Source: National Concrete Masonry Association, Herndon, Va.

Effects of Confinement Reinforcement on Bar Splice Performance – Summary of Research and Design Recommendations documents four testing phases to determine the effect of confining steel reinforcement on lap-splice strength in reinforced concrete masonry construction. The NCMA Research and Development Laboratory report concludes that confining reinforcement demonstrably enhances splice strength and enables shorter lap lengths for many configurations, and offers recommendations for modifying existing building code equations to account for horizontal confinement when determining lap splice lengths. 

The current report was prompted by research conducted in the 1990s, quantifying performance of lap splices in reinforced masonry construction and identifying failure modes not previously accounted for in masonry design standards. The study pointed to a need for longer lap lengths, which encourages longitudinal splitting of masonry along the length of the lap splice. As documented, the dominant failure mode of lap splices in masonry construction, when loaded in direct tension, is longitudinal splitting along the length of the lap; and, once developed, the crack propagates almost instantaneously, releasing the spliced reinforcing bars. Since spanning the longitudinal crack with reinforcement running transverse to the lap splice could mitigate crack propagation and increase the strength of the lap splice, NCMA’s most recent research aimed to quantify the effect of transverse reinforcement on confining the lap splice and document how detailing variables, e.g., location and quantity of confining reinforcement, influence performance.