Residual axial capacity of CFDST columns infilled with UHPFRC after close-range blast loading

•Experiment was conducted to investigate the residual capacity of blast damaged CFDST columns.•Key parameters that affected residual capacity were reported.•Differences in failure mode of circular and square cross sections were discussed.

Concrete-filled double-skin tubes (CFDST) consist of two concentrically placed steel tubes with concrete filled in between and they have more and more commonly been used in the field of civil engineering in recent years. A number of recent researches evidenced the excellent performance of CFDST columns under a variety of loading conditions. However, very limited knowledge is known about the residual axial capacity of CFDST columns following severe blast loadings. This paper presents an experimental study on the residual behaviours of ultra-high performance concrete infilled double-skin steel tubular columns after close-in blast loading. In total, eight CFDST columns, including 3 square ones and 5 circular ones, were first tested under different blast loads with two axial load levels. After the blast tests, all CFDST columns were transported to the laboratory and each of them was then subjected to static axially compressive load until failure. It was found that the CFDST columns with smaller permanent displacement had larger peak residual axial capacity and the CFDST columns which were not subjected to axial load during the blast test exhibited more ductile behaviour than those which were axially loaded during the blast test.