Seismic performance of a novel interior precast concrete beam-column joint using ultra-high performance concrete

In traditional precast reinforced concrete (RC) frame structures, the reinforcement details are usually complex in the joint zone, which makes the fabrication process difficult and thus affects the construction quality and speed. Ultra-high performance concrete (UHPC) exhibits substantially higher shear resistance and bond strength than normal concrete due to its much larger compressive and tensile strengths. As a result, the application of UHPC can significantly help reducing the amount of stirrups and anchorage length of the longitudinal bar in the joint zone of precast RC frames, which can obviously simplify the joint construction. This paper presents the cyclic tests of four interior precast UHPC/RC composite beam-column joints to evaluate quantitatively the effect of replacing the normal concrete by UHPC in the joint zone. Considering that the condition of steam curing is difficult to achieve in the actual construction environment, the non-steam-cured UHPC was adopted and proved to exhibit adequate compressive (> 120 MPa) and tensile strength (> 7 MPa) with the ultimate tensile strain larger than 1%. The main variables in this study are the anchorage methods, anchorage lengths and stirrup ratios in the joint zone. The cyclic load tests demonstrate that the cast-in-situ UHPC can work well with the precast concrete and there is no need of stirrups in the UHPC joint zone. With the use of UHPC instead of normal concrete, the anchorage length of the beam straight and headed bars can be decreased to 16d(b) and 8.1d(b), respectively. Therefore, the application of UHPC in the joint zone is practicable and can greatly ease the fabrication process, especially with the use of headed bars.