Design Of Square Footing

DESIGN OF SQUARE FOOTING Design Constants: fc’ = 21 MPa fc = 9.45 MPa fs = 124 MPa n = 10 γconrete = 23.6 kN/m3 Covering = 40 mm k = 0.432 j = 0.856 R = 1.75 va  0.09 f c '  0.412 MPa v p  0.17 f c '  0.779 MPa

LL = 1.9 kN/m2 Allowable Soil Pressure = 143 kPa Total Service Load, Ptotal: From design of axially loaded column P5 = 358.33 kN load @ 5th floor P = 5P5 + Weight of column 5 + Weight of column 4 + Weight of column 3 + Weight of column 2 + Weight of column 1 P = 358.33(5) + 0.2542 (4)(23.6) + 0.3352(4)(23.6) + 0.412 (4)(23.6) + 0.4752 (4)(23.6) + 0.532 (4)(23.6) P = 1872 kN Ptotal = P + 6% of P Ptotal = 1872 + ( 0.07 ) 1872 Ptotal =2003.04 kN Wt. of footing = 0.07(1872) = 131.04 kN Required Area: P S  total A A

2003 143

A = 14 m2 L2 = 14 L = 3.7 m

Try 3.7 m x 3.7 m Footing Effective Depth: 2003 3.7 2 Net Upward Soil Pressure = 146.31 kN/m2 Net UpwardSoil Pressure 

( From Bending ) d

M Rb

 1.585  M  146.31(3.7)(1.585)   2 

M = 680.13 kN-m d 

673.441x10 6 1.75(3700)

d = 324.09mm Says d = 350 mm Try d = 250 + 200

d =550 mm ( Check Shear ) V bd V = 144.9 ( 1.035 ) ( 3.7 ) V = 560.29 kN v

v

560.29 (10  3 ) 3.7(0.55)

v = 0.275 MPa < 0.412 MPa (safe)

( Check Punching Shear ) vp 

Vp

Ap Vp = 146.31 [(3.7)2 - (1.08)2] Vp = 1832.33 kN vp 

183.2.33 1.08(0.55)(4)

(10  3 )

vp = 0.771 MPa < 0.779 MPa (safe) Use d = 550 mm Steel Reinforcement: (Using 28 mm Ф bars) M As  f s jd As 

680.13x10 6 124(0.856)(550)

As = 11650.21 mm2  (d ) 2 N  As 4  2 4

(28) N  11650.12

N = 18.92 Says N = 19-28 mm Ф bars bothways Use 19-28 mm Ф bars bothways Check Bond Stress: V u  o jd V = 146.31 ( 1.585 ) ( 3.7 ) V = 858 kN u

858(1000)  (28)19(0.856)(550)

u = 1.09 MPa < 1.859 MPa (safe) Check for Weight: Total depth = 550 + 75 + 14 Total depth = 639 mm Wt. of footing = 0.639 (3.7)2 (23.6) Wt. of footing = 206 kN > 112.32 kN (safe)