Geotechnical Engineering

DHARM

SHALLOW FOUNDATIONS 645

Column loads:

Column A Column B

DL 540 kN 690 kN

LL 400 kN 810 kN

Distance c/c of columns = 5.4 m

Projection of footing beyond Column A = 0.5 m

Total Column Loads Column A Column B Total

DL + reduced LL 740 kN 1095 kN 1835 kN

DL + LL 940 kN 1500 kN 2440 kN

For uniform pressure under DL + reduced LL:

Let the distance of a resultant of column load from Column A be x m.

x =

1095 5 4

1835

×.

m = 3.22 m

Length L = 2(3.22 + 0.50) = 7.44 m Use 7.50 m

Width B =

1835

150 7 5×. m = 1.63 m say 1.65 m

Soil pressure under DL + LL:

Let the distance of resultant of column loads from Column A be x 1 m

x 1 =

1500 5 4

24 40

×.

.

m = 3.32 m

3.25 m from Column A to c.g. of footing ∴ e = 0.07 m

qmax =

2440

75 165

1 6007

.. 75

..
×.

+ × = 208 kN/m^2 < 225 kN/m^2 O.K.

qmin =

2440

75 165

1

6007

.. 75

.

.

×.

−

×

= 186 kN/m^2

Structural design of the footing will have to follow.

5.4 m 1.6 m

0.5

m

Section

L = 7.5 m

Plan

B = 1.65 m

Fig. 15.31 Rectangular combined footing (Ex. 15.4)
Example 15.5: Proportion a trapezoidal combined footing for uniform pressure under dead
load plus reduced live load, with the following data: