Mechanical properties of structural steels at high temperatures and after cooling down

Behaviour of mechanical properties of different steel grades at elevated temperatures need to be well known to understand the behaviour of steel and composite structures in fire. Quite commonly simplified material models are used to estimate the structural fire resistance of steel structures. In more advanced methods, for example in finite element or finite strip analyses, it is important to use accurate material data to obtain reliable results. To study thoroughly the behaviour of certain steel structure at elevated temperatures, one should use the material data of the steel obtained by testing. Extensive experimental research has been carried out in the Laboratory of Steel Structures at Helsinki University of Technology in order to investigate mechanical properties of several structural steels at elevated temperatures by using mainly the transient state tensile test method. In this thesis a collection of test results of the behaviour of mechanical properties of different steel grades at elevated temperatures is presented with analysis of the test results. The tests have been carried out at Helsinki University of Technology during the past about 12 years. The aim of these tests has been to evaluate the accuracy of existing design values for the mechanical properties of structural steel and to support other different research projects aimed at studying the behaviour of steel or composite structures in fire. The results are presented with a comparison to the European design standard (EN1993-1-2) for structural fire design of steel structures, which is already the officially accepted standard in the EU countries and certainly will be largely in use in the near future. The results are quite well adopted and referred in other different research projects. The main aim of this research was to provide results to other researchers and design engineers in the field of structural fire engineering to improve structural fire safety in the future.