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Re: A few questions for those who design concrete pools.

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Dennis,

	I haven't designed a pool for some time and I'm not very familiar with
the U.S. codes; but I do have a couple of comments/suggestions that may
be helpful.

	There are calculations, if not in ACI 318 then in other ACI
publications, dealing with crack width considerations.  These should be
followed for water containing structures.

	Ground water elevations are extremely important and often affected by
the pool.  Depending on whether or not you have under tank drainage and
whether or not said drainage is reliable the critical design condition
may be with the tank empty and ground water elevation at the ground
surface.

	Bouancy is also important.  I've seen underground tanks and known of
swimming pools lifted completely out of the ground when empty because
the effects of bouancy with a high water table were overlooked and the
subject structures were not properly anchored.

	Good luck with the swimming pool.

				Regards,

				H. Daryl Richardson

Structuralist wrote:
> 
> I know I have asked a few of these questions before, but I need to get
> a couple of opinions since I have had some conflicting responses. The
> questions have to do with the installation of Gunnite and the
> standards used.
> 
> 1. Does the Uniform Building Code (or 2000 IBC) make any specific
> reference to the structural design of Gunnite Pools?
> 2. While it may be sound practice to follow a concrete building
> standard for the clearance of reinforcing steel from earth and air,
> are there any specific standards of practice or published codes that
> mandate the placement and minimum clearance of steel in a swimming
> pool?
> 3. It is my understanding that the finish on most Gunnite Pools is
> considered a structural plaster used to provide a smooth surface. It
> is also my understanding that the plaster used is, essentially,
> concrete and can obtain the same strength as the concrete wall below.
> Is this valid?
> 4. It is my belief that all concrete (including Gunnite) cracks. The
> crack needs to be evaluated to prove if it is caused by defect or by
> normal processes such as temperature cracking (hairline). I also
> understand that most cracks will not cause sufficient leakage in a
> pool as the wetting of the concrete surface would tend to swell the
> concrete and essentially seal the crack. Is this a valid assumption
> for temperature and hairline cracks?
> 5. I've been told that the plaster finish on a pool is a waterproofing
> finish. Is this considered a valid assumption by most of you?
> 6. There are a few contractors in the area who specialize in the
> repair of Gunnite pools who rough up the surface of a pool considered
> to be a thin wall shell and who add an additional 4-inch shell of
> Gunnite within. There are alternatives that I believe are less costly
> - pool liners, Epoxy-injection and new plaster finishes etc. What
> alternatives have you used to repair minor cracks (no elevation
> changes and no cracks larger than approximately 1/32" in width) in a
> Gunnite Pools
> 7. Final questions: Is the City Inspector required to inspect the
> placement of the rebar cage before the Gunnite is shot on. If so, is
> the cage generally set on chairs to hold it away from the earth to
> allow for clearance between the earth and rebar (assuming that some
> standard or minimum clearance was originally specified by the design
> engineer)?
> 
> If you prefer, please feel free to email me privately with your
> response. If others want to know what the comments were, I'll be happy
> to post them on the Structuralist.Net or if you prefer, leave them on
> the SEAINT list.
> 
> Thanks in advance for those of you who respond.
> 
> Dennis S. Wish, PE
> Structural Engineering Consultant
> structures(--nospam--at)engineer.com
> 760.564.0884 - Phone
> 208.361.5447 - Efax

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