Behaviour of Grade 8.8 bolts under natural fire conditions - Tests and model

Recent full-scale experimental tests perfomed on steel andcomposite structures have demonstrated that the presence of tensile forces in axially-restrained beams during the cooling phase of a fire could lead to bolt failures. In order to understand this observation and design structures that are not prone to such a failure mode, it is essential to have a deep knowledge of the material behaviour of all the components, including bolts, during both the heating and the cooling phase. In the present article, the test set-ups and the results of the tensile and shear tests performed at the CSM (Italy) on Grade 8.8 bolts under heating-cooling cycles are described. Then, material laws are defined for characterising the mechanical behaviour of Grade 8.8 bolts under heating and cooling phases. these laws account for the non-reversibility of the mechanical properties of Grade 8.8 bolts