AS3600-2018 Bending factors? 1

[Tomfh]

I notice the phi factors for bending have changed, as have the rectangular stress block factors.

What's the background to these changes?

 

[rapt]

The old rectangular stress block was fairly inaccurate for concrete strengths over about 40MPa and gave some very misleading results, especially around decompression on column interaction diagrams.

RE the phi factors, some people thought that the old ones were too conservative given the improvements in materials technology etc. I cannot comment further or I could get in trouble.

 

[Tomfh]

Thank you rapt

Are the new phi factors in any way related to the change in stress block shape? Or are the two changes unrelated coincidence?

 

[Settingsun]

I'd guess that the new phi factors bring us closer to eurocode's partial factor results. No idea whether that's the basis though.

 

[rapt]

Tomnfh,

No relationship to the stress block changes. The stress block is now similar to the Canadian code stress block. There was a problem with the old stress block in that it did not predict the centroid of the force well in some situations. The only relationship to Eurocode is the addition of a reduction factor to allow for the concrete width reducing towards the compression face as the stress block derivation assumed a constant width. I had been requesting this for many years.

A "statistical" review of the phi factors was done and apparently showed they were low.

Nothing to do with Eurocode material factors either.