Project : Air Compressor Shed
Client : ONGC
DMM
FOUNDATION DESIGN Rev: R1
Date: 15/07/06
DESIGN OF STRIP FOOTING
The design is done for column nos. 16, 18 & 20 (Refer STAAD output sheets) of Grid B and is also applicable
for column nos. 22, 24 & 26 in Grid A.
It is observed from output forces obtained that Normal Service condition (Loadcase 11 from STAAD Output)
is critical. Hence, the footings are deisigned for forces in service/normal condition.
INPUT DATA
1 Column C1
Loads
Depth (along x) = 0.70 m P1 = 657 kN
Width (along y) = 0.70 m Mx1 = 332 kN
My1 = 171 kN
2 Column C2
Loads
Depth (along x) = 0.70 m P2 = 436 kN
Width (along y) = 0.70 m Mx2 = 322 kN
My2 = 543 kN
3 Column C3
Loads
Depth (along x) = 0.70 m P3 = 656.7 kN
Width (along y) = 0.70 m Mx3 = 332 kN
My3 = 171 kN
5 SBC of soil = 350 kN/m2
6 Restrained Width of Footing = 3.0 m
7 Density of concrete = 25.0 kN/m3
14.78
2 5.39 5.39 2.000
+ My
3.0
C1 C2 C3 Mx
X X
Y
Project : Air Compressor Shed
Client : ONGC
DMM
FOUNDATION DESIGN Rev: R1
Date: 15/07/06
C/L C/L of C2
Footing
C1 C2 C3
P1 P2 P3
1.650 1.650
600
Max. 47.6 45.4 39.45 39.45 31.35
Avg.pressure 46.5 42.4 39.5 35.4
CALCULATION FOR SIZE OF FOOTING
Total Load on footing P = P1 + P2 + P3
= 1749 kN
Self weight of footing = 665.1 kN
Size of footing required = 2414
350
= 6.898 m2
Length of footing reqd. L =
6.898
3.0
= 2.299 m say
Considering the max. base pressure, we have
Length of footing provided = 14.78 m
Total Moments on footing Mx = 986.0 kNm
My = 885.3 kNm
Max. Base Pressure = 2414 + 986.0 + 885.3
44.3 22.2 109.2
= 107.0 kN/m2 <350, SAFE
Let z be the distance of c.g of loading from column C1.
Taking moments about C1, we have
1749 x z =
( 657 x 0.0 + 436 x 5.4 + 657 x 10.8 ) + 885.3
Hence, z = 5.896 m from C1.
Shifting the centreline of footing to this location, we have
Left projection of footing from C1 = 1.494 m
Right projection of footing from C4 = 2.00 m
Project : Air Compressor Shed
Client : ONGC
DMM
FOUNDATION DESIGN Rev: R1
Date: 15/07/06
Project : Air Compressor Shed
Client : ONGC
DMM
FOUNDATION DESIGN Rev: R1
Date: 15/07/06
ANALYSIS OF FOOTING
Area of footing A = 44.34 m2
Sec. modulus Zxx = 1/6 x 14.8 x 3.0 2
= 22.2 m3
Zyy = 1/6 x 3.0 x 14.8 2
= 109.2 m3
P/A + Mxx / Zxx + Myy / Zyy = 39.45 + 44.47 + 8.106
= 92 kN/m2 OK
P/A + Mxx / Zxx - Myy / Zyy = 75.82 kN/m2
P/A - Mxx / Zxx + Myy / Zyy = 3.084 kN/m2
P/A - Mxx / Zxx - Myy / Zyy = -13.1 kN/m2
Along centreline of width of footing,
Max. pressure = 47.56 kN/m2
Min. pressure = 31.35 kN/m2
Base Pressure at left face of C1 = 45.75 kN/m2
Total Load on slab upto C1 = 46.46 x 3.0 = 139.4 kN/m
betn. C1-C2 = 42.41 x 3.0 = 127.2 kN/m
C2-C3 = 39.45 x 3.0 = 118 kN/m
after C3 = 35.40 x 3.0 = 106 kN/m
Shear Force to left of C1 = -139 x 2
= -279 kN
Shear Force to right of C1 = -279 + 657
= 377.9 kN
Shear Force to left of C2 = -127 x 5.39 + ###
= -308 kN
Shear Force to right of C2 = -308 + 436
= 128 kN
Shear Force to right of C3 = -106 x 1.65
= -175 kN
Shear Force to left of C3 = -175 + 657
= 481 kN
Project : Air Compressor Shed
Client : ONGC
DMM
FOUNDATION DESIGN Rev: R1
Date: 15/07/06
Point of Contraflexure between C1 & C2 = 377.9 = 2.970 m from C1
127
Point of Contraflexure between C2 & C3 = 128 = 1.083 m from C2
118
B.M under C1 = 139 x 2.00 2
2
= 279 kNm (sagging)
Average pressure from left edge upto C2 = ( 139 + 127) = 133 kN/m
2
BM at 2.97 m from C1 = 133 x ( 2.00 + 2.970 ) 2
- 657 x 2.97 + 171
2
= -475 kNm (hogging)
Average pressure from left edge upto C3 = ( 133 + 118) = 126 kN/m
2
B.M under C2 = 126 x 7.390 2 - 657 x 5.4 + 171
2
= -275 kNm (hogging)
BM at 1.083 m from C2 = 126 x ( 7.4 + 1.1 ) 2 - 436 x 1.083 - 657 x 6.47
2
+ 171 + 543
= -920 kNm (hogging)
B.M under C3 = 106 x 2.000 2
2
= 212 kNm (sagging)
Project : Air Compressor Shed
Client : ONGC
DMM Rev: R1
FOUNDATION DESIGN
Date: 15/07/06
DESIGN OF FOUNDATION SLAB
Geometry : Materials :
Length = 5390 mm Concrete - M 30
Breadth = 3000 mm Steel - Fe 500
Depth = 600 mm
Eff. Depth = 600 - 40 - 8 = 552 mm
Check for Bending Moment in Longitudinal Direction
Sagging Moment under C1
Mumax = 278.77 x 1.5 = 418.15 Kn-m(U.M)
Mu/bd2 0.4574 %Ast 0.00107
Ast 1773.2 mm2
Use 16 Tor ---- 26 Nos
I.e 5225 mm2 o.k
Hogging Moment between C1& C2
Mumax = -475.25 x 1.5 = -712.88 Kn-m(U.M)
Mu/bd2 0.7799 %Ast 0.00185
Ast 3063.8 mm2
Use 16 Tor ---- 26 Nos
I.e 5225 mm2 o.k
Hogging Moment under C2
Mumax = -274.8 x 1.5 = -412.2 Kn-m(U.M)
Mu/bd2 0.4509 %Ast 0.00106
Ast 1747.5 mm2
Use 16 Tor ---- 26 Nos
I.e 5225 mm2 o.k
Hogging Moment between C2 & C3
Mumax = -919.94 x 1.5 = -1380 Kn-m(U.M)
Mu/bd2 1.5096 %Ast 0.0037
Ast 6126.4 mm2
Use 18 Tor ---- 27 Nos
I.e 6867.2 mm2 o.k
Sagging Moment under C3
Mumax = 212.4 x 1.5 = 318.6 Kn-m(U.M)
Mu/bd2 0.3485 %Ast 0.00081
Ast 1345.1 mm2
Use 16 Tor ---- 26 Nos
I.e 5225 mm2 O.k
Check for shear :
Max shear = 481 x 1.5 = 722.16 kN
Pt = 0.004
= 8.400
uc = 0.459
Shear resisted by conc
= uc bd
= 0.459 x 3000 x 552
1000
= 760.38 kN O.k
Project : Air Compressor Shed
Client : ONGC
DMM Rev: R1
FOUNDATION DESIGN
Date: 15/07/06
Check for Punching Shear
Since, column C3 transmits heaviest load to the footing, punching shear will be checked only under
this particular column.
The critical section for punching shear is considered at a distance of d/2 from the periphery of the face
of the column.
Hence, peripheral size at critical section = 552.70 mm x 552.70 mm
Load from column C3 = 656.67 x 1.5 = 985.00 kN
Punching shear stress = 985 x 1000 = 0.807 N/mm2
2210.8 x 552
As per Cl.31.5.6. of IS 456-2000, we have
Permissible shear stress = k . c
where k = (0.5 + c ) or 1 whichever is less
where c = ratio of sides of column. = 1.0
and c = 0.25 fck = 1.4 N/mm2
Permissible shear stress = 1.0 x 1.4
= 1.4 N/mm2 Hence o.k
Check for Bending Moment in Transverse Direction
Projection of slab beyond column face = 1.15 m
Base pressure under slab = 92.033 kN/m2
Hence, B.M (unfactored) at column face = 92.033 x 1.15 2
2
= 60.857 kNm/m
Mumax = 60.857 x 1.5 = 91.2851 Kn-m(U.M)
Mu/bd2 0.0999 %Ast 0.00023
Ast 381.64 mm2
Use 16 Tor @ 110 c/c
I.e 1826.9 mm2 o.k
Min. Ast = 0.12%
= 662.4 mm2
