Stress-strain evaluation of steel-strapped high-strength concrete with modified self-regulating end clips

Abstract

High-strength concrete (HSC) is increasingly used in columns of building all over the world. Although it offers superior properties, it is relatively a brittle material. This study intends to improve the ductility of HSC using modified pretensioning confinement technique. It investigates the effects of the technique on the performance of the column and develops equations to predict the stress–strain. The basis of the technique is to apply a pretensioning force to relatively low-cost steel straps wrapped around the specimens. A modified end clip which is able to be self-regulated is used to secure the strap ends. The parameters studied include various spacing between straps and number of layers of straps. The confined specimens were tested in compression until failure under monotonic loading conditions, focusing particularly on the mode of failure, loads at peak and ultimate conditions and longitudinal and lateral strains in both concrete and straps. It was observed that the pretensioning technique using steel straps enhanced the ductility as well as the strength of the concrete as the confining ratio increases. Moreover, the layers of straps had also delayed the onset of volumetric expansion and therefore, the concrete failure. Based on the regression analysis, new equations of strength and strain for the confined HSC column have been developed to predict its stress–strain behavior.