Minimume Spacing between Top and Bottom Steel Mesh in Rfat Foundation??

[TekEngr]

Does any one can tell me what is the minimum spacing should be between Top and Bottom steel mesh in raft foundation as per American code or British code?
please also provide the ref.

 

[SlideRuleEra]

shahg123 - This was discussed in your recent thread, Link, but it is true you did not get a direct answer:

Codes do not require a minimum spacing between top and bottom rebar mats. Codes are not "cookbooks" where you "look-up" all the answers. The intend of a code is to keep an Engineer from producing a design that has flaws which have, over time, proven to cause problems.

Rebar mat spacing is a human judgment decision. There is no "problem" spacing the mats with near zero spacing, the software that you have used confirmed that. However a dose of engineering judgment indicates that near zero spacing is a waste of materials.

In your other thread, I essentially agree with the discussion and advice you received from SemiPE, clear spacing of 100 mm is a reasonable minimum.

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[Teguci]

Minimum clear spacing = (dt + db)/2

Currently looking at an old (1950s) 1-way slab that is only 4" thick (100 mm). Cover is 3/4" with top and bottom steel mats. Not ideal to anchor to, but it spans 10'-0" fairly well. Every other 1/2" diameter bar (reinforcing is 6" oc) is bent to transition from top to bottom reinforcing.