Spread/individual/isolated

footings

Course 5

March 2009

Which one is?

NP 112 – 2004 the new design code

1st design stage – geotechnical design

the footing dimensions

Df,min = max {Df1, Df2}

Df1 = hî + 10…20cm

Df2 = h poor soil

pmax ≤ α ppl

ppl = ml ( ● B ● N1 + q ● N2 + c N3)

q = ● Df

N1, N2, N3 = f( )

.max 2

6 y

ef

MNp

B L B L

N My

Load type

Effective pressure

in GF

CENTRIC

ECCENTRIC ON 1

DIRECTION

ECCENTRIC ON 2

DIRECTIONS

STAS 3300/2-85

N.P. 112-04 ( )

ef plp p

.max1, 2 ( )

ef plp p

.max1, 4 ( )

ef plp p

s s t tDeformation Limit State –

ultimate state

Deformation Limit State –

service state

Soil fill

Impervious soil

layer

i

n

ii

pz

t hE

s i

1

100

1 2

1 2

.1 1 2 3 4 .2 1 2 3 4( ) ( )p zM net c c c c F net c c c c F

actiunea fundatiei F actiunea fundatiei F

p p

stress induced by the footing F1 stress induced by the footing F2

the point of interest where

settlement is evaluated

The 2nd design stage

the structural design

• setting the stiffness option

• rigid foundation

• flexible foundation

• setting construction materials

• setting the other dimensions to complete

the foundation element(s)

• compute the necessary reinforcement as

area and no of bars – only if made of r.c.

• drawing plans of foundation details

Rigid individual footing

Foundation block made o plain concrete &

reinforced concrete pad

3D view of a rigid individual footing

Flexible

Individual

Footing

Flexible Precast

Individual Footing

Socket

footing

Rigid individual footings

When there is only the foundation block

2nd design stage – the foundation height

the rigidity angle condition tg αeff ≥ tg αmin

H

Foundation block

made of plain concrete C4/5 or C8/10

)(5,0 s

effbB

Htg

the minimum rigidity angle

Effective pressure C4/5 C8/10

(kPa)

200 1,15 1,05

250 1,30 1,15

300 1,40 1,30

350 1,50 1,40

400 1,60 1,50

600 2,00 1,85

α

Rigid individual footing

Foundation block made o plain concrete &

reinforced concrete pad

2nd design stagedimensions of the reinforced concrete pad

5,0...4,0

65,0...5,0

L

l

B

b

L

l

B

b

cc

cc

40

0;

6

minmin

minmax

2minmax,

c

c

cccc

c

Rif

R

bl

M

lb

GN

)1(;65,0

25,0

300min,

tgtg

lh

mmh

cc

c

hc

2;

2

32

minmax21

21

minmax1

0

medc

medcy

ccccx

blM

llbM

Reinforcement conditions

network of bars;

pmin = 0,1% (OB37) and 0,075% (PC52) on each direction;

min = 10mm;

dmin = 100mm and dmax = 250mm;

the longitudinal bars from the column are entering with 250mm more than the anchorage length within the pad.

3rd design stagethe height of the foundation block

the rigidity angle condition tg αeff ≥ tg αmin

2max,

6

BL

M

LB

GGNp

yfc

eff

Dfq

R

H

R’Q

R’

L’ L

2eB

BB’ 2eL

eL

eB

CONDIŢIA DE VERIFICARE Q < m Rm = 1/1,20, coeficientul condiţiilor de lucruN N Nq c; ; se determin ţie de caracteristicile de calcul

determinate pentru = 0,95, sau determinate cu

relaţiile:

ă func

{

0 0

1

2

3

5

10

2030

50

100

0,5 0,5 1,01,0

Nc

N

Nq

NcN Nq; ;

tg oI

0,1

0,2

0,3

0,4

0,50,60,7

0,80,91,0

0,1

0,20,30,4

0,50,60,70,80,9tg o=

1,0

tg tg

i

i

0 0,5 1,0

0,1

0,2

0,3

0,40,5

0,60,7

0,80,91,0

0,1

tg o=1,0

tg tg

0,20,3

0,4

0,50,6

0,7

0,8

0,9iq

iq

0 0,5 1,0

0,1

0,2

0,3

0,40,5

0,60,7

0,80,91,0

tg tg

ic

ic

0,1

0,2

tg o=1,0

0,3

0,4

0,50,6

0,70,80,9

STAS 3300/2-1985 SNIP II-15-74

SNIP II-15-74

T.G.L. 11464-1970

T.G.L. 11464-1970

SOLICITARE COEFICIENŢII DECAPACITATE PORTANTĂ

COEFICIENŢIIDE ÎNCLINARE

COEFICIENŢII DE FORMŢIEI

ĂAI TĂLPII FUNDA

Fundaţie continuă

Fundaţie continuă

Bearing capacity – Ultimate Limit State