A Simple Finnish Method for the Structural Fire Design of Composite Structuresby Timo Inha, Tampere Univ of Technology, Tampere, Finland,
Document Type: Proceeding Paper
Part of: Composite Construction in Steel and Concrete II
The structural fire design of composite structures in Finland has previously been based on furnace tests, which are expensive and take too much time to arrange. With the increasing prominence of composite constructions and steel constructions, it has thus been necessary to evolve a simple calculation model for their structural fire design. While the Finnish method is akin to those involving reductions, the concept of `reduction' should be understood in a different sense from that implied in Eurocode 4, for example. In order to obtain a simple basis for manual calculations, the cross-section is transformed to contain parts having only constant material properties. For this purpose a reduction in the size of the cross-section has to be made. The method is based partly on tabulated data and partly on calculation, the size of the cross-section being determined first from tabulated data, after which the fire temperatures of the parts of the steel section and the reinforcing bars are determined from tabulated data or from the temperature distribution of concrete cross-section. Finally, the flexural resistance, shear resistance and other properties needed can be checked easily employing a reduced concrete cross-section with material properties equal to those prevailing at +20 °C, reduced parts of a steel section with material properties equal to those prevailing at the appropriate fire temperatures and reinforcing bars with material properties equal to those prevailing at their fire temperatures.
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