Experimental Study of Offset Mechanical Lap Splice Behavior

Abstract

Mechanical lap splices can be an attractive alternative to conventional lap splices for applications that include providing continuous spiral reinforcement in columns, reducing the reinforcement ratio in splice regions, and splicing new reinforcing steel to existing steel in patches or structural additions. This study investigates the behavior of two commercially available offset mechanical splice systems in the context of currently-prescribed acceptance test methods and criteria. The mechanical splices were tested in direct tension with the splice both restrained and unrestrained from rotating. The splices were additionally tested in air under prescribed fatigue loading conditions. Finally, the splices were tested in place in 4.7 m (15 ft 5 in.) long concrete beams under both monotonic and fatigue loading conditions and their behavior is assessed. The findings indicate that an increase in reinforcement bar diameter resulted in a decrease in performance for each of the performance criteria considered, although most specimens still passed the criteria. The direct tension (DT) test was not necessarily as conservative as commonly assumed. The splice capacity determined by the DT test was greater than that determined by the restrained tension (RT) test, presumably due to friction between the kinked bar and coupler. The rupture of the bar at the stress raiser associated with contact between the kinked bar and coupler was the most commonly observed failure mode in DT tests, and pullout failure was the most common failure mode observed for the RT tests. There was no noticeable degradation of the in-place splice behavior resulting from fatigue conditioning as a stress range of 138 MPa (50 ksi) applied for 10,000 cycles. Recommendations based on the findings from this study are presented.