# 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
• Hello,

In RCDC the effective depth of a beam is calculated in the fllowing manner.
If D is the total depth and d is the effective depth, then
d = D - Clear Cover - 16mm -12.5mm
d= D- Clear Cover -28.5mm

Here, clear cover thickness includes stirrup dia. For effective depth calculation it is assummed that 2 layers of reinforcement is present and effective depth is calculated from the top most fibre to the mid depth of spacer bar. Though it is conservative in some cases, but we are in safer side. Considering this fact, a value of 16mm is considered as the bar dia of bottom most layer reinforcement. Then 25mm spacer bar is considered for which we take half the depth in claculation as 25/2=12.5mm.

After getting the d value it is again rounded down to nearest 5mm interval, which in turn make the aforementioned 28.5mm value, 30mm.

Can you please check and let me know if this matches with your calculation?

Thanks & regards,

Abhisek M

Global Technical Support

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• d = D - Clear Cover - 16mm -12.5mm
d= D- Clear Cover -28.5mm

Issue 1 : Does it take 16mm and 12.5mm (as quoted above) as the fixed values or these are based on User Input?

Also, referring to the link below, Q30 which says the assumed diameter of the bar, d1 as 20mm. how is it assumed.

Issue 2 : Can you please tell how the effective depth is calculated for say 3 number of layers.

Issue 3 : Can you confirm, if RCDC does or does not calculate effective depth based on the rebars and layers actually provided?

Issue 4 : Also, at beam different locations (say top left and top right) different rebars in different layers may be provided, say at top left one layer is provided and at top right 2 layers are provided. But RCDC is giving only one effective depth for entire beam. How is that being considered?