An exterior - 24 x 18 in. column with D = 170 kips, L 130 kips, and an interior 24 X 24 in. column with D = 250 kips, L = 200 kips are to be supported on a combined rectangular footing whose outer end cannot protrude beyond the outer face of the exterior column (see Fig. 16.1). The distance center to center of columns is 18 ft 0 in., and the allowable bearing pressure of the soil is 6000 psf. The bottom of the footing is 6 ft below grade, and a surcharge of 100 psf is specified on the surface. Design the footing for f' = 3000 psi and f, = 60,000 psi. 412,000 lb 18" x 24" column 24" sq. col. 620,000 lb