The spreadsheet to calculate ultimate moment capacity of a reinforced or prestressed concrete section under combined axial load and biaxial bending, last presented here, has been updated to use the QuadBrent solver, rather than the Excel Goal Seek function, for better performance. The new solver function reduces the time to calculate the neutral axis angle from about 1 second down to 2 to 5 milliseconds, which is quite a respectable improvement in performance.

The new file can be downloaded from ULS Design Functions, including full open-source code.

The screenshot below shows the new FindNAAng function, which returns the calculated Neutral Axis angle for the specified combination of axial load and biaxial bending:

As in the previous version, the Neutral Axis angle may be entered manually on the input sheet, or updated automatically with the Adjust NA Angle button:

An output summary is given on the input sheet (as shown above) or detailed output data is provided on the Out sheet. Alternatively interaction diagrams may be plotted for a range of neutral axis angles, as shown below:

See the previous post, or download, for more details.

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