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Re: Minimum Slab Reinforcing

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Josh,
 
Look at 7.12.2.1: 0.0018 is applicable to "gross concrete area", meaning that you need to use the full thickness to calculate the total (T&B) reinforcement, or 1/2 thickness for top or bottom rebars.  I always make each layer separately - rather than both layers combined - compliant with this requirement.
 
V. Steve Gordin, SE
Irvine CA
 
 
 ----- Original Message -----
Sent: Thursday, September 04, 2008 11:28
Subject: Minimum Slab Reinforcing

In ACI 318, section 10.5.4, the code states that the minimum flexural reinforcement for slabs and footings should be the same as given in 7.12 (which is the temperature / shrinkage requirements). 

 

I?ve interpreted this to me that regardless of what the area of steel required by analysis is, you can never let your total slab reinforcing (As_top + As_bottom) be less than the minimum amount required for temperature and shrinkage. 

 

Now, I?ve got another engineer who is arguing that the Asmin = 0.0018 * Agross requirement applies for BOTH the top steel reinforcing and the bottom steel reinforcing.  Since temperature and shrinkage controls the design of most relatively thick mat foundations, this interpretation would effectively double the amount of steel required in these mats. 

 

Any opinions?  Has anyone heard of someone interpreting this section of code in this manner? Is it common? 

 

Sincerely,  

 

Josh Plummer, SE