Pad Footing Capacity

This tool calculates the soil bearing, concrete flexure, and concrete shear capacity of an isolated pad or spread footing

Code:
CA flagCSA A23.3
D(kip)

Dead load

Constraints
min: 0
L(kip)

Live load

Constraints
min: 0
q_a(ksf)

Allowable soil bearing pressure

Constraints
min: 0
q_u(ksf)

Ultimate soil bearing pressure

Constraints
min: 0
b_c(in)

Column width

Constraints
min: 0
h_c(in)

Column depth

Constraints
min: 0
B_f(ft)

Footing width

Constraints
min: 0
L_f(ft)

Footing length

Constraints
min: 0
t_f(in)

Footing thickness

Constraints
min: 0
cover(in)

Concrete clear cover to reinforcing

Constraints
min: 0
f_c(ksi)

Specified concrete strength

Constraints
min: 1step: 0.5
f_y(ksi)

Specified reinforcing steel yield strength

Constraints
min: 0step: 1
ϕ_c

Resistance factor for concrete

Constraints
min: 0step: 0.01
ϕ_s

Resistance factor for reinforcing steel

Constraints
min: 0step: 0.01
layer

Bottom lowest layer of reinforcement (for effective depth calculation)

barx/qty_x

Quantity and size of bottom reinforcement bars. X-bars are parallel to x. Y-bars are parallel to y.

Constraints
min: 2
bary/qty_y

Quantity and size of bottom reinforcement bars. X-bars are parallel to x. Y-bars are parallel to y.

Constraints
min: 2
BfBfLfLfxxyytftf

Calculation Steps:

    Calculate design loads
    Pf = 2953 kip, Ps = 2260 kip
    • P_s

      Service axial load

      kip
    • P_f

      Factored axial load

      kip
    Geometric properties
    • d

      Depth to primary reinforcing

      in
    • d_v

      Shear depth, normally taken as 0.9d

      in
    • α_1

      Stress modification factor for equivalent stress block

    • β_c

      Column aspect ratio (long/short)

    • β_f

      Footing aspect ratio (long/short)

    • A_c

      Column area

      ft²
    • A_f

      Footing plan area

      ft²
    • A_2

      Effective bearing area under load dispersion

      ft²
    • S_2

      Footing section modulus about the B_f axis

      ft³
    • S_3

      Footing section modulus about the L_f axis

      ft³
    • x

      Cantilever length in B_f direction

      ft
    • y

      Cantilever length in L_f direction

      ft
    • f_v

      √fc in MPa, coverted back to ksi, for convenience in concrete shear equations.

      ksi
    Soil bearing
    Usoil = 95% (Qsls = 95%, Quls = 85%)
    • q_s

      Service bearing pressure

      ksf
    • q_f

      Factored bearing pressure

      ksf
    • Q_sls

      Service bearing utilization ratio

    • Q_uls

      Ultimate bearing utilization ratio

    • U_soil

      Governing soil utilization ratio

    Concrete bearing
    Ubearing = 82%
    • B_r

      Concrete bearing resistance

      kip
    • U_bearing

      Concrete bearing utilization ratio

    Punching shear
    Upunching = 55%
    • b_o

      Critical punching shear perimeter

      in
    • A_o

      Area inside punching shear perimeter

      ft²
    • v_f

      Factored punching shear stress

      ksi
    • λ_s

      Size effect factor for punching shear

    • α

      Punching shear coefficient

    • v_c

      Punching shear resistance

      ksi
    • U_punching

      Punching shear utilization ratio

    One way shear (x)
    Ushear = 87%
    • β_x

      One-way shear coefficient

    • V_cx

      One-way shear resistance

      kip
    • V_fx

      Factored one-way shear

      kip
    • U_shear_x

      One-way shear utilization ratio

    One way shear (y)
    Ushear = 96%
    • β_y

      One-way shear coefficient

    • V_cy

      One-way shear resistance

      kip
    • V_fy

      Factored one-way shear

      kip
    • U_shear_y

      One-way shear utilization ratio

    Flexure (x)
    Using 21-25M9.5 --- Uflexure = 78%
    • M_fx

      Factored bending moment

      kip-ft
    • d_x

      Effective depth for x-direction flexure

      in
    • A_sx

      Area of reinforcing steel

      in²
    • a_x

      Equivalent stress block depth

      in
    • M_rx

      Factored flexural resistance

      kip-ft
    • s_avg_x

      Average bar spacing

      in
    • L_bar_x

      Bar length within footing plan

      ft
    • U_flexure_x

      Flexural utilization ratio

    Flexure (y)
    Using 18-25M11.5 --- Uflexure = 86%
    • M_fy

      Factored bending moment

      kip-ft
    • d_y

      Effective depth for y-direction flexure

      in
    • A_sy

      Area of reinforcing steel

      in²
    • a_y

      Equivalent stress block depth

      in
    • M_ry

      Factored flexural resistance

      kip-ft
    • s_avg_y

      Average bar spacing

      in
    • L_bar_y

      Bar length within footing plan

      ft
    • U_flexure_y

      Flexural utilization ratio

    User Notes: