Why does RCDC give me more rebar than Necessary

Question

Good day, I tried using RCDC 9.2 for my concrete design and it is over reinforcing my beam section. 
 
 I have a single span beam of 6m with a property of .23X.45. and a mid-span moment of 90kNm 
 from my manual design, I am getting 4Y16. but rcdc is giving me 5Y16 why?

Abhijeet Gundaye · Accepted Answer

Hi RCDC is now available in STAAD.pro with limited features. in STAAD. pro advance you will get all features of RCDC. click on below link RCDC /cfs-file/__key/communityserver-discussions-components-files/5932/RCDC-features-for-STAAD.pro-_2800_Basic_2900_-license-users.pdf 
 
 As RCDC basic version is available to design column, walls and beams, Concrete design module is removed. In RCDC user will get more options to design these elements.

Abhisek M · Answer

Hello, 
 I guess this has been done considering detailing criteria. If you go to Settings> Preferred bar spacing you can see the minimum spacing criteria mentioned. For 230mm width by default 3 nos of rebars are set. If that is the case, program will place 3 rebars in the bottom layer and try to place additional required rebars in 2nd layer. Now as bottom layer is having 3, for symmetry it provides at least 2 at 2nd layer though the requirement is 1. You can make it 4 in preferred rebar spacing settings and then try. If using 4 the spacing become too less, the program may not allow. In that case you may change the clear cover from general design settings to accommodate 4 rebars in a single line. Hope this helps. 
 
 If you still not satisfied please share the file with us.

Abhijeet Gundaye · Answer

Hi Detailed design calculation sheet is available in RCDC. please go to reports tab and generate it. i would request you to share STAAD and RCDC file to provide you more clarity in design. There are lot of options for design and detailing of reinforcement in RCDC. You can cross check the required steel in RCDC with your hand calculations. validations sheet for IS and ACI codes are available in below link, 
 IS code Validation sheets 
 https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/47981/is-456--2000-is-13920-2016_5f00_design-validation-documents 
 ACI -M Validation sheets 
 https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/47574/aci_5f00_318m_5f00_validation-sheets

Why does RCDC give me more rebar than Necessary

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