Shear strength and drift capacity of fiber-reinforced concrete slab-column connections subjected to biaxial displacements

Results from the tests of three large-scale slab-column subassemblies subjected to combined gravity load and biaxial lateral displacements are presented. The main purpose of the experimental program was to investigate the use of randomly oriented steel fiber reinforcement as a means to increase connection punching shear strength and deformation capacity. The connection of Specimen SB1 was reinforced with regular strength (1,100 MPa) fibers, 30 mm long and 0.55 mm in diameter, while the connection of Specimen SB2 featured high-strength (2,300 MPa) fibers, 30 mm long and 0.38 mm in diameter. Both types of fibers were targeted at a 1.5% volume fraction. The connection of Specimen SB3, on the other hand, was reinforced with shear studs, designed according to the 2008 American Concrete Institute Building Code. All three connections were subjected to a gravity shear ratio of approximately 1/2 during application of biaxial lateral displacements. The use of fiber reinforcement in the connection region resulted in superior deformation capacity compared to the connection with shear stud reinforcement. Average connection rotation, just before punching, was approximately 0.04 rad in the two fiber-reinforced concrete connections. On the other hand, shear stud reinforcement seems to have had little effect on connection ductility. The connection with shear stud reinforcement failed at an average rotation of 0.023 rad. Inspection of this connection after the test indicated a breakout failure of the concrete engaged by the second line of studs accompanied by severe bending of the bottom steel rail.