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RE: z factor for crack control

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Serviceability is a major concern to water treatment structures.  As a
result there is a good section with references, charts, etc. in the ACI
350, Sec. 2.6.6.  The Z value is based on 2" cover or less.  The
recommended Z is 115 k/in and is based on exposure to alkaline liquids
greater than ph of 5, or exposure to sulfate solutions less than 1500

The Z value should stay the same for greater cover.  The larger covers
should be considered as added protection.

I hope this helps.

Harold Sprague
Black & Veatch
From: JENSEN(--nospam--at)
To: seaoc(--nospam--at)
Subject: z factor for crack control
Date: Friday, August 08, 1997 6:37AM

I have been facing a little dilemma lately regarding the crack control
provisions in section 10.6 of the ACI code and would appreciate some

I am designing grade beams and mat slab for a large under/ above ground
parking structure in Korea.  Local water table conditions are terrible,
the structure must be designed assuming water to the ground surface or
even a few meters above at flood stage.  To add to the problems, the
structure is located in a highly marine environment.

Looking at 10.6.5 in the code, I would venture a guess that a z value of
145 is not sufficient for this situation (Yes, i remembered to reduce
value for the slab, for all you nitpickers out there!).  What sort of
number would be appropriate for this scenario and how can I justify
it?  I have also tossed around the idea of simply increasing the cover
and leaving the z at 145.

Any help you can give would be greatly appreciated.
Thanks in advance.

Wade Jensen