Confining stress path-based compressive strength model of axially compressed circular concrete-filled double-skin steel tubular short columns

Previous investigations have shown that the confining stress paths (CSPs) of confined concrete significantly affected the compressive behaviour of confined concrete in fibre-reinforced polymer (FRP) confined concrete or concrete-filled steel tube (CFST) columns. Unlike the concrete in FRP-confined concrete or CFST columns, which is only confined by external materials, e.g., FRP sheet or steel tube, the concrete in concrete-filled double-skin steel tubular (CFDST) columns is confined by both the external and internal steel tubes. Due to different confinement mechanisms, the CSPs of confined concrete in CFDST columns may be different from those in FRP-confined concrete or CFST ones, but they have not been investigated so far. In this paper, the CSPs of confined concrete in circular CFDST stub columns were experimentally investigated, and their corresponding influences on the compressive strength were also discussed. It is shown that the CSPs of confined concrete induced by the external tube are considerably influenced by column variables, whereas those generated by the internal tube found no obvious trend. Moreover, the results suggest that the compressive strength of confined concrete in specimens with a confinement coefficient eta less than 2.731 is CSP-dependent, based on which, a compressive strength model of confined concrete considering the CSP effect is developed for circular CFDST columns. Based on this model, a CSP-based compressive strength model for estimating the ultimate strength of CFDST columns is proposed, and comparison with existing models against the collected test data indicates a higher accuracy of the predictions for the proposed model.