Single footing, strip footing and mat foundations are designed automatically according to ACI Chapter 13.
Ag = gross area of concrete section, in2
As = area of nonprestressed longitudinal tension reinforcement, in2
dpile = diameter of pile at footing base, in.
D = dead load
E = earthquake load
Eh = effect of horizontal seismic forces
Em = seismic load effect including overstrength
Emh = effect of horizontal seismic forces, including overstrength
Ev = vertical seismic effect applied in the vertical downward directio
fc' = specified compressive strength of concrete, psi
fy = specified yield strength for nonprestressed reinforcement, psi
F = load due to fluids with well-defined pressures and maximum heights;
L = load due to lateral earth pressure, ground water pressure, or pressure of bulk materials;
Lr = roof live load
Pa = maximum allowable compressive strength of a deep foundation member, lb
R = rain load
S = snow load
Vn = nominal shear strength, lb
Vu = factored shear force at section, lb
W = wind load
ϕ = strength reduction factor
Allowable Axial Strength
According to ACI 220.127.116.11, ASCE/SEI Section 2.4 and allowable strength specified in ACI Table 18.104.22.168 can be used to design a depp foundation member.
Basic Combinations given in ASCE/SEI Section 2.4 are shown below;
It shall be permitted to design a deep foundation member using allowable strength specified in ACI Table 22.214.171.124 if the two conditions given below are satisfied. If one of these two conditions is not satisfied, a depp foundation member should be designed using strength design in accordance with ACI 13.4.3.
The deep foundation member is laterally supported for its entire height
The applied forces cause bending moments in the deep foundation member less than the moment due to accidental eccentricity of %5 of the member diameter or width
Strength design in accordance with this section can be used for all deep foundation members.
According to ACI 126.96.36.199, the strength design of deep foundation members should be in accordance with Column Required and Design Strength title using the compressive strength reduction factors of ACI Table 188.8.131.52 for axial load with no moment, and the strength reduction factors of ACI Table 21.2.1 for tension, shear and combined axial force and moment.
According to ACI 184.108.40.206, overall depth of pile cap should be selected such that the effective depth of bottom reinforcement is at least 12 inches.
According to ACI 220.127.116.11, pile caps should be designed such that condition 1 is satisfied for one-way foundations and condition 1 and condition 2 are satisfied for two-way foundations. These two conditions are given below,
ϕVn ≥ Vu , where Vn should be calculated in accordance with One-Way Shear Strength title.
ϕvn ≥ vu , where vn should be calculated in accordance with Two-Way Shear Strength title.
According to ACI 18.104.22.168, calculation of factored shear force one any pile cap section should be in accordance with conditions given below;
Entire reaction from any pile with its center located dpile/2 or more outside the section shall be considered as producing shear on that section.
Reaction from any pile with its center located dpile/2 or more inside the section shall be considered as producing no shear on that section.
For intermediate positions of pile center, the portion of the pile reaction to be considered as producing shear on the section shall be based on a linear interpolation between full value at dpile/2 outside the section and zero value at dpile/2 inside the section.