Effectiveness of Steel Fibers as Hoops in Exterior Beam-to-Column Joints under Cyclic Loading

Abstract

In this study, the seismic performance of reinforced concrete beam-column joint subassemblies reinforced with steel fiber was evaluated through experiments. A total of seven specimens were used, and four steel fiber-reinforced specimens were planned based on the amount of steel fiber; the presence or absence of hoops of joints, and the spacing of hoops arranged in the beam. The steel fibers used were determined to have properties that could be used to replace the minimum shear reinforcement in beams proposed by ACI 318. To evaluate the seismic performance quantitatively, a loading protocol was applied based on the displacement control protocol of ACI 374. Experimental results showed that reinforcement of steel fiber improves the shear strength of the joint itself. The shear strength of the joint increased as the amount of steel fiber was increased. However; the increase rate of the shear strength of the joint decreased with increasing steel fiber content. A large seismic performance improvement was confirmed when the hoop spacing on the beam was widened and the steel fiber was used with the hoop of the joint. Simultaneous reinforcement of steel fiber and the hoop with increased hoop spacing on the beam caused more damage on the beam and reduced the joint shear strength. Seismic performance evaluations according to ACI 374 showed that performance similar to that of the hoop rein forced joint can be expected when steel fiber with 2% volume fraction is used instead of the hoop in the joint region.