Shallow Foundation for a Concrete Column
Shallow Foundation for a Concrete Column
(OP)
Hello,
I am designing a shallow concrete foundation for a 2ft x 2ft column. I have a concern because my moment (450 ft*k) is considerably greater than the axial load (70 ft*k). This is creating a large eccentricity at the base (e=450/70 = 6.4ft). To make this work on a shallow foundation I would need the width of the foundation to be e<b/6 so b = 38.5ft. This seems way to excessive for a 2ftx2ft column. Can somebody please tell me if there are any other methods of looking at this foundation?
Thanks!
I am designing a shallow concrete foundation for a 2ft x 2ft column. I have a concern because my moment (450 ft*k) is considerably greater than the axial load (70 ft*k). This is creating a large eccentricity at the base (e=450/70 = 6.4ft). To make this work on a shallow foundation I would need the width of the foundation to be e<b/6 so b = 38.5ft. This seems way to excessive for a 2ftx2ft column. Can somebody please tell me if there are any other methods of looking at this foundation?
Thanks!






RE: Shallow Foundation for a Concrete Column
RE: Shallow Foundation for a Concrete Column
- For a single column, use a drilled pier foundation
- For a column located near other columns, use a "pump handle" to an adjacent column. Basically, the pump handle is a big grade beam beam that transfers resisting moment to the troublesome footing.
- Provide a really big footing that everyone will question your sanity about.
RE: Shallow Foundation for a Concrete Column
RE: Shallow Foundation for a Concrete Column
TEGUCI, Unfortunately I don't have an option to drill or install piles. I have to resort to a shallow foundation.
JOSHPLUM, I am already 1.5 m under ground and cannot go any lower. Is there any other solution other than having a huge foundation with an extraordinary amount of concrete?
RE: Shallow Foundation for a Concrete Column
If this is not possible, then it sounds like it's the bite the big footing option today.
Mike McCann
MMC Engineering
RE: Shallow Foundation for a Concrete Column
RE: Shallow Foundation for a Concrete Column
RE: Shallow Foundation for a Concrete Column
Mike McCann
MMC Engineering
RE: Shallow Foundation for a Concrete Column
So, putting a grade beam between the two columns will me strength laterally but not longitudinally (long with width). I am expecting this to be a combined foundation anyways.
RE: Shallow Foundation for a Concrete Column
Mike McCann
MMC Engineering
RE: Shallow Foundation for a Concrete Column
RE: Shallow Foundation for a Concrete Column
RE: Shallow Foundation for a Concrete Column
RE: Shallow Foundation for a Concrete Column
See attached page from "Design Of Concrete Structures" by Winter, Urquhart, O'Rourke & Nilson. a = (Mr-Mo)/Rv. I normally use this primarily for retaining walls... the pressure results are in kips/ft. or lbs./ft., but you simply divide by footing width "b" (into the paper) and you get psf results for an isolated footing.
I think most would agree that being within the middle third is desireable, but sometimes it's impractical.
RE: Shallow Foundation for a Concrete Column
RE: Shallow Foundation for a Concrete Column
I was thinking the same thing. I would not design this by trying to stay inside the kern.
I was going to run a couple of number for this. However, the loads stated in the post do not match what is in the later provided sketch.
RE: Shallow Foundation for a Concrete Column
Based on the comments I have changed my loads to unfactored and placed my foundation 5ft under ground to further stabilize the foundation. So my eccentricity has gone down to e=(308k*ft)/(150k) = 2.1ft. This would still keep me out of the middle third if I go with a width of 9ft (2.1 > B/6, 1.5).
I am also considering offsetting the column on my foundation by the required difference so the resultant can be positioned in the middle third (2.1-1.5 = 0.6m).
But Spats has made a legitimate point and I need to check for overturning and actually I might not even need to offset the column. Most of the resources that I have obtained does not even mention check overturning on shallow foundations. Ultimately I might even be able to decrease the width if overturning is adequately satisfied in the medium density soil.
Spats, in your formula shouldn't it just be (M resisting / M overturning) ?
RE: Shallow Foundation for a Concrete Column
RE: Shallow Foundation for a Concrete Column
RE: Shallow Foundation for a Concrete Column
I suggest you look at the anchorages as hokie has suggested or the whole thing could end up the the river.
RE: Shallow Foundation for a Concrete Column
But looking at the cable on the saddle situated at the top of the tower there are two different angles, one for the incoming cable (from main span) and outgoing cable (to deadman) this combined with the dynamic movements induces a frictional load on the tower top. As many have said, 25% might be an exaggeration of that load.
RE: Shallow Foundation for a Concrete Column
RE: Shallow Foundation for a Concrete Column