Behaviour of Galvanized High Strength Grade 10.9 Bolts Under Fire Conditions

In the last decades structural fire design has changed essentially. In the past the structural integrity of single elements was mostly proven by load tables which were based on fire tests. The introduction of the "hot" Eurocodes (Parts 1-2) offers the possibility to assess the resistance even of complex structural systems under fire conditions. For this purpose a calculation can be made according to the Eurocodes taking into account the relevant material behaviour which is mainly known for structural steel and concrete elements. The material behaviour is defined in the ECs by stress strain curves, depending on the temperature. Even for connections design rules are given in the Eurocodes. The resistance of bolts and welding seams under fire conditions can easily be calculated using global reduction factors which depend on the element temperature. The global reduction factors for bolts are currently valid for all grades. The experience shows that either differing alloying materials or varying treatment methods can lead to a relevant change in the ultimate strength. These two points have an important influence on the production process of galvanized high strength grade 10.9 bolts. Due to this tension tests on specimens and galvanized bolt assemblies have been carried out in order to evaluate the behaviour under fire conditions. The results will give on one hand the possibility to verify the reduction factors for grade 10.9 bolts given in the Eurocode and on the other hand a more precise understanding of high strength bolt behaviour under fire conditions. The paper will describe the state of the art, the elaborated tests in more depth and present results.