Civil Engineering Reference
In-Depth Information
Figure 12.17
Two-way footing bar spacing diagram.
Design of Steel in Short Direction (Figure 12.17)
7
9
Lever arm
2
12
2.75 ft
2.75
2
M
u
(2.75)(14.0)(4.71)
249.3 ft- k
M
u
(12)(249,300)
(0.90)(168)(19.5)
2
52 psi
bd
2
200
60,000
0.0033
k
Use
larger of
or
3
4000
60,000
0.00316
A
s
(0.0033)(168)(19.5)
10.81 in.
2
use 18 #7 bars (10.82 in.
2
)
Reinforcing in band width
Total reinforcing in short direction
2
2
1
2
3
Use
3
18
12 bars in band width
Subsequent check of required development lengths is OK.
12.10
COMBINED FOOTINGS
Combined footings support more than one column. One situation in which they may be
used is when the columns are so close together that isolated individual footings would run
into each other [Figure 12.18(a)]. Another frequent use of combined footings occurs
where one column is very close to a property line, causing the usual isolated footing to ex-
tend across the line. For this situation the footing for the exterior column may be com-
bined with the one for an interior column, as shown in Figure 12.18(b).
