Circular shaped foundation for wind turbines 6

[M.Honda]

Hi all,
For wind towers/turbines, a spread footing might be an option. It can either be rectangular or circular, yet in most cases I have seen so far (from colleagues and in the internet) circular sloped footings are used (smaller thickness as u go away from the center, like attached in the first two images below). I understand that they definitely have high probability of overturning since a wind turbine can extend to a height of 100 m and thus they heavily rely on gravity to resist this overturning (circular footings can extends to 20 m diameter with a thickness over 3 m).

My question are:

1. What are the benefit of circular footings compared to rectangular ones? why are they more adopted for wind turbines? (constructability? economical aspects? structural aspects?)
2. Why using sloped ones not regular ones?
3. In the second image, why such sudden decrease in thickness is made? is it for economical purposes?

If you do not see it, you cannot design it!

 

[JLNJ]

I think the answer to all three of your questions is, "To reduce materials and save money."

With small column footings, it is much easier and simple to excavate for a square or rectangular footing and pour that footing as a uniform thickness. If you save a spoonful of concrete but make the design and construction 10x more difficult, what have you saved?

For really large footings, it makes more economical sense to use a round and/or tapered footing because you are saving many, many yards of concrete and many, many pounds of steel compared to a uniform thickness square footing. You also lose some mass, so minimizing the footing for stress demands needs to be balanced with the overturning factor of safety.

 

[HTURKAK]

Pls find below my responds to your questions;

1. What are the benefit of circular footings compared to rectangular ones? why are they more adopted for wind turbines? (constructability? economical aspects? structural aspects?)

- Circular ftgs are common for wind towers , chimneys.. Hexagonal ftgs could also be option for moderate height. If the load direction is variable ( in this case wind, sometimes seismic), rectangular ftg could not be an option.The benefit is, obtaining equal resistance for all directions.


2. Why using sloped ones not regular ones?

- For economy..you will need max . ht around tower center.

3. In the second image, why such sudden decrease in thickness is made? is it for economical purposes?

- IMO, meaningless.. the use of single slope without sudden decrease is better .. The sudden decrease will complicate the top reinf.

 

[JoshPlumSE]

1. What are the benefit of circular footings compared to rectangular ones? why are they more adopted for wind turbines? (constructability? economical aspects? structural aspects?)
Octagonal footing are often used for similar supports (vertical vessels, monopole communications towers). From a materials standpoint circular and octagonal footings are just more efficient and cost effective.

2. Why using sloped ones not regular ones?
That's not something I've seen with vertical vessels and monopoles. But, those are usually pretty light. So, maybe tapering it is more efficient for resisting punching shear while still conserving material.

Another possibility would be the dynamic aspect of wind turbines. You might want some extra mass near the pole to help control vibration.


3. In the second image, why such sudden decrease in thickness is made? is it for economical purposes?
Not sure, that's not something I've done before. If I had to guess, I'd think it could be something related to punching or anchor rods pullout cones.

 

[dik]

Depending on the 'wind rose', I can even envision eliptical shaped footings... if you have enough of them to build...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[1503-44]

Octagonal shapes are even easier to construct than a hexagons and result in a more uniform soil loading. Large rectangular or square patterns should be avoided due to higher soil bearing loads and longer moment arms at the corners.

Octagonal foundation design appears in this study of foundations for large vertical vessels typically found in refineries.

 

[1503-44]

The website uploader is broken.

Here's a link to my Dropbox,

https://www.dropbox.com/s/foz0w3iwwjlse81/109ce0168.pdf?dl=0