Foundation Design

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DESIGN OF FOUNDATION:
1.0 Footing Data
Unit Weight of Concrete
Grade of Concrete
Net SBC
Increament factor for BC
Concrete cover

25.00
30.00
200
1.00
75.00

SBCnet
fbc

Depth of foundation below ground level ,dfgl
Pedestal height above Ground level
Tenion load
Unit Weight of soil
Angle of internal friction
Coeffcient of friction
FOS against Overturning
FOS against sliding

mm

0.95 m
0.50
6.40
18.00
30
0.50
2.00
1.5

γs
φ
µ

X-Dirn
350
1000
0

Pedestal Size(mm)
Footing Size(mm)
Eccentricity,e(mm)

kN/m3
2
N/mm
kN/m2

m
kN
kN/m3
degree

Z-Dirn
450
1000
0

Y-Dirn
50
900
0

Load acting at(Top
of Pedestal/Bottom of Footing):
Axial
Load
Load,
Shear,
Moment,
case/Node
Py(kN) Shear, Fx(kN)
Fz(kN)
Mx(kNm)
number
2.769
2.753
0.2
0
D.L+W.L
Gross SBC

=

fbc x SBCnet + γs x dfgl

Moment,
Mz(kNm)
2.355

=

2

=

217 kN/m

2.77
0.20
1.00
0.76

2.0 Vertical load acting at bottom of foundation
Axial Load
Weight of Pedestal
Area of foundation ( Provided )
Load due to soil

Py
Wp
A
Ws

Lp x Bp x (Hp) x 25
L*B
γs*(dfgl - D)*(A - (Lp x Bp))

=
=
=
=

kN
kN
m2
kN

Weight of footing

Wf

A*D*25

=

22.50 kN

Total Vertical Load

Pv

Py+Wp+Ws+Wf+Wgs+Wll

=

26.22 kN

3.0 Moment acting at bottom of foundation(about x-axis)
Moment
Moment due to lateral force
Moment due to eccentricity (ez)

Mx
Mlfx
Mecc

Fz * dforc
(Py+Wp)*ez

=
=
=

0
0.19
0.00

kNm
kNm
kNm

Moment acting at bottom of foundation

Mxx

Mx+Mlfx+Mecc

=

0.19

kNm

Mxx/Pv

=

0.007

m

Eccentricity along Z-Direction from cg of Footing, ez'

<
B/6

4.0 Moment acting at bottom of foundation(about z-axis)
Moment
Moment due to lateral force Fx
Moment due to eccentricity (ex)

Mz
Mlfz
Mecc

Fx * dforc
(Py+Wp)*ex

=
=
=

2.355
2.61535
0.00

kNm
kNm
kNm

Moment acting at bottom of foundation

Mzz

Mz+Mlfz+Mecc

=

4.97

kNm

Mzz/Pv

=

0.190

m

Eccentricity along X-Direction from cg of Footing, ex'

>
L/6

5.0 Bearing Pressure Calculation:Eccentricity along X-Direction from cg of Footing, ex'
Eccentricity along Z-Direction from cg of Footing, ez'
Teng Value

k

Mzz/Pv
Mxx/Pv

=
=

0.190
0.007

=

2.199

m
m

Maximum Bearing Pressure
Minimum Bearing Pressure

fmax
fmin

kPv/A
Pv/A(1-6ex'/L-6ez'/B)

Bearing capacity Ratio

BCR

fmax/Gross SBC

2
27.36 kN/m
2
25.08 kN/m

=
=
=
Safe

0.13

6.0 Check for Stability:X-Direction
Overturning Moment
Restoring Moment
Stability Ratio

Mo
Mr=Pv x L/2
Mr/Mo

=
=
=

0.19 kNm
13.11 kNm
69.01

Z-Direction

Pv x B/2

=
=
=

4.97 kNm
13.1121 kNm
2.64

>2 Safe

>2 Safe

7.0 Check for Sliding:X-Direction
Sliding Force
Resisting Force
Sliding Ratio

Hs
Hr = µPv
Hs/Hr

=
=
=

Z-Direction

2.753 kN
13.11 kN
4.76
>1.5 Safe

=
=
=

0.2 kN
13.1121 kN
65.5603
>1.5 Safe

8.0 DESIGN FORCE CALCULATIONS:8.1 X-Direction:Pressure variation :Maximum Pressure
Minimum Pressure
Design Moment:Distance from left edge to face of pedestal
Distance from right edge to face of pedestal
Moment at west face of pedestal
Moment at east face of pedestal
Design Moment
Mxu
One way Shear:Effective Depth

Pv/A(1+6ex'/L)
Pv/A(1-6ex'/L)

27.36*0.325*1000*0.325/2
27.36*0.275*1000*0.275/2

dx

Distance from left edge to d distance from west face of pedestal
Distance from right edge to d distance from east face of pedestal
Shear at d distance from west face of pedestal
27.36*0
Shear at d distance from east face of pedestal
27.36*0
Design Shear at d from face of pedestal
Vxu
Max Vx
Shear Stress at critical section
As per Clause 3.4.5.8 of BS 8110 Part1,
Alllowable Shear Strength of concrete

=
=

2
27.36 kN/m
2
25.08 kN/m

=
=
=
=
=

0.325
0.275
1.45
1.03
1.45

=

817.00

=
=
=
=
=
=

0.8170
0.000
0.000
0.00
0.00
0.00

m
m
kNm/m
kNm/m
kNm/m

m
m
m
kN/m
kN/m
kN/m
2

=

9 Z-Direction:Pressure Variation:Maximum Pressure
Minimum Pressure
Design Moment:Distance from top edge to face of pedestal
Distance from bottom edge to face of pedestal
Moment at north face of pedestal
Moment at south face of pedestal
Design Moment
Mzu

=
0.00 N/mm
(0.79*0.2^(1/3)*max of((400/817,1)^0.25/1.25*(30/25)^(1/3))
2
N/mm
0.459

Pv/A(1+6ez'/B)
Pv/A(1-6ez'/B)

56.05*0.325*0.325/2
56.05*0.325*0.325/2

=
=

2
56.05 kN/m
2
kN/m
-3.60

=
=
=
=
=

0.325
0.325
2.96
2.96
2.96

m
m
kNm/m
kNm/m
kNm/m

10 Punching Shear Force:At face of the pedestal
Critical section of at a distance 2d from face of footing
Critical perimeter
A
B

Area with the perimeter

=
=
=
=

2A + 2B
1167.000
1267.000
4868.00

-478589.0000
8.38E+06 mm^2
40.460
kN

mm

Punching shear force

VEd

=
=
=

Shear Stress

d
vRd,c

=
=

817
0.01

=

0.8 Roof of Fck

=

4.38

(As Per Cl 3.7.7.2 of BS 8110 : Part 1:1997, max shear strength is max of
0.8(fcu)1/2 and 5N/mm2)

mm
N/mm2

N/mm

2

11 Design of Bottom Reinforcement:Thickness of footing
Clear Bottom cover
Clear Top cover

D
Cb
Ct

=
=
=

Characteristic strength of concrete

fck

=

30 N/mm2

Characteristic strength of steel

fy

=

500 N/mm2

Effective Thickness of Footing

=

900 mm
75 mm
75 mm

817.00 mm

Mx = Base Pressure * Width of Footing * Cantilever projection
Mx =
1.223
kN.m
K

K'

Minimum Percentage of Steel
Provide Reinforcement
No of Rod Required
Provide number of Reinforcement
Provide Area of Steel
Provide

=
M / Fck*b*d^2
=
0.000
=
0.156
K
<
K'
(No need Compression Reinforcement)
Z
=
d*(0.5+SQT (0.25-k/0.9)
Z
=
817
mm
0.95*d =
776.15
mm
As
=
3.62
mm^2
=
0.13 %
=
1062.1 mm^2
=
14 mm
=
10.58104771
=
5.6
=
1134.093333 mm^2
14.00 mm Dia @

150.00 mm both ways

12 Check Uplift:
Tension in Pedestal
=
Total Vertical load in Footing =
Factor of safety

=

6.40 kN
25.47 kN
3.979042969 > 1

Safe

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