Mechanical material behaviour of ultra-high-strength structural steel S960QL in case of fire

Due to their good strength-to-weight ratio, high-and ultra-high-strength structural steels are increasingly used in multi-storey and industrial buildings in the form of plate material, pipes and sections. For structures with fire protection requirements, how-ever, the use of high-strength structural steels is currently in-hibited by a lack of knowledge regarding temperature-and rate-dependent material behaviour. Comprehensive knowledge of the material behaviour is a basis for a realistic modeling of the load-bearing behaviour of steel structures. Within the framework of the FOSTA-research project P 1502, systematic investigations of the structural material behaviour of ultra-high-strength steels are carried out in terms of an extensive tensile test program. The aim of the project is to characterise the mechani cal material behaviour during all phases of a fire, in-cluding the cooling phase of natural fire scenarios. The paper addresses the material behaviour of quenched and tempered steel S960QL in fire. Steady state and transient state tensile test results are presented and used for the characterisation of the material behaviour during the heating phase of a fire and the comparison to common material models. In addition, the results of natural fire tests for the evaluation of the material behaviour in the cooling phase and the residual behaviour are presented.