Civil Engineering Reference
In-Depth Information
Total bars required:
122
6
12
=
−
9.66 spaces
Use 10-No.7, 9 ft-4 in. long (each way)*
(6) Footing dowels
Footing dowel requirements are different for sway and non-sway frames. For the sway frame, with wind
moment transferred to the base of the column, all of the tensile forces produced by the moment must be
transferred to the footing by dowels. The number and size of dowel bars will depend on the tension development
length of the hooked end of the dowel and the thickness of the footing. The dowel bars must also
be fully developed for tension in the column.
For the non-sway frame, subjected to gravity loads only, dowel requirements are determined as follows:**
(a) For 16
16 in. column (Table 7-2):
φ
P
nb
= 566 kips
Minimum dowel area = 1.28 in.
2
Since
P
nb
> P
u
= 512 kips, bearing on concrete alone is adequate for transfer of compressive force.
Use 4-No.6 dowels (A
s
= 1.76 in.
2
)
φ
(b) Embedment into footing (Table 7-3):
For straight dowel bars,
h
≥
db
+ 3 in.
db
= 17 in. for No.6 dowels with f
c
= 3000 psi
h = 27 in. > 17 + 3 = 20 in. O.K.
For hooked dowel bars,
≥
db
+ r + d
bd
+ 2d
bf
+ 3 in.
r = 3d
bd
= 3
h
0.75 = 2.25 in.
(ACI Table 7.2)
h = 27 in. > 17 + 2.25 + 0.75 + (2
0.875) + 3 = 24.75 in. O.K.
* 13-No.6 or 8-No.8 would also be adequate.
** The horizontal forces produced by the gravity loads in the first story columns are negligible; thus, dowels required for
vertical load transfer will be adequate for horizontal load transfer as well.
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