Combined Footing Design BS8110

Tech.Form-029cd : BS_Design of Combined Footing_BS8110 29/10/2014 1:25 PM

(Ref. Code : BRITISH)

P1

Total Weight of Combined Fdn : A. LOADING DATA :

(refer to page

Load P

M'x

Ultimate

M'z

Fx

Fz

Pu

M'ux

M'uz

Fux

Fuz

(Jt.#3) (heavily-loaded pt.)

Perm.

42.00

0.00

1.00

1.00

0.00

Temp.

122.00

0.00

23.00

20.00

0.00

Pt. No.2

soil = 119.76 kN

(unit : kN, kN-m)

Service

Case Pt. No.1

)

1800.00

40.00

40.00

0.00

0.00

1600.00

20.00

10.00

0.00

0.00

F1

foot. =

94.18 kN

surch.=

2.16 kN

misc.=

0.00 kN

0.00

0.01

1.00

0.00

Temp.

122.00

0.00

23.00

20.00

0.00

qap (perm.) =

140.00 kN/m²

qat (temp.) =

186.00 kN/m²

pt.2

5 -D16

. . . . . . . . . . . . . . . . . .

Allow. Soil Bearing Pressure , qa ;

42.00

F2

G.L

Fw = 216.10 kN

(Jt.# 4)

Perm.

P2

pt.1

Sd h

MARK : F12A

H

DESIGN OF COMBINED FOOTING

z

z

10 -D16

x Foot. Dimen.,

Col. Dimen.,

C. CHECK OF SOIL BEARING PRESSURE L=

5.00 m

B=

2.00 m

H=

0.40 m

C.1 at Permanent Condition P=

84.00 + Fw =

300.10 kN

ez = Mx/P =

0.000 m 0.013 m

h=

0.30 m

ex = Mz/P =

0.45 m

qp = P / (L B) (1 + 6ez / B + 6ex / L

l=

0.55 m 0.70 m

=

Conc. Cover,

cc =

50.00 mm

Unit Wt. of Soil,

ws =

18.00 kN/m³

P=

d=

Conc. Strength,

fcu =

25.00 mPa

Steel Bar Yield,

fy =

420.00 mPa

P=

326.00 mm

244.00 + Fw =

244.0 + Fw =

460.10 kN

F = (Fx² + Fz²)½ =

40.00 kN

Coeff. of friction, ff =

0.60

< qap Ok.!

=

6.90

0.85

0.85

3.30

(x2)

L

D.2 against Overturning (use temporary case) 460.10 kN

Overturning Moments ;

0.000 m

Mox =

0.0 kN-m

ex = Mz/P =

0.222 m

Moz =

102.0 kN-m

qt = P / (L B) (1 + 6ez / B + 6ex / L 58.25 kN/m²

(x1)

> 1.50 Ok.

ez = Mx/P =

=

l

Factor of Safety = ff P / F

C.2 at Temporary Condition

Least Eff.depth,

E. FLEXURE DESIGN

30.47 kN/m²

b

D.1 against Sliding (use temporary case)

b= Sd =

Soil Depth,

D. CHECK OF STABILITY

B

B. FOUNDATION DATA :

Resisting Moments ; Mrx =

Factor of Safety about X-axis ;

< qat Ok.

= Mrx / Mox =

460.10 kN-m

Mrz = 1150.25 kN-m Factor of Safety about Z-axis ;

n.a

= Mrz / Moz =

11.28

> 1.50 Ok.

(BS 8110 Part 1 : sec.3.4.4.4) ( Note : In cases where, ex > L/6 or ez > B/6, it becomes necessary to provide Top Reinforcements )

E.1 Determine net ultimate upward soil pressure ;

E.2 X-direction Reinforcement (top or bottom) Muz = qmax(L²/8)B-Pu1(L/2-x1) =

E.3 Z-direction Bottom Reinforcement

C. Axial,

Pu = 3400.00 kN

Eccentri.,

ez = Mux / Pu =

0.018 m

Kx = Muz / ( fcu B d² ) =

ex = Muz / Pu =

0.112 m

Zx = d [ 0.5 + ( 0.25 - Kx / 0.9 )½ ] < 0.95d =

qmax = Pu/(L B)(1+6ex/L+6ez/B) =

403.60 kN/m²

qmin = Pu/(L B)(1-6ex/L-6ez/B) =

276.40 kN/m²

Min.x =

qave = ( qmax + qmin ) / 2 =

340.00 kN/m²

Use

(BS 8110 Part 1 : sec.3.7.7)

F.1 Punching at column face

=

2000.00 mm

vp = Vup / ( bo d ) =

2.63 mPa

vc = 0.8 (fcu)½ or 5 mPa

4.00 mPa > vp Ok.

308.54 mm

Asz' = Muz / ( 0.87 fy Zx ) 5375.44 mm²

0.0024 (B) (H) = 1920.00 mm²

Min.z =

-D16

0.0024 (L) (H) = 4800.00 mm²

Use < Min.x N.G!)

G. CHECK FOR WIDE BEAM SHEAR

606.03 kN-m 0.046 < 0.156

Zz = d [ 0.5 + ( 0.25 - Kz / 0.9 )½ ] < 0.95d

Asx' = Muz / ( 0.87 fy Zx ) 4195.04 mm² 5

Mux = qmax {[(B-b)/2]²}L/2 = Kz = Mux / ( fcu L d² ) =

10

-D16

(Asz = 2010.00 mm²

< Min.x N.G!)

(BS 8110 Part 1 : sec.3.5.5 & Table 3.9)

G.1 X- Direction (at inside of column face 1)

Vup = Pu1 - qave (l) (b) = 1715.85 kN bo = ( l ) 2 + ( b ) 2 =

0.084 < 0.156

291.94 mm

(Asx = 1005.00 mm² F. CHECK FOR PUNCHING SHEAR

447.50 kN-m

G.2 Z- Direction (at a dist."B / 4" from face)

Vux = qmax (x1+l/2)B -Pu 891.90 kN

Vux = qmax {(B - b)/4}L =

vx = Vux / ( B d ) = 1.37 mPa 1/3 1/4 1/3 vcx = [ 0.79 (100Asx/Bd) (400/d) (fcu/25) ] / 1.25

vz = Vuz / ( L d ) = 0.48 mPa 1/3 1/4 1/3 vcz = [ 0.79 (100Asz/Ld) (400/d) (fcu/25) ] / 1.25

=

0.36 mPa < vx N.G!

=

781.98 kN

0.33 mPa < vx N.G!

(Note : shear enhancement factor of 2d/av as allowed in BS 8110 sec.3.4.5.10 was not applied here to account for an additional factor of safety.)

designed and prepared by : nzh