Soil bearing capacity for trapezoidal footing

[imvok3r]

Hi guys,
my first post here
I want to know how should i calculate soil bearing capacity using hansen method for trapezoidal footing?
thank you very much in advance

 

[oldestguy]

In most cases rupture bearing capacity does not govern. Settlement does. I'd approximate the area(to equal a rectangle) for that estimate.

 

[imvok3r]

that's true
but i need the bearing capacity
do you think that the equal rectangle with same length as trapezoidal would be good for that too?

 

[oldestguy]

If I really had to have a number, I'd work up an actual test in the lab where a plunger device, such as a unconfined compressive test machine would use a rectangular "foot" for one test and a trapezoidal "foot" for another, with same area for each, on the same material,such as a uniform sand or the same material as the job site. Relating that density to field density and test boring info, adopting the rectangular for the design number might be acceptable. At least you would see if the assumptions for rectangular would apply.

 

[fattdad]

step 1: Approximate the change of stress using an equivalent-area square or rectangle.
step 2: Use the principal of superposition to assemble squares and rectangles of the approximate shape as the trapezoidal footing.
step 3: With all the discrete stress changes known, sum them all up and contrast the delta sigma v for each. If they are the same (close enough), then you'll know if the approximation is okay.

Evaluate multiple points in the plan dimension. Not just below the center of the footing.

It is all about the settlement; however.

f-d

ípapß gordo ainÆt no madre flaca!

 

[oldestguy]

The definition of "bearing capacity" may need to be clarified. In my view it is what pressure is considered acceptable, such as with8in some limit of settlement. In the view of many it is the pressure, set by a safety factor, against soil rupture. In that case settlement is not in the picture, but fortunately at a safety factor of 3 the settlement result9ing out there usually is tolerable. Either way might be termed "bearing capacity" for the pressure determined.

 

[dik]

I'd check to see that the centroid of the trapezoid was 'near' the centroid of the load to make the load distribution similar.

Dik

 

[oldestguy]

Perhaps with a little more from you as to why you need "bearing capacity". Why does it have to be related to soil rupture and maybe not settlement? The term alone can mean many things. It depends on the structure, risk tolerable, etc. Is thee a code that requires a safety factor?