filled. The first level of the tower, consistingof four corner elements and the trussed beams, is nowcomplete.Pre-assembly of the following levels also takes place

on the ground. Mobile foundations made up of prefabri-cated concrete plates are arranged next to the actualtower. Pre-assembly of the next levels is carried out inthe same way as described for the first level. In cold re-gions, this can also be done under a special cover, whichallows temperature-independent assembly and providesoptimum conditions for grouting. Each level of the hy-brid2 tower is lifted into position, placed on grout andaligned by a hydraulic device. The same procedure is re-peated as often as necessary. The upper end of the hybrid2

tower is built on the adapter ring. This ring is also posi-tioned and aligned on grout. After completion of the con-crete tower, the external prestressed steel tendons areinstalled and reach from the foundations to the adapterring. The prestressing cables have no anchor points on thereinforced concrete corner elements so as to avoid unbal-anced forces. After the necessary prestressing force for theconcrete tower has been applied, installation of the steeltube tower can begin. This is done in the same way aswith assembled wind turbines.For assembly of the hybrid2 towers it is necessary to

use a mobile truck crane rather than a crawler crane be-cause of weight optimization. (A comparison of thesetwo cranes is shown in Fig. 3.) This has significant ad-vantages when choosing the location of the wind turbineand also helps to reduce costs considerably. A crawlercrane has to be brought to the construction area withthe help of special transports and is assembled on site.In contrast, the mobile truck crane is self-propelled andbecause it consists of much less equipment, it can be de-livered with normal trucks. Additionally, there is lesseffort involved in securing access to the building site,

Fig. 3 Comparison of a mobile crane and a crawler crane for a wind turbine (Liebherr Werk, 2014)

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which is important since the large wind turbines areerected mainly in rural areas or forests. A hybrid2

tower with 8 levels can be assembled in five days.The costs of using a crawler crane for a completeconcrete cross-section amount to 100,000 €, includingassembly and dismantling, but not including personalcosts. In contrast, the costs of using a mobile craneare less than half this sum. Furthermore, considerablecosts arise if the assembly work is interrupted be-cause of bad weather conditions or high wind speeds.On average, 10 days are lost during the assembly of

one wind turbine. The rate per lost day for the mo-bile truck crane is only about 65 % of that of thecrawler crane. In addition, the smaller mobile cranecan be used for lifting even at high wind speeds, andthus downtimes are minimized. All this shows thatthere are many complications with regard to the con-struction and operation of wind turbines, and costscan increase significantly. With the help of BuildingInformation Modelling methodology during planning,assembly and operation, the participation of all stake-holders can be optimized.

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Performance improvement techniques and methodologies:Prefabrication and Building Information ModellingAmong the methodologies and processes which are avail-able for improving the efficiency and productivity of agiven construction project, Building Information Model-ling (BIM), prefabrication, modularization and off-sitetechniques must be highlighted. An example of this canbe found in a study carried out by a committee of expertsof the National Research Council (NRC) in 2008 to definethe existing possibilities of improving the productivity andcompetitiveness of the construction industry in theUnited States. In this study, both BIM and off-site tech-niques were classified among the five key measureswith a capacity to enhance overall performance by im-proving quality, time and cost efficiency, and sustain-ability. Moreover, the study underlined the fact thatefficient implementation of BIM methodology and theuse of off-site manufactured components will lead to achange in the way of working in the industry, mainlybased on open collaboration (National Research Coun-cil, 2009).The aim of the research is to present a new design for

wind turbine towers at a time when attention is focusedon breaking up information silos and improving projectperformance by transforming standard construction pro-cesses into more industrialized ones.

PrefabricationHighly industrialized sectors, such as computer or auto-motive manufacturing, have reached a level of automa-tion that has significantly increased their productivityand efficiency. This has led to discussions as to why theconstruction industry has not implemented techniquesand methodologies aimed at enhancing performance assuccessfully as other industrialized sectors have done.Prefabrication is one of the techniques which could bringabout higher levels of automation by creating synergieswith BIM capabilities.Prefabrication and modularization processes and tech-

nologies are based on the fabrication and assembly of theelements “off-site” and their subsequent transportation toand installation at the construction site in question. Thesetechniques are associated with considerable time and costreductions and noticeable quality improvements due totheir efficient use of resources (National Research Council,2009).The benefits of prefabrication and modular construc-

tion have been highlighted in different studies. In 2011McGraw Hill Construction focused on improved prod-uctivity as being one of the main advantages and em-phasized the following aspects: shortening of overallproject schedule, reduction in costs and wastage (espe-cially with respect to the construction site itself ) and

higher level of on-site safety (McGraw Hill Construc-tion, 2011).Reducing on-site construction activities leads to time-

saving and consequently to cost-saving. Prefabricationenables on-site work to be done at the same time asother tasks are being carried out off-site. It also cutsthe project-related budget in a number of ways: not somany expensive on-site tasks, fewer on-site resources,less risk of paying overtime, elimination of unexpectedcosts (McGraw Hill Construction, 2011). Moreover,prefabrication offers more quality and greater reliabilitysince controls are more effective under off-site condi-tions and there is generally a higher level of precisionthan is the case with on-site procedures (NationalResearch Council, 2009). Finally, there is also a sub-stantial decrease in wastage (i.e. less on-site debris),which means a benefit for the environment as well(McGraw Hill Construction, 2011).The study conducted by McGraw Hill Construction

highlighted three further factors that are contributing tothe increased use of prefabrication in the constructionindustry: lean construction (thanks to higher productivity),BIM (which is starting to be more widely implemented),and green construction (which is growing rapidly inimportance). In fact, the contribution made be BIMmethodology towards improving the productivity ofprefabrication has been highlighted as an incentive forspreading the use of this technique in the constructionindustry as a whole (McGraw Hill Construction, 2011).

Building Information ModellingThe implementation of information technologies is cur-rently playing an important role in the constructionindustry. However, compared to other industries suchas automotive or aircraft manufacturing, constructionstill has a long way to go in this respect. Extensive ap-plication of information technologies such as BuildingInformation Modelling (BIM) would support the effi-cient implementation of industrial processes, e.g. pre-fabrication and off-site construction (Nawari, 2012).The performance of a project is invariably enhanced

by improving interoperability, such as can be achievedby implementing information technologies like BIM.The main advantages of this methodology include: man-agement of information among stakeholders and duringall phases, visualization, scheduling, cost estimation, andmaterials tracking. BIM also helps to optimize decision-making processes. In addition, the comprehensive datamanagement system of BIM enhances data accuracy andreduces unnecessary data reentry tasks. By offering anautomatic answer to changes in design, BIM enables de-signers and engineers to observe the immediate conse-quences of their actions. Errors in design are easilyidentified whereas errors which originate from the

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inconsistency of 2D drawings are eliminated thanks to the3D model. A multidisciplinary assessment of the modelcan be developed and future defects and errors eliminatedbefore the construction phase. Finally, BIM supports life-cycle management and has important post-constructionbenefits related to management and operation processes;this is due to fact that the model acts as the main sourceof information and includes all design and as-built infor-mation (Eastman et al. 2011). It should be rememberedthat effective BIM implementation requires collaborationamong stakeholders as well as integrated processes, butthis will in itself reduce fragmentation in the industry(National Research Council, 2009).

Results and DiscussionBenefits of the new hybrid towerThe main advantage of the new structure used for thehybrid2 tower is cost-saving, especially with regard totransportation and assembly. The cost-saving process ac-tually starts in the precast factories during production ofidentically constructed concrete elements for the entiretower. Only one formwork is necessary for precasting allthe elements, which leads to a reduction in productioncosts. The inclination of the tower is made possible bythe variation in length of the truss beams. These beamscan be produced accurately in the factories and are easyto deliver to the construction site due to their low self-weight. Based on this principle, it is possible to constructtowers of different heights by varying the number oflevels. After the elements have been delivered with con-ventional trucks to the construction site, each level ispre-assembled on the ground. The self-weight a hybrid2

tower is reduced by the use of trussed beams and the re-sultant open structure; thus smaller cranes are used foron-site construction than is the case with full-concretetowers. When each level of the hybrid2 tower has beenpre-assembled, it is placed on top of another one andthe joints are grouted. The above mentioned procedureleads to a reduction in the time needed for constructionand assembly. In summary, this construction principleimproves both static and dynamic performance as wellas optimizing transportation and assembly processes.Building Information Modelling makes a significant con-tribution to the development, planning and assembly ofthe hybrid2 tower.

Benefits of combining Building Information Modellingmethodology and prefabrication processesConstruction industry is currently characterized bythe growing implementation of industrialization andcomputerization processes, this leads to the growingpresence of prefabrication and Building InformationModelling presence. Their advantages are noticeable.The combination of BIM methodology and

prefabrication processes generates important syner-gies. On the one hand, BIM provides greater reliabilityand precision and, on the other hand, the materials andmanufacturing processes involved in prefabrication gainsignificantly in quality. All in all, the productivity of con-struction projects is increased (McGraw Hill Construc-tion, 2011). Moreover, increasing implementation of BIMmethodology may well boost prefabrication as a whole.With the help of BIM methodology, it is possible to createmodel-driven prefabrication where off-site processes canbe developed and handed over to the manufacturers(McGraw Hill Construction, 2011).Thanks to its high level of accuracy, BIM functions as

a source of information for fabrication and constructionprocesses. These processes are facilitated by the model’s3D definition of the elements. The practice is currentlywidespread in the steel industry and has also been suc-cessfully applied to precast elements. The model con-tains all the details needed for the fabrication processesand enables more complex elements to be constructedoff site than was possible with 2D techniques (Eastmanet al. 2011).The fact that successful off-site production is based on

effective information exchange between stakeholderscalls for an efficient information management systemlike BIM. This system has the capacity to select the re-quired data at the right moment for each stakeholder.Prefabrication processes need well-functioning coordin-ation and collaboration among the stakeholders, so thathigh quality products reach the construction site ontime. BIM is the ideal tool for integrating the varioustasks involved in the prefabrication process. Its 3Dvisualization capacity and information management andcommunication systems are key features in generatingessential synergies (Nawari, 2012).This paper describes a modular wind turbine made

of prefabricated elements, but attention has also beenfocused on how this prefabrication process can be sup-ported by new information technologies. BIM not onlyprovides 3D visualization of the tower (somethingwhich in fact was already possible in the past withoutimplementing BIM methodology), but also handles in-formation management and supplies relevant data toeach of the stakeholders when needed. The BIM modelcontains updated information on the individual projectand can be used to check the current status of each ofthe prefabricated elements, no matter whether they areunder production, ready to be shipped or already onsite.The next step of this research project will be the

transformation of the BIM model to the project’s mainsource of information for supporting the various manu-facturing and on-site placement processes as well asfuture maintenance activities.

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Further steps to be undertaken in this research projectOn the one hand, the new design presented in thispaper includes already prefabricated elements in orderto increase the efficiency. On the other hand, BIM hasbeen proposed as the perfect complement for prefabri-cation, based on the proven advantages of this method-ology. The aim of this research group is to develop aBIM model, which will be the main source of informa-tion of the project during the whole life cycle of theturbine. The prefabricated elements can be previouslydefined and modeled as BIM objects stored in a libraryfor immediate use; in these objects the detailed defin-ition of the elements properties is included. As a fur-ther development materials and prefabricated elementslogistic planning supported by BIM will be developed.

ConclusionsIn Germany today special focus is being put on the de-velopment of renewable energies, especially wind power.The increase in the hub height of wind turbines meansthat tower structures have to be more massive. This, inturn, leads to higher transport and assembly costs. Thepresent paper describes the design and construction ofthe hybrid2 tower.Hybrid2 towers are currently being developed as part

of a research project at the Technische Hochschule Mit-telhessen (University of Applied Sciences) in the State ofHesse in Germany together with Oberhessisches Spann-betonwerk GmbH. The mission statement driving thedevelopment of the new hybrid2 towers for onshorewind turbines is associated with optimizing the perform-ance of the supporting structure. The new tower conceptreduces the amount of material used, and thus theweight of the tower itself decreases remarkably. More-over, hybrid2 towers are designed to cut transport andassembly costs dramatically.Due to the high dynamic loads to which it is exposed,

a wind turbine only has a lifetime of some 20 years. Thetraditional wind turbine is set for reconstruction andthere will be widespread repowering. All this means thatnew and more efficient wind turbines will replace oldwind turbines at the same location. Planning and costestimations with respect to deconstruction and othertasks during the life cycle of a wind turbine will have tobe dealt with. This is why good cooperation amongstakeholders is so necessary. Such cooperation is facili-tated by Building Information Modelling methodology.However, this is not the only advantage of BIM. The

current research aims at implementing BIM method-ology from the early design phases, so that the modelbecomes the centralized source of information. It re-mains to be said that BIM can enhance prefabricationprocesses and optimize the performance of a hybrid2

tower during its complete life cycle.

Competing interestsThe authors declare that they have no competing interests.

Authors’ contributionsMK and JM carried out the development of the hybrid towers, such as theconstruction processes, the structural design, assembling and benefits of thehybrid² tower. LA and JD carried out the general inefficiency problems inconstructions, the performance improvement techniques andmethodologies like BIM and prefabrication as well as the benefits ofcombining them. The background and conclusions were composed incooperation. All authors read and approved the final manuscript.

AcknowledgementsThe hybrid2 towers were developed by the Technische HochschuleMittelhessen* (Giessen, Germany) together with the precast companyOberhessisches Spannbetonwerk (Nidda, Germany). The project (HAproject no. 352/12-42) is funded within the framework of the HessenModellProjekte, financed with funds from LOEWE (Landes-Offensive zurEntwicklung Wissenschaftlich-ökonomischer Exzellenz**, Förderlinie 3:KMU-Verbundvorhaben).* University of Applied Sciences** State Offensive for the Development of Scientific and Economic Excellence

Received: 20 August 2015 Accepted: 29 December 2015

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doi:10.1186/s40327-015-0032-4Cite this article as: Alvarez-Anton et al.: Optimization of a hybrid towerfor onshore wind turbines by Building Information Modeling andprefabrication techniques. Visualization in Engineering 2016 3:.