Composite Column Design to EN1994-1-1

[Charlie95]

Hi Engineers,

I am a graduate engineering the process of doing composite column design to EN 1994-1-1.

To check the column for axial compression, there are 2 methods;

1) Use European buckling curves
2) Use second order analysis, considering member imperfections.

Please could someone clarify in which instances to use either method. I have considered the column to be pinned bottom and top. I cannot see how the buckling curves can be used as all structural elements are likely to have some sort of member imperfections?

Thanks in advance.

 

[Settingsun]

I'm not familiar with EN1994 specifically, but column curves are typically ways of reducing the design axial capacity to account for imperfections. You can then compare that reduced capacity to analysis results that don't account for imperfections. Basically, instead of a very accurate analysis giving larger stresses, you get lower stresses from your analysis and compensate on the capacity side of the equation.

The non-linear analysis option is more complex but you just get the result straight from the analysis. I don't know about Europe, but I'd consider this to be less common by far than using the curves.

 

[HTURKAK]

Hi Charlie95 (Structural),

- If the column subject to axial compression only ;
You can use both methods .(European buckling curves or second order analysis with equivalent geometrical bow imperfections )

- If the column subject to combined compression and bending , you can use ONLY second order analysis with equivalent geometrical bow imperfections .

GOOD Luck ..

 

[Settingsun]

Hturkak, do you say that curves can only be used for pure compression based on clause 5.2.2(6)(c)? I don't read it that way. Yes, it refers to members in compression, but not pure compression. It seems similar to the requirements of Aus/US codes (that I actually use so understand better), which allow column curves with K=1.0 when second order elastic analysis has been done. Is there some other clause that clarifies this?

PS: are the buckling curves defined in this code? I ran a text search and found the term used four times but none of them showed the curves or provided a cross reference.

 

[HTURKAK]

Dear steveh49 ,

-I have copied and pasted the relevant clause 5.2.2(6)(c),

(c) for members in axial compression, by the use of buckling curves to account for second-order effects in the member and member imperfections, see 6.7.3.5. This verification should take account of end forces from global analysis of the structure including global second-order effects and global imperfections when relevant, and should be based on a buckling length qual to the system length.

I understand only compression . Because the subject standard otherwise uses the term ( combined compression and bending )

- Pls look Table 6.5 : Buckling curves and member imperfections for composite columns.

 

[Settingsun]

I don't like the wording, as has often been the case in my limited exposure to eurocodes. A member in compression and bending is of course in compression. The native English phrase for what they mean would be 'pure compression' or something similar. I've found the Designers Guide and it says, in its discussion of clause 5.2.2, that the use of 'compression member' is meant to include non-vertical members (ie not just columns) but later, in section 6, says it means pure compression. It surprises me that the eurocodes provide rules restricted to these fictional members.

IMO it would be better if the British Standards Institute were given the job of writing the base version of the codes and these translated to the continental languages as BSI were better technical writers in the past. Though that may not be the case now, I suppose.

 

[HTURKAK]

Dear steveh49 (Structural),

I fully agree with you.. I do not know the language of original text ( could be also German , French ..). I checked the situation from the website JRC ( Joint Research Centre )

https://eurocodes.jrc.ec.europa.eu/

And found the following document free of charge..

https://eurocodes.jrc.ec.europa.eu/doc/WS2008/EN1994_4_Hanswille.pdf

 

[Settingsun]

Thanks, Hturkak.