Axial compressive performance of water cooling high strength concrete-filled steel tubular columns after high temperature

The degradation of mechanical properties of high strength concrete-filled steel tubular columns after fire is one of the possible causes of building collapse. Meanwhile, water cooling is the most commonly used fire extinguishing method. This paper presents 20 high strength concrete-filled steel tubular(HSCFST) columns after high temperature under axial compression, including 14 water cooling HSCFST. With the maximum temperatures, cooling methods, constant temperature durations and concrete strengths as variation parameters, the axial compressive performance of HSCFST was discussed. The results show that with the increase of temperature, the peak load, initial stiffness and energy absorption of HSCFST increase firstly and then decrease while the ductility coefficient is contrary. The average ultimate bearing capacity of water cooling HSCFST after being exposed to 800 degrees C degrades by 35.5% in comparison to that of specimens at 20 degrees C. The properties of water cooling specimens were improved compared with natural cooling specimens. The higher concrete strength specimens show better fire resistance. A bearing capacity calculation model of HSCFST was proposed, which considered the different cooling methods and the materials degradation. The calculation results were in good agreement with test results.