Effective Second Moment of Area (AS 5100.5) 1

[handofthelion]

Hi all,

I have a quick question about the formula presented in AS 5100.5:2017 (Australian bridge code for concrete) for the effective second moment of area:

This formula seems counter-intuitive to me - as the service moment (M*s) increases, so does the effective second moment of area. I thought this should be the other way around as increased moment leads to further development of flexural cracking and therefore a less stiff section. This would also be in line with the formula in AS 3600, in which an increase in the service moment results in a decrease of stiffness.

Keen to hear everyone's thoughts on this, thanks!

my structural engineering blog

 

[IDS]

The equation is wrong!

The corrected equation is attached, taken from the AS 3600 draft for public comment, issued earlier this year.

The corrected version is essentially the same as the Eurocode 2 requirements, and has been shown to give much better results for lightly reinforced sections at just over the cracking moment.



Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[handofthelion]

Ok makes sense, thanks for clarifying this!

my structural engineering blog