Experimental and numerical study on axial compressive behaviors of reinforced UHPC-CFST composite columns

•RU-CFST columns consisted of peripheral reinforced UHPC and inner CFST were proposed.•The compressive strength and ductile of RU-CFST column was significantly promoted compared to the reinforced UHPC column.•The composite effects as well as the failure mechanism of RU-CFST columns were revealed based on the proposed FE model. To improve the fragility of UHPC columns, reinforced UHPC-concrete filled steel tube (RU-CFST) columns conjugated of peripheral reinforced UHPC and inner CFST were proposed. An axial compressive test program consisting of three RU-CFST columns and one reinforced UHPC (RU) column was conducted to study the effects of steel tube thickness and stirrup spacing on the compressive behaviors of RU-CFST columns. The test results indicated that the sudden drop of load beyond the ultimate load was effectively improved and the compressive strength as well as ductile of the RU-CFST columns were significantly promoted compared to that of the RU column. Based on the experimental results, three-dimensional FE models were developed to simulate the axial compressive performance of the RU-CFST columns, and their accuracy was confirmed by the test results. With the validated FE model, the effects of steel tube thickness, stirrup spacing and core concrete strength on the compressive behaviours of RU-CFST columns were further investigated. Finally, calculating method considering the contribution ratio of the inner CFST component was developed to predict the ultimate bearing capacity of the RU-CFST columns.