Design of Shallow Foundation (Isolated Footings)

OBJECTIVE OF CHALLANGE

• To know general design procedure of spred footing with hard calculation
• To practice how inputs can be collabrated and arrivef as data for calculations ( how assumptions are helpful wen certain input is not available)

• OBJECTIVE OF CHALLANGE

  • To know general design procedure of spred footing with hard calculation
  • To practice how inputs can be collabrated and arrivef as data for calculations ( how assumptions are helpful wen certain input is not available)

    Procedure

    Steps involved in the design of footing

    Find out GROSS SOIL PRESSURE &FOTTING AREA

    After that NET SOIL PRESSURE /ACTUAL AREA OF FOOTING DEPTH

    Using IS -456-2000 clause 34.4

    One way shear check in thatDesign shear steress is less than shear capacity

    Two way shear check

    Steps involved in fotting design

    1 calculation of gross soil pressure for footing area

    2 calculation of net soil pressure for flexural and shear design

    3Intial depth of footing calculation

    4One way shear check

    5Two way shear check

    6 the settlement for footing

    GROSS SOIL PRESSURE &FOTTING AREA

  • Unfactored load with surcharge + self weight of footing / allowable soil pressure
  • =(2000/1.5*1.1)150=9.78m2
  • Assuming we have suare footing
  • 9.78 =3.12 meter side footing
  • Consider 3,2 m sided isolated fotting

  NET SOIL PRESSURE /ACTUAL AREA OF FOOTING DEPTH

  • Factored load /actual area of footing
  • 2000/1000(3.2*3.2)
  • Pn=195.3kN/m2
  • Assume depth of footing 500mm and checking for strss as per IS -456 -2000 clause 34.4
  • Footing base bearing area /loaded area <-2
  • the max value we can adopt from this is 2only

    FLEXURAL REINFORCEMENT

    • Conversion of net pressure into uniformity distributed load

    =195*3.2=625kN/m2

    • Bending moment due to UDL over a cantilever section

    Wl3/2=625*1*1.6/2

    M=800kNm

    • reinforcement cal
    • n

    Assume Fy=500N/mm2 ,in result Ast required=4350mm2

    If we provide 16mmdia rebar at 125mm spacing ,the actual rebar provided =3200/125*210

    As per =5146mm2

    ONE WAY SHEAR CHECK
  • In the footing the net force cutting footing at criticle position at one side Shear force in the one way shaded area

  • Shear force in the one way shaded area

    0.95*3.2*195.3kN

  • • Shear stress capacity of section as per IS -456-2000 table -19 (include rebar)

    =0.425

    • Design shear force at one way cut face

    =593.7*1000(3200*4500)=0.412N/mm2

    • Design shear steress is less than shear capacity

    Hence ok

  • • ONE WAY SHEAR stress CHECK

    In the footing the net force cutting footing at criticle position at one side

    Shear force in the one way shaded area

    0.95*3.2*195.3kN

    • Shear stress capacity of section as per IS -456-2000 table -19 (include rebar)

    =0.425

    • Design shear force at one way cut face

    =593.7*1000(3200*4500)=0.412N/mm2

    • Design shear steress is less than shear capacity

    Hence ok

  • 
  • • TWO WAY SHEAR STRESS CHECK

    Shear force in the TWO way shaded area

    (3.2*3.2)*(0.85*0.85)*195.3kN

    • Design shear force at two way cut face

    =1859*1000/93400*450)=1.215Nmm2

    • Shear stress capacity of section as per IS -456-2000 clause 31.6.1

    =0.25*fck =1.25N/mm2

    • Design shear steress is less than shear capacity

    Hence ok

  • 
  • RESULT: ALL THECALCULATION OF ONE WAY SHEEAR TWO WAY SHEAR ,GROSS SOIL PRESSURE ,FLEXURAL REINFORCEMENT CALCULATED