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RE: Joints and Spacing in Concrete Tank?

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We just finished an underground concrete reservoir, square in plan, and
245 feet by 245 feet by 20 feet high.  To keep it water-tight, we
designed in pour closure strips, about 6 feet wide across both
directions, I recall in two locations over the 245 ft. dimensions. The
closure pour-backs were placed after I think it was about 30 days to
allow for shrinkage of the base pours.  (Played he!! with a quick
construction schedule, though.)  Water-stop was used at pour strips, and
reinforcing was continuous across the pour strips.  Contract required
the contractor to route and grout (epoxy) any cracks wider than hairline
(don't remember the specified width).  There were a few cracks that had
to be treated.  Overall, though, a successful job, now watering lawns
throughout La Jolla.

Bob Garner, S.E.

-----Original Message-----
From: Jeremy South [mailto:jslist(--nospam--at)apt38.com]
Sent: Tuesday, August 02, 2005 1:52 PM
To: seaint(--nospam--at)seaint.org
Subject: Joints and Spacing in Concrete Tank?

I'm designing my first rectangular concrete tank (aeration basin) for
a wastewater treatment facility. The tank is approximately 100' feet
long with circular ends. There is a free-standing wall on the inside
of the tank that separates the tank into 2 - 12' wide ditches. The
tank will be an above ground tank approximately 12' deep.

I'm familar with the PCA guide for the Design of Rectangular Concrete
Tanks (5th Ed.)

I have designed the side walls as cantilevers using the appropriate
factors discussed in the ACI codes. The walls are 12" thick with 2
layers of steel. I feel very comfortable with the design.

However, I am still confused regarding the joint layout and spacing.
The design guides I've used so far don't provide much information
regarding joint spacing for the main walls.

The PCA information I've found generally recommend limiting the joint
spacing in the walls to about 20'-0 OC max. I have seen other similar
tank wall designs where they push the joint spacing up to 50 or
60'-0...this seems excessive to me.

Given the design aids in the PCA publication, I'm looking at joints at
about 35' OC for the T&S reinforcement I'm using. However, I'm still
confused about whether to use expansion joints, construction joints
only, or a combination of the two.

Generally, what is the recommended spacing or "rule of thumb" for
spacing of joints both in the vertical side walls and slab?

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