Reinforcement bars used in reinforced concrete structures aren't exactly of the size that is mentioned on the design. Generally a structural engineer would design a structure suppose say a beam to have 4 bars of Ø16 at the bottom. This Ø16 mentioned in the design intent is the nominal size, it isn't necessary that the bars being used will have exactly 16mm as their diameter. The production of reinforcement bars even in very controlled environment doesn't ensure that the bar would have an exact diameter of 16mm throughout its length.
As a result of this inconsistency in the size of the bar to avoid the failure of design the nominal size is considered for area calculation while detailing a section actual size is considered. For an instance if a section is detailed with the nominal bar diameters it may occur that the reinforcement may just not fit into the section, this is also called as a tight section.
The custom add in excel provides the user an ability to get the actual bar size from the nominal bar size. Just add the spreadsheet as an add in an you should be able to see the command Abar() in the prompts, follow the methods shown in the video.
Spreadsheet can be downloaded here:
The code that is used in the formula is as follows:
Function Abar(NominalSize As Integer) As Variant
'Array is used instead of switch case
Dim ActualSizes(1 To 100) As Variant
'Array is indexed by the size of the bar
ActualSizes(5) = 5
ActualSizes(6) = 8
ActualSizes(8) = 11
ActualSizes(10) = 13
ActualSizes(12) = 14
ActualSizes(16) = 19
ActualSizes(20) = 23
ActualSizes(25) = 29
ActualSizes(32) = 37
ActualSizes(40) = 46
ActualSizes(50) = 57
'Add more if required
Abar = ActualSizes(NominalSize)
If Abar = 0 Then
Abar = "Size out of scope"
End If
End Function