Structural Concrete - Hassoun

7.8 Splices of Reinforcement 277
Figure 7.12
Lap-splice failure due to the development of one or more cracks.
1. Class A splices: These splices have a minimum length l st = l d and are used when (a) one-half
or less of the total reinforcement is spliced within the required lap-splice length; and (b) the
area of tensile reinforcement provided is at least twice that required by analysis over the
entire length of the splice. The length l d is the development length of the bar, as calculated
earlier.
2. Class B splices: These splices have a minimum length l st = 1.3l d and are used for all other
cases that are different from the aforementioned conditions. For example, class B splices are
required when all bars or deformed wires are spliced at the same location with any ratio of
(A s provided)/(A s required). Splicing all the bars in one location should be avoided when
possible.
3. l d in classes A and B splices is calculated without the modification factor of (A s required)/
(A s provided).
4. When multiple bars located in the same plane are spliced at the same section, the clear spacing
is the minimum clear distance between the adjacent splices. For staggered splices, the clear
spacing is taken as the minimum distance between adjacent splices.
5. When bars of different size are lap spliced in tension, splice length shall be the larger of
l d of the larger bar and the tension lap-splice length of the smaller bar (ACI Code, Section
25.5.2.2).
6. Lap splice shall not be used for bars larger than no. 11 because of lack of adequate experimental
data (ACI Code, Section 25.5.1.1).
7.8.3 Lap Splice in Compression, l sc
The lap-splice length of the reinforcing bars in compression, l sc , should be equal to or greater
than the development length of the bar in compression, l dc (including the modifiers), calculated
earlier (Eq. 7.14). Moreover, the lap-splice length shall satisfy the following (ACI Code,
Section 25.5.5.1):
l sc =(0.0005f y d b ) for f y ≤ 60,000psi (7.16)
l sc =(0.0009f y − 24)d b for f y > 60,000psi (7.17)
For both cases, the lap-splice length must not be less than 12 in. Table 7.5 gives the lap-splice
length for various f y values. If the concrete strength, f ′ c, is less than 3000 psi, the lap-splice length,
l sc , must be increased by one-third. When bars of different sizes are lap spliced in compression,
splice length shall be the larger of l dc of larger bar and compression lap splice l sc of smaller bar.
Lap splices of no. 14 and no.18 to no. 11 and smaller shall be permitted.