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Dames en here,

Ladies and gentlemen, coming from the Netherlands my first thoughtwas to do this presentation in Dutch. It sounds a lot like Afrikaans andwould make my job a lot easier. After giving it some thoughts I decidedotherwise: the risk would be to high that you would only understandhalf of it. So, English will take me more effort but also will give moreoptimal results.

My name is Axel Jacobs and I am here to tell you more aboutoptimisation of foundation designs for wind turbines. For over 20 yearsnow, I work as a full time civil consultant for wind energy projects. Thehead office of my company ABT is located in the Netherlands but weare involved in projects around the world. Recently ABT has formed apartnership with the South African engineering firm Gibb for windenergy projects in Africa. I think that our firms form a strongcombination of local and specialised knowledge.

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The foundation is the connection of the wind turbine with earth. Ittransfers all loads coming from the turbine to the earth. Foundationscome in all sorts and dimensions. This not only depends on the type ofwind turbine, or the hub height, or the wind speed etcetera, butmaybe more importantly it depends on the soil conditions and terrainfeatures. These last items can vary substantially. A variation whichbrings allong the largest un-certainties of a project, and thereforemaybe the largest risks.In South Africa so called gravity foundations are the most common.These gravity foundations are “simply” big circular reinforced concretebases, which are put directly on the soil.

Now that you also have an idea on what a foundation could look like, Iam going to jump to directly to what this presentation is about.

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The foundation is the connection of the wind turbine with earth. It transfers all loadscoming from the turbine to the earth. Foundations come in all sorts and dimensions.This not only depends on the type of wind turbine, or the hub height, or the wind speedetcetera, but maybe more importantly it depends on the soil conditions and terrainfeatures. These last items can vary substantially. A variation which brings allong thelargest un-certainties of a project, and therefore maybe the largest risks.In South Africa so called gravity foundations are the most common. These gravityfoundations are “simply” big circular reinforced concrete bases, which are put directly onthe soil.

Now that you also have an idea on what a foundation could look like, I am going to jumpto directly to what this presentation is about.

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The foundation is the connection of the wind turbine with earth. It transfers all loadscoming from the turbine to the earth. Foundations come in all sorts and dimensions.This not only depends on the type of wind turbine, or the hub height, or the wind speedetcetera, but maybe more importantly it depends on the soil conditions and terrainfeatures. These last items can vary substantially. A variation which brings allong thelargest un-certainties of a project, and therefore maybe the largest risks.In South Africa so called gravity foundations are the most common. These gravityfoundations are “simply” big circular reinforced concrete bases, which are put directly onthe soil.

Now that you also have an idea on what a foundation could look like, I am going to jumpto directly to what this presentation is about.

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The foundation is the connection of the wind turbine with earth. It transfers all loadscoming from the turbine to the earth. Foundations come in all sorts and dimensions.This not only depends on the type of wind turbine, or the hub height, or the wind speedetcetera, but maybe more importantly it depends on the soil conditions and terrainfeatures. These last items can vary substantially. A variation which brings allong thelargest un-certainties of a project, and therefore maybe the largest risks.In South Africa so called gravity foundations are the most common. These gravityfoundations are “simply” big circular reinforced concrete bases, which are put directly onthe soil.

Now that you also have an idea on what a foundation could look like, I am going to jumpto directly to what this presentation is about.

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The foundation is the connection of the wind turbine with earth. It transfers all loadscoming from the turbine to the earth. Foundations come in all sorts and dimensions.This not only depends on the type of wind turbine, or the hub height, or the wind speedetcetera, but maybe more importantly it depends on the soil conditions and terrainfeatures. These last items can vary substantially. A variation which brings allong thelargest un-certainties of a project, and therefore maybe the largest risks.In South Africa so called gravity foundations are the most common. These gravityfoundations are “simply” big circular reinforced concrete bases, which are put directly onthe soil.

Now that you also have an idea on what a foundation could look like, I am going to jumpto directly to what this presentation is about.

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The foundation is the connection of the wind turbine with earth. It transfers all loadscoming from the turbine to the earth. Foundations come in all sorts and dimensions.This not only depends on the type of wind turbine, or the hub height, or the wind speedetcetera, but maybe more importantly it depends on the soil conditions and terrainfeatures. These last items can vary substantially. A variation which brings allong thelargest un-certainties of a project, and therefore maybe the largest risks.In South Africa so called gravity foundations are the most common. These gravityfoundations are “simply” big circular reinforced concrete bases, which are put directly onthe soil.

Now that you also have an idea on what a foundation could look like, I am going to jumpto directly to what this presentation is about.

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The foundation is the connection of the wind turbine with earth. It transfers all loadscoming from the turbine to the earth. Foundations come in all sorts and dimensions.This not only depends on the type of wind turbine, or the hub height, or the wind speedetcetera, but maybe more importantly it depends on the soil conditions and terrainfeatures. These last items can vary substantially. A variation which brings allong thelargest un-certainties of a project, and therefore maybe the largest risks.In South Africa so called gravity foundations are the most common. These gravityfoundations are “simply” big circular reinforced concrete bases, which are put directly onthe soil.

Now that you also have an idea on what a foundation could look like, I am going to jumpto directly to what this presentation is about.

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This scale measures the degree of optimisation of a design inrelation to savings and risks.It ranges from a conventional design to an optimised design.****************I am sorry to say that in a lot of projects a conventional designis were it stops. Design optimisations are not even consideredor the design is thought to be optimised, but is reality is farfrom optimised. How come?The most important reason is the perception that optimisationleads to lower safety and higher risks.******************As I will explain later, this reason is a misconception. Arelationship between level of optimisation and risk levels isnot as obvious as it might seem.******************I would like to bring forward that we, as a green industry,should consider the impact of our activities on the

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environment. Our aim should be to pursuit an optimal designin order to save materials and to minimise CO2 emisions. Bydoing so also substantial cost savings can be achieved.Is that possible?

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Let’s look at the statistic facts, based on a large number ofprojects were we have been involved over the last years.I’ve made a comparrison between a conventional design andan optimised design.

Besides cost savings, material amounts are reducedsubstantially as well as the amount of CO2. When you knowthat 1 ton of cement causes 1 ton of CO2 emmisions, you canimagine that making a foundation isn’t that environmental-friendly at all. So every ton CO2 saved has an big impact onthe CO2 footprint of the project as a whole.

I will let you look at it for a moment. You can judge foryourselves whether the additional effort is worthwhile.

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An example:

Something went wrong here. Most people would say: thefoundation has failed leading to collapse of the wind turbine.Let’s look at it in a different way: the concrete base is toostrong! Not even a crack.So, I would say: possibilities for optimisation.

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Let’s step away from wind energy for a moment.

Steve Fisher is a South African extreme kayaker and has a veryinteresting story to tell about risk. We don’t have the time now, butwhen you have a 10 minutes to spare you should look up Steve’s TEDxtalk on the internet.

Risk, Steve says, is doing something that has never been done before.That could be kayaking down this waterfall. How do you handle therisks?

Steve has a 5-points list of tools that you need. The first three tools(equipment, physical conditions and location) are pre-conditions (orthe information) that depend on the challenge ahead. Once thesethree are in place it becomes possible to develop the last two, skillsand experience.

The more you develop these skills and experience the easier itbecomes to judge the risks of the next waterfall.

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So, knowing these tools, we can say that you cannot be surethat the risks in the upper situation are less than the lowerpicture.When the lady in the upper picture has no skills andexperience at all she can still take a larger risk than the guy inthe lower picture who has been doing this for years.

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The real risks are the ones that were not identified as risks,and to identify risks you will need your toolbox.

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And on the other side….You only really know risks when you know were the edge is!Were you know that you can’t go further. And this edge canonly be found through experience.

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With this in mind we now step back to the safety concept that is used to design afoundation.

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In general the value of the strength (Resistance R) should bemore than de loads (S) in order to have a safe structure.

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To make it a little bit more difficult, both the loads and thestrength have a certain variation. Most design codes introduceso-called partial safety factors (load factors and materialfactors) in order to achieve sufficient low failure probability.As an example: the so-called characteristic load Sk ismultiplied by a loadfactor to get the design load S.

Let’s take a look at an example of this variation of materialproperties.

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A site where we found a very fine sand which, in combinationwith water can lead to quick sand like behaviour.

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And at this picture you see a site where we have rock. Socompletely different from the other situation.

Note that we are now talking about the first three tools fromour risk-toolbox! We are gathering information about thelocation, materials, loads, ground water, soil etcetera. This isimportant input for our design works and the more precise itis, the better we can asses the risks.

Back to the theory…

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So, Resistance should be more than Load. In order to provethat, we need a model. Let’s say that models are the skills andexperience tools from our risk-toolbox.There are two important laws of modelling.

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A model is not equal to reality! It is always an approximation.That means that the results should also not be treated asreality.The second law is: rubbish in equals rubbish out. The designershould be aware that the way a structure is modelled alsoinfluences the outcome. Model assumptions influence theoutcome.

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This graph shows the relationship between time devoted toanalysis and accuracy. We can say that when we can achieve100% accuracy, we have exactly reproduced reality. Level I toIV stand for the different ways of modelling, ranging from lowto high accuracy.

When we would translate this into the safety model we seethe following.

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The more in-accurate the model is, in general the more over-dimensioned the structure becomes. The problem is that thiseffect is not visible to the designer. He actually only sees thatR is more than S. The conclusion of the designer could than bethat the design very optimised, forgetting the accuracy of themodel!

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When looking at a level I analysis we are talking about themost in-accurate way of modelling. Most conventional designsdon’t go further than level I (or maybe level II) modelling! Thisis an analytical design method which uses all kinds ofsimplifications in order to make it comprehensible. Formulasare used to describe overall behaviour. In order to describebehaviour in a single formula, assumptions and simplificationsare needed.

It seems that a level I design always lead to over-dimensionedstructures and therefore is “to save”. But there we could bewrong. We said before that the real risks are the ones thatwere not identified as risks. When using a analytical designmethod it is easy to overlook a possible failure mechanism orthe used model is not suited to verify a certain failuremechanism. This is exactly the reason why the codes andguide lines are mostly quite extensive. They need to protect

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the designer, who uses level I modelling against forgettingmechanisms.

Codes and guide lines actually translate skills and experiencefrom experts into rules that also make it possible forunexperienced designers to design a foundation. Designerswho do not know were the edge lies. However to compensatefor the lack of experience these rules need to be conservative.

On the other hand the codes do also allow for the use ofadvanced level IV modelling.

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Opposite to level I modelling a level IV model uses the realgeometry of the foundation including all internal components(like reinforcement and tower anchorage). Also the real, non-linear material behaviour is modelled. This model actuallyshows the behaviour of the structure under increased loadingand the interaction of all components. For concrete thismeans that realistic crack patterns develop and you canactually see the stress distribution in the reinforcement steel.The real failure mechanism becomes apparent. So instead ofguessing what failure mechanism will occur, all failuremechanisms are implicitly verified and the real weak spot canbe found.Simplifications need not to be done.

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To conclude we can say the following:1. By optimising the foundation design we can achieve

substantial savings in CO2 emmisions, material usage andcosts.

2. Optimisation can be done without compromising safetymargins according to the codes.

3. Pre-conditions to be able to optimise are “information”,“skills” and “experience”. If one of them is missing orincomplete, the risks can become to high.

Steve Fisher said: “Risk is doing something that has neverbeen done before”. I would say that we have done it beforeand in order to go forward we should do it again: We cannotrisk not going down the waterfall!

I thank you for your attention, Dankie vir die aandag.

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