# Strip Footing Capacity

This tool calculates the bearing, shear, and flexural capacity of a strip footing in accordance with CSA A23.3

Materials:
psi
ksi
Geometry:
in
in
in
in
in2
ft
kip
kip
ksf
ksf

## Output:

1. Definitions
• ϕc = Resistance factor for concrete
• ϕs = Resistance factor for reinforcing steel
• fc = Specified concrete strength (psi)
• fy = Specified reinforcing steel yield strength (ksi)
• λ = Concrete density modification factor; 1.0 for normal density concrete
• As = Area of reinforcing steel (in2)
• α1 = Stress modification factor for equivalent stress block
• β = Cracked concrete shear factor
• d = Depth to primary reinforcing (in)
• B = Width of footing (in)
• Lf = Footing length (ft)
• tw = Wall thickness (in)
• Cover = concrete cover to centroid of reinforcing (in)
• qa = Allowable bearing resistance for service conditions (ksf)
• qult = Ultimate bearing resistance (ksf)
• qs = Service bearing demand (ksf)
• qu = Factored ultimate bearing demand (ksf)
• dv = Shear depth, normally taken as 0.9d (in)
2. Calculate soil bearing stresses
• Ps = (D + L)/Lf = (10 + 5) / 1 = 15 kip/ft
• Pu = max[1.4D, 1.25D + 1.5L] / Lf = max[14, 20] / 1 = 20 kip/ft
• qs = Ps / B = 15 / (18/12) = 10 ksf --> Service bearing capacity exceeded! Revise design
• qu = Pu / B = 20 / (18/12) = 13.33 ksf --> Ultimate bearing capacity exceeded! Revise design
3. Calculate shear capacity at critical section, located 'dv' away from the face of the wall
• d = h - cover = 30 - 3 = 27 in
• dv = max[0.9d, 0.72h] = 0.9 (27) = 24.3 in
• β = 0.21 if h < 14in or (B-tw < 2dv)). Else β = 230/(1000 + dv*25.4). --> β = 0.21
• tw + dv > B --> Vu = 0 kip
• Vc = ϕc λ β √fc Lf dv = (0.65) (1) (0.21) (0.852) (1) (24.3) = 33.9 kip
• Vu / Vr = 0 / 33.9 = 0 --> okay
4. Calculate the flexural capacity at the critical section, located at the face of the wall
• Mu = qu Lf (B-tw)2 / 2 = (13.33) (1) (18 - 12)2 / 2 = 240 kip-in = 20 kip-ft
• Mr = ϕs As fy (d - a/2), where a = (ϕs As fy) / (ϕc α1 fc Lf)
• Mr = (0.85) (5) (60) (27 - 5.449/2)
• Mr = (255) (24.276)
• Mr = 6190 kip-in = 515.85 kip-ft
• Mu / Mr = 20 / 515.85 = 0.04 --> okay