Rusted Mezzanine Columns 3

[dylansdad]

Good day folks,
We are in the process of submitting a proposal to renovate an old (1940 construction, riveted connections) Industrial building. The "wet end", which is of course the worst end, is exhibiting rusted columns at the mezzanine (13'-4" AFF). It appears that some attempt was made previously to strengthen the flanges by welding on plates. It might also be just the product of rusting. My question would be how to repair (if possible) the columns at this level. The columns at the ground floor show evidence of rust but not at the same magnitude. The mezzanine is a 5" slab on beams. I would appreciate any suggestions. I include a typical mezzanine/column interface along with a view from ground floor to underside of mezzanine. Thanks in advance for any responses/suggestions.

 

[dylansdad]

I will reply to my post with the other picture. Don't know how that happened.

 

[JAE]

Here are the steps I would take:
1. Have the columns carefully cleaned of the rust - removing the rust down to bare steel.
2. Include some partial concrete removal around the column to also reveal some of the column below the floor to understand the depth of the distress below.

3. Measure the remaining "good" steel and calculate new section properties for this area.

4. Do a load take-off of the mezzanine - analyzing the design loads coming down on the column and verifying if the column is intended to take any moment at its base (probably not).

5. With the new Pu axial load, check the cross section for compression. Keep in mind that this small base length doesn't need to be checked for buckling - only axial stress as this is not the portion of the column that will buckle. Buckling is more dependent upon the middle length of the column and its properties there.

6. If the column, as is - with reduced section properties - is OK then repaint the steel, repatch the concrete, and take steps to ensure no further moisture/distress can occur to the column.

7. If the column is not OK, simply add plate steel to increase section properties of the damaged length, repaint, repatch the concrete and take steps to ensure no further moisture/distress can occur to the column.

 

[dylansdad]

Thanks for your response. I was thinking along the same lines.

 

[msquared48]

As a side note, I would try to look at the cause for the rust and eliminate it or the same thing will just happen again.

The pipe to the left that is also entering the concrete slab - is it an electricalconduit, or could it carry a small electrical charge? If so, there could be some electrolysis happening here. A Zinc attached to the column might help prevent further rusting.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[hokie66]

Agree with JAE about the procedure to follow, and with Mike that you should find out why the corrosion occurred. Based on similar experience, I think the corrosion is not too bad, and will probably not extend into the concrete due to the protection offered by the concrete alkalinity.

 

[dylansdad]

Msquared: Not too sure about the pipe to the left. I think it is a process pipe and not electrical in nature.

All: This column is one of many at this level. See another one where the web (take my word for it) is rusted clean through. Again, this is in a highly corrosive atmosphere and all comments regarding future protection is duly noted and appreciated.

 

[hokie66]

Follow JAE's procedure. If many of the columns are as for the last one, you may want to reinforce them all with the same detail to simplify things. Then coat the bases with a high performance organic coating, followed by casting a protective, sloped plinth around each column to divert the corrosive material.

 

[beton1]

Great procedure by JAE, and Hokie beat me to punch about encapsuling with concrete. Is this a paper mill or other corrosive type environment?

 

[dylansdad]

Manufacturer of lay-in ceiling tile.

 

[csd72]

I would tell them to prop the floor above before carrying out any work, who knows how badly corroded these are.