Experimental behavior of interior and exterior steel-concrete composite NPS® beam-column joints

This paper presents the results of an experimental program involving a series of seven full scale composite steel-concrete beam-column joints part of the "New Performance System" (NPS®). The NPS® is a novel steel-concrete composite moment resisting frame that utilizes steel wrapped reinforced concrete (RC) columns and steel-concrete composite beams, reinforced with steel truss elements made with bottom plates to double as partial formwork. Prior to this project, no experimental evidence was available to provide insight into the performance of the NPS®. In addition to the four interior and the three exterior NPS® specimens, two moderately ductile reinforced concrete (one interior and one exterior) beam-column joints, designed per Eurocode requirements and intended to serve as reference, were tested in the experimental program. The specimens were tested under quasi-static reversed cyclic horizontal loading, with a constant axial load applied to the column. The variables considered were the moment continuity solution through the beams and joint region, the level of shear reinforcement provided within the joint panel zone, and the presence/absence of additional shear reinforcement in the beam end-regions. The experimental results demonstrated that, if properly designed, the NPS® can achieve adequate strength, stiffness, ductility and energy dissipation, meeting modern seismic performance objectives. The analysis of the experimental results further demonstrated that, if properly detailed, the NPS® can meet or surpass the performance of a traditional Eurocode compliant RC specimen, designed to achieve moderate ductility.