Windmill foundations with FEA 6

[mendinho]

Dear mates,

I need to desing a square reinforced concrete foundation for several windmills in the North of Spain using finite elements. The dimensions vary from 10 to 15 metres length and 1 to 1.5 m depth.

My first idea is to perform a very simple linear static analysis to estimate the amount of steel. Then, I will confirm the reinforcement using a 3D model with nonlinear materials for concrete and steel.

I would like to know if there is any kind of academic work, book, paper and such that can help me to build the model and to check some results. Any advice or comment will be useful and helpful. Thanks a lot.

Note: The FEM software I have is Cosmos/m (Ansys like but a bit cheaper).

 

[JoeTank]

There hae been numerous such foundations, all designed without resorting to FEA. Sounds like a bit of overkill design-wise. Is there anything unique about the structure or loadings that requires FEA? A good starting point would be a concrete structures handbook (Fintel, but that's and old reference)) that shows design examples of similar structures such foundations for a tall stack.

Joe Tank

 

[JStephen]

This actually sounds more like a class assignment. Typically, this kind of foundation wouldn't use FEA.

One of the issues to consider is that you may have partial loss of contact of the bearing area.

 

[mendinho]

Thank you very much for your kind help.

You are right, Stephen, it sounds a bit like an academic assignment but, surprisingly, the amount of concrete needed for wind turbine foundations is one of the most expensive items used in the process. The design with FEA was, in fact, a client requirement.

Thank you for the reference, Joe. Unfortunately, the Handbook of concrete engineering by Mark Fintel is going to be hard to find. I will try with an equivalent concrete manual. The only special issue is the connection between the steel mast and the concrete foundation and that is all.

 

[civilperson]

Square reinforced foundation for the high moments caused by lateral loads are very inefficient since the wind can blow in many directions and only the leeward fraction is available to provide soil pressure for stability. Circular reinforced rings and large diameter drilled piers are much more cost effective for wind turbine foundations.

 

[JStephen]

Consider also a circular slab with center pedestal, with the slab below grade, so weight of soil over the slab resists uplift.

 

[GregLocock]

stars for you two. Sound slike a bit of thought will get you a lot further than a puter.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[mendinho]

After long and hard talking to my client the result was a square foundation. I must admit that I would prefer to use an octogonal foundation because plane framework can be used and it is nearly as efficient as a circular one. Sometimes it is difficult to change the building tradition.

 

[csd72]

mendinho,

The reason why square foundations are normally used is that it is easier to dig a square hole. For an octagonal foundation they will probably just dig a square hole and backfill the corners after.

Why are you using formwork if this is in ground? The formwork will be more expensive than the concrete!

As far as the finite element is concerned, this is a waste of your clients money. There are no elements in this simple design that can be refined by the analysis.