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# Slender Concrete Column Design AS3600

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## Slender Concrete Column Design AS3600

(OP)
Hi Guys

Does anyone have any tricks for designing slender concrete columns where the Le/r ratio starts getting higher than 50.

I am noticing a large fall away in strength for columns with high Le/r.

Does anyone know how to reduce the effective length factor, I normally use a ke=0.85 for braced columns and sometimes get it down to 0.8 by calculating buckling effective lengths in FE packages. I haven't explored too much into the graphs used in AS3600 for the calculation of effective length factors.

Does anyone have a good justification to not consider the minimum eccentricity provisions of AS3600?

I have attached the 2 column design curves for an 800x300 column for Le/r's of 25 and 60. I have walked passed many columns thru the city which are very slender so I am looking for a way to push my columns skinnier.

Thanks and regards

### RE: Slender Concrete Column Design AS3600

1. Increase the column dimensions. But that's probably not the answer you're looking for.
2. Can you brace it at mid height? Perhaps a couple of CHS braces would work without being too obvious.

### RE: Slender Concrete Column Design AS3600

(OP)
Yeah, they both weren't really the answers that I was hoping for. Good answers, but I was hoping someone had some tips on how I can push my columns right to the limit like justifying that the 0.05*D min moment isn't required.

### RE: Slender Concrete Column Design AS3600

Why is it so important? Are you trying to keep an architect happy?
Better to sleep well at night.

### RE: Slender Concrete Column Design AS3600

(OP)
Yeah, the architect likes skinny columns and so do I.

### RE: Slender Concrete Column Design AS3600

Those slender columns in the city look too skinny to me.

### RE: Slender Concrete Column Design AS3600

I don't like to push the b'ndy to much. I know some engineers used to consider blade columns as blade walls, but this practice has been stopped with the 2009 code.

http://www.nceng.com.au/
"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

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