Structural Concrete - Hassoun

7.4 Development Length in Compression 265
Table 7.2 Development Length I d
(in.) for Tension Bars and f y
= 60 ksi (ψ t
= ψ e
= λ = 1.0)
Development Length I d
(in.)—Tension Bars
f ′ c = 3ksi
f′ c = 4ksi
Bar Number Bar Diameter (in.) Conditions Met Other Cases Conditions Met Other Cases
3 0.375 17 25 15 21
4 0.500 22 33 19 29
5 0.625 28 41 24 36
6 0.750 33 50 29 43
7 0.875 48 72 42 63
8 1.000 55 83 48 72
9 1.128 62 93 54 81
10 1.270 70 105 61 92
11 1.410 78 116 68 102
The ACI Code, Section 25.4.9.2, gives the basic development length in compression for all bars as
follows:
l dc = 0.02d bf y
λ √ ≥ 0.0003d b f y (7.14)
f c
′
which must not be less than 8 in. (ACI Code, Section 25.4.9.1). The development length, l dc ,may
be reduced by multiplying l dc by R s = (A s required)/(A s provided). For spirally reinforced concrete
compression members with spirals of not less than 1 in. diameter and a spacing of 4 in. or less, the
4
value of l dc in Eq. 7.14 may be multiplied by R sl = 0.75. In general, l d = l dc × (R s or R sl , if applicable)
≥ 8 in. Tables 7.3 and 7.4 give the values of l dc /d b when f y = 60 ksi.
Table 7.3
Values of l d
/d b
for Various Values of f
c ′ and f y
(Compression Bars),
λ = 1.0, Minimum I dc
= 8in.I dc
∕d b
= 0.02f y
∕λ √ f ′ c ≥ 0.0003f y
f ′ (ksi)
c
3 4 5 or more
f y = 40 ksi 15 13 12
f y = 60 ksi 22 19 18
Table 7.4 Development Length, I dc
(in.), for Compression Bars (f y
= 60 ksi), λ = 1.0
Development Length, I dc
(in.) when f ′ c =
Bar Number Bar Diameter (in.) 3 ksi 4 ksi 5 ksi or More
3 0.375 9 8 8
4 0.500 11 10 9
5 0.625 14 12 12
6 0.750 17 15 14
7 0.875 20 17 16
8 1.000 22 19 18
9 1.128 25 22 21
10 1.270 28 25 23
11 1.410 31 27 26