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RE: Allow. Stresses for Cast-in-Place Piles

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Larry,

I am not sure I understand the question. The allowable stress requirement is
for piles (or caissons more specifically) under axial, compressive loading.
Those stresses are meant to include some allowance for imperfections and
load eccentricity. If the caisson is to be supporting lateral loads, you may
design the caisson as a beam (LRFD and all) or, rather, a
compression-flexural element. In this case, you may waive about the 1/3
requirement if the amount of steel is significant. The magnitude of lateral
loading will depend on the diameter of the caisson if there are lateral
earth pressures involved.

I am not sure why is there lateral loading and where the 1,000 lb/lf came
from. A geotechnical engineer should give you the lateral load magnitude for
your particular case...

	Jesús Gómez, Ph.D., P.E.
	Associate                                          
	Schnabel Engineering
	jgomez(--nospam--at)schnabel-eng.com


-----Original Message-----
From: lrhauer(--nospam--at)earthlink.net [mailto:lrhauer(--nospam--at)earthlink.net]
Sent: Thursday, June 24, 2004 10:07 AM
To: SEAOC
Subject: Allow. Stresses for Cast-in-Place Piles


Sec. 1808.2.2 of the UBC/CBC requires that uncased cast-in-place piles be
designed for 1/3 the allowable concrete stress and compressive stress of the
reinf steel. I am working on a job which requires underpinning of a one
story Type V structure with settlement problems due to about 8 feet of fill
beneath the structure. Although I haven't designed the piles yet, which will
be flag poled from the bedrock below and pinned at the top, I am concerned
that applying the traditional 1,000 plf creep in the fill area as a lateral
load on the piles will produce some pretty horrendous piles.

Are other engineers following this 1/3 allowable stress requirement, (and
anyone with advice to give is appreciated)?

Thanks in advance,

Larry Hauer S.E.



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