footing design-F6DESIGN OF FOOTING :( Sample calculations for
Footing F6 - Supporting C6 group of columns )Load from columnFX
=0.000kNFY=0.000kNFZ=2100kNBase Pressure is less than SBC Hence
SAFEMoment @ x-axis MX=6kN.mMoment @ y-axis MY=5kN.mNo Tension at
base Hence SAFEUltimate design forcesMxFX =0.000kNFzSafe in One way
ShearFY=0.000kNFxFZ=2100.000kNMyMoment @ x-axis MX=6.000kN.mSafe in
Two way ShearMoment @ y-axis MY=5.000kN.mH =0mmHSBC
=250kN/m2UBC=375kN/mFactor of Safety against SBC. Is =1.01Bx
=2600mmD1By =2300mmD1 =800mmSafety against Bearing CapasityDepth at
Edge (D2) =300mmEff. Cover =50mmBxColumn Width parallel to x-axis (
Cx ) =600mmColumn Width parallel to y-axis ( Cy )
=300mm12120120Charectoristic strength of concrete(fck)
=20N/mmCharectoristic strength of Steel(fy) =415N/mmWt
=92.35CxDESIGN OF FOOTING :CyVolume =3.694ByM.I. @ x-axis
=Bx*By/12=2.6361833333m4Zxx =Ixx/(By/2)=2.2923333333M.I. @ y-axis
=By*Bx/12=3.3687333333m4Zyy =Iyy/(Bx/2)=2.5913333333Self weight of
the footing =92.35kNForces at the Base of the footing.FX
=0.00kNFY=0.00kNFZ=2192.35kNMoment @ x-axis MX=6.00kN.mMoment @
y-axis MY=5.00kN.mMax Base Pressure (Pmax)
=(Fz/A)+(Mx/Zxx)+(My/Zyy)=371.16kN/mCorner 2Min. Base Pressure
(Pmin) =(Fz/A)-(Mx/Zxx)-(My/Zyy)=362.07kN/mCorner 4Base Pressure at
Corner 1 =(Fz/A)+(Mx/Zxx)-(My/Zyy)=367.3kN/mBase Pressure at Corner
3 =(Fz/A)-(Mx/Zxx)+(My/Zyy)=365.93kN/m362.07365.93Bearing Pressure
Diagram atBase of the footing.43Distance to the edge600of footing
from column face =1m300( Parrel to x-axis )1368.89Distance to the
edgeof footing from column face =1m1( Parrel to xyaxis )12Dia of
R/F Bar =12mm367.3371.16369.68Moment @ y-axis
=(369.68)1x2.3x1/2+0.5x(371.16-369.68)2.3x((2/3)x1)x1=426.27kN.mArea
of Steel Required
=(0.5xfck)/fy{1-SQRT(1-(4.6xB.M./fckBd))}Bd(Parallel to x-axis
)=1913mmMoment @ x-axis
=(368.89)2.6x1x1/2+0.5x2.6(371.16-368.89)((2/3)x1)1=481.52kN.mArea
of Steel Required
=(0.5xfck)/fy{1-SQRT(1-(4.6xB.M./fckBd))}Bd(Parallel to y-axis
)=2208mmMin. area of steel required =0.12 %=540mmNo of 12 mm dia
Bar =17NosSpacing =120mmSay 100 c/cNo of 12 mm dia Bar
=20NosSpacing =120mmSay 100 c/cCHECK FOR SHEAR.1.Check for one way
shear.Critical section is at effective depth from face of
support.Taking Critical axis parallel to y-axisAverage Bearing
Pressure =(371.16+370.79+365.93+365.56)/4=368.36kN/m0178Max S.F
=368.36x(0.25x2.3)=211.81kNTaking Critical axis parallel to
x-axisAve. Bearing Pre.
=(371.16+370.66+367.3+365.99)/4365.56=368.7775kN/mMax S.F
=368.7775x(0.25x2.6)362.07365.93=239.71kN750362.07365.93Max S.F.
=239.71kN750750365.99370.660.25367.3367.3371.16371.161370.79Depth
of footing at critical section0.25=+((750-)/1)x0.25=187mmWidth of
footing at this section=2100mmThis width is parellel to the axis
for which S.F. is critical.Max Shear stress=Max. S.F. / Shearing
Area=239710/(2100x187)=0.611N/mmPermissible shear stress
:(Tuc)Shear area =2100 x 187 = 392700 mmParrel to x-axis pt
=0.489%Parrel to x-axis pt =0.576%b =0.8fck/6.89ptb =1.134(Tuc)
=(0.85/6b)x(SQRT(0.8fck)x(SQRT(1+ 5b)-1)(Tuc) =0.791N/mmAs shear
stress is less than permissible stress O.K.1.2945990182.Check for
Two way shear.1.8061389338Critical section is at d/2 distance from
the support.365Total unbalanced Shear Force at
critical362.07363.00365.93Section.375362.07365.93Ave. Base Pressure
on Area Within CriticalSection .=( 364.42 + 366.42 + 368.81 +
366.81 ) / 4=366.615kN/m363.49364.42366.42367.351050Ave. Base
Pressure on total area of footing=( 362.07 + 365.93 + 371.16 +
367.3 ) / 4366.81368.81375=366.615kN/m365.881350369.74Net Unbalance
Shear at critical SectionS.F =366.615 x 2.6 x 2.3 - 366.615 x 1.35
x 1.05=1672.68kN367.3367.3371.16371.16Depth at Critical
Section370.23=250 + ( 750 - 250 ) x ( 0.625 / 1
)368.23=563mmPerimeter of footing at critical section0.625=2 x (
1350 + 1050 )=4800mmArea resisting Two way Shear=563 x
4800=2702400mm750Shear stress at critical Section=1672680 /
2702400=0.619N/mm0.6253751Permissible Shear Stress=ks TcTc =0.25 x
fck1/2=1 x 1.118Tc =1.118N/mm=1.118N/mmks =0.5 + Cx/Cyks =1Shear
stress is within limit.Hence SAFEAs ks is less than one henceks
=1
