# RCDC Beam design - effective depth Calculation

Bentley Team,

How is the effective depth for beam being calculated for a beam with two or more numbers of layers in RCDC software?

Please provide the basis and validation for the same.

I could find some formula related to effective depth in FAQ in the link below, but that is not giving correct value for the design I have.

Parents
• Hi,

Effective depth, d = 450 (Overall Depth) - 30 (Clear cover) - 16 (for layer 1) - 25 (spacer bar between layer 1 and layer 2) - 16/2 (upto centre of layer 2) => d = 371mm = 370mm (rounded off).

But actual provision is 3 layers of 12 dia bar as per design, as per which calculation should be as follows,

Effective depth, d = 450 (Overall Depth) - 30 (Clear cover) - 12 (for layer 1) - 13.33 (Two third of aggregate size or bar dia, whichever is higher) - 12/2 (upto centre of layer 2) => d = 388.67mm = 385mm (rounded off).

So RCDC is basically calculating lesser effective depth than required. Is that correct?

Also confirm if my assumptions are correct.

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Children
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