Eccentric footing 1

[Gus14]

For footings with an eccentricity greater than kern distance where strap beams, mat foundation, the combined footing are not possible options. I have found the attached formula to simplify eccentric footing design a lot. Since the footing width reduces qmax, I end up with very wide footings with a short length (a sketch is attached in the replies). The formula suggests that overturning is not possible because the resultant of soil pressure shares the same line of action with the column load, but I am still wondering if further checks are necessary regarding footing stability, or if I am miss interrupting the formula.

 

[Gus14]

The wide footing sketch >>

 

[HTURKAK]

What is the reason for the combined footing is not possible option? . If the resultant force is only vertical force and coincides with the footing area, OT moment will not develop.. Is this the question?

If this is a real question, pls post some descriptive sketches , dwg etc. to get better responds..

 

[Gus14]

My questions :
1) is using the formula attached to size a footing eliminates the need to check against overturning moment?
Since the soil reaction resultant has the same line of action as the column load with equal value and opposite direction, I would say YES, but I am not sure.

2) The formula suggests that increasing the footing width ( regardless of the footing length in the direction of the eccentricity ) decreases the qmax substantially. therefore, Is the footing length only controlled by punching, wide beam shear, and moment?

 

[HTURKAK]

Dear Gus14 (Civil/Environmental)(OP),

I do not look to web everyday.. I just see your last post.. Below find my responds to your specific questions,

1- Yes .. with the foundation set up,and provided that, the column load is only vertical ..no moment, no horizontal force..

2- My answer will be yes up to a certain limit.. Instead of width , If you increase the length, you will increase the weight and reduce the eccentricity also.You are expected to check punching shear, wide beam shear and bending..

If you post your specific case with descriptive sketches ,you can get better valuable responds.

 

[Gus14]

Thank you for replying, I will consider applying a reasonable value of moment for additional saftey.