Building Concrete Columns in the Soil

[dl5150]

Will a concrete column supported by soil buckle? Can we say that the effective length factor K=0 for this condition and therefore makes the critical buckling load Pcr undefined?

 

[structSU10]

Are you refering to a column that is confined on all sides by the soil? or is this an element that only has soil on one side? One way to explore this is by doing a P-delta analysis, modeling your soil as a spring at regular intervals. I would think that buckling would not control in most cases, but a very slender element in poor soil may be a different story.

 

[JLNJ]

I would limit the capcity similar to that of a reinforced concrete drilled shaft.

 

[JedClampett]

No, you can't use K=0. The soil, unless it's compacted more than you would want to adjacent to a column, will not provide lateral bracing. Use an effective length of base to top.
Once buckling commences, the forces are pretty large. A small lateral movement is all it takes to get it started. To activate even the active pressures, takes more movement than it would take to start buckling.

 

[wannabeSE]

It sounds more like a foundation pier or pile. The 2006 IBC section 1808.2.9.1 states: "Any soil other than fluid soil shall be deemed to afford sufficient lateral support to the pier or pile to prevent buckling . . ."

 

[BAretired]

There was just one case in memory when the soil was deemed inadequate to provide lateral support to the pile. It wasn't liquid, but it was extremely soft. Ordinarily, piles are considered laterally braced by the soil but it is a matter of engineering judgment.

BA

 

[JedClampett]

Maybe I'm misinterpreting this, but from the question, I was thinking it was a column on a spread footing, and backfilled around it. For a cast in place concrete pier, I would expect the loads to be low compared to the concrete strength and bucking and lateral support is not an issue, hence the code direction.
But sometimes we have to support a structure with columns below grade. This happens when there's a building or a portion of a building constructed on a deep excavation. Before the excavation is filled, we have columns constructed on footings and the backfill installed around them.

 

[BAretired]

The North Elevation and the top half of the South Elevation act pretty much as a shearwall. The bottom half of the South Elevation needs to be assessed as a kind of frame.

Continuous bond beams would seem to be a good idea above and below each opening and at floor level.



BA

 

[hokie66]

Wrong thread, BA. Don't you just hate it when that happens?

 

[JedClampett]

Maybe the OP was wrong?

 

[BAretired]

Yes, wrong thread. Please ignore my comment.

BA