Compression element slenderness AS3600

[BentEng]

Hi

I know this topic has been beat around a bit before on here but with the new AS3600 I was hoping there would be some clarification regarding Wall v Column design, namely slenderness and second order bending effects, moment magnifier etc.

Without going into seismic and ductility, lightly loaded slender columns are still significantly hindered by the moment magnifier for second order effects, and Section 11 can still gives significantly larger capacities, with significantly less reinforcement.

Is there anything new in the 2018 AS3600 that changes/clarifies this at all? I'm trying to find anything that explicitly states when it is or isn't appropriate to use section 11. Has anyone had any further thoughts on this since the last threads about this?

Again considering gravity loads for now, and probably limiting to 50MPa concrete.

 

[rapt]

No.

But it is a worry that a simplified method like that in 11 which has no specific checks on slenderness is less conservative than the more refined calculation method in section 10! On checks we did before the 2018 code, singly reinforced walls performed very badly when checked by section 10.

Also, I have pointed out previously to the AS3600 committee that the simple slenderness method in section 10 can be overly conservative compared to other codes (Eurocode) for columns with low M* / N* values (small eccentricity) but no one has had time to review it fully yet.

 

[BentEng]

RAPT,

In your opinion (maybe you can't say) is the eurocode method the best/(most accurate) for slender RC columns/compression elements?

It sounds like AS3600 CL11 might be unconservative but CL10 moment magnifier might be too conservative..?

I've had a look at BS8110 (which I believe is where our CL11 simplified method comes from) and unfortunately I can't find anything more there that might explicitly state when you can't use the simplified method.

 

[rapt]

The Eurocode approach seems more logical to me. What is actually right or wrong I do not know, but the AS method in chapter 10 is very conservative in my opinion for columns with relatively small moments.

In any case where you really need to look at slenderness I would be using 2nd order analysis according to 10.2.2 or 10.2.3.

 

[BentEng]

RAPT,

When you say eurocode method, to clarify, are you referring to the nominal curvature method?