1) The document describes the design of a combined footing to support interior and exterior columns. Load and dimension data is provided for the columns. 2) The footing is designed to be 10.95 sqm in area and 300mm deep. Reinforcement is designed for the longitudinal and transverse beams of the footing. 3) Steel reinforcement is specified for the top and bottom of the longitudinal beams as well as the transverse beams connecting the columns. Distribution steel is also specified.

1. Combine Footing Design
Given Data:
At exterior column:
Pu at exterior column= 515.2 KN
Mux at exterior column =2.5 KN-m
Muy at exterior column =24.4 KN-m
Exterior Column Dimension=375x375 mm
Structure Design of RCC Building Manual and Excel

2. Combine Footing Design
Given Data:
At interior column:
Pu at interior column= 713.7 KN
Mux at interior column =4.5 KN-m
Muy at interior column =19.2 KN-m
Interior Column Dimension=375x375 mm
Fc’=28 MPa
Fy =420 MPa
Allowable Bearing Capacity = 1 tsf (95) KPa
Depth of Footing = 4 ft (1.2m)
Structure Design of RCC Building Manual and Excel

3. Combine Footing Design
Solution:
Pu at exterior footing = 1.1x 515.2 = 566.5 KN
Pu at interior footing = 1.1x 713.7 = 785.4 KN
Service Load = (566.5+785.4)/1.3 = 1039.92 KN
x ’ = 𝑃2𝑥𝑆
=785.4/1.3𝑥3.277
= 1.903 m
𝑅 1039.92
x1 = 0.1875
Length of footing = 2x(x’+x1) ≅ 4.2 m
Width of footing =
𝑅
= 1039.92
≅ 2.6 m
𝑞𝑥𝐿 95𝑥4.2
FinalArea of footing = 4.21x2.6=10.95 m²
Structure Design of RCC Building Manual and Excel

4. Combine Footing Design
Solution:
Center of Gravity = 3.277 / 2 = 1.6385 m
Center of Rigidity= (515.2x0+713.7x3.277)/(515.2+713.7)
= 1.9032 m
Structure Design of RCC Building Manual and Excel

5. Combine Footing Design
Pu = 1229x1.1= 1351.9 KN
qu= Pu/Af = 1351.9/(10.95)
= 123.80 KPa
Approximate depth of footing for exterior, H =
𝑃 + 1.5𝑀𝑥 + 1.5𝑀𝑦
+60 mm
/(0.01α𝑓𝑓𝑐′)
H =
/(0.01x30x28)
566.5/1.3 + 2.5𝑥𝑥/1.3 + 1.5𝑥𝑥𝑥.𝑥/1.3
+60 mm = 286 mm ≥ 250mm
Structure Design of RCC Building Manual and Excel

6. Combine Footing Design
Approximate depth of footing for interior, H =
𝑃 + 1.5𝑀𝑥 + 1.5𝑀𝑦
+60 mm
/(0.01α𝑓𝑓𝑐′)
H = 1.3
785.4
+ 1.5𝑥4.5
+ 1.5𝑥19.2/1.3
1.3
/(0.01x𝑥0x28)
+60 mm=298 mm ≥ 250mm
Take H=300 mm
Structure Design of RCC Building Manual and Excel

7. Combine Footing Design
SFD & BMD
At Point B:
• 321.88x0.187= 60.2 KN
• -566.5+60.2 = - 506.3 KN
At Point C:
• 321.88x3.277= 1054.8 KN
1054.8-506.3 = 548.5 KN
• 548.5-785.4 = - 237 KN
Structure Design of RCC Building Manual and Excel

8. Combine Footing Design
SFD & BMD
At Point D:
• 321.88x.736= 237 KN
Structure Design of RCC Building Manual and Excel

9. Combine Footing Design
SFD & BMD
At Point B:
• 60.2x0.187/2 = 5.63 KN-m
At Point C:
• 506.3 x X/2= ?
X=?
-566.5+60.2 + 321.88X=0
X=1.573 m
506.3 x 1.573/2= 398.2 KN-m
398.2 – 5.63 = 392.6 KN-m
Structure Design of RCC Building Manual and Excel

10. Combine Footing Design
SFD & BMD
• 548.5x1.704/2 = 467.3 KN-m
• 467.3-392.6= 74.722 KN-m
At Point D:
• 237x0.736/2 = 87.216 KN-m
• Diff = 87.216-69.12= 12.5 KN-m
Structure Design of RCC Building Manual and Excel

11. Combine Footing Design
One way Shear Check :
Max Shear, V = 548.5 KN
Max One way shear on right of int col, V =
548.5 – (.375-.240)x321.88 KN =411 KN
One Way Shear Capacity, φVc=0.75x0.17x√𝑓𝑓𝑐𝑓 x bxd = 411
0.75x0.17x √28x1000x d /1000 = 411 KN
d =234mm.
Again H remains same
Structure Design of RCC Building Manual and Excel

12. Combine Footing Design
Two way Shear / Punching Check :
Take H as 425mm because 300mm fails in Two way later.
Effective depth of footing , d = 425x– 60 = 365mm
Perimeter, bo = 2x(c1+d/2)+(c2+d)
Perimeter, bo =2x(375+365/2)+(375+365)
=1855 mm
Β = 375/375 = 1
Structure Design of RCC Building Manual and Excel

13. Combine Footing Design
φVc = lesser of
1) = 0.75x0.33 x λ x √𝑓𝑓𝑐𝑓 x bo x d
= 0.75x0.33 x 1 x √28 x 1855 x 365 = 886.72 KN
Β
2) = 0.75x0.17 x (1+2
)λ x √𝑓𝑓𝑐𝑓 x bo x d
1
= 0.75x0.17 x (1+2
) x 1 x √28 x 1855 x 365 = 1370 KN
b𝑜
3) = 0.75x0.083 x (αxd +2)x λ x √𝑓𝑓𝑐𝑓 x bo x d
1605
= 0.75x0.083 x (30x240
+2)x 1 x √28 x 1855 x 365 =1762kN
Structure Design of RCC Building Manual and Excel

14. Combine Footing Design
So,
φVc = 886 KN
Actual Shear , Vu = Col load - qu x {Af- (c1+d/2)(c2+d)}
= 512-123.8x {10.95-(375+365/2)/1000
x(375+365)/1000}
= 477.6 KN
So,
φVc > Vu (Depth is Ok)
Structure Design of RCC Building Manual and Excel

15. Combine Footing Design
Two way Shear / Punching Check :
Effective depth of footing , d = 425x– 60 = 365mm
Perimeter, bo = 2x(c1+d)+2x(c2+d)
Perimeter, bo =2x(375+365)+2x(375+365)
=2960 mm
Β = 375/375 = 1
Structure Design of RCC Building Manual and Excel

16. Combine Footing Design
φVc = lesser of
1) = 0.75x0.33 x λ x √𝑓𝑓𝑐𝑓 x bo x d
= 0.75x0.33 x 1 x √28 x 2960 x 365 = 1415 KN
Β
2) = 0.75x0.17 x (1+2
)λ x √𝑓𝑓𝑐𝑓 x bo x d
1
= 0.75x0.17 x (1+2
) x 1 x √28 x 2960 x 365 = 2187 KN
b𝑜
3) = 0.75x0.083 x (αxd +2)x λ x √𝑓𝑓𝑐𝑓 x bo x d
1605
= 0.75x0.083 x (𝑥0x240
+2)x 1 x √28 x 2960 x365 =2467 kN
Structure Design of RCC Building Manual and Excel

17. Combine Footing Design
So,
φVc = 1415 KN
Actual Shear , Vu = Col load - qu x {Af- (c1+d)(c2+d)}
= 714-123.8x {10.95-(375+365)/1000
x(375+365)/1000}
= 646 KN
So,
φVc > Vu (Depth is Ok)
Structure Design of RCC Building Manual and Excel

18. Combine Footing Design
Area of Steel :
Top Longer Steel:
Bending Moment, Mu = 392.6 KN-m
𝑏𝑑2
R= 𝑀𝑢
= 1.1158
W=0.85𝑓𝑓𝑐′
= 0.85𝑥28
= 0.056667
𝑓𝑓𝑦 420
Ro = Wx(1- 1 − 2.614𝑥𝑅
) = 0.00307 > 0.002 (OK)
𝑓𝑓𝑐𝘍
Area of Steel = Ro x b x d = 0.00303 x 2600 x 365 = 2924 𝑚𝑚2
#19 @ 230 c/c
Structure Design of RCC Building Manual and Excel

19. Combine Footing Design
Area of Steel :
Bottom Longer Steel Under Interior Column:
Bending Moment, Mu = 74.722 KN-m
𝑏𝑑2
R= 𝑀𝑢
= 0.215
W=0.85𝑓𝑓𝑐′
= 0.85𝑥28
= 0.056667
𝑓𝑓𝑦 420
Ro = Wx(1- 1 − 2.614𝑥𝑅
) = 0.00057 < 0.002 (Provide minimum steel)
𝑓𝑓𝑐𝘍
Area of Steel = 0.002x b x h = 0.002 x 2600 x 425 = 2215 𝑚𝑚2
#16 @ 215mm c/c
Structure Design of RCC Building Manual and Excel

20. Combine Footing Design
Area of Steel :
Bottom Longer Steel Under exterior Column:
Bending Moment, Mu = 5.63 KN-m
Here moment is much lesser but for additional safety we ‘ll provide
Minimum area of steel.
Area of Steel = 0.002x b x h = 0.002 x 2600 x 425 = 2215 𝑚𝑚2
#16 @ 215 c/c
Structure Design of RCC Building Manual and Excel

21. Combine Footing Design
Area of Steel :
Design of Transverse Beam Under Exterior Column:
Approximate width of beam = c1+d/2
= 375+365/2 = 557.5 mm
Load on transverse beam = Pu/B = 714/2.6 = 197.69 KN/m
Bending Moment, Mu = Load x 𝑙2 / 2
=197.69x
(2600/2−375/2) 2
2
=123 KN – m
Structure Design of RCC Building Manual and Excel

22. Combine Footing Design
Area of Steel :
Design of Transverse Beam Under Exterior Column:
Bending Moment, Mu = 123 KN-m
𝑏𝑑2
R= 𝑀𝑢
= 1.656
W=0.85𝑓𝑓𝑐′
= 0.85𝑥28
= 0.056667
𝑓𝑓𝑦 420
Ro = Wx(1- 1 − 2.614𝑥𝑅
) = 0.00456 > 0.002 (Ok)
𝑓𝑓𝑐𝘍
Area of Steel = 0.00456x b x d = 0.00456 x 557.5x 365 = 929 𝑚𝑚2
#19 @ 140mm c/c or #25 @ 275mm c/c
Structure Design of RCC Building Manual and Excel

23. Combine Footing Design
Area of Steel :
Design of Transverse Beam Under interior Column:
Approximate width of beam = c1+d
= 375+365 = 740 mm
Load on transverse beam = Pu/B = 714/2.6 = 273.8 KN/m
Bending Moment, Mu = Loadx 𝑙2 / 2
=273.8x
(2600/2−375/2) 2
2
=170.4 KN – m
Structure Design of RCC Building Manual and Excel

24. Combine Footing Design
Area of Steel :
Design of Transverse Beam Under Exterior Column:
Bending Moment, Mu = 170.4 KN-m
𝑏𝑑2
R= 𝑀𝑢
= 1.992
W=0.85𝑓𝑓𝑐′
= 0.85𝑥28
= 0.056667
𝑓𝑓𝑦 420
Ro = Wx(1- 1 − 2.614𝑥𝑅
) = 0.00553 > 0.002 (Ok)
𝑓𝑓𝑐𝘍
Area of Steel = 0.00456x b x d = 0.00553 x 740x 365 = 1394 𝑚𝑚2
#19 @ 145mm c/c or #25 @ 245mm c/c
Structure Design of RCC Building Manual and Excel

25. Combine Footing Design
Area of Steel :
Distribution Steel:
Area of Steel = 0.002x b x h = 0.002 x 1000 x 425 = 850 𝑚𝑚2
#16 @ 200 c/c
Structure Design of RCC Building Manual and Excel