Maximum Soil Pressure Under Combined footing with eccentricity

[E720]

As I was studying for the PE Exam I came across this question. I have attached a drawing of a combined footing. Depending on the loads there can be some eccentricity in the reaction. What would be the maximum soil pressure under the footing a)if the resultant fell within the middle third and (b) if the resultant was outside the middle third. Also when I check the eccentricity for the middle third rule should I compare it against L/6 or L'/6 (see attached for definitions of L and L'). Any good references on this type of question? Any help is appreciated.

I know the posting guidelines say no students but I am not a student and feel like this forum is an appropriate place to post this. If not, I am happy to take it down.

Thanks.

 

[BAretired]

(a) pmax = R/A + R.e/S where A = B*L; S = B*L²/6; B = footing width

(b) pmax = 2*R/A where A = 3*B(L/2-e)

When e = L/6, it is precisely at the edge of the middle third, so when e > L/6, R is outside the middle third.

BA

 

[JStephen]

See attached.

 

[E720]

Thanks