Gamma (AS3600-2009 Cl 8.1.3)

[asixth]

I noticed today that the ? is given in Clause 8.1.3 as 1.0-0.003*fc whereas the draft code was given as 1.05-0.007*fc. Is this a typo given in the new code. It varies vastly from the old code for all concrete grades.

 

[rapt]

asixth,

Yes, it is a typo. The draft figure is correct.

Standards already know about the problem.

No one knows why it changed as there was no discussion about it to question it at the time, though I have pointed out to them that the rectangular stress block figures are not very logical and need to be completely reviewed. They tried to keep the old logic and extend it, so that 0 - 50MPa stayed the same as previously), rather than developing new consistent logic. Consequently, the results are a mess in some cases. They now agree with me on this and hopefully it will be completely rewritten next release of the code.

 

[IDS]

Standards already know about the problem.

I wonder if/when they are planning to tell us.

The attached file shows design ultimate moment capacity to the new code, draft, and 2001 version for a section subject to significant axial load.

The maximum difference (for 55 MPa concrete) was 8% higer moment resistance with the new code. The difference reduced for lower and higher axial load. Not a huge difference, but enough to cause approval problems if nothing else.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/