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.
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 -12.5mmd= 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,
Global Technical Support
Abhisek M said:d = D - Clear Cover - 16mm -12.5mmd= 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?
Request you to kindly note following:
At design time the number of layers of reinforcement is assumed as under to arrive at the effective depth, d:
Agree of the part on how RCDC takes no. of layers into account during auto design. But what I observed is the following. Say my beam depth is 550mm as per which 2 layer will be assumed by RCDC. So effective depth is calculated based on 2 layers of rebar that is,
d = 550 (overall depth) - 30 (clear cover) - 16 (bar dia) -12.5 (spacer bar dia/2) = 491.5 = 490 (rounded off)
But as per design (auto-design), only 1 layer of reinforcement is provided consisting of 3 no. of 12 dia bars. But still effective depth corresponding to 2 layers is being used for design.
Also the usage of 16mm and 12.5mm is doubtful as provided is only 12mm bars.
If you can again refer to my previous reply and provide solutions issue-wise, it will be highly appreciated. Thank you.
It would be useful if we can have an example based in which we can take this further.
You can provide us with a live example which you are doing manually and we will help you with validation oh how RCDC is doing it. You can share your own manual calculation by taking an example into consideration.
I have attached a sample file. If you refer Beam B5, top right is provided with 3 layers of rebar. In that case how is the effective depth being calculated? Based on the solution given by Abhisek M I presume that it is calculated as below:
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.
Request you to please check and confirm.