Development of connections between hybrid steel truss-FRC beams and RC columns for precast earthquake-resistant framed construction

Results from an investigation aimed at developing a moment connection for a new earthquake-resistant framing system that consists of precast hybrid fiber reinforced concrete (FRC)-encased steel truss beams and reinforced concrete (RC) columns are presented. Various connection schemes between the precast hybrid beams and RC columns were experimentally evaluated for adequate moment and shear transfer during large displacement reversals. From results of four large-scale beam-column subassembly tests, a connection scheme that features external steel rods for moment transfer and a bolted connection between the embedded steel truss and the RC column for shear transfer is proposed. The steel rods are external to the beams to facilitate installation and inspection, but can pass through or outside the precast column, depending on the beam width-to-column width ratio. Force transfer between the truss chords and the external rods is achieved through steel members forming a horizontal truss. The connection components are designed to remain elastic, forcing the inelastic activity to occur in the hybrid beam. Test specimens constructed with these connection details exhibited displacement capacities exceeding 4.0% drift, with full hysteresis loops and good strength and stiffness retention capacity. Inelastic rotations concentrated in the hybrid beams and accounted for most of the applied drift, while the connection members behaved elastically, as intended in design.