Leaderboard

According to ACI 318-08 in the commentary of section 7.12.1.2 its said "Where structural walls or columns provide significant restraint to shrinkage and temperature movements, the restrain of volume changes causes tension in slabs, as well as displacements, shear forces, and flexural moments in columns or walls. In these cases, it may be necessary to increase the amount of slab reinforcement required by 7.12.2.1 due to the shrinkage and thermal effects in both principal directions (see References 7.7 and 7.16)." So according to these two references we are allowed to increase the minimum steel ratio depending upon the restraint of the structure. Now the question is to which extent are we allowed to increase this ratio to which you quoted ACI COMMITE REPORT 224R-01. What reference 7.16 ( Gilbert, R. I., “Shrinkage Cracking in Fully Restrained Concrete Members,” ACI Structural Journal, V. 89, No. 2, Mar.-Apr. 1992, pp. 141-149.)* quoted by ACI R7.12.1.2 suggests is that minimum steel ratio should be greater than 0.45%. For through understanding please download the paper given below and read it but for brevity let me quote the statement from the discussion of this paper "For a maximum design crack width of 0.3 mm (as is commonly specified in codes of practice), it appears that for the restrained slabs tested in this study a reinforcement area of greater than about 270 mm2 (ρ = 0.0045) would be satisfactory" * you can also download it from https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&ved=0CC4QFjAA&url=http%3A%2F%2Fwww.scribd.com%2Fdoc%2F48305786%2Fshrinkage-cracking-in-restrained-reinforced-concrete-members&ei=MtooUtmAIpDLswb-zIHgAQ&usg=AFQjCNFdUzeJmxmkPw3K5S1_oXde_bak4g&sig2=DXzeQ2UG9dwzrB81bTZ03g 48305786-shrinkage-cracking-in-restrained-reinforced-concrete-members.pdf

The statement taken out from ACI document only covers shrinkage cracks in reinforced concrete structures. Hence, it is regarding serviceability limit states. In order to fully understand it, one should know what they mean by 'acceptable level', or 'acceptable design limits'. There must be a paper regarding that, which needs to be studied. You should check latest ACI code; I think. they have not included this provision in the latest code. They are continuing older provision of 0.18/0.2 %. It look like as if they have not taken the recommendation of this committe seriously. It is a confusion.