Effect of Confinement and Gauging on the Performance of MMFX High Strength Reinforcing Bar Tension Lap Splices

Six beam specimens were tested with MMFX bars spliced in a constant moment region. Test variables included the use of transverse reinforcement and its spacing, and the number of spliced bars in the beam specimens. In all specimens, the bar size, concrete strength, splice length and the bar cover was held constant. Splice confinement was varied using transverse reinforcement.

The splice lengths were instrumented with strain gauges to monitor bar stress distribution along the splice length. Four of the beam specimens included two spliced bars, with two of those specimens part of a collaborative test program mandating strain gauges on splice ends only. The remaining two specimens had three spliced bars to compare the behavior of the interior splice to that of the exterior splice. The interior splice was thought to be confined less than the exterior splice; however no difference in behavior was noted.

Test results were compared with computed values using current development length equations. Stress variation along bars was linear. More splice confinement provided increased splice capacity. At high working stress levels (80-100 ksi) crack widths exceeded code serviceability requirements for Grade 60 reinforcement. No difference was noted in splice behavior when the splice length was gauged compared to the splice ends gauged only.