Pile CAP Design Example + 2 piles

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3/25/2015

RC PILE CAP DESIGN (BS8110:PART1:1997) TEDDS calculation version 2.0.02

Loaded width - x

2 Pile Cap, height h

s e ex

b P1

x

 P2

e

L Pile Cap Design – Truss Method Design Input - 2 Piles - No Eccentricity Number of piles;

N=2

ULS axial load;

Fuls = 31500.0 kN

The ultimate load per pile;

Fuls_pile = Fuls/2 = 15750.0 kN

Characteristic axial load;

Fchar = 21500.0 kN

The characteristic load per pile;

Fchar_pile = Fchar/2 = 10750.0 kN

Pile diameter;

 = 1800 mm

Pile spacing;

s = 4500 mm

Pile cap overhang ;

e = 200 mm

Overall length of pile cap;

L = s +  + 2  e = 6700 mm

Overall width of pile cap;

b =  + 2  e = 2200 mm

Overall height of pile cap;

h = 3000 mm

Dimension of loaded area;

x = 1500 mm; (parallel to pile cap)

Cover Concrete grade;

fcu = 40.0 N/mm2

Nominal cover;

cnom = 100 mm

Tension bar diameter;

Dt = 32 mm

Link bar diameter;

Ldia = 10 mm

Depth to tension steel;

d = h – cnom - Ldia - Dt/2 = 2874 mm

Pile Cap Forces Compression within pile cap;

Fc = Fuls/(2  sin()) = 20002.5 kN

Tension within pile cap;

Ft = Fc  cos() = 12330.4 kN

Compression In Pile Cap - Suggested Additional Check Check compression diagonal as an unreinforced column, using a core equivalent to pile diameter Compressive force in pile cap;

Pc = 0.4  fcu    2/4 = 40715.0 kN PASS Compression Cl. 3.8.4.3

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2 Calc. by

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3/25/2015

Tension In One Truss Member Characteristic strength of reinforcement;

fy = 500 N/mm2

Partial safety factor for strength of steel;

ms = 1.15

Required area of reinforcement;

As_req = Ft /(1/ms  fy) =28360 mm2

Provided area of reinforcement;

As_prov = Ast = 33778 mm2

Tension in truss member;

Pt = (1/ms  fy)  As_prov = 14686.3 kN PASS Tension Cl. 3.11.4.2

Max / Min Areas Of Reinforcement Minimum area of tension steel;

Ast_min = kt  Ac = 8580 mm2

Maximum area of tension steel;

Ast_max = 4 %  Ac = 264000 mm2 Area of tension steel provided OK Cl. 3.12.6 & Table 3.25

Shear Applied shear stress Aplied Shear stress;

V = Fuls / 2 = 15750.0 kN

Width of pile cap shear plane;

bv = min( b, 3   ) = 2200 mm

Design shear stress;

v = V / (bv  d) = 2.49 N/mm2

Allowable shear stress;

vallowable = min ((0.8 N1/2/mm)  (fcu ), 5 N/mm2 ) = 5.00 N/mm2 Shear stress - OK Cl. 3.4.5.2

Design concrete shear strength Determine concrete shear strength on the section at distance / 5 inside face of pile: Cl. 3.11.4.3 & fig. 3.23

Shear stress - Table 3.8; vc_25 = 0.79  r1/3  max(0.67, (400 mm/d)1/4)  1.0 N/mm2 / 1.25 = 0.34 N/mm2 Shear stress - Cl. 3.4.5.8 & fig. 3.5;

vc = vc_25  ( min( fcu, 40 N/mm2 ) / 25 N/mm2 )1/3 = 0.40 N/mm2

Spacing;

av = min( 2  d, max( ( s / 2 - / 2 + / 5 - x / 2 ), 0.1 mm )) = 960 mm

Enhanced shear stress;

vc_enh = min( vallowable , 2  d  vc / av) = 2.41 N/mm2 Concrete shear strength - NOT OK, provide MINIMUM links

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Sheet no./rev.

3 Calc. by

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3/25/2015

Deflection Check (Cl 3.4.6) Redistribution ratio;

b = 1.0

Design service stress in tension reinforcement;

fs = 2  fy  As_req /(3  As_prov  b) = 279.9 N/mm2

Modification for tension reinforcement; factortens = min( 2, 0.55 + (477 N/mm2 - fs)/(120  (0.9 N/mm2 + Ft /(bd )))) = 1.126 Modified span to depth ratio;

modfspan_depth = factortens  basicspan_depth = 22.5

Span of pile cap for deflection check;

Ls = 4500 mm

Actual span to depth ratio;

actualspan_depth = Ls /d = 1.57 PASS - Deflection