Combined FoundationDesign of Raft
Foundation31.0500.4790.60.751.53.68101.0500.750.7501.50.750FGL1.252.00.75Unit
Wt Of Soil =1.8T/m3Density Of Water =1T/m3Unit Weight Of Concrete
=2.5T/m3Comp. strength of concrete fc =30N/mm2Yield strength of
steel fy =415N/mm2Coefficient Of Friction m =0.5Net SBC =8T/m2Gross
SBC =13.6T/m2 ------ Where increase in SBC is allowed.Length Of
Foundation Lf =3mWidth Of Foundation Wf =3.6mThickness Of
Foundation Tf =0.75mFounding Depth Df =2m`Length Of Pedestal Lp
=0.4mWidth Of Pedestal Wp =0.6mHeight Of Pedestal Hp
=1.25mSelfweight Of Foundation =3 x 3.6 x 0.75 x 2.5=20.25TBuoyant
selfweight Of Foundation =3 x 3.6 x 0.75 x 1.5=12.15TSelfweight Of
Soil =1.8 x 1.25 x ( 3 x 3.6 - 0.6 x 0.4 x 4 )=22.14TBuyoant
selfweight Of Soil =0.8 x 1.25 x ( 3 x 3.6 - 0.6 x 0.4 x 4
)=9.84TSelfweight Of Pedestal =2.5 x 0.6 x 0.4 x 1.25 x 4=3TBuoyant
selfweight Of Pedestal =1.5 x 0.6 x 0.4 x 1.25 x 4=1.8TTotal weight
without buoyancy =20.25 + 22.14 + 3=45.39TTotal weight with
buoyancy =12.15 + 9.84 + 1.8=23.79TLoad On Column A1:- (At Founding
Level)Col. No.Comb No.Load
CombinationFORCE-XFORCE-YFORCE-ZMOM-XMOM-YMOM Z7110
(SELF+WL+X)-0.1840.105-0.017-0.0400.42211
(SELF+WL-X)0.0972.2030.0330.070-0.22312
(SELF+WL+Z)0.141-4.62-0.926-2.130-0.32413
(SELF+WL-Z)-0.2286.9250.9412.1600.52514-0.196-0.868-0.141-0.3200.45615
(SELF+PO+WL+X)-0.336-1.916-0.166-0.3800.77716
(SELF+PO+WL-X)-0.0560.182-0.116-0.2700.13817
(SELF+PO+WL+Z)-0.012-6.64-1.074-2.4700.03918
(SELF+PO+WL-Z)-0.384.9040.7931.8200.87Load On Column B1:- (At
Founding Level)Col. No.Comb No.Load
CombinationFORCE-XFORCE-YFORCE-ZMOM-XMOM-YMOM Z9110
(SELF+WL+X)-0.2123.0320.0510.1200.49211
(SELF+WL-X)0.0580.9320.0020.010-0.13312
(SELF+WL+Z)0.378-3.629-0.206-0.470-0.87413
(SELF+WL-Z)-0.5327.5950.260.601.22514-0.223.4920.0690.1600.51615
(SELF+PO+WL+X)-0.3554.5410.0930.2100.82716
(SELF+PO+WL-X)-0.0842.4410.0440.100.19817
(SELF+PO+WL+Z)0.235-2.12-0.165-0.380-0.54918
(SELF+PO+WL-Z)-0.6759.1050.3020.6901.55Load On Column A2:- (At
Founding Level)Col. No.Comb No.Load
CombinationFORCE-XFORCE-YFORCE-ZMOM-XMOM-YMOM Z8110
(SELF+WL+X)-0.1840.1050.0170.0400.42211
(SELF+WL-X)0.0972.203-0.033-0.080-0.22312
(SELF+WL+Z)-0.2236.973-0.943-2.1700.51413
(SELF+WL-Z)0.136-4.6680.9272.130-0.31514-0.2580.592-0.097-0.2200.59615
(SELF+PO+WL+X)-0.398-0.455-0.072-0.1700.92716
(SELF+PO+WL-X)-0.1171.642-0.122-0.2800.27817
(SELF+PO+WL+Z)-0.4386.413-1.032-2.3701.01918
(SELF+PO+WL-Z)-0.078-5.2290.8381.9300.18Load On Column B2:- (At
Founding Level)Col. No.Comb No.Load
CombinationFORCE-XFORCE-YFORCE-ZMOM-XMOM-YMOM Z10110
(SELF+WL+X)-0.2133.032-0.051-0.1200.49211
(SELF+WL-X)0.0580.931-0.00200-0.13312
(SELF+WL+Z)-0.5287.546-0.259-0.601.21413
(SELF+WL-Z)0.373-3.5810.2060.470-0.86514-0.354.888-0.093-0.2100.81615
(SELF+PO+WL+X)-0.4855.937-0.118-0.2701.12716
(SELF+PO+WL-X)-0.2153.837-0.069-0.1600.49817
(SELF+PO+WL+Z)-0.80110.452-0.326-0.7501.84918
(SELF+PO+WL-Z)0.1-0.6750.1390.320-0.23Summary Of Loads :- ( At
foundation level)JOINTLOADFORCE-XFORCE-YFORCE-ZMOM-XMOM-YMOM
Z71-0.1840.105-0.017-0.0400.4220.0972.2030.0330.070-0.2230.141-4.62-0.926-2.130-0.324-0.2286.9250.9412.1600.525-0.196-0.868-0.141-0.3200.456-0.336-1.916-0.166-0.3800.777-0.0560.182-0.116-0.2700.138-0.012-6.64-1.074-2.4700.039-0.384.9040.7931.8200.8781-0.1840.1050.0170.0400.4220.0972.203-0.033-0.080-0.223-0.2236.973-0.943-2.1700.5140.136-4.6680.9272.130-0.315-0.2580.592-0.097-0.2200.596-0.398-0.455-0.072-0.1700.927-0.1171.642-0.122-0.2800.278-0.4386.413-1.032-2.3701.019-0.078-5.2290.8381.9300.1891-0.2123.0320.0510.1200.4920.0580.9320.0020.010-0.1330.378-3.629-0.206-0.470-0.874-0.5327.5950.260.601.225-0.223.4920.0690.1600.516-0.3554.5410.0930.2100.827-0.0842.4410.0440.100.1980.235-2.12-0.165-0.380-0.549-0.6759.1050.3020.6901.55101-0.2133.032-0.051-0.1200.4920.0580.931-0.00200-0.133-0.5287.546-0.259-0.601.2140.373-3.5810.2060.470-0.865-0.354.888-0.093-0.2100.816-0.4855.937-0.118-0.2701.127-0.2153.837-0.069-0.1600.498-0.80110.452-0.326-0.7501.8490.1-0.6750.1390.320-0.23Moment
On C.G :Due to
FyJOINTLOADFXFYFZMXMYMZ71-0.1840.105-0.017-0.079--0.07920.0972.2030.033-1.653--1.65330.141-4.62-0.9263.465-3.4654-0.2286.9250.941-5.194--5.1945-0.196-0.868-0.1410.651-0.6516-0.336-1.916-0.1661.437-1.4377-0.0560.182-0.116-0.137--0.1378-0.012-6.64-1.0744.98-4.989-0.384.9040.793-3.678--3.67891-0.2123.0320.051-2.274-2.27420.0580.9320.002-0.699-0.69930.378-3.629-0.2062.722--2.7224-0.5327.5950.26-5.697-5.6975-0.223.4920.069-2.619-2.6196-0.3554.5410.093-3.406-3.4067-0.0842.4410.044-1.831-1.83180.235-2.12-0.1651.59--1.599-0.6759.1050.302-6.829-6.82981-0.1840.1050.0170.079--0.07920.0972.203-0.0331.653--1.6533-0.2236.973-0.9435.23--5.2340.136-4.6680.927-3.501-3.5015-0.2580.592-0.0970.444--0.4446-0.398-0.455-0.072-0.342-0.3427-0.1171.642-0.1221.232--1.2328-0.4386.413-1.0324.81--4.819-0.078-5.2290.838-3.922-3.922101-0.2133.032-0.0512.274-2.27420.0580.931-0.0020.699-0.6993-0.5287.546-0.2595.66-5.6640.373-3.5810.206-2.686--2.6865-0.354.888-0.0933.666-3.6666-0.4855.937-0.1184.453-4.4537-0.2153.837-0.0692.878-2.8788-0.80110.452-0.3267.839-7.83990.1-0.6750.139-0.507--0.507Total
Reactions On foundation:TOTALLOADFXFYFZMxx1Mxx2MxxMzz1Mzz2Mzzdue to
FYExternalMxx1+Mxx2due to
FYExternalMzz1+Mzz21-0.7936.27400004.391.826.2120.316.26900-0-0-1.908-0.7-2.6083-0.2326.27-2.33417.0775.3722.4471.1730.531.7034-0.2516.2712.334-17.078-5.36-22.4381.3180.571.8885-1.0248.104-0.2622.1420.592.7326.4922.368.8526-1.5748.107-0.2632.1420.612.7529.6383.6313.2687-0.4728.102-0.2632.1420.612.7523.341.084.428-1.0168.105-2.59719.2195.9725.1896.4192.348.7599-1.0338.1052.072-14.936-4.76-19.6966.5662.378.936Check
For stability :-a) Against Overturing :- (Check is done only for
with buoyancy case)It is ensured that all the four corners of
foundation are in compression for all the load cases.This means
foundation will not loose contact and safe against overturning.b)
Against Sliding :- (Check is done only for with buoyancy case)Total
Sliding ForcesRestoring
ForcesLoadFxFzResultantExternalSoil,Fdn,Total0.5*(1+2)F.O.S.ResultLoadPedestalLoad121+21-0.79300.796.27423.7930.06415.0419.04Safe20.3100.316.26923.7930.05915.0348.48Safe3-0.232-2.3342.356.2723.7930.0615.036.4Safe4-0.2512.3342.356.27123.7930.06115.046.4Safe5-1.024-0.2621.068.10423.7931.89415.9515.05Safe6-1.574-0.2631.68.10723.7931.89715.959.97Safe7-0.472-0.2630.548.10223.7931.89215.9529.54Safe8-1.016-2.5972.798.10523.7931.89515.955.72Safe9-1.0332.0722.328.10523.7931.89515.956.88SafeCheck
For Bearing Preasure:Check For Pressure At All The Corners (With
Buoyancy)LoadFy FromSoil+
FdnFyMxxMzzFy/AMxx/ZxxMzz/Zzz1+2-31+2+31-2+31-2-3Load+Ped12316.27423.7930.06406.212.7801.151.633.933.931.6326.26923.7930.059-0-2.6082.7800.482.33.263.262.336.2723.7930.0622.4471.7032.783.460.325.926.56-0.36-146.27123.7930.061-22.4381.8882.783.460.355.896.59-0.33-1.0358.10423.7931.8942.7328.8522.950.421.641.735.014.170.8968.10723.7931.8972.75213.2682.950.422.460.915.834.990.0778.10223.7931.8922.7524.422.950.420.822.554.193.351.7188.10523.7931.89525.1898.7592.953.891.625.228.460.68-2.5698.10523.7931.895-19.6968.9362.953.041.654.347.641.56-1.74pmax
=8.46t/sqmpmin =-2.56t/sqmCheck For Pressure At All The Corners
(With0ut Buoyancy)LoadFy FromSoil+
FdnFyMxxMzzFy/AMxx/ZxxMzz/Zzz1+2-31+2+31-2+31-2-3Load+Ped12316.27445.3951.66406.214.7801.153.635.935.933.6326.26945.3951.659-0-2.6084.7800.484.35.265.264.336.2745.3951.6622.4471.7034.783.460.327.928.561.64146.27145.3951.661-22.4381.8884.783.460.357.898.591.670.9758.10445.3953.4942.7328.8524.950.421.643.737.016.172.8968.10745.3953.4972.75213.2684.950.422.462.917.836.992.0778.10245.3953.4922.7524.424.950.420.824.556.195.353.7188.10545.3953.49525.1898.7594.953.891.627.2210.462.68-0.5698.10545.3953.495-19.6968.9364.953.041.656.349.643.560.26pmax
=10.46t/sqmpmin =-0.56t/sqmCALCULATION FOR LOSS OF CONTACT AREA
:4CxB=3.64CyL =3mDepth of foundation below F.G.L2.0MLength of
foundation(L)3MWidth of foundation(B)3.60MTotal vertical load on
foundation(P)31.8TMoment about X axis(Mx)25T-mMomoent about Y
axis(My)9T-mArea = L x B(A)10.8m2Zxx = L x B 2 / 6(Zxx)6.48m3Zyy =
B x A 2 / 6(Zyy)5.40m3ex = My / Pex0.28mB / 6 =0.600mECCENTRICITY
IS OUTSIDE KERNCx = (L / 2) - exCx1.22mCy = (B / 2) - eyCy1.01mP
min = (P / A) - (Mx / Zxx) - (My / Zyy)-2.58T/m2-25.8N/mm2FOOTING
IS IN TENSIONex / L0.09ey / B0.22For corresponding (ex / L) and (ey
/ B) value of =3.1Maximum edge pressure =9.13T/m2Safe bearing
capacity =8.0T/m2Allowable gross bearing capacity
=8*1.25+1.8*2=13.6T/m2Calculation for loss of contact
area4.91.931.563.62.044.10.52.450.55% Loss of contact area
=23.22%Check For Sheara) Two Way ShearLimit State
Method3.60.750.75Critical Section =At distance d/2 from face of
columnConcrete Grade =30N/mm2Column DetailsLength =400mmWidth
=600mmFoundation DetailsLength =1500mmWidth =3600mmEffective Depth
=675mmPercentage Of Steel =0.2%Punching LoadMaximum Load on Column
=9.105TPunching Shear =9.105 x ( 1.5 x 3.6 - 1.075 x 1.275 )1.5 x
3.6P =7TonShear Resistance Of Concrete (Vc)=vc x bc x d -----Refer
to clause no. 31.6.3.1 of IS 456where vc =ks x tcks =0.5 +
bc-----should not be greater than 1bc =Short Side Of ColumnLong
Side Of Column=400600=0.667ks =1tc =1.37N/mm2bc =Appropriate
perimeter at distance d/2Length of critical section =1075mmWidth of
critical section =1275mmPerimeter of critical section =4700mmDepth
Required =1050001.37 x4700=16.31mmShear Resistance =1.37 x 4700 x
675 / 10000434TB) One Way
Shear1.50.8253.6-0.1250.88-0.130.751.5Critical Section =At distance
d from face of columnMaximum Pressure =6.335T/m2---- For without
Buoynacy ConditionAt LengthLength at critical section =3600mmWidth
at critical section =-125mmShear Force =6.335 x 3.6 x -0.125=-3TAt
WidthLength at critical section =1500mmWidth at critical section
=825mmShear Force =6.335 x 1.5 x 0.825=8TDesigned Shear Stress
=8TCorresponding Length =1500mmAllowable Shear Stress
=0.33N/mm2----Refer Table 19 of IS 456k =1---- Refer clause no.
40.2 of IS 456tc =0.33N/mm2Depth Required =1200000.33 x
1500=243mmDesign Of Foundationa) Calculation of reinforcement at
bottomMaximum Pressure =10.46T/m2--- Without Buoyancy Load CasePre.
due to pcc & fdn wt =( 20.25 + 22.14 ) / ( 3 x 3.6
)=3.93T/m2Net causing moment =6.53T/m2Maximum Projection of fdn
=0.75mBending Moment =6.53 x 0.75 x 0.75 / 2=1.84TmAst =0.5 x fck x
b x d1 -(4.6 x Mu )fyfck x b x d2Ast =113.57mm2Min. percentage of
re-bar =0.12%Ast =900mm2Use16mm dia barsArea of bar
=200.96mm2Spacing =200mmProvide Spacing =150Area Provided
=1339.73mm2Provide 16 mm dia Bars @ 150 mm spacing bothwaysb)
Calculation of reinforcement at topArea Load =6.53T/m2Max.
Projection of fdn =1.5mBending Moment =6.53 x 1.5 x 1.5 /
10=1.47TmAst =0.5 x fck x b x d1 -(4.6 x Mu )fyfck x b x d2Ast
=90.69mm2Min. percentage of re-bar =0.12%Ast =900mm2Use16mm dia
barsArea of bar =200.96mm2Spacing =223mmProvide Spacing =150mmArea
Provided =1339.7333333333mm2Provide 16 mm dia Bars @ 150 mm spacing
bothwaysSummary Of Design :-Length Of Footing :-3000mmWIdth Of
Footing :-3600mmDepth Of Footing :-750mmReinforcement :-At Top
:-Provide 16 mm dia Bars @ 150 mm spacing bothwaysAt Bottom
:-Provide 16 mm dia Bars @ 150 mm spacing bothways
