Lessons for pilescap

1. Design note for Bored pile BP140
Ultimate load U = 10925.6 kN
Ultimate moment Mu = 100 kNm
Colum size a = 400 mm
b = 400 mm
Pile size (diameter or side of square) D = 1400 mm
Side cover cs = 75 mm
Cover of pile cap c = 75 mm
Compressive strength of concrete f'c = 25 MPa
Yield strength of steel fy = 400 MPa
Steel diameter DB = 20 mm
As1 = 314 mm2
Minor Steel diameter DB = 12 mm
As2 = 113 mm2
Clear edge cd = 150 mm
Pile type Bored pile
Location of foundation BP140
Solution
Concrete design strength
c = 1.5
fc = 25/1.5
fc = 16.67 MPa
Steel design strength
s = 1.15
fs = 400/1.15
fs = 347.83 MPa
Cap dimensions are
A = max(D,a) + 2*150 = 1400+ 2*150
A = 1700 mm
B = max(D,b) + 2*150 = 1400+ 2*150
B = 1700 mm
Suppose the height is
h = 1200 mm OK !
Wc = 86.7 kN
Wcu = 1.35*86.7
= 117 kN
Page 8 , DesignNote 1BP140

2. P = Wcu + U
= 11042.6
P = 11042.6 kN
Equivalent side C of quare pile
C= (pi()*D^2/4)^0.5
= (PI()*1400^2/4)^0.5
C= 1241 mm
Effective height of cap varies from 0.75 to 0.9 of pile or column
Take  = 0.9
d = 0.9*Max(1241, 400, 400)
d = 1117 mm
h = 1117+75
h = 1192 mm
the height multiple = 50 mm
Take h = 1200 mm, d = 1125 mm
Bottom reinforcement in A direction
Asx= P*(C-a)/(8*d*fs)
= 11042.6*1000*(1241-400)/(8*1125*347.83)
= 2966.6 mm2 = 1913.9 mm2/m
Suppose the spacing is multiples of 50 mm
mlt = 50 mm
Spacing = 150
Asx= 10DB20 = 3140 mm2
Or Asx= DB20@150 mm = 2093 mm2/m
Bottom reinforcement in B direction
Asy = P*(C-b)/(8*d*fs)
= 11042.6*1000*(1241-400)/(8*1125*347.83)
= 2966.6 mm2 = 1913.9 mm2/m
Suppose the spacing is multiples of 50 mm
mlt = 50 mm
Spacing = 150 mm
Asy = 10DB20 = 3140 mm2
Or Asy = DB20@150 mm = 2093 mm2/m
Check the bending reinforcement
d = 1603 mm
s = 100*10^6/(1700*(1603)^2*16.67)
s = 0.0014 <= 0.088, OK!
In combination with moment and axial force, the tie force can be calculated using a unique
axial load P equal to
Page 9 , DesignNote 1BP140

3. s = 0.85*(1-(1-2.353*0.0014)^0.5)
s = 0.0014
As = 0.0014*1700*1603*16.67/347.83
As = 182.8 mm2 = 107.5 mm2/m
Spacing 2900
As = DB20@2900 mm = 108 mm2/m
Vertical bars
Asx = DB20@150 mm = 2093 mm2/m
Asy = DB20@150 mm = 2093 mm2/m
The minimum reinforcement ratio is 400 mm2/m
Amin = 400 mm2/m
DB = 12 mm ,
As1 = 113.1 mm2
As = DB12@282 mm =401 mm2/m
Suppose the spacing is multiples of 150 mm
mlt = 150 mm
Spacing = 150 mm
As = DB12@150mm = 754 mm2/m
In conclusion
Top reinforcement in A direction Asx,t = DB12@150mm = 754 mm2/m
Top reinforcement in B direction Asy,t = DB12@150mm = 754 mm2/m
Bottom reinforcement in A direction Asx,b = DB20@150 mm = 2093 mm2/m
Bottom reinforcement in B direction Asy,b = DB20@150 mm = 2093 mm2/m
Horizontal reinforcement As,h = DB12@150mm = 754 mm2/m
Page 10 , DesignNote 1BP140