Design of Footing for Edge Column1

5/27/2018 Design of Footing for Edge Column1

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DESIGN OF FOOTING FOR EDGE COLUMN

Data :-

Load from side or edge column = 200 KN

Column size = 230 x 230 mmSBC of soil =120 KN /m

2

Concrete Mix =M20

Steel Grade = Fe 415Clear cover of bottom slab =50 mm

Design :-

1. SIZE OF FOOTING :

Load on column P =200 KNSelf weight of footing 10% = 20 KN

-------Total load on soil P1 220 KN

---------

SBC of soil =120 KN/m2

Area of footing required = 220 / 120 =1.83 m2

Provide 1.50 x 1.50 m square footing.

Area provided =2.25 m2 > 1.83 m2

2. NET UPWARD SOIL PRESSURE :

Load from column =200 KN

Area of footing =2.25 m2

Net upward soil pressure p =200 / 2.25 =88.90 KN/m2

< 120 KN/m2(SBC) O.K.

3. FOOTING SLAB :

Provide overall depth of slab =250 mm

Bending moment = 88.9 x 0.6352/2


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=17.90 KN.m

Factored moment Mu =1.5 x 17.90 =26.90 KN.m

K=Mu /b d2 = 26.90 x 106/ 1000 x 1822 = 0.81

100 Pt from Table 2 of Design Aid =0.236

Ast = 0.236/100x1000x 182 =430 mm2

Provide 10 RTS @ 150 mm C / c (Ast=524 mm2

430 mm2 ).

Distributors:

Minimum Ast =0.20/100x1000x 250 =500 mm2

Provide 10 RTS @ 150 mm C / c (Ast=524 mm2

500 mm2 )


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4. BEAM DESIGN :

Load /m run on beam

Load from footing slab } = 56.50 KN/m

88.90 x 0.635

Self weight of beam assuming size as 300 x 600 mm

0.30 x (0.60 0.25) x 25 =26 KN/m

--------- Total udl w = 59.10 KN/m ----------Span l =1.50 m

Maximum bending moment =wl2/2

= 59.10 x 1.502/2

= 66.49 KN.m

Factored B.M. =1.50 x 66.49

=99.74 KN.m

Torsional moment =88.90 x 0.6352/2

=17.92 KN.m

Tu = 1.5 x 17.92 =26.88 KN.m

Mt = Tu (1+ D/b) = 26.88 (1 + 0.60/0.30)1.7 1.7

= 47.44 KN.m

Mu > Mt


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Equivalent B.M. Me = 99.74 + 47.44

= 147.18 KN.m

K = 147.18 x 106 = 1.77

300 x 5262

100 Pt from Table 2 of Design Aid = 0.553

Ast = 0.553 x 300 x 526 100

=872.63 mm2

Provide 3 Nos. 20 RTS 2 bottom. Provide 3 Nos.

16 RTS @ top. (Ast = 942 mm2 > 872.63 mm2 ).

Check for shear:

Maximum Shear Force = 59.10 x 1.50 = 88.65 KN.

Factored SF Vu = 1.5 x 88.65 = 132.98 KN.

Equivalent Shear Ve = Vu + 1.6 Tu /b

= 132.98 + {1.6 x 26.88 x10 3/300 }

= 132.98 + 143.36

=276.34 KN

Shear stress = 276.34 x 103

300 x 526

=1.75 N/ mm2 < 2.80 N/mm2 O.K.

Pt = 942 x100

300 x 526

=0.60


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c from Table 61 Design Aid =0.51 N/mm2

Asv = Tu Sv + Vu Sv b1d1(0.87 Fy) 2.5 d1 (0.87 Fy)

b1= 300-25-25-20-8 =222 mm

d1= 600- 50-8-10-50-8-8=466 mm

Asv= (0.87 x fy) = 26.88 x 106 + 132.98 x 103

Sv 222 x 466 2.5 x 466

= 260 + 114.24

= 374.24 mm

Asv x( 0.87 fy) = (1.75 -0.51) x 300 Sv

=372 mm

Using 8 RTS stirrups spacing Sv = 2x 50x0.87x415 372

= 97 mm

Using 4 legged stirrups spacing Sv = 2x 97=194 mm say

180 mm c/c

X1 =shorter dimension of hoop stirrups

=300-40-8=282mm.

y1=longer dimension of hoop stirrups

=600-32-16=552mm.


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Spacing of stirrups provided should not exceed the least

of (i) x1 =282 mm

(ii) (x1 + y1 ) = (282 + 552) =208.50 mm4 4

(iii) 300 mm.

Provide 8 RTS 4 legged stirrups @ 150 mm c/c.

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Design of Footing for Edge Column1