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RC combined footing spreadsheet
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COMBINED FOOTING DESIGN PROGRAMME USING LIMIT STATE METHOD
General information
300 260.87
Concrete grade = 25
20.00 11.33
1.04
= ###
= ###
250
3.00
18.00
0.30
0.30
Sizing the footing
Footing group F6
272.00 440.00
Resultant force, R = 712.00
Distance b/n the two columns, x 1.00
= 0.62
Projection from the face of the lighter co 0.60
Footing length L (m) = 2.74 Use 2.80m
Depth, D (m) 0.30
Effective depth, d (m) = D - 0.05 = 0.25
= 193.90
= 3.67
Footing width, W (m) = A/L = 1.34 Use 1.40m
= 213.35
= 381.35
= ###
= ###
= 79.32
= ###
Longitudinal reinforcement
136.00
N = 0.19
B = 1 -(1 - 2*N)^0.5 = 0.22
= ###
= 416.67
20.00
314.29
= 134.50
= 754.29
Final
Transverse reinforcement
44.51
N = 0.06B = 1 -(1 - 2*N)^0.5 = 0.06
= 705.31
= 416.67
14.00
154.00
= 218.34
= 369.60
Final
Take rho = rmin = 0.002
fyk = fyd= fyk/1.15
fck =concrete grade/1.25 = fcd= 0.85*fck/1.5
fctd = 0.21*((fck)^0.67)/1.5 = Allowable punching resistance of concrete, Vup(KPa) = 0.5fctd(1+50*rho)
Allowable wide beam shear resistance of concrete, Vud (KN/m2) = 0.25fctd(1+50*rho)
Allowable bearing pressure, Pall (KPa)
Foundation depth, fd (m)
Unit weight of soil, γs (KN/m3)
Width of column 1, a1 (m)
Width of column 2, a2 (m)
Loads: P1 (lighter) and P2 (heavier) (KN)
= P1 + P2
Centroid of the footing from P1, e = (P2 * x)/R
= 2*(r + a1/2 + e)
Net soil pressure, Pnet (KPa) = Pall-[D*γc+ (fd-D)*γs]
Actual area, A(m2) = R/Pnet
Punching shear (column 1) Vp1 (kN) = P1-Pnet (a1+d)^2
Punching shear (column 2) Vp2 (kN) = P2-Pnet (a2+d)^2 Punching shear stress (column 1) Vps (KPa)
= Vp1/(4(a1+d)*d) Punching shear stress (column 2) Vps (KPa)
= Vp2/(4(a2+d)*d)
Wide beam shear (column 2) Vw2 (KN) = P2-Pnet[(r+2e+(a1+a2)/2+d-x)W]
Wide beam shear stress (column 2) Vws (KPa) = Vw2/(b*d)
Design moment, Md (KN-m/m) = (Md*10^6/fcd*b*d^2)
As = B*fcd*b*d/fyd
Asmin = 0.5/fyk*b*d
Diameter Φ (mm)
Asing = 3.14*Φ^2/4
Spacing for As = Asing*1000/As
Spacing for Asmin = Asing*1000/Asmin
use Φ20 c/c 130
Design moment, Md (KN-m/m) = 0.5*(P2/(1*W)) ((W-a2)/2)^2 = (Md*10^6/fcd*b*d^2)
As = B*fcd*b*d/fyd
Asmin = 0.5/fyk*b*d
Diameter Φ (mm)
Asing = 3.14*Φ^2/4
Spacing for As = Asing*1000/As
Spacing for Asmin = Asing*1000/Asmin
use Φ14 c/c 200
