INTEGRATION METHOD. Considering a footing of dimensions: Bx = 1.70 m, By = 1.50 m. P=15 t. (axial load) It is desired to calculate the stress at a depth of z = 1.20 m, and at a location in plan xo = 0.8 m, i = 0.7 m. The modified expression of the vertical force is: /2 3dQ 02 = 2nZ2 (xo - x) 2 + (i - y) 2 dx d 2TZ2 (x or - x) 2 + (10- y) 2 + N The limits of integration are: xi=0 m, xf= 1.70 m; yi= 0 m, yf= 1.50 m. Integrating by the Simpson 1/3 rule, with 6 intervals, produces the following results