The influence of percentage of bars lapped on performance of splices

Most design codes encourage the staggering of lapped splices in a section, such that a portion of the bars in the cross section remains continuous throughout the lap zone. A penalty on lap length may be imposed if all bars are lapped at one section. In the literature, however, almost all tested specimens have had all reinforcement lapped at the same section. This paper presents results of tests carried out to shed some new light on the behaviour of lap splices where only a portion of bars is lapped. To this end, four point bending tests were carried out on 24 full-scale beams with all or part of the longitudinal reinforcement lap spliced at mid-span. The beams were reinforced with either 16 or 20 mm diameter rebars, included two grades of concrete and various lap splices configurations, all confined by links. All the beams were designed with the same concrete cover and with the minimum amount of transverse reinforcement permitted by MC2010, equal to 50 % of the area of the lapped bars. The resistance and the residual strength of the splices were measured and compared with the results of specimens with continuous bars and with all bars lapped. The results show that lapping only a portion of bars at a section impairs splice strength, although some post-peak strength is maintained by the continuous bars. These outcomes raise questions over the validity of EC2 and ACI 318-11 provisions which allow a reduction in lap-length when splices are staggered.