Previous posts in this series have looked at the analysis of beams where the steel stress is within the elastic range, and the concrete stress is sufficiently low that the assumption of linear elastic behaviour in compression is a reasonable approximation. I now move on to analysis for the ultimate limit state, where some or all of the steel is past its yield stress, and the concrete compression zone may be analysed as having a constant stress, close to its failure stress.

The file ULS Design Functions.zip contains User Defined Functions (UDF’s) that will find the ultimate bending capacity of any reinforced or prestressed concrete section (defined by rectangular or trapezoidal layers) with any number of layers of reinforcement, when subject to a specified axial load. As for the elastic design functions, the analysis uses a closed form solution, rather than an iterative procedure. The current version follows the Australian Standards AS 3600 or AS 5100. Other codes will be added to future versions. Details of the procedure will be given in later posts.

Screen shots:

Input, circular section

Output, circular section

Interaction diagram

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Very neat spreadsheet… Thank you for releasing the code under GPL. Nice to see another Structural with a CopyLeft soul… I’ve added a slenderness check to NZS 3101, and am in the process of implementing the NZ code as Code = 3 (No EN here! lol). Quite impressed with your work; Well done!

Let me know if you want me to toss the finished result back your way. Happy to oblige.

Cheers,

YS

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YoungStructural – Thanks for the comments. I’d certainly be interested in seeing your implementation of the NZ code. You can either post a link here or email me at Gmail (DougAJ4).

Also watch out for a new spreadsheet which I’ll be posting in the next few days with cut-down versions of both the elastic and ULS programs to use with rectangular sections with two layers of reinforcement. These have simplified data input, and are more convenient when checking multiple sections on rectangular members.

Doug

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