Experimental study on random temperature field of ultra-high performance concrete filled steel tube columns under elevated temperature

Due to the change of microstructure and increased heterogeneity of ultra-high-performance concrete (UHPC) in comparison with normal concrete, the thermal properties of UHPC are much less uniform within the material. Consequently, the fire performance of UHPC filled steel tubes (UHPCFST) columns are affected by the random distribution of temperature within the concrete. In order to study the distribution of the random temperature field within UFPCFST columns under elevated temperature, high temperature tests on 16 circular UHPCFST columns subjected to the ISO-834 standard fire and a linear heating mode are carried out. The average temperature, temperature difference, temperature probability density distribution and the temporal and spatial correlation of the random temperature field are investigated. It is found that the columns with more steel fiber and coarse aggregate contents have higher temperature, small temperature gradient and higher temperature difference. It is also found that the correlation of the zero-centered temperature in the circumferential direction between different time is strong when the temperature continues to rise or fall. The aims of this paper is to provide the reference for the analysis of temperature field of UHPCFST considering the heterogeneity of UHPC core.