Thermal behaviour of steel columns with steel sheet - mineral wool fire protection

A product development project was carried out to find out such a mineral wool fire protection system for steel columns, which would meet the requirements corresponding to different fire resistance times. The primary demand imposed on the structure was to be industrially fabricated to ensure better quality of the product and lower costs of workmanship. Galvanised steel sheet casing systems containing different combinations of mineral wool of various densities, air gaps and aluminium foils between multiple layers of mineral wool were selected and investigated experimentally to find out the influence of different structural factors on the fire resistance (steel temperatures) of the columns. Besides, the columns were tested using two different test arrangements (assemblage of the column in the furnace) in order to be able to evaluate the comparability of test results obtained when using different test procedures. The efficiency of different protection systems is compared by the aid of steel temperatures of the columns or virtual heat resistances calculated for separate insulation layers or the total protection. The effective thermal conductivity of the insulation material is calculated from the test results at various times during the test and it is presented as a function of the average temperature of the insulation. The calculated values were verified by comparing the temperatures measured with those calculated by the nonlinear finite element method (ADINAT) using the determined values of thermal conductivity. It could be seen that by using these temperature dependent values of thermal material properties the calculated and measured temperatures agreed very well. An analytical calculation method to determine the temperature development in the structure was developed. Using proper constant average values for thermal material properties and linearising the heat exchange between the environment and the structure the steel temperatures can be predicted considerably well whereas the temperature distribution inside the insulation can not be determined very accurately