Behavior of Ultrahigh-Performance Concrete Confined by Steel

Abstract

Ultrahigh-performance concrete (UHPC) offers a superior alternative to normal-strength concrete (NSC) due to its significantly higher compressive and tensile strengths, improved ductility, and enhanced durability. This paper presents an experimental study of the stress-strain behavior of UHPC confined by conventional transverse steel reinforcement. Test results are compared with two confinement models, as well as a large amount of available data on steel-confined NSC and high-strength concrete (HSC), and limited data available for UHPC confined by fiber-reinforced polymers (FRP). The study shows a potential threshold of confinement ratio beyond which the confinement effectiveness of UHPC exceeds that of HSC and nears that of NSC. This may have implications on the minimum level of confinement reinforcement for UHPC. For the most part, steel reinforcement is more effective than FRP as the confining device for UHPC, except for the very high end of confinement ratios, where FRP may become more effective. For the same confinement ratio, steel-confined UHPC has a larger ultimate strain than FRP-confined UHPC. Of the two types of FRP, glass leads to a higher ultimate strain than carbon, primarily due to its lower elastic modulus, and hence higher deformability. Additional research on larger-scale columns can help develop requirements for confinement reinforcement of UHPC.