Eccentric compression behaviour and assessment of CFET short columns offering spherical-cap gaps

Abstract

This paper designs and tests a total of 14 specimens to explore the effect of load eccentricity and spherical-cap gap on the compressive strength, ductility, failure modes, and strain distribution of the concrete-filled elliptical steel tubular (CFET) short columns with spherical-cap gaps. A finite element (FE) model of the eccentrically-pressured CFET short column is established by taking the characteristics of spherical-cap gap and elliptical cross-section into consideration. Extensively parametric studies on the impact of various geometric and material variables are further developed via FE analytical models. Intensive mechanical responses, such as the contact pressure between concrete core and hollow steel section (HSS) and the compressive stress at the mid-height cross-section, are presented as well. Based on the comparison between the test results and the predicted data obtained from the design provisions in specifications EN 1994–1-1, AISC 360–16, and GB 50936–2014, proper design formulae for evaluating the eccentric compressive strength of the CFET-SG short columns are proposed. The research results show that the existence of the spherical-cap gap significantly weakened the interaction between the HSS and the concrete core, leading to a reduction in the eccentric compressive strength and ductility behaviour. The concrete around the gap region appeared brittle collapse due to the shrinking confining effect of the HSS, and the HSS exhibited inward and outward local buckling because of the lack of concrete supporting action. The observations of this paper may furnish a scientific reference for the performance evaluation and prevention measures of CFET short columns with spherical-cap gap defects.