The RC Design Functions spreadsheet has been updated (to Version 8.04) with the addition of a CircU function for ULS design of circular reinforced concrete sections under combined bending and axial load. The new version, including full open-source code, may be downloaded from:
Typical input and output are shown in the screen-shots below:
The function has 3 options for the design concrete stress block: rectangular, bi-linear, and parabolic-linear. For the non-rectangular stress blocks the strain limits and parabolic curve exponent are set to Eurocode 2 requirements.
Comparing rectangular stress block results for AS 3600, Eurocode 2, and ACI 318, for 32 and 50 MPa concrete the AS 3600 results are significantly more conservative for intermediate axial loads, and the Eurocode results are less conservative above the balance load: