Direct Embedded//Buried Steel Columns for Buildings
Direct Embedded//Buried Steel Columns for Buildings
(OP)
I used to work in the electric utility industry, and we used direct embedded steel poles on transmission lines all the time. I now have a situation with a proposed interior building mezzanine where the allowable soil bearing is poor, and we need to go to bedrock for bearing. The bedrock is about 15 feet down. I am thinking that direct embedded steel columns, bearing on a concrete leveling pad in the base of 2 foot diameter hole might get me the axial bearing capacity I need along with the lateral stiffness (from the embedment and floor slab at grade) for the lateral loads on the mezzanine. I don't know that any has done this before, but seems the same premise as a pole barn structure.
I don't think corrosion will be a significant concern given the interior location, surrounding concrete slab, and that in my experience most corrosion takes place in the first 12" of soil or so as it needs oxygen. However, I could add a sacrificial steel collar at ground line to provide extra steel cross section if corrosion is a concern (this is done on transmission poles).
Thoughts?
I don't think corrosion will be a significant concern given the interior location, surrounding concrete slab, and that in my experience most corrosion takes place in the first 12" of soil or so as it needs oxygen. However, I could add a sacrificial steel collar at ground line to provide extra steel cross section if corrosion is a concern (this is done on transmission poles).
Thoughts?






RE: Direct Embedded//Buried Steel Columns for Buildings
You say that you are embedding the columns for moment resistance, so be sure you have flange and web stiffeners at the point where the column exits the slab. I would not embed a hollow section like this, since it cannot be effectively stiffened as a one-piece column. Generally, a leave out would be around the column at the slab would prevent slab movement from compromising the column, and having the stiffener at slab level could present a problem. I would probably have a round form (same as the bore hole) extend to top of slab and fill to that level as the column is embedded, to allow vertical slab movement.
The other issue will be compatibility with the other structure. If the mezzanine is founded on rock and the surrounding building is not, there could be issues.
RE: Direct Embedded//Buried Steel Columns for Buildings
I really can't imagine any director of code enforcement allowing it for a dwelling.
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Direct Embedded//Buried Steel Columns for Buildings
Anyway- some other issues. If you'd normally have a steel erector doing their work after the concrete is finished, then you'd have to have both onsite to work this. If the steel erector doesn't have a good way to hold (or maybe to adjust) the exact location when the beam is set, you could have issues. And you may run into the "We've never done it like that before" syndrome.
Utility poles should mainly have a moment load, not much vertical load, and that detail could be poor for vertical loading- may still require a baseplate, for example.
RE: Direct Embedded//Buried Steel Columns for Buildings
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Direct Embedded//Buried Steel Columns for Buildings
I did forensic structural engineering in the area, and our stock in trade could have been sub-slab and sub-structure moisture-related problems. I also spent 5 years working in a 890,000 building where the slab had continually heaved, year by year, for more than 20 years, due to moisture-driven expansion of the underlying clay, at a rate of about 1/2" per year. The vertical rise was nearly uniform throughout the slab (a bit higher on the irrigated, uphill side of a nearly flat lot), and was 8-10 inches on the high side when I left there.
RE: Direct Embedded//Buried Steel Columns for Buildings
RE: Direct Embedded//Buried Steel Columns for Buildings
M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)
RE: Direct Embedded//Buried Steel Columns for Buildings
I would be backfilling these embedded columms with concrete.
Our original design had them on augered concrete piers (caissons). However, we are looking at the embedded option to help reduce hole size, and save money on rebar and anchor bolts.
Money is the big driver on this project, so we are looking at all means possible to shave some costs.
RE: Direct Embedded//Buried Steel Columns for Buildings
I agree that dropping a steel column into a boring, truing it up, maybe hanging some beams on it, and then concreting it in seems like an easy solution, but I doubt the contractor has ever done it, so it would be priced at a premium. Also, how much overhead space do you have to hoist the columns and feed them in to the boring. (How about space for the drill rig?)