Restoring force model of high‐strength concrete‐encased CFST composite columns

Abstract

SummaryTo investigate the seismic behavior of high‐strength concrete‐encased concrete‐filled steel tube (HSC‐encased CFST) composite column, eight specimens with a high axial compression ratio were tested under lateral cyclic loading and constant axial compressive loading in this paper. Key points on the load–displacement skeleton curve of the composite columns were obtained based on the experimental results. The test parameters include the axial compression ratio, volume stirrup ratio, stirrup form, and the diameter‐width ratio. All specimens failed in the flexural mode, with the crushing of compressive concrete and losing of vertical load‐carrying capacity. The ductility and deformation capacity decrease with the axial compression ratio increasing, and enhancing the volume stirrup ratio within 1.33–1.63% can provide an effective confinement of composite column. The ultimate strength of specimen with the octagonal stirrup is 23.8% higher than that with well stirrup, and the ductility and load‐carrying capacity are enhanced due to the increase of diameter‐width ratio. A degrading trilinear restoring force model of HSC‐encased CFST composite column with a high compression ratio is proposed. The comparisons made between calculated results and test results show such a high agreement, which indicates the proposed restoring force model is applicable to such HSC‐encased CFST composite column. It provides a theoretical basement for further research on the nonlinear dynamic analysis of such CFST composite column.