Terzaghi's Equation with more than one column

I've been send to do a project about the construction of a building. Throughout the project I had a doubt I couldn't solve and wish you could help me with:

When we are working with foundations, we can apply Terzaghi's formulas to get the bearing capacity of the ground. However, in everything I've read they always use a single column. How can I apply the formulas having the weight of the building and a more than one column?

• Please only put one question in each post. Also, putting more information in your question will result in a better question and hopefully better answers. – hazzey Apr 12 '17 at 16:20

$$B'=B-2e_B$$ $$L'=L-2e_L$$