Tests and analysis on the temperature field within concrete filled steel tubes with or without protection subjected to a standard fire

The temperature fields within twelve concrete filled steel tubular columns with or without fire protection when exposed to the ISO-834 standard fire curve (ISO-834, 1975) have been experimentally investigated and the results are presented in this paper. The main parameters varied in the tests are: (1) Sectional types, square and circular; (2) Sectional dimensions from 299mm to 800mm; (3) Thickness of fire protection coat from 14mm to 35mm. A derivation has been given for the surface temperature of concrete-filled tubular columns. Nonlinear finite element analysis has been carried out to calculate the temperature field for the members with and without fire protection. The theoretical predictions are in good agreement with the experimental data. It has been found that the increasing of tube dimensions results in a temperature reduction in the section. The effect of tube dimensions on temperature reduction is more significant for the core concrete than for the steel surface. Within a three-hour fire time, the reduction in temperature due to the increase in tube dimensions becomes less significant when the outer sectional dimension exceeds about 400 mm. The work in this paper provides a basis for further theoretical study on the fire resistance of concrete filled steel tubular columns.