Temperature analysis of heavily-insulated steel structures exposed to fire

An exact analytical one-dimensional solution of the temperature response of insulated steel structures is derived and a closed form solution is given for a structure exposed to the ISO 834 standard curve.

Alternative approximate solutions are also given where all the heat capacity is assumed lumped in the steel core; only one third of the insulation heat capacity is then considered. It is also shown that approximate solution schemes given elsewhere strongly underestimate the temperature rise in structures protected with heavy insulations system. In addition the theoretical background of a proposed NORDTEST test method on how to obtain the thermal properties of an insulation system is outlined. Finally a numerical calculation scheme is recommeded.