Pile as spring below foundation

[aslam]

plz see attachment and discuss

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plz see attachment and discuss

[oanm2000]

Excellent!
It's a good solution for modelling the pile as support.
I ever use the 0.25*fc*Apile, but I calculate the settlement of the pile ever, evaluating the effective stress and deformation along the pile (so long and so boring). But the suggestion is equate to the formula: the maximun allowable settlement for a pile must be between 0.0075*d and 0.016*d (d is the pile diameter). The 0.01*d is a very good aproximation I think and a good sollution...
Where you found this information Aslam?... Is very good
Thanks a lot

[aslam]

Dear oanm2000 ,

It is from ETABS manual published by ATKINS - DUBAI.

I have following queries regarding this article.

Kv represent end bearing resistance of pile ?
Kh = 0.1 Kv, Kv represent frictional resistance of pile ?

Generally frictional resistance of pile >>>> end bearing resistance, (when depth of pile (& thus surface area) is large and cohesion of soil is good)
then why Kh=0.1 Kv

If we have pile with single or multi bulbs, we have to consider bulb dia in equation of Kv?

If we have piles in group, it is neccesary to reduce Kv ? (i.e. pile efficiency)

[oanm2000]

Dear Aslam:
Kh is the horizontal balasts coeficient or horizontal balast module.
According to Bowles (1996) Ks or Kv is = qadm*4000, with qadm in Ton/m2, but Kv in KN/m3
According to Monet (1994) Ks or Kv (in Kg/cm3) depend on of bearing capacity (in Kg/cm2) to this depth, calculate from the Nspt value.
Wherever...
According to Tsudik (1992) the Kh or Ksh is from 0.1 to 0.5 Kv (or Ksv), according to the soil type. Kv and Kh in Kg./cm3...
Then, I supose, the idea is take the most unfavourable value
Regards

[ErnestoIII]

for piles on rock, you can use the normal spring equation for columns assuming the pile/column would fail first rather than the rock.

ks = AE/L

[AK12]

Tried to download the file but not possible. Could you please reupload the file.
Thanks

plz see attachment and discuss

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[essenza]

Very interesting topic. To be honest i never agree modeling pile in SAFE using point spring but there are "no other choice"...what i mean by no other choice is not related with the fact that this is the best and most used method for office design but really because SAFE is the only software that compatible with ETABS.:P

Currently what I'm doing is modeling the whole pile raft in ETABS export it to SAP2000 to model the nonlinear spring of the soil presented by q-z, t-z and p-y spring and soil beneath the raft with area spring (I just don't know how to model nonlinear spring in ETABS, hope anybody can help with this). After that run the nonlinear analysis and voila. This nonlinear soil-pile-structure interaction becomes more cumbersome in combination with dynamic. I believe this is the reason why SAFE point spring model is "the best easiest and hopefully conservative choice" so far.

[jagur]

hey friend i agree with essenza,
can anybody give EDB file as a simple example for design foundation with Etabs?

[hessian]

upload the file again plz

[jpver]

I am a practicing structural and geotechnical engineer but I am no longer using ETABS as I am more focus now on bridges. Looking at all the threads of this topic, it looks like you are modelling incorrectly and may not necessarily conservative. The pile should have both the lateral and vertical springs. The lateral springs control the lateral displacement that includes pile displacement (so with moment) and lateral building drift. Without these springs, you will have large bending moment in the piles and displacements unless you use the basement walls to carry all the lateral forces. But even then, when the basement walls move laterally it also moves the piles. In this case, without the lateral springs included in the piles it will just move freely which gives a higher moment and displacement.

An if you have large drift because of no lateral springs or fixities at the base, you will have to increase the stiffness (EI) of the building. When you increase the stiffness, you are also increasing the mass and then increase the earthquake forces.

If it can not be done in SAFE/ETABS, use another software to model correctly the interaction of the foundation and the soil. Assume your building structure to be fixed at the base when using ETABS, and transfer all your forces to another software modelling correctly the soil and the basement or raft.