Footing result

This is a sample calculation. Enter your own footing to run a real check.

Strap footing Pad 1 96 × 96 in Pad 2 108 × 108 in Strap 18 × 36 in, 168 in c/c h 24 in qa 4 ksf f′c 4,000 psi fy 60 ksi #5 bottom bars

PASS

All checks pass: pad 1, pad 2 and the strap beam.

Equilibrium and pad reactions

The strap carries the eccentric exterior column load to the interior pad. Moments about the pad 2 center give the pad reactions; each pad is then checked as an isolated footing under its reaction.

R₁ (pad 1 reaction, factored): 226.15 kip
R₂ (pad 2 reaction, factored): 333.30 kip

Quantity	Value
R₁ (pad 1 reaction, service, kip)	159.72
R_1,u (pad 1 reaction, factored, kip)	226.15
R₂ (pad 2 reaction, service, kip)	239.72
R_2,u (pad 2 reaction, factored, kip)	333.30
W_strap (strap self-weight, kip)	9.45
e₁ (column 1 offset from pad 1 center, in)	18.0
L_strap (center-to-center distance of the pads, in)	168.0

Static equilibrium; column 1 moved toward the property line by e₁ ACI 318-19 §13.2.1

Pad 1: exterior column

PASS

Soil bearing, overturning and sliding

PASS

D/C bearing (q max / q net) 0.72

q_max (maximum service pressure): 2.50 ksf
q_net (net allowable pressure): 3.46 ksf

Quantity	Value
q_max (maximum pressure, ksf)	2.50
q_min (minimum pressure, ksf)	2.50
q_net (qa less overburden and self-weight, ksf)	3.46
e_L (eccentricity from M_L, in)	0.00
B/6 (kern limit for e_L, in)	16.00
e_B (eccentricity from M_B, in)	0.00
L/6 (kern limit for e_B, in)	16.00
Footing self-weight (kip)	19.20
Soil weight above footing (kip)	15.36
F_resist (friction resistance, kip)	79.86
FS_ot (overturning factor of safety, minimum 1.5)	N/A (no overturning moment)
FS_slide (sliding factor of safety, minimum 1.5)	N/A (no lateral force)
Bearing (q_max ≤ q_net)	Satisfied
Kern (e within B/6 and L/6, full contact)	Within kern
Overturning (FS ≥ 1.5)	Satisfied
Sliding (FS ≥ 1.5)	Satisfied

Service loads; friction-only sliding resistance ACI 318-19 §13.2.1 · §13.2.2

Flexure

PASS

L-direction bars (parallel to L)

D/C moment 0.39

φMn (design moment capacity): 396.24 kip-ft
Mu (factored moment at column face): 157.05 kip-ft

Quantity	Value
b (design width, in)	96.0
d (effective depth, in)	20.69
A_s,req (steel required for M_u, in²)	1.70
A_s,min (minimum steel, in², §13.3.3.2)	4.15
Bars (number of #5 bars)	14
A_s,prov (steel provided, in²)	4.34
s (center-to-center spacing, in)	6.88
Clear spacing (in, minimum max(d_b, 1 in), §25.2.1)	6.25
a (stress block depth, in)	0.80
φMn (design moment strength, kip-ft)	396.24
Status	PASS

B-direction bars (parallel to B)

D/C moment 0.40

φMn (design moment capacity): 384.03 kip-ft
Mu (factored moment at column face): 157.05 kip-ft

Quantity	Value
b (design width, in)	96.0
d (effective depth, in)	20.06
A_s,req (steel required for M_u, in²)	1.75
A_s,min (minimum steel, in², §13.3.3.2)	4.15
Bars (number of #5 bars)	14
A_s,prov (steel provided, in²)	4.34
s (center-to-center spacing, in)	6.88
Clear spacing (in, minimum max(d_b, 1 in), §25.2.1)	6.25
a (stress block depth, in)	0.80
φMn (design moment strength, kip-ft)	384.03
Status	PASS

γ_s (fraction of short-direction steel in the central band, §13.3.3.3)

1.000

φ = 0.90; critical section at the column face ACI 318-19 §13.2.7.1 · Table 21.2.2 · §25.2.1

One-way shear

PASS

L-direction bars (critical section parallel to B)

D/C shear 0.46

φVc (design shear capacity): 97.80 kip
Vu (factored shear at d from the face): 45.50 kip

Quantity	Value
ρ_w (A_s,prov / (b_w·d))	0.0022
V_c (concrete shear strength, kip)	130.40
φV_c (design shear strength, kip)	97.80
V_u (factored shear, kip)	45.50
Status	PASS

B-direction bars (critical section parallel to L)

D/C shear 0.49

φVc (design shear capacity): 95.82 kip
Vu (factored shear at d from the face): 46.97 kip

Quantity	Value
ρ_w (A_s,prov / (b_w·d))	0.0023
V_c (concrete shear strength, kip)	127.76
φV_c (design shear strength, kip)	95.82
V_u (factored shear, kip)	46.97
Status	PASS

φ = 0.75; no shear reinforcement ACI 318-19 §13.2.7.2 · Table 22.5.5.1

Punching shear

PASS

D/C punching shear 0.34

φVc (design punching capacity): 562.49 kip
Vu (factored punching demand): 193.68 kip

Quantity	Value
d_avg (average effective depth, in)	20.38
b_o (critical perimeter at d/2, in)	145.5
Area inside perimeter (in²)	1,323
β (long side / short side of column)	1.00
α_s (location factor, §22.6.5.3)	40
v_c (a) (4λ_sλ√f′c, psi)	253.0
v_c (b) ((2 + 4/β)λ_sλ√f′c, psi)	379.5
v_c (c) ((2 + α_sd/b_o)λ_sλ√f′c, psi)	480.8
v_c governing (minimum of (a), (b), (c), psi)	253.0
V_c (v_c·b_o·d, kip)	749.98
φV_c (design punching strength, kip)	562.49
Critical perimeter fits in the footing	Yes

φ = 0.75; concentric loading only ACI 318-19 §22.6.4.1 · Table 22.6.5.2

Development length

PASS

L-direction bars

D/C development length 0.32

Quantity	Value
l_d (development length, in)	14.2
l_d adjusted (reduced for excess steel, minimum 12 in, in)	12.0
l_avail (available length beyond the critical section, in)	37.0
c_b (cover or half spacing term, in)	3.31
ψ_t (casting position)	1.00
ψ_e (coating)	1.00
ψ_s (bar size)	0.80
ψ_g (grade)	1.00
Status	PASS

B-direction bars

D/C development length 0.32

Quantity	Value
l_d (development length, in)	14.2
l_d adjusted (reduced for excess steel, minimum 12 in, in)	12.0
l_avail (available length beyond the critical section, in)	37.0
c_b (cover or half spacing term, in)	3.31
ψ_t (casting position)	1.00
ψ_e (coating)	1.00
ψ_s (bar size)	0.80
ψ_g (grade)	1.00
Status	PASS

Straight bars in tension, no hooks ACI 318-19 §13.2.7.1 · Eq. 25.4.2.4a · Table 25.4.2.5

Column to footing interface

PASS

D/C bearing on concrete 0.19

φB_n (design bearing strength): 1,131.52 kip
Pu (factored load): 226.15 kip

Quantity	Value
A₁ (loaded area, in²)	256
A₂ (supporting area (frustum base), in²)	4,096
φB_n (design bearing strength, kip, §22.8.3.2)	1,131.52
A_s,dowel,min (minimum dowel area, in², §16.3.4.1)	1.28

Feasible dowel sizes

Sizes whose compression development length fits in the footing depth. A design aid; detailing is the engineer’s responsibility.

Bar	Number	l_dc (in)
#4	7	9.5
#5	5	11.9
#6	3	14.2
#7	3	16.6
#8	2	19.0

φ = 0.65 for bearing ACI 318-19 §22.8.3.2 · §16.3.4.1 · §25.4.9.2

Pad 2: interior column

PASS

Soil bearing, overturning and sliding

PASS

D/C bearing (q max / q net) 0.85

q_max (maximum service pressure): 2.96 ksf
q_net (net allowable pressure): 3.46 ksf

Quantity	Value
q_max (maximum pressure, ksf)	2.96
q_min (minimum pressure, ksf)	2.96
q_net (qa less overburden and self-weight, ksf)	3.46
e_L (eccentricity from M_L, in)	0.00
B/6 (kern limit for e_L, in)	18.00
e_B (eccentricity from M_B, in)	0.00
L/6 (kern limit for e_B, in)	18.00
Footing self-weight (kip)	24.30
Soil weight above footing (kip)	19.44
F_resist (friction resistance, kip)	119.86
FS_ot (overturning factor of safety, minimum 1.5)	N/A (no overturning moment)
FS_slide (sliding factor of safety, minimum 1.5)	N/A (no lateral force)
Bearing (q_max ≤ q_net)	Satisfied
Kern (e within B/6 and L/6, full contact)	Within kern
Overturning (FS ≥ 1.5)	Satisfied
Sliding (FS ≥ 1.5)	Satisfied

Service loads; friction-only sliding resistance ACI 318-19 §13.2.1 · §13.2.2

Flexure

PASS

L-direction bars (parallel to L)

D/C moment 0.54

φMn (design moment capacity): 452.70 kip-ft
Mu (factored moment at column face): 248.94 kip-ft

Quantity	Value
b (design width, in)	108.0
d (effective depth, in)	20.69
A_s,req (steel required for M_u, in²)	2.70
A_s,min (minimum steel, in², §13.3.3.2)	4.67
Bars (number of #5 bars)	16
A_s,prov (steel provided, in²)	4.96
s (center-to-center spacing, in)	6.76
Clear spacing (in, minimum max(d_b, 1 in), §25.2.1)	6.13
a (stress block depth, in)	0.81
φMn (design moment strength, kip-ft)	452.70
Status	PASS

B-direction bars (parallel to B)

D/C moment 0.56

φMn (design moment capacity): 438.75 kip-ft
Mu (factored moment at column face): 248.94 kip-ft

Quantity	Value
b (design width, in)	108.0
d (effective depth, in)	20.06
A_s,req (steel required for M_u, in²)	2.79
A_s,min (minimum steel, in², §13.3.3.2)	4.67
Bars (number of #5 bars)	16
A_s,prov (steel provided, in²)	4.96
s (center-to-center spacing, in)	6.76
Clear spacing (in, minimum max(d_b, 1 in), §25.2.1)	6.13
a (stress block depth, in)	0.81
φMn (design moment strength, kip-ft)	438.75
Status	PASS

γ_s (fraction of short-direction steel in the central band, §13.3.3.3)

1.000

φ = 0.90; critical section at the column face ACI 318-19 §13.2.7.1 · Table 21.2.2 · §25.2.1

One-way shear

PASS

L-direction bars (critical section parallel to B)

D/C shear 0.65

φVc (design shear capacity): 110.60 kip
Vu (factored shear at d from the face): 71.94 kip

Quantity	Value
ρ_w (A_s,prov / (b_w·d))	0.0022
V_c (concrete shear strength, kip)	147.47
φV_c (design shear strength, kip)	110.60
V_u (factored shear, kip)	71.94
Status	PASS

B-direction bars (critical section parallel to L)

D/C shear 0.68

φVc (design shear capacity): 108.36 kip
Vu (factored shear at d from the face): 73.87 kip

Quantity	Value
ρ_w (A_s,prov / (b_w·d))	0.0023
V_c (concrete shear strength, kip)	144.48
φV_c (design shear strength, kip)	108.36
V_u (factored shear, kip)	73.87
Status	PASS

φ = 0.75; no shear reinforcement ACI 318-19 §13.2.7.2 · Table 22.5.5.1

Punching shear

PASS

D/C punching shear 0.45

φVc (design punching capacity): 624.34 kip
Vu (factored punching demand): 286.72 kip

Quantity	Value
d_avg (average effective depth, in)	20.38
b_o (critical perimeter at d/2, in)	161.5
Area inside perimeter (in²)	1,630
β (long side / short side of column)	1.00
α_s (location factor, §22.6.5.3)	40
v_c (a) (4λ_sλ√f′c, psi)	253.0
v_c (b) ((2 + 4/β)λ_sλ√f′c, psi)	379.5
v_c (c) ((2 + α_sd/b_o)λ_sλ√f′c, psi)	445.7
v_c governing (minimum of (a), (b), (c), psi)	253.0
V_c (v_c·b_o·d, kip)	832.45
φV_c (design punching strength, kip)	624.34
Critical perimeter fits in the footing	Yes

φ = 0.75; concentric loading only ACI 318-19 §22.6.4.1 · Table 22.6.5.2

Development length

PASS

L-direction bars

D/C development length 0.29

Quantity	Value
l_d (development length, in)	14.2
l_d adjusted (reduced for excess steel, minimum 12 in, in)	12.0
l_avail (available length beyond the critical section, in)	41.0
c_b (cover or half spacing term, in)	3.31
ψ_t (casting position)	1.00
ψ_e (coating)	1.00
ψ_s (bar size)	0.80
ψ_g (grade)	1.00
Status	PASS

B-direction bars

D/C development length 0.29

Quantity	Value
l_d (development length, in)	14.2
l_d adjusted (reduced for excess steel, minimum 12 in, in)	12.0
l_avail (available length beyond the critical section, in)	41.0
c_b (cover or half spacing term, in)	3.31
ψ_t (casting position)	1.00
ψ_e (coating)	1.00
ψ_s (bar size)	0.80
ψ_g (grade)	1.00
Status	PASS

Straight bars in tension, no hooks ACI 318-19 §13.2.7.1 · Eq. 25.4.2.4a · Table 25.4.2.5

Column to footing interface

PASS

D/C bearing on concrete 0.18

φB_n (design bearing strength): 1,768.00 kip
Pu (factored load): 333.30 kip

Quantity	Value
A₁ (loaded area, in²)	400
A₂ (supporting area (frustum base), in²)	4,624
φB_n (design bearing strength, kip, §22.8.3.2)	1,768.00
A_s,dowel,min (minimum dowel area, in², §16.3.4.1)	2.00

Feasible dowel sizes

Sizes whose compression development length fits in the footing depth. A design aid; detailing is the engineer’s responsibility.

Bar	Number	l_dc (in)
#4	10	9.5
#5	7	11.9
#6	5	14.2
#7	4	16.6
#8	3	19.0

φ = 0.65 for bearing ACI 318-19 §22.8.3.2 · §16.3.4.1 · §25.4.9.2

Strap beam

PASS

D/C flexure (top steel) 0.99

D/C shear 0.76

D/C development length 0.51

A_s,prov (steel provided, 7 #5 bars): 2.17 in²
A_s,req (steel required): 2.15 in²

Quantity	Value
Mu (maximum factored moment, kip-ft)	300.00
Vu (maximum factored shear, kip)	26.15
A_s,req (steel required for M_u, in²)	2.15
A_s,min (minimum steel, in², Table 9.6.1.2)	1.92
Bars (number of #5 bars)	7
A_s,prov (steel provided, in²)	2.17
φMn (design moment strength, kip-ft)	302.70
V_c (concrete shear strength, kip)	45.41
φV_c (design shear strength, kip)	34.06
l_d (development length required, in)	33.9
l_avail (clear length between pad edges, in)	66.0
Status	PASS

φ = 0.90 flexure, 0.75 shear; top steel; no shear reinforcement designed ACI 318-19 §22.2 · §22.5 · Eq. 25.4.2.4a

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