Recommended rebars maximum change in diameters

[ramihabchi]

Hi,
Our design team use the following rule while designing RC walls,beams,slabs and foundations:
Ratio of main mesh diameter to additional rebars must be less than 1.7 and higher than 1/1.7
And ratio of diameters of two lapped rebars must be less than 1.7.
Is this rule(or a similar rule) available in any Codes?if you know a code that recommend such a limitation on rebars diameter which is?
If you can also explain the reason behind it.

 

[Lomarandil]

I've heard of similar rules (at least 2 imperial bar sizes or 4mm diameter between bar sizes) to aid in field inspection.. hard to tell 12mm from 14mm, but 10mm to 14mm is pretty clear.

But I haven't seen anywhere that had a guideline like that codified as a definite rule.

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The name is a long story -- just call me Lo.

 

[BridgeSmith]

I don't believe there's anything in th AASHTO bridge design spec limiting the sizes of bars that can be lapped. It does have minimum area of reinforcing requirements for transverse distribution steel as a percentage of the area of the main reinforcement. This only applies to slabs subject to truck wheel loads.