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RE: Cracks on floor slabs

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Minimum strength reinforcement is each face. Minimum shrinkage and temperature reinforcement is normally the total at a cross section.

For a fully restrained concrete member, the minimum shrinkage and temperature value could be as high as .006 - .007 and the strength value about 3/4 of this.


At 03:32 PM 5/09/2006, you wrote:
Thanks for your reply Gil.  I appreciate it.
 
The way I understand it, the temperature reinforcement of 0.0018 - 0.002 should be for each face of the slab and not the total for both top and bottom.  Am I right?


Gil Brock <gil(--nospam--at)raptsoftware.com> wrote:
You have answered your own question.
Minimum reinforcement for slabs is normally in the order of .0018 to .02 times the concrete area as long as there is no restraint. The 1.4/Fsy figure is a very approximate (and incorrect) version of this for T beams again without restraint.
In your case the shear walls are restraining the slab shortening leading to full depth shrinkage cracks. Significant shrinkage problems will continue for several years with minor further shrinkage for the next 10 to 20 years. If the concrete is very young, filling with epoxy will not work long term. You will need to repaid them again in future.
Talk to a concrete repair company that understands restrained shrinkage cracking.  



At 05:01 PM 2/09/2006, you wrote:
Thanks for your reply James.
 
It is a 240mm thick flat slab supported by shearwalls and columns.  Cracks appear perpendicular (almost) to shearwalls and reinforcement provided parallel to shearwalls are only 10mm rebars spaced at 200mm O.C. top & bottom.  Crack widths at slab soffit are 0.2mm - 0.5mm and some goes through the slab.

"Kestner, James W." <jkestner(--nospam--at)somervilleinc.com> wrote:
Could be many, many causes. We would need more descriptive info.
 -----Original Message-----
From: The Best Always [ mailto:the_best_always(--nospam--at)yahoo.com]
Sent: Wednesday, August 30, 2006 5:43 AM
To: seaint(--nospam--at)seaint.org
Subject: Cracks on floor slabs

Hi everyone,
Can anyone assist me on cracks on floor slabs of highrise buildings?
Regards to all
 
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Regards  Gil Brock
Prestressed Concrete Design Consultants Pty. Ltd. (ABN 84 003 163 586)
5 Cameron Street Beenleigh Qld 4207 Australia
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