Effect of UHPC jacketing on the shear and flexural behaviour of high-strength concrete beams

Abstract

Ultra-high performance concrete (UHPC) is an advanced material which shows high compressive strength, tensile resistance, toughness and durability when compared to conventional concrete. One of the potential applications of UHPC is in the retrofit of ageing or deteriorated reinforced concrete structures. However, limited research exists on the use of UHPC to strengthen higher strength concrete members (with compressive strength exceeding 80 MPa). This paper examines the ability of UHPC to improve the shear and flexural performance of high-strength concrete (HSC) beams. As part of the tests two shear-deficient HSC beams built without stirrups, and having 15M or 20M bars (steel ratios of 1.6% and 2.4%), were retrofitted with a thin UHPC jacket and tested under four-point bending. The results are compared to a control set of HSC beams built with and without stirrups. The effect of steel ratio in the retrofitted beams was also investigated. The results show that the UHPC jacketing significantly increased the shear capacity by 40–125% in the shear-deficient HSC beams, allowing the beams to reach their full flexural resistance. The UHPC retrofit also allowed for improved flexural performance, with increases of 80–85% in stiffness, 20–35% in flexural strength and 40–180% in ductility when compared to the control beams built with stirrups. The failure mode and ductility in the UHPC retrofitted beams was affected by the longitudinal steel ratio, with the failure transitioning from bar fracture to concrete crushing as the steel ratio in the reference HSC beams was increased from 1.6% to 2.4%. To supplement the engineering case, finite element modelling is used to study the influence of other retrofit types, as well as the shear-span-to-depth ratio.