Numerical analysis and design of thin-walled RECFST stub columns under axial compression

Abstract Round-ended elliptical concrete-filled steel tube (RECFST) column is a novel type of composite member which is gradually used in engineering practices (i.e. piers and arches) because of its low flow resistance coefficient and reasonable distribution of major-minor axis. However, little attentions to the structural behavior of RECFST columns have been paid. This paper makes an attempt to conduct a numerical analysis on the axial compressive performance of RECFST stub columns. Firstly, an equivalent constitutive model for the confined round-ended concrete of the RECFST column was proposed. Following this, a nonlinear finite element (FE) modeling considering contact interactions of the type of thin-walled CFST column was developed and verified by the test results in terms of axial load (N) - longitudinal shortening (δ) curves and failure modes. The influence of extensive parameters, including diameter-to-thickness ratio, aspect ratio and cross-section area etc., on the performance of thin-walled RECFST stub columns under axial compression was estimated as well. The analytical results demonstrated that the axial compressive strength of thin-walled RECFST stub columns was substantially improved with the increase of the steel strength, the concrete strength and the cross-section area, and the trend of the N-δ curves was obviously affected by the confinement factor. Finally, two simplified design methods to predict the axial compressive strength of thin-walled RECFST stub columns were established on the basis of the simple superposition approach and the unified theory. The studies may provide a considerable reference for designing this type of structures in engineering practice.