Geotechnical Engineering

DHARM

646 GEOTECHNICAL ENGINEERING

Allowable soil pressures:

150 kN/m^2 for DL + reduced LL

225 kN/m^2 for DL + LL

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 not to exceed 0.5 m.

Resultant 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 us use equal projections beyond columns A & B.

L′ = 5.4 m

L = L′ + 2e 1 = 5.4 + 2 × 0.5 = 6.4 m.

Total area required, A = 1835/150 = 12.23 m^2

x, distance of resultant column load from the left edge = 3.22 + 0.5 = 3.72

3.22 m 2.18 m

740 kN R = 1835 kN 1095 kN

L = 5.4 m¢

L = 6.4 m

0.5 m Section 0.5 m

3.7 m 2.7 m

Col. A Col. B

Plan

2440 kN

C.G.

e = 0.12 m

B = 1.05 m 2 B = 2.85 1

Fig. 15.32 Trapezoidal combined footing (Ex. 15.5)

∴ B 1 =^23121223

64

3372

64

A 1

L

x

L

F −

HG

I

KJ

= ××F −

HG

I

KJ

.

.

.

.

= 2.85 m

B 2 =^2 2 12 23

(^164)
A
L
−=B
×.
.

• 2.85 = 1.05 m