Rectangular Footing Aspect Ratio
Rectangular Footing Aspect Ratio
(OP)
Hi all,
I feel sure this is an easy question, but I can't seem to find an answer in ACI 318 or my concrete textbook. But when calculating applied pressure to the soil through a rectangular footing, I'm sure you cant count on your whole footing area to bear evenly if it's 2'x10' for example. In my specific problem I'm trying to find a required footing width for a strip footing with axial loads of about 20-kips every 10 feet, with qa=2000psf. So if i choose 18" for the width, the problem works out if you have a bearing area of 1.5'x10', but I'm sure that extreme of an aspect ratio doesn't bear evenly. Are there any provisions or rules of thumb you all could direct me to?
I feel sure this is an easy question, but I can't seem to find an answer in ACI 318 or my concrete textbook. But when calculating applied pressure to the soil through a rectangular footing, I'm sure you cant count on your whole footing area to bear evenly if it's 2'x10' for example. In my specific problem I'm trying to find a required footing width for a strip footing with axial loads of about 20-kips every 10 feet, with qa=2000psf. So if i choose 18" for the width, the problem works out if you have a bearing area of 1.5'x10', but I'm sure that extreme of an aspect ratio doesn't bear evenly. Are there any provisions or rules of thumb you all could direct me to?






RE: Rectangular Footing Aspect Ratio
I've heard it proposed that a "rigid" footing with uniform soul stress assumed ought not cantilever more than 5X the footing thickness.
This sounds like a one way footing to me. A real strip footing in the conventional sense. Are your loads transmitted to the footing through a continuous wall? Is it a basement wall situation with columns on top?
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Rectangular Footing Aspect Ratio
RE: Rectangular Footing Aspect Ratio
RE: Rectangular Footing Aspect Ratio
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RE: Rectangular Footing Aspect Ratio
RE: Rectangular Footing Aspect Ratio
Now that I know that there's not a concrete wall on your footing, the 18" width makes me a bit nervous. Small accidental eccentricities in the cross footing locations of those 20 kip loads may have significant impacts. At potentially 18"W x 30"H, your footing is starting to feel more like a grade beam or a stocky wall. I'd hate to see it roll over.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Rectangular Footing Aspect Ratio
RE: Rectangular Footing Aspect Ratio
RE: Rectangular Footing Aspect Ratio
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.