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Transcript of C5
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