Civil Engineering Reference
In-Depth Information
Table 7.2
Simplified Development Length Equations
#6 and
smaller bars and
#7 and
deformed wires
larger bars
Clear spacing of bars being developed
or spliced not less than
d
b
, clear
cover not less than
d
b
, and stirrups or
ties throughout
d
not less than the
code minimum
d
b
f
y
25
f
d
b
f
y
20
f
d
d
c
c
or
Clear spacing of bars being developed
or spliced not less than 2
d
b
and clear
cover not less than
d
b
3
f
y
3
f
y
d
d
b
d
d
b
Other cases
c
c
f
f
50
40
1.5. Based on this value and the appropriate values of
, the expressions in Table 7.2
were determined.
For SI values, see Section 12.2.2 of the 318M- 02 Code.
If a minimum cover equal to
d
b
and a minimum clear spacing between bars of 2
d
b
(or
a minimum clear spacing of bars equal to
d
b
, along with a minimum of ties or stirrups) are
used, the expressions in Table 7.2 can be used. Otherwise it is necessary to use the more
rigorous ACI Equation 12-1.
The author feels that the application of the so-called simplified equations requires al-
most as much effort as is needed to use the longer equation. Furthermore, the develop-
ment lengths computed with the “simpler” equations are often so much larger than the
ones determined with the regular equation as to be uneconomical.
For these reasons the author recommends the use of Equation 12-1 for computing de-
velopment lengths. In using this long form equation, however, you may very well like to
assume that
K
tr
0, as the results obtained usually are only slightly more conservative
than those obtained with the full equation.
The author uses Equation 12-1 with K
tr
0 for
all applications after this chapter.
Examples 7.3 and 7.4, which follow, present the determination of development
lengths using each of the methods that have been described in this section.
EXAMPLE 7.3
The #7 bottom bars shown in Figure 7.9 are epoxy coated. Assuming normal weight concrete,
f
y
60,000 psi, and
c
f
3500 psi, determine required development lengths
(a)
Using the simplified equations of Table 7.2.
(b)
Using the full ACI Equation 12-1 with the calculated value of
K
tr
.
(c)
Using ACI Equation 12-1 with
K
tr
0.
