Structural Detailing of Reinforcement for Economy - Simplified Design of Reinforced Concrete Buildings - page 238

⎛ ⎞

f y ψ t ψ e
25

d = ⎜ ⎟ d b For No. 6 and smaller bars

λ ʹ f c

⎝ ⎠

⎛ ⎞

f y ψ t ψ e
20

d = ⎜ ⎟ d b For No. 7 and smaller bars

λ ʹ f c

⎝ ⎠

where

˜ d = development length, in.

d b = nominal diameter of bar, in.

f y = specified yield strength for bar, psi

› = specified compressive strength of concrete, psi

ψ = reinforcement location factor

t

= 1.3 for horizontal reinforcement so placed that more than 12 in. of fresh concrete is cast below
the bar being developed or spliced

= 1.0 for other reinforcement

ψ = coating factor e

= 1.5 for epoxy-coated bars with cover less than 3d b or clear spacing less than 6d b

= 1.2 for all other epoxy-coated bars

= 1.0 for uncoated reinforcement

The product of ψ t and ψ e need not be taken greater than 1.7.

λ = lightweight aggregate concrete factor

= 1.3 when lightweight aggregate concrete is used, or

= 1.0 for normal weight concrete

The above equations are valid for clear spacing of bars being developed or spliced not less than d b ,
clear cover not less than d b and stirrups or ties not less than the code minimum, or clear spacing not
less than 2d b and clear cover not less than d b (ACI 12.2.2). For cases where the reinforced bars are
closely spaced, or the provided cover is less than d b , the development length must be increased ACI
R12.2.

For 4000 psi normal weight concrete and uncoated reinforcing bottom bars:

˜ d = 38 d b for No. 6 and smaller bars

˜ d = 48 d b for No. 7 and larger bars