1. Anchor
Channel Systems
2. HAC
Portfolio
3. HAC
Applications
A reduction in development length is permitted in limited
circumstances. If the flexural reinforcement provided exceeds
the amount required to resist the factored moment required by
analysis, reduction of development length is allowed. In such a
case, ACI 318-14, §25.4.10 allows to be multiplied by (A s,required /
A s,provided ).
Additional requirements
ACI 318-14, §18.8.5.3 For bar sizes No. 3 through No. 11, ℓ d , the
development length in tension for a straight bar, shall be at least
the greater of (a) and (b):
(b) 3.25 times the length in accordance with 18.8.5.1 if the depth
of the concrete cast in one lift beneath the bar exceeds 12 in.
The ACI concept of development length is based on the
attainable average bond stress over the length of embedment of
the reinforcement.
If a reinforcing bar provides the required development length,
the reinforcing bar will yield before it is pulled-out of the
concrete. In situations where the force at the reinforcing bar is
less than its yield strength, ACI 318 allows reducing the excess
reinforcement.
9. Special Anchor
Channel Design
10. Design
Software
Pullout strength of reinforcing bar per ACI
318-14 with (c b + K tr )/d b < 2.5
11. Best
Practices
R25.4.2.2 This provision recognizes that many current practical
construction cases use spacing and cover values along with
confining reinforcement, such as stirrups or ties, that result in a
value of (c b + K tr )/d b of at least 1.5. Examples include a minimum
clear cover of d b along with either minimum clear spacing of 2d b ,
or a combination of minimum clear spacing of d b and minimum
ties or stirrups. For these frequently occurring cases, the
development length for larger bars can be taken as
ℓ d = [f y ψ t ψ e /(20λ√(f′ c )]d b . In the formulation of the provisions in
ACI 318-95, a comparison with past provisions and a check of
a database of experimental results maintained by ACI 408.1R
indicated that for No. 6 deformed bars and smaller, as well as
for deformed wire, the development lengths could be reduced
20 percent using ψ s = 0.8. This is the basis for the No. 6 and
smaller bars and deformed wires column of Table § 25.4.2.2.
12. Instructions
for Use
13. Field Fixes
14. Design
Example
With less cover and in the absence of minimum ties or stirrups,
the minimum clear spacing limits of 25.2.1 and the minimum
concrete cover requirements of 20.6.1.3 result in minimum
values of c b equal to d b . Thus, for “other cases,” the values are
based on using (c b + K tr )/d b = 1.0 in Eq. (25.4.2.3a).
As long as minimum cover of d b is provided along with a
minimum clear spacing of 2d b , or a minimum clear cover of db
and a minimum clear spacing of d b are provided along with
minimum ties or stirrups, then ℓ d = 47d b . The penalty for spacing
bars closer or providing less cover is the requirement that
ℓ d = 71d b .
§ 25.4.2.2 For deformed bars or deformed wires, ℓ d shall be
calculated in accordance with Table 25.4.2.2.
The simplified development length equation for a reinforcing bar
in tension is as follows:
ACI 318-11 Equation (25.4.2.3a) for deformed bars in tension
can be recast in terms of an equivalent bond stress equation as
follows:
A sfy = τ bond πd b ℓ d
τ bond is the equivalent bond stress
Substituting A s = πd b 2 /4, the following expression for bond
can be derived from the development length equation given in
Section 12 2 3:
y
N p , R =
d
æ 3 ö
= ! d , prov ç ÷ l
è 40 ø
Spacing and cover No. 6 and smaller bars and
deformed wires No. 7 and larger bars
Clear spacing of bars or wires being developed or
lap spliced not less than db, clear cover at least d b ,
and stirrups or ties throughout ℓ d not less than the
Code minimum
where
( f = ) s
Table 8.3.1.1 (ACI 318-14 Table 25.4.2.2) —Development length for deformed bars and deformed wires in tension
or
Spacing and cover No. 6 and smaller bars and
deformed wires No. 7 and larger bars
Spacing and cover No. 6 and smaller bars and
deformed wires No. 7 and larger bars
æ f y y t y e
ç
ç 25 l f '
c
è ö
÷ d
÷ b
ø æ f y y t y e
ç
ç 20 l f '
c
è ö
÷ d
÷ b
ø
æ 3 f y y t y e
ç
ç 50 l f '
c
è ö
÷ d
÷ b
ø æ 3 f y y t y e
ç
ç 40 l f '
c
è ö
÷ d
÷ b
ø
Clear spacing of bars or wires being developed or
lap spliced at least 2 db and clear cover at least d b
Other cases
æ c + k tr ö æ 1 ö æ 1 ö
÷ ÷ ç ç ÷ ÷
÷ ÷ ç ç
f c ' ç ç b
è d b ø è y t y e y s ø è d b ø
ACI 318-14, §18.8.5.4 Straight bars terminated at a joint shall
pass through the confined core of a column or a boundary
element. Any portion of ℓ d not within the confined core shall be
increased by a factor of 1.6.
Pullout strength of reinforcing bar per ACI
318-14, §25.4.2.3
8. Reinforcing
Bar Anchorage
.5 times the length in accordance with 18.8.5.1 if the depth
(a) 2
of the concrete cast in one lift beneath the bar does not
exceed 12 in.
8.3 PULLOUT STRENGTH OF
STRAIGHT REINFORCING
BARS
7. Anchor Channel
Design Code
ℓ d shall not be taken less than 12 in.
6. Loading
p d s 2, R
4
æ 10 ö
N p , R = ! d , prov p d b ç ÷ l
è 3 ø
é
ö ù æ 1 ö
æ c + k tr
÷ ÷
f c ' ê min ç ç b
, 2 . 5 ÷ ÷ ú ç ç
d
b
ø û è y t y e y s ø
è
ë
Pullout strength reduction ∅-factor
ACI 318-14 development length equation does no require a ∅
factor to be applied to the development length equation. An
allowance for strength reduction is already included in the
expression for determining development length. R25.4.1.3
When calculating the pull-out strength of the reinforcing
reinforcing bar, per ACI 318-14, §17.4.2.9 a reduction factor, ∅ of
0.75 shall be applied to the nominal pull-out rebar strength.
206
A reduction of development length in accordance with 25.4.10.1
is not permitted for (a) through (e): (a) At non-continuous
supports
(b) At locations where anchorage or development for f y is
required
(c) Where bars are required to be continuous
(d) For headed and mechanically anchored deformed
reinforcement
(e) I n seismic-force-resisting systems in structures assigned to
Seismic Design Categories D, E, or F
5. Base material
Reduction of development length for excess
reinforcement
4. Design
Introduction
Cast-In Anchor Channel Product Guide, Edition 1 • 02/2019
207