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

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Forgive the code developers. When the limit state design provisions "ultimate strength" were written, you could not design columns of any type with "working stress design". You were forced to use "ultimate strength" design.

The geotechs did not start to convert to limit state until very recently. Since it was rendered impossible to design columns using allowable stress, a lot of practitioners ignored this requirement.

Technically it is still a requirement in the code. It should not govern, but it should be checked for propriety. Strength design took over the concrete design community in the 1970's. You may have to get an old CRSI or ACI just to get a handle on the allowable stresses in a circular reinforced concrete member.

There are many references to allowable stress in reinforced concrete that will have to be purged in code cycles to come.
Harold Sprague

From: lrhauer(--nospam--at)
Reply-To: <seaint(--nospam--at)>
To: SEAOC  <seaint(--nospam--at)>
Subject: Allow. Stresses for Cast-in-Place Piles
Date: Thu, 24 Jun 2004 07:06:30 -0700 (GMT-07:00)

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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