Comparative behavior of circular precast UHPC columns with hoops and spiral reinforcement

Ultra-high performance concrete (UHPC) offers outstanding mechanical properties that can greatly influence the future of our structures. Despite the remarkable durability and high tensile and compressive strength of UHPC, its widespread use in large structural applications remains limited. This limitation is attributed to several factors such as the relatively high cost of the material and the slow development of large-scale production technology and procedures. In light of these challenges, the objective of this research is two-fold: first, demonstrate the successful fabrication of four full precast UHPC columns using economic mixture and construction-scale production in a precast plant setting, and next, compare the axial behavior of the fabricated circular columns with different transverse reinforcement detailing. The study carefully considers the choice of lateral confinement and spacing along the height of the column (spiral and hoop reinforcement with 1.5 in and 3 in spacing). The paper presents the global and local behavior that include load capacity, stiffness, axial and reinforcement strains, and ductility. The spirally confined column with 1.5 in spacing showed 26 % higher ductility than the counter hoop reinforced column, while both configurations showed a significant increase in ductility of 34 % when the transverse reinforcement spacing is reduced from 3 to 1.5 in. The research shows that the ACI design reduction factor for conventional concrete (0.65) and the accidental eccentricity reduction factor (0.8) for hoops are unnecessarily conservative and might be increased to 0.75 and 0.85, respectively as for the spiral reinforcement in the case of UHPC columns.