Civil Engineering Reference
In-Depth Information
(
)
2
⎣
⎦
V
u
=
q
u
A
f
−
c
1
+
d
q
u
4
+φ
q
u
2
+φ
q
u
4
⎛
⎜
⎞
⎟
⎛
⎜
⎞
⎟
(
)
= 0
d
2
v
c
+
v
c
c
1
d
−
A
f
−
A
c
4
f
c
ʹ
where A
c
= area of the column = c
1
2
and v
c
= . Fig. 7-4 can be used to determine d for footings with
› = 3, 4, 5 and 6 ksi: given q
u
and A
f
/A
c
, the minimum value of d/c
1
can be read from the vertical axis.
Square footings, that are designed based on minimum flexural reinforcement will rarely encounter any one-
way or two-way shear problems when supporting square columns. For other footing and column shapes, shear
strength will more likely control the footing thickness. In any case, it is important to ensure that shear strength of
the footing is not exceeded.
7.5.1
Procedure for Simplified Footing Design
(1) Determine base area of footing A
f
from service loads (unfactored loads) and allowable (safe) soil pressure q
a
determined for the site soil conditions and in accordance with the local building code.
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