Civil Engineering Reference
In-Depth Information
8.7
SPECIAL BAR DETAILS AT SLAB-TO-COLUMN CONNECTIONS
When two-way slabs are supported directly by columns (as in flat plates and flat slabs), transfer of moment
between slab and column takes place by a combination of flexure and eccentricity of shear (see Chapter 4,
Section 4.4.1). The portion of the unbalanced moment transferred by flexure is assumed to be transferred over
a width of slab equal to the column width c plus 1.5 times the slab thickness h on either side of the column.
For edge and interior columns, the effective slab width is (c+3h), and for corner columns it is (c+1.5h). An
adequate amount of negative slab reinforcement is required in this effective slab width to resist the portion of
the unbalanced moment transferred by flexure (ACI 13.5.4). In some cases, additional reinforcement must be
concentrated over the column to increase the nominal moment resistance of the section. Note that minimum
bar spacing requirements must be satisfied at all locations in the slab (ACI 13.3.2). Based on recommendations
in Reference 8.7, examples of typical details at edge and corner columns are shown in Figs. 8-7 and 8-8.
˜
n1
˜
n2
˜
n2
˜
n3
˜
n1
4
Larger of
3
or
3
Larger of
3
or
3
Std. hook
(typ.)
1
/
4
(A
+
s1
)
Note 1
≥
A
+
A
+
A
+
0"
0"
0"
s2
s3
s1
Std. hook
or anchored
to develop
F
y
0.12
5
˜
n1
0.12
5
˜
n2
0.1
2
5
˜
n2
0.12
5
˜
n3
6"
˜
n1
˜
n2
˜
n3
(a) Beams without closed stirrups
˜
n1
˜
n2
˜
n2
˜
n3
˜
n1
4
Larger of
3
or
3
Larger of
3
or
3
Std. hook
(typ.)
A
-
Note 2
A
-
A
-
0"
0"
0"
s3
s2
1
/
4
(A
+
s1
)
Note 1
≥
A
+
0"
A
+
0"
A
+
0"
s2
s3
s1
0.12
5
˜
n1
0.12
5
˜
n2
0.1
2
5
˜
n2
0.1
2
5
˜
n3
˜
n3
6
"
˜
n1
˜
n2
One piece closed stirrups or U-stirrups
with 135
∞
hook required for shear type
(b) Perimeter beams
Notes: (1) Larger of
1
/
4
(A
+
or mechanical or welded splice (ACI 7.13.2.2 and 7.13.2.3)
(2) Larger of
1
/
6
(A
-
s1
) or
1
/
6
(A
-
s2
) but not less than two bars continuous or spliced with Class B splices
or mechanical or welded splice (ACI 7.13.2.2)
s1
) or
1
/
4
(A
s2
) but not less than two bars continuous or spliced with Class B splices
Figure 8-3 Recommended Bar Details for Beams
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