Civil Engineering Reference
In-Depth Information
Figure 14.33
Development length requirements for positive-moment reinforcing.
compression reaction, such as when there is a column below but not when a beam frames
into a girder, an increase of 30% in the value to is allowed. The values
described here are summarized in Figure 14.33; a brief numerical illustration for a simple
end-supported beam is provided in Example 14.3.
M
n
/
V
u
1.3
M
n
/
V
u
EXAMPLE 14.3
At the simple support shown in Figure 14.34, two uncoated #9 bars have been extended from the
maximum moment area and into the support. Are the bar sizes satisfactory if
f
y
c
60 psi,
f
3 ksi,
b
12 in.,
d
24 in., and
V
u
65 k, if normal sand-gravel concrete is used, and if the reaction is
compressive? Assume cover for bars
2
clear.
A
s
f
y
0.85
f
(2.00)(60)
(0.85)(3)(12)
3.92
SOLUTION
a
c
b
a
2
3.92
2
M
n
A
s
f
y
d
(2.00)(60)
24
2644.8 in.- k
c
side cover
2
1.128
2
2.564
k
1
2
c
one- half to c. to c. spacing of bars
(12
2
2
1.128)
3.436
