Structural Detailing of Reinforcement for Economy - Simplified Design of Reinforced Concrete Buildings - page 250

Lap splices, welded splices, and mechanical connections are permitted when the bar stress is tensile;
end-bearing splices must not be used (ACI 12.16.4.1). According to ACI 12.14.3, full welded splices and full
mechanical connections must develop in tension at least 1.25 A b f y . When the bar stress on the tension face of
the column is less than or equal to 0.5 f y , lap splices must be Class B if more than one-half of the bars are
spliced at any section, or Class A if half or fewer of the bars are spliced and alternate splices are staggered by
the tension development length ˜ d (ACI 12.17.2). Class B splices must be used when the bar stress is greater
than 0.5 f y .

Lap splice requirements for columns are illustrated in Fig. 8-9. For factored load combinations in Zone 1, all
column bars are in compression. In Zone 2, the bar stress f s on the tension face of the column varies from zero
to 0.5 f y in tension. For load combinations in Zone 3, f s is greater that 0.5 f y . The load combination that
produces the greatest tensile stress in the bars will determine which type of lap splice is to be used.
Load-moment design charts (such as the one in Figs. 5-17 through 5-24 in Chapter 5) can greatly facilitate the
design of lap splices for columns.

Typical lap splice details for tied columns are shown in Fig. 8-10. Also given in the figure are the tie spacing
requirements of ACI 7.8 and 7.10.5 (see Chapter 5). When a column face is offset 3 in. or more, offset bent
longitudinal bars are not permitted (ACI 7.8.1.5). Instead, separate dowels, lap spliced with the longitudinal
bars adjacent to the offset column faces must be provided. Typical splice details for footing dowels are given
in Chapter 7, Fig. 7-7.

8.8.3 Example: Lap Splice Length for an Interior Column of Building #2, Alternate (2) Slab and

Column Framing with Structural Walls (Non-sway Frame)

In this example, the required lap splice length will be determined for an interior column in the 2nd story; the
splice will be located just above the 9 in. floor slab at the 1st level.

(1) Column Size and Reinforcement

In Example 5.7.2, a 16 16 in. column size was established for the entire column stack. It was
determined that 4-No.8 bars were required in both the 1st and 2nd floor columns.

(2) Lap Splice Length

Since the columns carry only gravity loads, all of the column bars will be in compression (Zone 1 in
Fig. 8-9). Therefore, a compression lap splice is sufficient.

From Table 8-4, the minimum compression lap splice length required for the No.8 bars is 30 in. In this
situation, No.3 ties are required @ 16 in. spacing.

According to ACI 12.17.2.4, the lap splice length may be multiplied by 0.83 if ties are provided with
an effective area of 0.0015hs throughout the lap splice length.