Pile Cap Design

GENERAL DETAILS OF THE PILES, COLUMNS AND PILE CAP Axial load on column= 35000 kN Column size = 1200 mm x 1200mm square Pile diameter = 1500 mm No. of piles connected by the pile cap = 4 Center to center distance in between piles = 4500 mm

D

C 1200 mm

1200 mm

4500 mm

1500mm

B

A

4500 mm a N

C

C

d

T

N/2

N/2

2L = 4500 mm As this is a symmetric structure

TAB = TBC

=

TCD = TDA=



N 3L2  a 2 12 Ld



Average effective depth of pile cap = 2500 mm Total depth can be taken as about 2625mm allowing for 75 mm cover and bar spacing Width of the cap = 4500+750 X 2+250 X 2 = 6500 mm

TAB = TBC = TCD = TDA=

TAB = TBC



N 3L2  a 2 12 Ld



7688.33 103 N = TCD = TDA= 0.87  460 N / mm 2

= 7688.33 kN TAB = TBC = TCD = TDA = 0.87 fy As 7688.33 kN = 0.87 X 460 As As =

7688.33 10 3 N 0.87  460 N / mm 2

= 19211.22 mm2 Assume 32 mm bars No of bars =

19211.22 = 23.887 bars   322  4

Hence provide 24 Nos of 32 mm diameter bars @ 270 mm spacing As provided

= 24 X 804.25 = 19302 mm2 in both directions

Distribute the bars along the section uniformly as Spacing of piles = 3 times pile diameter 4500 = 3 X 1500 Min r/f check 100 As 100 19302  2   0.2263  0.13 bh 6500  2625

Hence more than minimum provided Check for shear 100 As 100 19302  2   0.238 bd 6500  2500

Corresponding shear resistance 1/3

1/4

1/3

 100 As   400   fcu  0.79         bvd   d   25  

m

0.79  .238  1  1.2  1/3



= 0.416 N/mm2

1.25

1/4

1/3

Enhanced shear resistance value  

2d Vc av 2  2500  0.416 1200

= 1.733 N/mm2

35000 103 2 Shear stress along the critical section = 6500  2500 =1.0938N/mm2 < 1.733 N/mm2 Hence ok for shear and no shear reinforcement needed Check for punching shear Punching shear check is not necessary as Spacing of piles =3 times pile diameter 3750 =3 X 1500 Shear at the face of the column =

35000 103 4 1200  2500

= 2.917 N/mm2 < 4.38 = 0.8 fcu Anchorage Anchorage length

= 37 times diameter of the main bar = 37 X 32 = 1184 mm

Horizontal binders Use 25 % of main steel required as horizontal binders Binders

= 0.25 X 19211.22 = 4802.805mm2

Hence provide 16 T20 bars as horizontal binders at 150 mm spacing Reinforcement provided as binders= 314.2 x 16 = 5027.2 mm2

Detail drawing of the pile cap

DESIGN OF A PILE CAP

NAME

:

R.M. RIFDY

INDEX

:

080425E

COURSE

:

BSc Eng

MODULE

:

CE4240 COMPUTER ANALYSIS OF STRUCTURES