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RE: Uplift on Belled Drilled Pier

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Rich,

My edition is the 3rd, copyright 1982. (I bought it new in '82 for
$38.00 while still at university.) In the 3rd edition, Section 4-11 is
titled "Bearing Capacity Of Foundations With Uplift Or Tensions Forces"
and Section 16-13 is titled "Tension Piles - Piles For Resisting
Uplift". The Ppb reference in section 16-13 sends you back to 4-11.

Another excellent reference is "Principles Of Foundation Engineering",
4th edition 1999, by Braja M. Das. Section 10.10, Uplift Capacity Of
Drilled Shafts, offers a good discussion of the subject. Das presents
step by step procedures for calculating estimates of the net uplift
capacities for deep and shallow drilled shaft foundations with bells in
both sand and clay.

Both references are based on the research of Meyerhoff and Adams (1968).

And, as I believe others have already pointed out, verify the bell is
dimensioned such that the tension forces will not shear it from the
shaft. 

If you are having trouble locating these resources, please feel free to
contact me privately.

-Brent



-----Original Message-----
From: richard lewis [mailto:rlewistx(--nospam--at)juno.com] 
Sent: Friday, November 14, 2003 08:33 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Uplift on Belled Drilled Pier


Brent,

Which edition of Bowle's do you have.  I have the 5th edition.  I can't
find this information.  Section 16-13 discussed static pile capacity. 
Section 16-14 discusses tension piles but I don't find the text you
give.  It discusses a factor called Ppb which is the pullout capacity of
the bell but goes on to state most tension piles are straight shafts and
don't have bells.  Then it never mentions it again.  My section 4-11 is
"Bearing Capacity using the Cone Penetration Test".

Thanks for your help.

Rich

On Thu, 13 Nov 2003 09:22:38 -0800 "brkoch" <brkoch(--nospam--at)pacbell.net> writes:
> Rich,
> 
> Within Bowles' Foundation Analysis and Design this subject is
> discussed
> in sections 16-13 and 4-11.
> 
> From Section 16-13:  "The pullout resistance can be estimated using
> the
> shaft skin resistance + the pile weight and the method of Sec 4-11. 
> If
> the soil is reasonably competent and the base enlargement is on the
> order of 2D, the pullout capacity of the pile should be about 2x 
> the
> shaft skin resistance plus pile weight."
> 
> Equations are presented in section 4-11 which are NOT based the 
> truncated quasi-conical soil pull out zone observed in model and full
> scale testing. The equations do include the effects of the footing 
> and
> soil weight as well as passive pressure friction resistance on a
> cylindrical surface defined by the diameter of the footing (or bell
> diameter in your case) with additional factoring based on shape and
> internal friction. The equations estimate an ultimate capacity and
> should be reduced by an appropriate factor of safety.
> 
> If you would like more info, please contact me privately. Thanks.
> 
> Sincerely,
> Brent
> 
> 
> -----Original Message-----
> From: richard lewis [mailto:rlewistx(--nospam--at)juno.com]
> Sent: Thursday, November 13, 2003 08:18 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Uplift on Belled Drilled Pier
> 
> 
> I am working on a drilled pier foundation for a pre-engineered
> metal
> building.  There are significant uplift loads on the frames.  I will 
> be 
> belling the bearing ends of the piers.  For uplift resistance I know 
> I
> can use skin friction.  But for the bell contribution, how is 
> uplift
> resistance calculated?  Is it the weight of a soil wedge based on 
> the
> angle of friction?
> 
> Thanks.
> 
> Rich
> 
> 
> 
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