Eng. Khalid Footing-Design

8/6/2019 Eng. Khalid Footing-Design

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Footing Design


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Types of Footing

Wall footings are used tosupport structural walls that

carry loads for other floorsor to support nonstructuralwalls.


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I solated or single footingsare used to support single

columns. This is one of themost economical types of footings and is used whencolumns are spaced atrelatively long distances.

Types of Footing


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C ombined footings usuallysupport two columns, or

three columns not in a row.Combined footings are usedwhen two columns are soclose that single footingscannot be used or when onecolumn is located at or near a property line.

Types of Footing


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C antilever or strap footingsconsist of two single

footings connected with a beam or a strap and supporttwo single columns. Thistype replaces a combinedfooting and is moreeconomical.

Types of Footing


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R afted or mat foundationconsists of one footingusually placed under theentire building area. Theyare used, when soil bearingcapacity is low, columnloads are heavy single

footings cannot be used, piles are not used anddifferential settlement must

be reduced.

Types of Footing


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P ile caps are thick slabsused to tie a group of piles

together to support andtransmit column loads to the

piles.

Types of Footing


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D istribution of Soil Pressure

When the column load P is applied on the centroid of the footing, a

uniform pressure is assumed todevelop on the soil surface below the footing area. However the actual distribution of the soil is not

uniform, but depends on may factors especially the composition of the soil and degree of flexibility of the footing.


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D istribution of Soil Pressure

Soil pressure distribution in cohesionless soil.

Soil pressure distribution in cohesivsoil.


11/60

Ecc entri cally load ed footings


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E ccentrically loaded footings E xample Isolated Footing D .L = 900 kN L.L = 450 kN

Ms = 150kN.m Mu=200kN.m q all =200kpa

M


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A rea require d app roxim a te d

4

125.25.3

2

2

3

3

)(

2

)(

9.8

75.8

5.25.3

75.610200

10)450900(

200/20

3

m I

m A

mmuse

mq

P A

kPamt q

net all

s g

net all

!!!

v

!v

v!!

!!

v

kPa I C M

A P

kPa I

C M A P

P M e

s s

s s

L

7.1249.8

150

75.8

1 350

7.1 839.8

150

75.8

1 350

5 83.0111.01 350150

25.3

25.3

65.3

6

!v

!

!v

!

!!!!!

Check stress

183.7124.7


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Ul timate pressure under footing

k a I

k a I

kN kN

uu

uu

u

u

1 669.8

20075.8

1 800

2459.8

200

75.8

1 800.200

18

00)

450(6.

19

002.

1

2

5.3

25.3

}v!

}v

!

!!!

245

245

166


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Check Punching Shear

? A

1 7985.25.3

5.24 641000/37205 303

2575.0

3

'

:equationsuitablecolumn thesquareFor

3720)4005 30(4

4)2451 662451 66( kN V

kN d b f

V

isV

cb

U

oc

o

!v}

!vvv!!

!!

J J

J


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Check Beam Shear

5.5 67

5.2*5 3.05.1*224522 3

facecolumnfromat

1 3.82 81000/25005 306

2575.0

C

C

k

d

k

J

J

!

!

!vvv!


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directionlong /1 67 5.1 31 34 610005 3000254.0

0 .002542500*5 30*250 .859.0

65 7.2*102-1-1

420

25*85.0

305d,2500 b.

2.6

57)

1(7

5.63)7

5.

0(

25.79

1)

1()7

5.

0(

75.63)5.2)(5.1)(211245(

25.791)5.2)(5.1(211facecolumnfromdat

22

2

6

21

21

2

1

musecmmm A

mmmk P P M

k P

k P

M

S

J

V

}!vv!

!

v!

!! !!!

!!!!

Bending moment design

L ong d ire ction 245

245

166

3.5m


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directionshort1.1010 6010005 30002.0

0 .0023500*5 30*250 .859.0

71 9.25*102-1-1420

25*85.0

305d,3500 b

.25.71 95.05.312

1 66245

f acecolumnf romdat

22

2

6

c

kN

S

U

U

}!vv!

!

v

!

!!

!

v!

V

Bending moment design

Sh ort d ire ction245

245

166

2.5m


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0 .832 .4

2

1

2

1 .42 .53.5

!!

!!

F

F

C entral band of short direction = 0.83 As = 0.83 (10.1)=8.6cm 2

C entral band ratio =


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14/ m7J 142J 142J

1 6/m7J


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Footing DesignPart IIC ombined footing


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E xam ple 1D esign a combined footing As shown

k at q net all 200/202

)( !!225 mm N f c !d

2420 mm N f y !


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Dimension calc u la tion T h e b ase d imension to get uniform d istribute d load

x2=6.2m x1=0.2m

800 kN 1200 kN

x

2000kN

A

800(0.2)+1200(6.2)=2000(x)x = 3.8m

2x =7.6 m

800 kN 1200 kN

T ry thickness=80cm


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kPa Pa

A P

q

mq

P A

k P P kPamt q

uu

net all

s g

su

net all

1 90101 908.1*6.7

102 600

8.1*6.71010200

102000

2 600)2000(3.1)(3.1,200/20

33

2

3

3

)(

2

)(

!v!v!!

}!vv!!

!!!!!

A rea require d


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C h eck for pun ch ing Sh eard = 730 mm

oK 8.8751 90*765.0*1 3.1)3.1(800

602 71000/22 6073012

25

22 6073030275.0

12

'2

3.20 621000/22 607303

2575.0

3

'

22 6011 30)765(2

V k V

k d b f bd V

k d b f

V

mmb

c

oc s

C

oc

C

o

J

EJ J

J J

!!

!vvv

v!

!

!vvv!!

!!A

1.13m

0.765


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? A

o 4.1 31 71 90*1 3.1*1 3.1)3.1(1200

5.1 33221000/452073012

25

4520

73040275.0

12

'2

4.41241000/45207303

2575.0

3

'

4520)400730(4

V kN V

kN d b f

bd

V

kN d b f

V

mmb

cU

oc s

oc

o

J

EJ J

J J

!!

!vvv

v

!

!

!vvv!!

!!

B


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Dr aw S. F.D & B .M. D

Stress under footing = 190 *1.8 = 342 kN/m


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34.762f acecolumnf romat.

25.8211000/1 800730625

75.0

C U

U

C

V V

kN d V ax

kN V

J

J

!p

!vvv!

C h eck for be am s h earb = 1800mm, d = 730mm


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Top /209 5.2 82 84 7100073000 39.0

0 .00 391 800*730*250 .859.0

1 366*102-1-1420

25*85.0

307d,8001 b.

1366

22

2

6

musecmmm A

mmmm

mkN ve

S J

V

!!vv!

!

v

!

!!!

Ben d ing moment L ong d ire ction

Bottom /1 67 4.1414401000800001 8.0

0 .000 71 800*730*250 .859.0

24 6.7*102-1-1420

25*85.0

307d,8001 b

.7.24 6

22

min

min2

6

musecmmm A

mmmm

mk M ve

S J

V V

!!vv!

!

v!

!!!


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Ben d ing moment Sh ort d ire ction

/147 116.1101765800001 8.0

765*730*250 .859.0

141 .6*102-1-1

420

25*85.0

307d,765 b

6.1412

4.08.12

765.0

)765.0*8.1(

1040

22

min

min2

6

2

musecmmm A

mmmm

M

S J

V V

!!vv!

v!

!!

!

v!

Under Colum n A


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/147 116.1101765800001 8.0

11 30*730*250 .859.0

212 .33*102-1-1

420

25*85.0

307d,11 30 b

33.2122

4.08.12

1 3.1)1 3.1*8.1(

15 60

22

min

min2

6

2

musecmmm A

mmmm

M

S J

V V

!!vv!

v

!

!!

!

v!

Under Colum n B

Shrinkage Reinforcement in short direction

/147 116.1101765800001 8.022

min musecmmm AS J !!vv!


34/60


35/60

Footing DesignPart III

C ombined footing, strip footing, & Mat foundati


36/60

E xam ple 2D esign a combined footing As shown

k amt q net all 1 80/1 82

)( !!225 mm N f c !d

2420 mm N f y !


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x1=0.2m x2=4.2

m

1200 kN 750 kN

x

1950kN

A750(4.2)+1200(0.2)=1950 (x)x = 1.75m

3

2

21

21 L

B B

B B

x

!


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m B

m B

B

B L B B B B x

B B

B B

B B

L B B

mq P

A

kPamt q

net all

s

g

net all

4

1

2 9.045.175.1335.4

55

32

5

5.22

8.1035.42

8.102

8.10

101 80101 950

,200/20

1

2

2

2

21

21

21

21

21

21

2

3

3

)(

2

)(

!!

!

!

!

!

!

!

!

!v

v!!

!!

A rea require d

kPa Pa

A

P q uu 2 35102 35

8.10

101 9503.1 33

!v!v!!


39/60

C h eck for pun ch ing Sh earh= 750mmd = 732 mm

oK 6.1 3762 35*733.0*0 65.1)3.1(1200

52221000/25 9066512

25

25 9066530275.0

12

'2

4.21 601000/25 906653

2575.0

3

'

25 9010 65)732(2

V k V

k d b f bd V

k d b f

V

mmb

c

oc s

C

oc

C

o

J

EJ J

J J

!!

!vvv

v!

!

!vvv!!

!!A

B 1=4m

B 2=1m


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B

o 5.8962 35*633.0*965.0)3.1(800

52 731000/22 3166512

25

22 31

66530275.0

12

'2

5.1 8541000/22 316653

2575.0

3

'

22 31965)633(2

V kN V

kN d b f

b

d V

kN d b f

V

mmb

cU

oc s

C

oc

C

o

J

EJ J

J J

!!

!vvv

v!

!

!vvv!!

!!


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Dr aw S. F.D & B .M. D


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mk

wl M

wave

.11 748

65.3705

8

705)2 35940(2 3522

max

32

!!!

!! M max

68270.0975 !v

10 92)70.0(15 60 !v

E m pirical S. F.D & B .M. D

m

Convert trapezoida l load to rectang le

Clear distance between co lumnB in mom ent des ign = av e . width = 2.5m


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668critical)mostthe(f acecolumnf romat.

6961000/1 700665

6

2575.0

1 7007.15.1)(21

0 .150 .815at)(21

35.4965.0

C U

U

C

L

x

V V

kN d V Ma x

kN V

mmm

x yb

J

J

!p

!vvv!

!!v

!v!

C h eck for be am s h eard = 665mm

Y =1.5m

1m

4m

x

b


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Top /1 601 201 995100066500 3.0

0 .00 32 600*665*250 .859.0

12 60*102-1-1420

25*85.0

307d

.12 60

22

2

6

musecmmm A

mm

mk M ve

S J

V

!!vv!

!

v!

!!


ottom /149 5.1 31 3501000750001 8.0 22min musecmmm A S J !!vv!

2 60060.25.1)(2135.4

25.2 !!v! mbTop

Bottom


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Ben d ing moment Sh ort d ire ction

2001 333325733665005.0

0 .005733*665*250 .859.0

5 83. 5 7*102-1-1

420

25*85.0

665d

6.5 832

4.075.32

733.0

)733.0*75.3(

15 60

22

2

6

2

J

V

usecmmm A

mm

M

S !!vv!

!

v!

!

!

v!

Under Colum n A

mmmb 35005.35.1)(21' 35.462.3 !!v!

mmmmb 375075.32

45.3!!!

mmmb 144044.15.1)(21' 35.4633.0 !!v!


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146 6.86.854633750001 8.0

633*665*250 .859.0

84 .6*102-1-1

420

25*85.0

665d,633 b

6.842

3.022.12

633.0

)633.0*22.1(975

22

min

min2

6

2

J

V V

usecmmm A

mmmm

M

S !!vv!

v!

!!

!

v!

Under Colum n B

Shrinkage Reinforcement in short direction /149 5.1 31 3507501000001 8.0 22min musecmmm A S J !!vv!

mmmmb 122022.12

144.1 !!!


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Reinforcement detai ls


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E xam ple 3 ( S tri p footing)D esign a combined footing As shown

k amt q net a ll 200/202

)( !!225 mm N f c !d

2420 mm N f y !


49/60


Assume L1=0.6 x1=5.2m

800 kN 1280 kN

x

3040kN

A

800(0.6)+1280(5.1)+960(10.6)=3040 (x)x = 5.65m,2(x)=11.3m

L2=11.3-

(10.6)=0.7

960 kN

x2=10.7m L2


50/60

mmmq

A

k amt q

net a ll

s g

net a ll

8.13.119.1 6101 80103040

,1 80/1 8

2

3

3

)(

2

)(

v}!vv

!!

!!

kPa Pa

A P

q uu 1 95101 958.13.111030403.1 3

3

!v!v

v!!


51/60

C h eck for pun ch ing Sh earh = 700 mmd=630mm

oK 1.145 71 95*0 3.1)3.1(12 80

65 841000/41206301225

4120

63040275.012

'

2

5.32441000/41206303

2575.0

3

'

4120))400630(4

2 V k V

k d b f

bd

V

k d b f

V

mmb

c

oc s

C

oc

C

o

J

EJ J

J J

!!

!vvv

v

!

!

!vvv!!

!!

B

E xampl e

Y ou ca n che ck o ther colum ns

D S F D & B M D S d f i


52/60

Dr aw S. F.D & B .M. D Stress under footing = 195 *1.8 = 351 kN/m


53/60

3.70 6)100 9(7.0f acecolumnf romat.

75.70 81000/1 80063062575.0

C U

U

C

V V

kN d V Ma x

kN V

J

J

!}p

!vvv!

C h eck for be am s h earb = 1800mm, d = 630mm


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Top /22

9 6.3333621000

630005

3.0

0 .005 31 800*630*250 .859.0

1 365*102-1-1420

25*85.0

307d,8001 b

.1 366

22

2

6

musec

mmm A

mmmm

mkN M ve

S J

V

!!vv!

!

v

!

!!

!


Bottom /148 6.1212 601000700001 8.0

1 800*730*250 .859.081*102

-1-1420

25*85.0

307d,8001 b

.7.24 6

22

min

min2

6

musecmmm A

mmmm

mk M ve

S J

V V

!!vv!

v!

!!!

Design Sh ort d ire ction as ex am ple 1 (lecture 11)


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Reinforcement detai ls


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M a t Foun da tion


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C h eck for pun ch ing Sh ear


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M odified load

Genera l Examp le, Ref. 2


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Genera l reinforcement detai ls

Eng. Khalid Footing-Design

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Transcript of Eng. Khalid Footing-Design