AS3600-2009 fire rating for columns

[pwht1]

Hey everybody,

I refer you to table 5.6.4 note 1: "The first order eccentricity"... blah blah... "e/b has been taken as <=0.025 with emax = 100mm". I take it this clause limits the table usage to columns with tiny moments and high axial loads.

For example I'm designing a 600 by 300 column which is 4000mm high. I'm taking the effective length as 4m because only the 300mm wide face is attached to the slab, thus I can't use table 5.6.3 as it is limited to columns with an eff. length less then 3m. My fire actions are 380kN and 195kNm respectively which give an e=513mm! Which means that I can't use table 5.6.4 either cause e must be less then 100mm. Apart from using the Eurocode 2, referenced in clause 5.3.1, how else do I get a fire-rating for this column?

I think this eccentricity limit is a little over the top and should be reviewed, anyone else care to comment?

 

[pwht1]

Hmmm no comments, much like the response I got from the 10 senior engineers that I work for.......Seriously, no one has reviewed the fire tables in AS3600 - 2009?

 

[rowingengineer]

pwht1,
I don't know of anyone that is using AS3600-2009 part 5 for design. See this thread for discussion on this chapter, and note that the committee is reviewing this chapter and other errors. thread744-264534

Rapt, if you happen to pass by, do you know what happened at the committee meeting?


A clear conscience is usually the sign of a bad memory

 

[pwht1]

Thanks rowingengineer. Good to know that it is being looked at.

 

[rapt]

The section of fire that you are questioning is not being changed as far as I know. I had a look at EC code on this and their requireemnts are basically the same. Columns ourside the range covered by the table have to be designed using the provided design method for fire that AS3600 refers you to. And the AS3600 tables are a direct copy of EC code.

There is supposed to be an amendment coming out shortly to fix some of the problems with the code, while other problems have been referred back to sub-committees to sort out. Presumably they were too complex for a quick fix. Dont know when this will be finalised.

 

[pwht1]

I finally got my hands on a copy of the EC code.

I noticed that is has numerous tables in Annex C that deals with more variable actions then the single table in AS3600. Thankfully they have a few that require "e=0.5b with e<200mm".

The criteria that e/b =<0.025 ratio is not it the Eurocode either. The Aussies have added in an 0, the eurocode says e/b=<0.25.

Fire-rating for unbraced columns may be found in a "Country's National Annex" according to EC, where is that in AS3600?

Also, why is the a columns effective length different for fire-rating purposes?

 

[rapt]

pwht1,

Actually the e/b limit of .25 is in the EC code (I have a draft copy but it should not have changed much) in clause 5.3.3 for Method B which is one of the 2 simplified methods offered in AS3600. It is basically the same as the AS3600 method, both the table and the limitations.

It refers to Appendix C to extend this table to cover more columns and to Appendix B for calculation methods to cover any section (on which both Appendix C and clause 5.3.2 and 5.2.2 in EC are based.
THis is the part that is not in AS3600. I assume it will be covered in the Commentary when it si written (at least I will be trying to get it in there) but I cannot be sure at this stage.

 

[apsix]

It is basically the same as the AS3600 method, EXCEPT the e/b limit is 0.025 (not 0.25) in AS3600.
This is the point of pwht1's post, the usefulness of T.5.6.4 is severely limited.

 

[rapt]

Oops missed that part. It is probably another typo in AS3600. I will check.

 

[rapt]

THis problem was on Dgens original list of problems with the fire rules and has been modified to .25 in accordance with EC in the AS3600 amendment that is due shortly.

 

[pwht1]

Thanks rapt and apsix. I'm still not too sure what's to be done with sway frames though.

 

[rapt]

pwht1,

You use one of the 2 calculation methods in Appendix B of EC2 if not covered by 5.6.3 in AS3600.