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RE: Crack control for swimming pool.

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ACI 224R, Table 4.1, does show a recommended crack width of 0.004 inch for
water retaining structures. However, ACI 350-01, R10.6.4, states that
environmental structures (liquid-containing structures) with "normal
exposure" may be designed for z=115 corresponding to a crack width of 0.010
inch, and using a maximum concrete cover value of 2-inches. 

There has been some recent discussion on the 350 committee regarding the
0.004 inch crack width in ACI 224R. It is generally felt that this should
apply to concrete elements in direct tension, such as walls of circular
tanks, but should not apply to flexural cracks. Flexural cracks should not
be a significant leakage problem since they are not full depth, but they
should be controlled due to potential corrosion. 

ACI 350 has retained the "z-formula" for crack control even though ACI 318
has gone to a different formula. It is felt that the new formula does not
provide adequate protection for environmental engineering concrete
structures.  

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

-----Original Message-----
From: Bill Marczewski [mailto:bmarczewski(--nospam--at)pndast.com]
Sent: Tuesday, February 18, 2003 12:45 PM
To: SEOC Engineering Forum (E-mail)
Subject: Crack control for swimming pool.


We are designing a swimming pool that has grade beams and one-way slabs
spanning between the grade beams.  Strength analysis does not require a lot
of reinforcing, however meeting the crack control requirements is becoming a
tedious iterative process, only to find out we can't achieve the appropriate
z-value.  We need a z-value of 43 corresponding to crack width,w = 0.004
inch (water retaining structures).  We need 3" of clear cover as we are
pouring the slab on grade, then expect soil settlement on the order of 12
inches per the geotechnical investigation.  I have tried a lot of different
bar sizes, and spacings.  Has anybody else been in a similar situation?
Thanks.


Bill S. Marczewski, P.E. 
Peratrovich, Nottingham & Drage, Inc. 
503-325-1250 Main; 503-325-9789 Fax 
bmarczewski(--nospam--at)pndast.com 
www.pnd-anc.com 

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