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What Rana means is to play with the wall stiffness modifiers till you get 25% base shear resisted by columns. This is different from standard stiffness modifiers applied to each structure irrespective of their geometry as per Section 10 of ACI. Thanks.

Sohaib, There are two standard ways to work with foundations: ASD and ULS. Please have a look at the two discussions below. The method you should adopt depends upon the codes you are following and recommendations in that code. http://www.sepakistan.com/topic/1519-deduction-of-overburden-from-bearing-capacity/ http://www.sepakistan.com/topic/1700-column-footing-size-for-high-snowfall-areas/ Thanks.

Here is the presentation that highlights the difference between two approaches for foundation design. Thanks. Use of Limit State Design in Foundation Engineering.pdf

I would like to draw your attention towards cut/fill levels. Footing resting on Fill If we are placing our footing on an area which is in fill than we have "0" ov.burdron pressure in this equation q(gross)= qnet + over.burdon, hence q(g) = q(net) And we need to take the fill pressure while designing the footing. Footing resting on cut If we are placing our footing on an area which is in cut than we have " ov.burdron" pressure exists in this equation q(gross)= qnet + over.burdon, hence we can increase out bearing capacity. And we need not to take this pressure while designing the footing,because what we have excavated we have put it again,and the difference of pressure will be nothing.

All three approaches exist there. First approach deducts over burden ( which is the most common approach) Second approach is to go straight a way with B.C at that depth, this has many observations and is not practiced widely because 1) Soil has to bear load of super structure along with load of foundation 2) Allowable B.C is calculated on certain assumptions as well which are catred for by placing a factor of safety of 2 to 3. But keeping in view the factor of safety, we calculate size of footing on service load. So factor of safety has already been relied up on in terms of sizing the footings. Third approach is to add up the weight of excavated soil in B.c values. This is generally done for deep excavations like two or three basements. But with that approach geotechnical engineer recommends that excavated surface should not be left open for longer period. If one has excavated the site and there comes a halt in construction after excavation then site must be rechecked by geotechnical engineer before placing of foundation. This is so because soil starts to get relaxed and if cracks get developed then provision of adding up weight of excavated soil does not remain valid.