Design of Shallow Foundation (Isolated Footings)
AIM: To design the footing by using the given data and check for one way shear and two way shear.
INTRODUCTION:Design the footing by using the IS 1893 code provisional .
PROCEDURE:
STEPS INVOLVED IN FOOTING DESIGN
- Calculation of gross soil pressure for footing area.
- Calculation of net soil pressure for flexure and shear design.
- Intial depth of footing calculation.
- Flexural reinforcemnt calculation.
- One way shear check
- Two way shear check
- Settlement check
Gross soil pressure for footing area
Area = P/qa
qa=150 Kn/sq m
P=2000/1.5=1333.33KN.
A=(1333.3+1.1)/150=9.78 sq m
Let assume the square footing
A=3.12mt
Net soil pressure & Intial footing depth
Pn=Factored load/Actual area of footing
Pn=(2000x1000)/(3.2x3.2)
Pn=195.3KN/sqm
Let assume depth of footing 500 mm and checking it for bearing stress as per Is 456-2000 C.34.4
Permissible bearing stress 0.45Xfc=11.25N/sq m
Permissible bearing stress multiplied with area factor =11.25x2=22.5N/sqm
Actual bearing stress at column base=(20x1000)/(400x400)=12.5N/sqmm
12.5N/sqmm<22>
Hence OK.
Flexural reinforcemnt calculation.
Conversion of net pressure into udl=195.3x3.2=625Kn/m
Bending moment due to udl area over acantilever section =wl^2/2=625x1.6x1.6/2=800KN-M
Reinforcement calculation as per IS 456-2000A-G
Provide 16mmdia at 125 mm spacing,the actual rebar provided=5146 sq mm
One way shear check
shear force in one way=Area xNet soil pressure=0.95x32x195.3=593.7 KN
Design shear stress at one way cut face
tv=(593.7x1000)/(320x450)=0.412 N/sq mm
shear stress capacity of sectio as per IS 456-2000,T-19
tc=0.45 N/sq mm
tv
Hence OK.
Two way shear check
Shear force in the two way =(3.2x3.2)-(0.85x0.85)x195.3=1895KN
Design shear stress at two way cut face
tv=1859x1000/340x450 =1.215 N/sq mm
Shear strees capacity as per IS 456-2000
C.31.6.3.1=0.25X(fck)^1/2=1.25 N/sq mm
< alt>
REPORT:
To complete design the footing by using the given data and check for one way shear and two way shear.