Kodur and Lie 1996
An experimental model was used to determine a numerical model which predicts fire behavior of fibre-reinforced concrete filled steel tubes. Concrete filled hollow steel columns have better economic effects and fire resistance.
Experimental Study, Results, and Discussion
Two circular HSS columns filled with steel fiber-reinforced concrete, without fire protection were tested to failure through fire. Two holes at the top and bottom on either side of the columns were drilled into the steel wall to provide ventilation for water vapor produced during fire exposure. Thermocouples were placed at midheight of the column to measure temperature. The columns had fixed-fixed end conditions and the load was applied for 45 minutes before the fire test and was maintained until no further axial deformation could be measured. The specimens failed when the hydraulic jack could no longer maintain the load, at a maximum speed of 75 mm/min. The goal of the testing was to develop data for a numerical model, in which the fire resistance is derived by calculating the strength of the column as a function of the fire exposure time. Overall, there is similarity between the calculated and measured steel temperatures, however the temperatures measured for the concrete are slightly lower than the calculated temperatures. Both columns expand at the beginning of the tests, and begin to contract leading to failure, and these results are similar to the calculated axial deformation vs. time curve however there are slight differences due to load, thermal expansion, bending, and creep. The effects of load and thermal expansion are significant towards the first few stages, and creep is more pronounced in the later stages. The numerical model defines the failure point as the instantaneous point in which the column cannot support the load, however failure in the experiment was not instantaneous. Overall, the model can accurately predict the fire resistance in the columns, and can also be used to calculate the fire resistance for other types of concrete.
Reference
Kodur, V. K. R and Lie, T. T. (1996). “Fire Resistance of Circular Steel Columns Filled With Fiber-Reinforced Concrete.” Journal of Structural Engineering, 122 (7), July, pp. 776-782