Design of Shallow Foundation (Isolated Footings)

Steps involved in footing design:-

1) Calculation of gross soil pressure for footing area.

2) Calculation of net soil pressure for flexural and shear design.

3) Initial depth of  footing calculation.

4) Flexural reinforcement calculation.

5) One way shear check.

6) Two way shear check.

GROSS SOIL PRESSURE & FOOTING AREA

Un factored load with surcharge + self weight of footing + allowable soil pressure

=(2000/1.50*1.1)/150=9.78m2

assuming we have square footing

√9.78 = 3.12m side footing

consider 3.2m sided isolated footing.

qu=2000*1.5/3.2*3.2=0.292KN/m2

factored shear force=Vu1=(0.292*3200)(1000-d)=934.4(1000-d)

assuming pt=0.25 for M25 grade.

hence τc=0.36

one way shear resistance Vc1=(0.36*3200*d)=(1152d)N

Vu1≤Vc1

934.4(1000-d)≤1152d

d>447.85mm

Two way shear

Assuming the effective depth of slab=d=448mm & computing the two way shear resistance at a critical section(d/2) from the face of column, we have the relation

Vu2=0.292{3200⊃2;-(450+d)⊃2;}=2756.61KN.

Design of  reinforcement

Mu=(292*1*0.50)=146KN-M

Mu/bd⊃2;=146000000/1000*500⊃2;=0.584

Ast=0.250*1000*500/100

Ast=1250mm⊃2;

using 20mm dia bars

spacing=1000*314/1250

251.2mm/c

Anchorage for column into footing=41d=41*20=820mm.