Effect of column base strength on steel portal frames in fire

In the UK, the design of steel portal frame buildings in fire is based on the Steel Construction Institute (SCI) design method, in which fire protection needs only be provided to the columns, provided that the column bases are designed to resist an overturning moment, M_OTM, calculated in accordance with the SCI design method. In this paper, a non-linear elastic-plastic implicit dynamic finite element model of a steel portal frame building in fire is described and used to assess the adequacy of the SCI design method. Both 2-D and 3-D models are used to analyse a building similar to the Exemplar frame described in the SCI design guide. Using the 2-D model, a parametric study comprising 27 frames is conducted. It is shown that the value of the overturning moment, calculated in
accordance with the SCI design method, may not be sufficient to prevent collapse of the frame before 890 °C.