Reinforcement detailing effects on axial behavior of full-scale UHPC columns

Ultra-high performance concrete (UHPC) applications are currently expanding worldwide from bridge deck joints and connections to full components and larger applications. UHPC has superior structural properties relative to other cementitious materials with multiple times the compressive and tensile strength, durability, and ductility. These outstanding mechanical properties of UHPC make it a strong candidate for full structural columns. The goal of this study is to provide experimental demonstration and reliable datasets of UHPC columns to validate current analytical procedures and inform future designs. This paper presents results and discussions from five full-scale UHPC columns tested at a 4 million-lb machine. The first objective is to analyze the experimental behavior of long UHPC columns with negligible slenderness effects and varying reinforcement details, i.e. different longitudinal, transverse, and fiber reinforcement ratios, under concentric axial loading. The second objective is to inspect the validity of ACI 318 equations for estimating the UHPC columns axial compressive strength. The results indicated that using the actual material properties of UHPC and longitudinal bars for ACI 318 equations overestimates the axial load capacity of columns with different reinforcement details by approximately 13% on average. Furthermore, a new strength reduction factor of 0.75 is suggested (instead of 0.85) for estimating axial capacity of UHPC columns with slenderness limit less than 30.