Rotation of a Pad Footing

[civeng80]

Im wondering if anyone has a paper on rotation of a pad footing with e>B/6 i.e. part of footing is detached from the soil.
I know that Bowles (5th edition) has an article on rotation of a pad footing but it assumes the base has full contact with the ground.

 

[Mccoy]

civeng, you probably refer to the so called 'rocking' phenomenon, you might want to start a search based on such password, the link provides an article which describes some analytic methods.

http://www.nzsee.org.nz/db/Bulletin/Archive/11(3)0141.pdf

 

[civeng80]

Hi Mccoy
The footing is under static load (no earthquake loads).
See illustration.
Regards

 

[Mccoy]

I don't know such solutions either but then, usually the regulations rule out the case where the pad is not in touch with the soil by the B/6 rule. Use of the effective area A' may lead to the region where e> B/6 but would that be acceptable in design practice?

 

[hokie66]

When loaded outside the kern, you just have a triangular pressure distribution on part of the footing. It is usual practice to restrict the maximum pressure to the same value as for uniform pressure. I am unaware of any procedure to calculate the rotation, and if there were, you would have to take it with a grain of salt...after all, this is soils engineering. I always try to use better solutions, deeper and less wide, or with rectifying perpendicular beams.

 

[civeng80]

I agree entirely. Bad practice having load outside of middle third (middle third rule)
But I'm faced with having to build footings adjacent to this bad detail.
Surprisingly the maximum bearing pressure is still less than the maximum allowable pressure, but the wall has tilted and caused some damage inside the building.
From site measurements its out of plumb by about 40mm (a bit less than 2 inches) but Im abit concerned it may tilt further, hence my question to the forum.
Oh Hokie66 how I wish you would have been the designer for that building !!