EN 1992-1-2 : unbraced columns

[blihpandgeorge]

I am designing an unbraced column (within a concrete sway frame building) and have some questions about to design for FRL. Prior to release of amemndment 1 in Dec 2019, the standard did not give any recommendations for unbraced columns at all. With release of amendment 1 in Dec 2019, Annex C now includes tables for unbraced columns.

I unfortunately have a few columns that sit outside of the Annex C (amdt 1-2019) primarily due to having higher eccentricities that those in the table. This is primarily with my columns that are towards the top of the building where there are gravity moments being transferred from different spans and little vertical load. Thus i have higher eccentricities (between 150-250mm)

Can anyone help with:
- background to the limit of eccentricty to 100mm
- how can i check my own values to use instead of the annex C tables? does anyone know of any examples? (i looked at B.3 but that seems to mention for braced columns only)
- any other approaches or comments?

 

[Agent666]

I'm guessing you'll have to go down the route of a rational buckling analysis, or perhaps look into the use of notional loads with the Direct Analysis Method from the AISC standard. The DAM is intended to be used in situations where assessment of buckling lengths isn't so clear cut.

A search on the internet should turn up links from AISC to the standard and many examples. There are also a number of videos on the AISC education channel on YouTube discussing the Direct Analysis Method which will help you understand the process.

 

[blihpandgeorge]

thanks - i wasnt aware of this approach, will check it out