Structural Concrete - Hassoun

484 Chapter 13 Footings
The minimum concrete thickness above the reinforcement in a pile footing is limited to 12 in.
(ACI Code, Section 13.4.2.1). For more design details of piles and pile footings, refer to books on
foundation engineering.
13.11 SI EQUATIONS
1. One-way shear:
2. Two-way shear:
φV c = 0.17λφ √ f ′ cbd (Eq. 13.3)
V c1
= 0.33λ √ f cb ′ 0 d (Eq. 13.6)
(
V c2
= 0.17 1 + 2 )
λ √ f ′
β
cb 0 d (Eq. 13.7)
( )
αs d
V c3
= 0.083 + 2 λ √ f
b
cb ′ 0 d (Eq. 13.8)
o
Other equations remain the same.
SUMMARY
Sections 13.1–13.4
1. General:
H = distance of bottom of footing from final grade (ft)
h = total depth of footing (in.)
c = wall thickness (in.)
q a = allowable soil pressure (ksf)
q e = effective soil pressure
W s = weight of soil (pcf)(Assume 100 pcf if not given.)
2. Design of Wall Footings. The design steps can be summarized as follows:
a. Assume a total depth of footing h (in.). Consider 1-ft length of footing.
b. Calculate q e = q a − (h/12)(150) − W s (H − h/12) (q a in psf).
c. Calculate width of footing: B = (total service load)/q e = (P D + P n )/q e . (Round to the nearest
higher half foot.) The footing size is (B × 1) ft.
d. Calculate the factored upward pressure, q u = P u /B where P u = 1.2P D + 1.6P L .
e. Check the assumed depth for one-way shear requirements considering d a = (h − 3.5 in.)
(Two-way shear does not apply.)
( B
V u = q u
2 − d − c )
(use kips.)
2