Partially Encasing an Already Installed Column in Concrete

[nick.n]

During the installation of an exterior column for pipe rack, we found that the survey information we were originally given was incorrect, and a few of our pedestals are now below grade. The footings are already poured and steel is on site, so any design changes would start to get expensive. I'm not comfortable having a cold joint in this pedestal, so cutting the column and doweling a pedestal extension isn't an option. I also don't want to increase the overturning moment on the footing by increasing the pedestal height.

The solution I've come up with is to encase the bottom 1 ft to 1.5 ft of the column in concrete. Debonding agent would keep the column from transferring load from the column to the concrete. I could use corner bars not doweled into the pedestal with ties to get minimum steel for the concrete. There are a few columns that have gussets for diagonal bracing that are going to create an issue. My thought is to extend the block as far as it needs to go to have the brace come out of the top of the concrete instead of the side, and have the bottom of the extension rest on the soil.

Does anyone have any suggestions on if this could be better? Or see anything that could go wrong? I've asked my team, but no one's done anything like this before.

 

[BSVBD]

nick.n...

Regarding the Steel Columnn contact with concrete, you could use a necessary thickness of expansion joint material between steel column and concrete (slab I presume?).

For the rest... Perhaps you can provide a detail?

You say, "extend the block as far as it needs to go to have the brace come out of the top of the concrete instead of the side, and have the bottom of the extension rest on the soil."

What is "the block"?

What does, "the brace come out of the top of the concrete instead of the side" look like?

What does, "the extension rest on the soil" look like?

 

[HTURKAK]

A sketch would help to get better responds . The piperack frame designed as pin conn. to the ftg . If this is so, i would consider steel short extension piece .



He is like a man building a house, who dug deep and laid the foundation on the rock. And when the flood arose, the stream beat vehemently against that house, and could not shake it, for it was founded on the rock..

Luke 6:48

 

[nick.n]

I've provided sketches for both the stand alone column and a column with a brace. I should have included this in the original post, but the whole purpose of this extra concrete is to protect the column.

 

[BSVBD]

nick...

I like your detail. It certainly helps understand and visualize!

The ONLY concern I would have is the debonding agent. I don't see how a +/-(1) MIL layer of agent would prevent the inevitable movement of the steel column and, perhaps, the bracing, to come into crack-potential contact with concrete casing.

Expansion joint material is at LEAST 1/4" thick. Could be thicker or layered for desired thickness.

Even a treated wood barrier between steel and concrete could be considered... but, not preferred by myself... just adding a suggestion.

Or provide a desired gap thickness to be filled with a heavy expansion caulk?

Other than that, the primary casing detail looks acceptable!

 

[AskTooMuch]

I don't get the point of this detail. What is your main concern?
It looks to me steel corrosion is the only concern here since it's below grade. Since this is a piperack, all steel and anchor bolts should be hot dip galvanized. You can also encase with concrete and use concrete "field fireproof" detail if you like that should be easier.

 

[AskTooMuch]

Also looks like only about 2' below grade, maybe just regrade the soil in that area since it's only a few pedestal/columns.

 

[HTURKAK]

Dear nick.n (Structural)(OP), your last post confused me. Just a simple question: Are the top of pedestal levels correct and only few of them are now below grade ?

Are the grade levels are not correct at some locations ? .
This is very typical that the way of piperack area should be flat. I will suggest you make grading .



He is like a man building a house, who dug deep and laid the foundation on the rock. And when the flood arose, the stream beat vehemently against that house, and could not shake it, for it was founded on the rock..

Luke 6:48