Masonry lap splice
The lap or development length of one bar size in grouted concrete masonry, to TMS 402-22 6.1.6 and 6.1.7. The equation is the same for strength and allowable stress design, so the LRFD / ASD switch is not shown.
Edition. The design basis is TMS 402-22 / TMS 602-22. The text of the 2022 code is not on hand. Section numbers come from TMS's cross-reference, the hook rule from TMS's 2022 handout, and the wording was read in TMS 402-13 and in a 402-16 summary table. The 402-22 equation numbers are not confirmed: the steps give the 402-13 ones.
Inputs of the masonry lap splice #
- Length to check: a lap, a straight bar's development, or a bar with a standard hook.
- Bar: No. 3 to 11, Grade 60 or 40, epoxy-coated or not. The length provided is checked against the length required.
- Masonry: f'm, wall thickness, the position of the bar: centre of the wall (cover worked out) or near a face (cover entered). Limit the f'm used is on by default at 4,000 psi; turn it off to use f'm as entered.
- Splice spacing: centre to centre of adjacent splices. K uses the clear distance between them; the bars spliced together do not count.
- Lap: contact or noncontact, with the distance between the bars.
- Transverse bars in the lap: off by default. On, with the conditions as inputs: a bar within 8 in. of each end, at most 1.5 in. clear of the lapped bars, fully developed. If any is not met, the lap is not reduced and the calculation says so.
Auto-design (editor toolbar) varies the length provided, in whole inches. Objective: the shortest length provided.
Checks performed #
| Check | Basis |
|---|---|
| Length required against provided | ld = 0.13 db² fy γ / (K √f'm), at least 12 in. (402-13 Eq. 9-16); K the least of the cover, the clear spacing and 9 db; γ 1.0, 1.3, 1.5; epoxy 150 percent |
| Transverse bars | ξ = 1.0 − 2.3 Asc / db^2.5, Asc at most 0.35 in.²; not below 36 db, and never longer than the lap without them (402-13 Eq. 9-18) |
| Standard hook | ldh = ld − γh db, γh 9.0 for No. 3 to 8, 8.0 for No. 9 to 11 (TMS 2022 handout) |
| Noncontact lap | Bars at most one-fifth of ld and 8 in. apart |
| Bar size | 6.1.3: db at most 1/8 of the wall and 1/3 of the grout space; bars at most 8 % of the grout space at a contact lap, 4 % elsewhere |
The drawings are the bars in elevation with the lengths, and a plan of the wall at the bars. Hook geometry is schematic.
Limitations #
- Concrete masonry. The clay masonry rules were not read for the 2022 code.
- The order of the epoxy factor and the reduction by transverse bars is this calculation's reading: epoxy first. The code's least length for a hook is not on hand, so none is applied beyond ld's 12 in. (to confirm against the code text).
- Welded and mechanical splices, joint reinforcement and wires are not sized. Seismic rules for where splices may sit are not checked.
Verification examples #
Verification status: 84 values compared in 79 examples (73 published, 6 hand calculations from the cited equations): 83 within tolerance, 1 recorded deviations. Code basis: written from an older edition, with the differences noted. Not yet compared line by line with the target edition.
Published: Masonry Designers' Guide Example 9.2-1 and Table 9.2.5, both as printed in TMS's ASD Night School 6 handout (March 2022, written to 402-16), slides 21 and 22: the cover, K and the 19.5 in. lap, and all 72 table values that have a number, at three f'm, three bar positions and nine bars. 71 agree. One is a recorded difference, on the Verification page: the table prints 12 in. for 12.27 in., where its other values round up. The dashes in the table are bars the size limit refuses here too.
Hand calculations, since no free example has them: epoxy, spacing governing K, a hook, transverse bars and the 36 db limit, the noncontact limit. The hook rule is from the 2022 handout. Nothing here is checked against the 402-22 text.