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Re: Composite columns

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On 10/27/06, Michael Hemstad <mhemstad(--nospam--at)mbjeng.com> wrote:
I have a rehab project, originally constructed about 1929, which has W8x31 columns protected with hard-rock concrete fireproofing.  These columns support only 1 floor and a roof currently; we are trying to add another floor.  The bottom floor of columns, to no one's surprise, are overstressed.  I am in the process of getting strengths on the concrete fireproofing, but as a guess it's probably in excess of 3000 psi.  The concrete section is 12 inches square.  There is no vertical reinforcing steel; the W8x31's are wrapped with number 10 wire at 12 inch pitch to help hold everything together. 
 
Transfer of force to the concrete, as far as I can see, can occur through bond, and direct bearing of the intersecting beams at the concrete shell.
 
Does anyone have any comment on considering these as composite columns?  They obviously do not meet the AISC requirements for reinforcing steel, either vertically or laterally.  However, I'm having a hard time with the idea of destroying all that concrete (the demolition costs will be very large--the concrete does not come off easily) in order to then go to the expense of welding plates on the columns.
 
Any background to the AISC requirements, or personal opinions, are appreciated.
 
Thanks,
Mike Hemstad
MBJ
Minneapolis, Minnesota

Mike-

Destroying all that concrete just add capacity would be a shame.

Your situation seems like a natural for an epoxy / fiber wrap of the columns.

Even if the building is not empty this is a fairly simple procedure.

Alternatively you could add some decent confining reinforcement & shotcrete or pressure grout it.

Using it "as is" would make me nervous but being in SoCal we have different issues.

cheers
Bob