Civil Engineering Reference
In-Depth Information
SOLUTION
From Table 7.1
1.0 for bottom bars
1.0 for uncoated bars
1.0 for #8 bars
1.0 for normal weight concrete
c
side cover of bars measured from center of bars
2
2
in.
or
1
2
c
one-half of c. to c. spacing of bars
in.
k
(a) Using ACI Equation 12-1 with
K
tr
0
c
K
tr
d
b
1.50
0
1.00
1.50
2.50
OK
f
y
c
d
60,000
(1.0)(1.0)(1.0)(1.0)
1.50
d
b
3
3
40
40
K
tr
d
b
c
f
3000
55 diameters
(b) Using Computed Value of
K
tr
and ACI Equation 12-1
A
tr
f
y
t
1500
sn
(2)(0.11)(60,000)
K
tr
0.367
(1500)(8)(3)
c
K
tr
d
b
1.50
0.367
1.0
1.867
2.5
OK
d
d
b
(1.0)(1.0)(1.0)(1.0)
1.867
60,000
3000
3
40
44 diameters
In determining required development lengths, there are two more ACI specifications
to keep in mind:
c
1.
Section 12.1.2 states that values of used in the equations cannot be greater
than 100 psi or MPa in SI. (This limit is imposed because there has not been a
sufficient amount of rese
arc
h on the development of bars in higher strength con-
cretes to justify higher values, which would result in smaller values.)
2.
When the amount of flexural reinforcing provided exceeds the theoretical amount
required and where the specifications being used do not specifically require
that the development lengths be based on
f
y
, the value of may be multiplied
by (
A
s
, required
/
A
s
, provided
) according to ACI 12.2.5. This reduction factor may not
be used for the development of reinforcement at supports for positive reinforce-
ment, for the development of shrinkage and temperature reinforcement, and for a
few other situations referenced in R12.2.5.
f
25
3
d
d
b
c
f
d
d
b
Instead of using ACI Equation 12-1 for computing development lengths, the ACI
in its Section 12.2 permits the use of a somewhat simpler and more conservative ap-
proach (as shown in Table 7.2 herein) for certain conditions. With this approach the
ACI recognizes that in a very large percentage of cases, designers use spacing and
cover values and confining reinforcing that result in a value of
c
K
tr
d
b
equal to at least
