Structural Detailing of Reinforcement for Economy - Simplified Design of Reinforced Concrete Buildings - page 242

field placing problems, mechanical connections or welded splices should be considered. The location of
construction joints, provision for future construction, and the particular method of construction may also make
lap splices impractical. In columns, lapped offset bars may need to be located inside the column above to
reduce reinforcement congestion; this can reduce the moment capacity of the column section at the lapped
splice location because of the reduction in the effective depth. When the amount of vertical reinforcement is
greater than 4%, and/or when large factored moments are present, use of butt splices—either mechanical
connections or welded splices—should be considered in order to reduce congestion and to provide for greater
nominal moment strength of the column section at the splice location.

Bars in flexural members may be spliced by non-contact lap splices (ACI 12.14.2.3); however, contact lap
splices are preferred since the bars are tied and are less likely to displace when the concrete is placed.

Welded splices gene rally require the most expensive field labor. F or projects of all sizes, manual arc-welded
splices will usually be the most costly method of splicing due to the costs of inspection.

Mechanical connections are made with proprietary splice devices. Performance information and test data should
be obtained d irectly from the manufacturers. Basic information about mechanical connections and the types of
proprietary splice devices currently is available from Reference 8.4. Practical information on splicing and
recommendations for the design and detailing of splices are given in Reference 8.5.

8.5.1 Tension Lap Splices

Tension lap splices are classified as Class A or Class B (ACI 12.15.1). The minimum lap length for a Class A
splice is 1.0 ˜ d , and for a Class B splice it is 1.3 ˜ d , where ˜ d is the tension development length of the bars. When
calculating the development length ˜ d the factor in ACI 12.2.5 for excess reinforcement must not be used, since
the splice classifications already reflect any excess reinforcement at the splice location. Also the minimum of
12 in. for ˜ d does not apply for lap splice.

The minimum lap lengths for Class A splices can be obtained from Table 8-1. For Class B splices, the
minimum lap lengths are determined by multiplying the values from Table 8-1 by 1.3. The effective clear
spacing between splices bars is illustrated in Fig. 8-2. For staggered splices in slabs or walls, the effective clear
spacing is the distance between adjacent spliced bars less the diameters of any intermediate unspliced bars
(Fig. 8-2a), The clear spacing to be used for splices in columns with offset bars and for beam bar splices are
shown in Figs. 8-2b and 8-2c, respectively.

In general, tension lap splices must be Class B except that Class A splices are allowed when both of the
following conditions are met: 1) the area of reinforcement provided is at least twice that required by analysis
over the entire length of the splice and 2) one-half or less of the total reinforcement is spliced within the
required lap length (ACI 12.15.2). Essentially, Class A splices may be used at locations where the tensile stress
is small. It is very important to specify which class of tension splice is to be used, and to show clear and
complete details of the splice in the Contract Documents.

8.5.2 Compression Lap Splices

Minimum lengths for compression lap splices is 0.0005f y d b for f y of 60,000 psi or less (ACI 12.16.1).
Minimum lap splice length for Grade 60 bars in normal weight concrete are given in Table 8-4. The values