Effect of Steel Fiber Volume Fraction on Cover Damage Control and Ductile Rod Development in Precast Concrete Beam–Column Ductile Connections

Precast concrete ductile connections are designed to dissipate energy through yielding of the ductile rods, but early cracking and cover spalling of the joint concrete have been reported to limit the plastic deformation developed by the rods. This study examines whether steel fibers suppress this damage in a connection whose joint transverse reinforcement has been reduced. Five full-scale interior beam–column subassemblies, one monolithic specimen and four DDC ductile connections, were subjected to reversed cyclic loading in accordance with ACI 374.1-05, with joint transverse reinforcement ratios of 1.59% and 0.79% and steel fiber volume fractions of 0%, 1% and 2% as the variables. Joint crack width, joint shear strain, and the strains in the joint transverse reinforcement and in the ductile rods were measured. When the transverse reinforcement ratio was halved without fibers, the joint crack width increased, yielding of the transverse reinforcement was recorded, and the lateral resistance retained in the third cycle at the acceptance drift level did not satisfy the strength criterion of ACI 374.1-05. With 1% of steel fibers in the same detail, the joint crack width decreased, and no yielding of the transverse reinforcement was recorded, but the secant stiffness around zero drift in the negative loading direction did not satisfy the stiffness criterion of ACI 374.1-05. With 2% of fibers, the joint crack width decreased further, the three acceptance criteria were satisfied, and load was sustained up to large story drift ratios. The maximum measured joint shear strain was lower than the strain at which the joint shear strength is developed; for the specimen with 2% fibers, this observation applies only up to the 2.0% drift level. One specimen was tested for each configuration; within the configurations tested, the steel fibers were observed to restrain crack propagation in the joint concrete and to affect the cyclic behavior of the connection.