construction architecture building management civil engineering installations

green foundations for wind turbines

The challengeConcrete is a wonderful building product and perfect for conveying the huge stresses inherent in a wind turbine into the ground. But it does have one disadvantage: cement is one of the largest causes of CO2 emissions. One ton of Portland cement actually produces 960 kg of CO2. This is inappropriate and it’s up to us as developers to find a solution. Other aspects also play a role in development. Preferably the foundations must be economical, construction time must be as short as possible, and above all, good quality and safety must be achieved. And all this against a background encompassing the huge variety of conditions (such as soil structure and terrain conditions) that are part of civil engineering projects.

The ABT solution The solution can be found in two ways:

Reduction of the quantity of concrete and steel •needed Reduction in CO• 2 emissions per m3 of concrete.

The green foundation solution.Reduction in CO• 2 emissions and cost savings through advanced computation methodsReduction in CO• 2 emissions and cost saving through fit-for-purpose approachReduction in CO• 2 emissions through development of the concrete compositionTime savings through development of the concrete •compositionReduction in environmental burden through life-•cycle considerationHigh quality through ABT involvement in execution •

Wind energy is green. Ideally we would also like the required foundations to be as green as possible. A challenge for which ABT has a solution …

Normal Green

Failure costs

Building costs

Engineering &quality control

Costs foundation

construction architecture building management civil engineering installations

Green foundations for wind turbines

Reduction in CO2 emissions and cost reductions through fit-for-purpose approachInvestment costs in the foundation of a wind turbine will vary depending on the ground conditions. A choice is often made for a standard foundation per wind turbine type. Often the only variation that can then occur per location, for example, consists of the length and dimensions of the foundation piling. But choosing this approach actually means by definition that no cost-optimised foundation is constructed. The standard foundation always has to suffice across all locations, and thus by definition it is over dimensioned. This is why ABT has advocated a per-project approach for years. This also means that a fit-for-purpose foundation (and sometimes even per wind turbine location) is designed per project. Experience has taught that this extra investment in engineering always pays for itself in a more economical foundation design

Time savings through development of the concrete compositionNormally the choice of a concrete strength is made on the basis of the concrete compressive stress under maximum load. Here it is assumed that this strength must be achieved after 28 days of hardening. But this actually ignores the fact that maximum stresses will only occur at a much later stage. Even more significantly, as long as the turbine is not rotating the load is still only a fraction of this maximum stress. This provides the opportunity to assemble the turbine just days after pouring the cement.

Reduction in CO2 emissions and cost reductions through advanced computation methodsABT has not stood still. Huge advances in wind turbine foundations have taken place. By integrating practical experience acquired into new development, it has been possible to optimise foundation design still further.The increase in turbine capacity and axis heights has also forced designers to take a new look at foundation designs. You cannot extrapolate a design for a small turbine to a large one without considering the risks entailed in such a scaling-up. Reason enough for ABT to apply advanced computing methods and finite element sums in order to further develop the design. This puts us in a better position to assess risks while above all discovering the opportunities for optimisation. The three-dimensional computing models approach reality far better than the simpler calculation models of the past. In summary, it can be concluded that, on the one hand, advanced computation is a necessity because of the increase in scale of wind turbine types, while on the other, it offers the advantage of savings in the design. It offers us a better insight, which enables safe optimisations in concrete and reinforcement steel to be achieved.

Reduction in CO2 emissions through development of the concrete composition In contrast to normal practice, as a designer ABT also involves itself in the composition of the concrete mixture. The usual state of affairs is that the designer stipulates a concrete strength and the contractor ultimately determines the actual composition. But we believe this ignores a number of vital issues:

To a considerable extent it is the concrete that is •responsible for the CO2 emissions in foundations. There are in fact possibilities for limiting this CO2 emission by the smart selection of a concrete mixture. In bulk concrete (a foundation is generally thick), a •quantity of heat is released during the setting process. If this is too much it can have a negative effect on the quality of the concrete construction. It is therefore important to take this into account when choosing the concrete mixture.

construction architecture building management civil engineering installations

Green foundations for wind turbines

Reduction in environmental burden through life-cycle considerationWhat happens to the foundation once the wind turbine is disassembled? Our experience with older wind turbines that have already been disassembled is that the old foundation is barely usable or not at all. Just the speed alone with which new wind turbine development occurs, dictates that any new and more efficient wind turbine with a high capacity will not be suited for the existing foundation. The only option that remains in 99% of cases is to demolish the existing foundations. And that’s a pity. Even more so given that most foundations still have years of life left in them. In construction design Dutch building rules generally assume a 50-year lifespan. In practice the lifespan is much longer. However, current developments in wind energy rather require an economic lifespan of 10 years. We are building too durably and too strongly! If an existing foundation cannot be easily recycled (or even upcycled), we are thus wasting effort. In designing foundations we already take into account the end of that foundation’s functional life.At the same time when designing the foundation we also make use of recycled materials. Here we take a more reduced lifespan into account (durability) and we take a balanced view of the required safety levels (strength).

High quality through ABT involvement in executionDesigning a wind turbine foundation is just one side of the coin. Carrying out the work correctly is the other, and as the designer we believe we should continue to be closely involved. You might say that the design work doesn’t stop in drawing a foundation and stipulating the specifications. We have two important reasons for this:

The quality of the work will only actually be achieved 1. during execution. It is important that the quality ABT envisages as the designer is also expressed in the construction execution. We can only continue to innovate if we learn from 2. practice through ongoing feedback. Things that don’t go as planned or practical solutions can only be incorporated into new designs if ABT is involved closely in the execution.

As designers we regard it as our responsibility to contribute acquired knowledge to the construction team during execution. Alongside the checking role there is thus also a supervisory one, where we support the contractor with the ultimate aim being a optimal result in quality and time … and thus reducing the risks for the principal.

construction architecture building management civil engineering installations

Green foundations for wind turbines

The companyABT has been closely involved in wind energy since the early 1980s. As a civil engineering consultant for wind energy projects, we might also label ourselves as pioneers. Through our involvement in a range of projects for a variety of principals, a large number of the problems that can occur during the preparation and construction of wind farms, have already been reviewed. And ABT has devised just as many solutions for these problems. With good results.

All the services under one bannerABT is a multidisciplinary bureau. Alongside civil engineering we also have specialists in building management, construction, architecture and technical installations. This means ABT can offer you a complete package of services.

Tasks and roles ABT can fulfil in your project: Designing foundations•Designing mast anchorage•Designing masts•Designing the (civil) infrastructure for wind farms•Drawing up specifications•Supervising tendering and awarding•Producing cost estimations•Supervising execution•Carrying out quality inspections•Exercising management•Carrying out feasibility studies•Carrying out loss investigations•Carrying out quick-scan location studies•

Further information? Then please contact Adviesgroep Civiele Techniek (Civil Engineering Advice Group)Telephone: +31 (0)26 368 35 00Fax: +31 (0)26 368 35 10E-mail: windenergie@abt.euInternet: www.abt.eu

ABT bvArnhemsestraatweg 358, VelpPO Box 82, 6800 AB Arnhem (Netherlands)Telephone: +31 (0)26 368 31 11

Delftechpark 12, DelftPO Box 458, 2600 AL Delft (Netherlands)Telephone: +31 (0)15 270 36 11

Kammenstraat 18B-2000 AntwerpTelephone: +32 (0)3 205 37 11

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