Members behavior of concrete-filled cold-formed steel oval hollow sections

Abstract

In the past several decades, concrete-filled steel tubular (CFST) members with conventional sections such as square, rectangular and circular sections have been widely used in structural applications, which have large deformability and good toughness because of the confinement stresses between the steel tube and the infilled concrete. Due to the increasing demand for aesthetic appearance and reliable structural performance, the oval hollow sections, including elliptical and semi-oval hollow sections, have been newly developed in the steel manufacturing industry. This research aims to investigate the members behavior of concrete-filled cold-formed steel oval hollow sections, and to develop design guidance for these novel sections. The experiment investigations in this research consisted of 20 material tests, 26 stub column tests, 52 beam tests and 98 short pin-ended column and beam-column tests. Eight cross-section series of concrete-filled cold-formed steel oval hollow sections, including four on elliptical sections and four on semi-oval sections, were included in the test program. Tensile coupons were extracted from each section and examined to obtain the corresponding material properties. Flexural behavior of concrete-filled cold-formed steel oval hollow sections was investigated through four-point bending tests. The pin-ended columns and beam-columns were loaded through a pair of knife edges with equal eccentricities at both ends. Accurate finite element models on concrete-filled cold-formed steel oval hollow section structural members, including stub columns, beams, pin-ended columns and beam-columns, were developed and validated against test results using Abaqus 6.19 software. The FEM results indicated that the models can reflect the essential test results, including the ultimate load-carrying capacities, failure modes and load-displacement responses. Based on validation of the finite element models, extensive parametric studies on 102 stub columns, 216 beams and 276 short pin-ended columns and beam-columns were performed. The test data as well as the numerical results were used to evaluate the feasibility of the existing design specifications, including the American specification, European code and Australian/New Zealand standard designated for conventional concrete-filled tubular sections, on concrete-filled oval sections including elliptical and semi-oval sections. The results indicated that the current design specifications are not able to provide accurate and reliable predictions for concrete-filled elliptical and semi-oval section members. New design rules are proposed in this study to improve the accuracy of the design strength predictions. Reliability analysis was performed for the current design rules and proposed design rules.