×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

No Pile cap needed below column

No Pile cap needed below column

No Pile cap needed below column

(OP)
Hi Guys

Simple question:

I have 1000diameter piles supporting a 300mm suspended ground slab and 350square columns directly ontop of pile.


Am I right to think that no pile cap is needed if the pile will not punch through the slab?

Do I treat the pile basically as a column and check direct/face shear and punching shear. If not a problem to thickening needed. So basically whether there is a column on top of the slab or not makes no difference to whether I need a thickening or pile cap, its all goverened by the possibility of the pile punching through the slab.

Of course if the pile is of a small diameter, there is a good chance I might need a thickening.

Cheers
 

RE: No Pile cap needed below column

I think this is no different than the requirements for the transfer of a load from a column above to column below through a floor slab. See requirements in 10.15 Transmission of column loads through floor systems.

RE: No Pile cap needed below column

You do not need a pile cap if the peripheral shear stress is acceptable around the pile periphery.

BA

RE: No Pile cap needed below column

Also check the following:
* bending in the slab (this assumes multiple piles are being used to support the column, which may not be the case)
* one way shear in the slab (probably won't control)

DaveAtkins

RE: No Pile cap needed below column

And as a foundation (other than the mechanical requirements) it is usual not to require a pile cap for piles directly supporting coaxial columns as long they are braced in X and Y directions; and yours are by your slab (even normally this would be thought to happen at ground level, and you have not THERE the lateral support). Normally, anyway would be good enough if the pile cantilevers vertically just little till the slab.

So the question would be refered to the ensured general stabilty of the building-structure-soil interaction, to be analyzed in the usual ways, i.e., for your problem, would not having some pile cap, or some pilecap restriction to displacement mean something that makes the foundation not work? If everything works, you know you have a sound foundation.

RE: No Pile cap needed below column

Ishvaag,
You bring up a valid point. If the column is not lined up with the centroid of the pile, then the induced moment will find its way into the slab based on joint stiffness. The slab will then have to be designed to take its share of moment.

I am not sure if you are in seismic country. If you are then you are required to tie your foundations together.

RE: No Pile cap needed below column

Assume that the pile will be eccentric to the column above due to construction tolerances and have a design ready to deal with this additional moment in the slab for both directions.  Essentially, your slab is your pile cap.

RE: No Pile cap needed below column

Is there a design moment in the column base? if so, will any additional moment caused by the eccentricity be significant? How was the reaction to that design moment to be distributed?
 

Michael.
Timing has a lot to do with the outcome of a rain dance.

RE: No Pile cap needed below column

With a 350 sq column on a 1000 dia pile it is likely that any base moment will go straight into the pile.
The presence or not of an isolated cap on that pile will hardly make any difference, as long as slab punching is not an issue.

RE: No Pile cap needed below column

Agree with apsix.  The pile will be much stiffer than the slab.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources