2 Piles Cap Design Bs8110 3516t

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RC PILE CAP DESIGN (BS8110:PART1:1997) TEDDS calculation version 2.0.07

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 - With Eccentricity Number of piles;

N=2

ULS axial load;

Fuls = 361.0 kN

Characteristic axial load;

Fchar = 246.0 kN

Pile diameter;

 = 150 mm

Pile spacing;

s = 450 mm

Eccentricity from centroid of pile cap;

ex = 75 mm

The characteristic load in pile, 1 is;

Fchar_pile_1 = Fchar  (s/2 - ex)/s = 82.0 kN

The characteristic load in pile, 2 is;

Fchar_pile_2 = Fchar  (s/2 + ex)/s = 164.0 kN

Pile cap overhang ;

e = 200 mm

Overall length of pile cap;

L = s +  + 2  e = 1000 mm

Overall width of pile cap;

b =  + 2  e = 550 mm

Overall height of pile cap;

h = 800 mm

Dimension of loaded area;

x = 300 mm; (parallel to pile cap)

Cover Concrete grade;

fcu = 25.0 N/mm2

Nominal cover;

cnom = 50 mm

Tension bar diameter;

Dt = 16 mm

Link bar diameter;

Ldia = 12 mm

Depth to tension steel;

d = h – cnom - Ldia - Dt/2 = 730 mm

Pile Cap Forces Maximum compression within pile cap;

Fc = max(Fc1, Fc2) = 245.7 kN

Maximum tension within pile cap;

Ft = max(Ft1, Ft2) = 49.5 kN

Tension In One Truss Member Characteristic strength of reinforcement;

fy = 460 N/mm2

Partial safety factor for strength of steel;

ms = 1.15

Required area of reinforcement;

As_req = Ft /(1/ms  fy) =124 mm2

Provided area of reinforcement;

As_prov = Ast = 804 mm2

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13/5/2015 Pt = (1/ms  fy)  As_prov = 321.7 kN

Tension in truss member;

Tension Cl. 3.11.4.2

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

Ast_min = kt  Ac = 572 mm2

Maximum area of tension steel;

Ast_max = 4 %  Ac = 17600 mm2 Area of tension steel provided OK Cl. 3.12.6 & Table 3.25

Shear Applied shear stress Shear force pile 1;

V1 = Fuls_pile_1 = 120.3 kN

Shear force pile 2;

V2 = Fuls_pile_2 = 240.7 kN

Width of pile cap shear plane;

bv = min( b, 3   ) = 450 mm

Shear stress pile 1;

v1 = V1/(bv  d) = 0.37 N/mm2

Shear stress pile 2;

v2 = V2/(bv  d) = 0.73 N/mm2

Allowable shear stress;

vallowable = min ((0.8 N1/2/mm)  (fcu ), 5 N/mm2 ) = 4.00 N/mm2 Shear stress - OK Cl. 3.4.5.2

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

Shear stress - BS8110-1:1997 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 Enhanced shear stress - Cl. 3.4.5.8 & fig. 3.5;

vc = vc_25  ( min(fcu, 40 N/mm2 )/25 N/mm2 )1/3 = 0.34 N/mm2 av_1 = min(2  d, max(s/2 + ex - /2 + /5- x/2, 0.1 mm)) = 105 mm av_2 = min(2  d, max(s/2 - ex - /2 + /5- x/2, 0.1 mm)) = 0 mm

Concrete shear strength - Case 1;

vc_enh_1 = min( vallowable , 2  d  vc / av_1 ) = 4.00 N/mm2

Concrete shear strength - Case 2;

vc_enh_2 = min( vallowable , 2  d  vc / av_2 ) = 4.00 N/mm2 Concrete shear strength - OK, no links reqd. for case 1 Concrete shear strength - OK, no links reqd. for case 2 Table 3.16

Note: If no links are provided, the bond strengths for PLAIN bars must be used in calculations for anchorage and lap lengths. Cl. 3.12.8.3

Clear Distance Between Bars In Tension (Cl 3.12.11.2.4) Bar spacing; spacingbars = max( 0mm, (b- 2 (cadopt + Ldia) - Dt)/(Lnt - 1) - Dt) = 121 mm Maximum allowable spacing;

spacingmax = min((47000 N/mm)/fs, 300 mm) = 300 mm

Minimum allowable spacing;

spacingmin = hagg + 5 mm = 25 mm Bar spacing OK

Clear Distance Between Face Of Beam And Tension Bars (Cl 3.12.11.2.5) Distance to face of beam;

Distedge = cadopt + Ldia + Dt/2 = 70 mm

Design service stress in reinforcement;

fs = 2  fy  As_req /(3  As_prov  b) = 47.1 N/mm2

Max allowable clear spacing;

Spacingmax = min((47000 N/mm)/fs, 300 mm) = 300 mm

Max distance to face of beam;

Distmax = Spacingmax /2 = 150 mm Max distance to beam edge check - OK

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Anchorage Of Tension Steel Anchorage factor;

factor =44

Type of lap length;

lap_type ="tens_lap"

Type of reinforcement;

reft_type = "def2_fy500"

Minimum radius;

rbar = 32 mm

Minimum end projection;

Pbar = 130 mm

Minimum anchorage length or lap length req’d;

Ltable 3.27 = factor  Dt = 704 mm

Check anchorage length to cl. 3.12.9.4 (b);

Lcl. 3.12.9.4 = 12  Dt + d/2 = 557 mm

Required minimum effective anchorage length;

La = max(Ltable 3.27, Lcl. 3.12.9.4) = 704 mm

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) = 47.1 N/mm2

Modification for tension reinforcement; factortens = min( 2, 0.55 + (477 N/mm2 - fs)/(120  (0.9 N/mm2 + Ft /(bd )))) = 2.000 Modified span to depth ratio;

modfspan_depth = factortens  basicspan_depth = 40.0

Span of pile cap for deflection check;

Ls = 1000 mm

Actual span to depth ratio;

actualspan_depth = Ls /d = 1.37 - Deflection