Design of Piles on Finite Element Software

[perfectaccess]

HI

If we have mat foundation carried by piles,and the piles are modeled as springs, we will define z stiffness for springs,to resist vertical loads,but what about horizontal load(in plane load),how it will be resisted in FE model.

Some people say define 10% of z spring stiffness in x&y,but I cant understand this.

I need to know,using finite element method how can I model the springs to study the horizontal in-plane load,and make sure that building is stable.(study earthquake effect)

Just Note that: I am using Safe

Regards

 

[KootK]

You've really only got two choices:

1) procure advice from a geotechnical engineer.
2) play geotechnical engineer yourself.

I don't recommend path #2. Regardless, here is some quality, free information: Link

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[IDS]

Excellent presentation.

The only thing I would add, that geotech engineers really should know, but like to ignore, is that in the typical working stress range, if the structure is reinforced concrete, the behaviour of the structure is even more non-linear than that of the soil.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[Trenno]

Well would you look at that...

Rob Day taught me Geotech at university.

 

[patswfc]

Heres a link to the Engineers Australia webinar where KootK's pdf comes from

http://mediavisionz.com/ea/2013/eav/130814-eav/index.htm#

Regards

 

[delagina]

shouldn't your piles have lateral stiffness as well per geotech report?
geotech report of piles usually provide a table or graph of horizontal load and lateral displacement of the piles

 

[perfectaccess]

Really Excellent presentation:
It has been said that the bigger the loading area is softer of elastic response.
Does this mean that bearing capacity for bigger foundation is less than smaller one?why?

Also, Could you please follow me in this points (What we do In designing piles, procedure)
1: we defined vertical stiffness for piles form test report
2 we define lateral stiffness for piles from test report
3. we make sure that model is stable in all direction
4.In general ,How we will Check Sliding and overturning of building if the building relying on piles

 

[KootK]

Does this mean that bearing capacity for bigger foundation is less than smaller one?why?

Do you do any work in wood? I sort of think of it like compression perpendicular to grain in wood design. The wood fibers, if they extend beyond the bearing area, tend to help support the load even though they are not, themselves, loaded directly. It's somewhat similar with soil. Obviously, the larger the loaded area, the less impact the material beyond the loaded area will have.

1: we defined vertical stiffness for piles form test report
2 we define lateral stiffness for piles from test report
3. we make sure that model is stable in all direction
4.In general ,How we will Check Sliding and overturning of building if the building relying on piles

1) I think vertical pile stiffness should come from the geotechnical engineer rather than being calculated by you based on the soil report.
2) I think lateral pile stiffness should come from the geotechnical engineer rather than being calculated by you based on the soil report.
3) Yes. Stable, in possession of enough capacity, and suitable with regard to movement. All your wheelhouse.
4) Overturning will be checked primarily by ensuring that the piles can generate a couple which would resist the overturning moment. This may require some of the piles to resist load in tension. Sliding can be checked using a number of resisting mechanisms which may or may not be assumed to be working in concert (usually your judgement). These may include pile lateral resistance, resisting soil pressure acting against vertical surfaces, and friction between the soil and foundation elements. Be wary of assuming friction resistance at the interface between a pile supported cap and the soil below.


I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[perfectaccess]

Thank you Ktootk
4) Overturning will be checked primarily by ensuring that the piles can generate a couple which would resist the overturning moment. This may require some of the piles to resist load in tension
Does that mean,if I check the pile for compression and tension forces under the applied loads(in FE model), and all the piles are within limit=====>the building is safe against overturning. but also,weight of the building play role in overturning?
Sliding can be checked using a number of resisting mechanisms which may or may not be assumed to be working in concert (usually your judgement). These may include pile lateral resistance, resisting soil pressure acting against vertical surfaces, and friction between the soil and foundation elements. Be wary of assuming friction resistance at the interface between a pile supported cap and the soil below.
As you said ,the sliding is combination between lateral force+ friction*weight+ passive soil pressure(example behind retaining walls).

Finally Ktootk,I am really thankful for your time ,to help me in this

Really Appreciate

 

[KootK]

Does that mean,if I check the pile for compression and tension forces under the applied loads(in FE model), and all the piles are within limit=====>the building is safe against overturning.

Yes. I`d do this by hand or spreadsheet but FEM would work to so long as you know what you`re doing.

Finally Ktootk,I am really thankful for your time ,to help me in this

You`re very welcome. I hope to see your input on one of my threads in the future.


I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[WARose]

Like someone else mentioned to you, you likely need the lateral stiffness for the pile from the geotechnical engineer. Sometimes they've given me a "depth to fixity" for the piles I want to use. From that (based on the stiffness of the pile) I've been able to figure the lateral and rotational stiffness of the pile at the tip and input that as a spring constant for the pile. Usually vertical stiffness does cause too many issues in a mat, although sometimes I might do an enforced displacement (representing differential settlement) to see what kind of forces this generates in the mat and so on.