Civil Engineering Reference
In-Depth Information
Figure 7.18
c
are different because the values for the footing and the column are different in this
case. The topic of dowels and force transfer from walls and columns to footings is dis-
cussed in some detail in Chapter 12. (The development lengths determined in this exam-
ple are for compression bars as would normally be the case at the base of columns. If
uplift is possible, however, it will be necessary to consider tension development lengths,
which could very well control.)
f
EXAMPLE 7.7
The forces in the column bars of Figure 7.18 are to be transferred into the footing with #9 dowels.
Determine the development lengths needed for the dowels (a) down into the footing and (b) up into
the column if
f
y
60,000 psi.
SOLUTION
(a)
Down into the footing,
db
0.02
d
b
f
y
f
(0.02)(1.128)(60,000)
3000
24.71
k
c
db
(0.0003)(1.128)(60,000))
20.30
Hence
d
24.71
, say 25
, as there are no applicable modification factors. Under no circumstances
may
d
be less than 8 in.
(b)
Up into column,
db
(0.02)(1.128)(60,000)
5000
19.14
db
(0.0003)(1.128)(60,000)
20.30
)
k
Hence
d
20.30
, say 21
(can't be
8
), as there are no applicable modification factors. (
An-
swer:
Extend the dowels 25
down into the footing and 21
up into the column.)
Note:
The bar details shown in Figure 7.18 are unsatisfactory for seismic areas as the bars should be
bent inward and not outward. The reason for this requirement is that the Code, Chapter 21, on seis-
mic design, stipulates that hooks must be embedded in confined concrete.
