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RE: Joints and Spacing in Concrete Tank?

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For a long cantilevered basin wall, I would typically provide
contraction joints at a spacing of 30 to 40-ft on center.  (See my other
email also sent today regarding joint types.)  I would extend the
contraction joint across the base slab in the same plane in your case. 


William C. Sherman, PE
(Bill Sherman)
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com

-----Original Message-----
From: Jeremy South [mailto:jslist(--nospam--at)apt38.com] 
Sent: Tuesday, August 02, 2005 2:52 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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