Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: Uplift on Belled Drilled Pier

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Please get yourself a copy of FHWA publication (FHWA-IF-99-025) on drilled piers. All your questions will be answered.

Angie Baughman <stecksy(--nospam--at)> wrote:
I would like to hear some more comments on this topic if
anyone can add to my questions below (and would like to
share your knowledge and expertise). I have been asked to
put some preliminary numbers together for some cost
comparisons using drilled piers versus one large mass of
concrete to anchor a structure against overturning (the
structures are bents that are supporting 2000 L.F. of a
continuous overhead conveying system located outdoors that
will be located about 40 feet above ground). There will
be about 25 of these bents (2 columns per bent, and the
bent is 8' center to center of columns) spaced in the 2000
L.F., so that is the owner?s reasoning behind spending the
time to do an analysis. The owner wants to see if using
drilled piers would offset the cost of excavation and
forming of spread footings (the spread footings would also
rely on the soil overburden to resist uplift). The soils
report and recommendations are in progress, so for now I
am using some low-end skin friction values that the
geotech recommended. (This is my first design experience
with drilled piers).

The equipment is available to do a belled pier, so I am
looking at both a straight-shaft or a belled pier.
However, the reference I was using (Principles of
Foundation Engineering by Das) stated that "For the
majority of drilled (belled) piers constructed in the
United States, the entire load-carrying capacity is
assigned to the end bearing only. However, in certain
circumstances, the end bearing capacity and the side
friction are taken into account."

Question #1: What and where would I find out what these
certain circumstances are? Would the Bowles reference
cover this?

Question #2: The owner?s design shows the 2 columns from
the bent setting directly on the drilled pier, (there will
be no cap connecting the two piers together, so they will
act independently), and the anchor bolts will be cast
directly into the drilled pier. This tells me that I will
need to run vertical steel the full length of the pier due
to the lateral loads (correct me if I am wrong). Is this
typical to run vertical steel the full length of the
drilled pier?

My preliminary numbers are showing that what the owner is
proposing to do is not going to be cost effective based on
the quotes he received for the unit cost of concrete to
excavate and form vs. the unit cost to do a drilled pier.
However, the owner is asking for an analysis of what he
wants to do, and not anyone?s opinion.

Angela Baughman, P.E.
Wausau, WI

******* ****** ******* ******** ******* ******* ******* ***
* Read list FAQ at:
* This email was sent to you via Structural Engineers
* Association of Southern California (SEAOSC) server. To
* subscribe (no fee) or UnSubscribe, please go to:
* Questions to seaint-ad(--nospam--at) Remember, any email you
* send to the list is public domain and may be re-posted
* without your permission. Make sure you visit our web
* site at:
******* ****** ****** ****** ******* ****** ****** ********

Do you Yahoo!?
Protect your identity with Yahoo! Mail AddressGuard