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9.0) Design of pile cap :

9.1) Pile cap is designed by Truss analogy method as per IRS CBC / Cl. 15.8.3.1 for ULS load cases . The truss model for the pile caps

is shown in fig 3A.Pile cap is checked for crack width for load cases 301 to 304 as per IRS CBC / Cl.15.9.8.2.1 (a).Critical section for

crack width is considered at the face of equivalent square pier.Critical section is considered at x - x & y - y as shown in Sketch - 1

Pile cap is also checked for bending and shear due to uplift forces.

Max pile reaction : Mem 401 = 6641 kN ( Ref Cl. 7.1.4 / Load Case 401 )

Max pile reaction : Mem 601 = 2511 kN ( Ref Cl. 7.2.4 / Load Case 405 ) TransverseEccentricity = 0.75 m

1.078 1.08

C/C distance between piles 1.5

Along Longitudinal direction = 3 m

Along Transverse direction = 3 m

C/C distance between C.G. of = 0.844 m 1.078 0.33

Pier quandrant 0.75

Dimensions of pile cap = 3

L B D Longitudinal

4.5 x 4.5 x 2.3 m

Pier size Pier Dia. = #REF! m 1.83 2.25

clear cover = 0.075 m 0.844

3

Dia. Of reinf. = 0.025 m

Effective depth d = 0.9 *( 2300 - 75 - 2.5 x 25 ) = 1946 mm

= 1.946 m

A) Total tension to be resisted by steel reinforcement in longitudinal direction

Considering max pile reaction at mem no. 401 :

Tensile force = Pile reaction x 1.078 = 6641 x 1.08 = 3678 kN

1.946 1.95

Area of steel required = 3678 x 1000 = 8456 mm2

0.87 x 500

80% of reinforcement is provided in pile strip and remaining is provided in the middle strip.

Provide Reinforcement

15 N T 25 i i A t 73632

Pil h d t i O K

301 401

501 601

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Tensile force = Pile reaction x 0.328 = 6641 x 0.33 = 1134 kN

1.921 1.92

Area of steel required = 1134 x 1000 = 2606 mm2

0.87 x 500

Provide Reinforcement

15 Nos. - Tor 25 giving Ast= 7363 mm2

Pile head strip O.K.

3 Nos. - Tor 25 giving Ast= 1473 mm2

Half Middle strip

Total As t= 8836 mm2

O.K.

B-2) Considering max pile reaction at mem no. 601 :

Tensile force = Pile reaction x 1.828 = 2511 x 1.83 = 2389 kN

1.921 1.92

Area of steel required = 2389 x 1000 = 5492 mm2

0.87 x 500

Provide Reinforcement

15 Nos. - Tor 25 giving Ast= 7363 mm2

Pile head strip O.K.

3 Nos. - Tor 25 giving Ast= 1473 mm2

Half Middle strip

Total As t= 8836 mm2

O.K.

Pt provided = 0.20 As t= 3927 mm2/m

The reinforcement will be provided with L-bend.

Thus basic development length = 42*bar dia. * 0.7 = 735 mm

Availble anchorage length = 750 - 75 = 675 mm > 735

UNSAFE: increase bend length

Length of standard hook with 90 degree bend is 10*bar dia.

In present case length hook will be 14*bar dia + ( 735 - 675 ) to satisfy the bevelopment length check

i.e. bend length required will be = 350 + 60 = 410 mm

Provide bend length of 450 mm > 410 SAFE

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9.1.2) Bending in pilecap due to uplift :

Piles are also subjected to uplift under ultimate loads. Thus pilecap will be subjected to bending causing

tension on pilecap top surface. Pilecap is designed by bending theory for this case.

As per appendix E, Member no. 501 & 601 are subjected to uplift & corresponding minimum force.

These are tabulated below :

Mem no. 501 601

Sr. Load ULS Load Combination V V total V

No. case kN kN kN

1 401 1.25DL+2SIDL+1.75LLa1 -56 823 767

2 402 1.25DL+2SIDL+1.75LLb1 16 493 509

3 403 1.25DL+2SIDL+1.75LLc1 565 1407 1972

4 404 1.25DL+2SIDL+1.75LLd1 63 920 983

5 405 1.25DL+2SIDL+1.6EQL2 345 2511 2855

6 406 1.25DL+2SIDL+1.6EQT2 73 143 215

7 407 1.25DL+2SIDL+1.25EQL2+1.75*0.5LLa3 -140 1967 1827

8 408 1.25DL+2SIDL+1.25EQL2+1.75*0.5LLb3 -108 1801 1692

9 409 1.25DL+2SIDL+1.25EQL2+1.75*0.5LLc3 166 2256 2422

10 410 1.25DL+2SIDL+1.25EQL2+1.75*0.5LLd3 -83 2015 1932

11 411 1.25DL+2SIDL+1.25EQT2+1.75*0.5LLa3 -353 118 -235

12 412 1.25DL+2SIDL+1.25EQT2+1.75*0.5LLb3 -321 -49 -370

13 413 1.25DL+2SIDL+1.25EQT2+1.75*0.5LLc3 -47 406 360

14 414 1.25DL+2SIDL+1.25EQT2+1.75*0.5LLd3 -295 165 -130

15 415 1.25DL+2SIDL+1.6WLL1 952 1022 1973

16 416 1.25DL+2SIDL+1.75*0.5LLa1+1.25*WLL2 -19 455 436

17 417 1.25DL+2SIDL+1.75*0.5LLb1+1.25*WLL2 17 291 307

18 418 1.25DL+2SIDL+1.75*0.5LLd1+1.25*WLL2 49 508 557

19 419 1.25DLC1 -1359 -1360 -2718

20 420 1.25DLC2 -1436 -1056 -2492

Total downward load on one side of pilecap = -2718 kN ----- Refer Load Case 419

Eqvivalent square of pier = #REF! m

Distance of pile from pilecap center = 1.5 m

Bending moment BM in pilecap @ face of (eqvivalent square) pier

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Design about x - x axis :

ULS moment = 69 kN-m

Concrete capacity = 305 kN-m > 69 Safe

Provided Y12 @ 200 c/c giving Ast= 565 mm2/m 0.18 %

(Note : Max bar in one layer = 10 Nos )

Ult. Moment capacity = 0.87 fy Ast z d = 75 kN-m/m Safe

z = (1-1.1 fy As/ fck b d ) *d = 0.95

z eff = 0.95

Shear reinforcement : ( Ref. IRS CBC / tab. 15 & 16 )

Shear stress = 2718 #REF! 0.319 = #REF! Mpa

s. Vc = 0.370 x 1.12 = 0.414 Mpa ####

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9.3.2) Design for bending in X-direction

Unit width = 1.000 m

Raft depth = 0.350 m

clear cover = 25 mm

Stirrup dia. = 0 mm

Deff = 0.32 m

Conrete grade = 20 MPa

12 @ 95

Ast= 1190 mm2/m Pt = 0.37 %

9.3.3) Check crack width :

SLS moment = 46 kN-m /m ( Refer Appendix- E, BM contour diagram for load case 301 )

Es = 195000 Mpa conc. Grad 20 Mpa

h = 350 mm Cover = 25 mm

d = 319 mm

pt = 0.0037 m = 14.00 m pt = 0.052248 n= 0.27520464

j = 0.908265 fst = 133 e1= 0.000681

cover = 25 mm spacing = 95 bar dia = 12 acr = 50.72

dc = 88 mm h = 350 (h-dc) = 262 e1= 0.000772

Strain Reduction #REF!

bt = 1000 a' = 350 As = 1190 #REF!

Mq = #REF! Mg = #REF! em = #REF!

Crack width = 3 acr.em/(1+2(acr-cnom)/(h-dc)) ( Cl 15.9.8.2.1 (a) ) = #REF! mm < 0.1

#REF!

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