Reference : Analysis of simple connections in steel structures subjected to natural fires
Dissertations and theses : Doctoral thesis
Engineering, computing & technology : Civil engineering
Analysis of simple connections in steel structures subjected to natural fires
[fr] Analyse des assemblages simples dans les structures métalliques soumises à un feu naturel
Hanus, François [Université de Liège - ULiège > Département Argenco : Secteur SE > Struct. en béton, struc. en bois et résist. au feu >]
University of Liege, ​Liege, ​​Belgium
Doctorat en sciences de l'Ingénieur
Franssen, Jean-Marc mailto
Jaspart, Jean-Pierre mailto
Dotreppe, Jean-Claude mailto
Plumier, André mailto
Simoes da Silva, Luis mailto
Zhao, Bin mailto
Vassart, Olivier mailto
[en] connections ; natural fire ; fire resistance
[en] Until recently, investigations on the fire resistance of steel joints have been neglected by structural engineers under the arguments that the design resistance of connections at room temperature is usually higher than the resistance of the connected members and that the temperature increases more slowly in the joint zone (high concentration of mass, low exposure to radiative fluxes) than in the adjacent beams and columns. However, brittle failures of connection components have been observed especially during the cooling phase of real fires for two main reasons: the high sensitive and non-reversible character of the resistance of bolts and welds at elevated temperatures and the development of high tensile thrusts. The present thesis is a contribution to the understanding of the thermo-mechanical behaviour of simple connections in steel beam-to-column joints subjected to natural fire conditions, with a special attention to the behaviour of these connections during the cooling phase.
The distribution of temperature in joints has been analysed by use of numerical models built in SAFIR software. The simplified methods presently mentioned in the Eurocodes are discussed and new methods, calibrated on the results of numerical simulations, are proposed in the present work to predict the temperature profile in steel beams and joints covered by a flat concrete slab under fire.
An existing method aimed at evaluating the distribution of internal forces in restrained steel beams (and by extension, in joints) under natural fire has been analysed in detail. Several modifications have been added in order to improve this method and to extend its field of application. The final version of this analytical method has been implemented and validated against numerical results.
An experimental programme aimed at characterising the mechanical behaviour of bolts and welds under heating and subsequent cooling is described in the present thesis. The properties of the tested specimens, the thermal loading applied to these specimens, the test set-ups and the results of the tests are reported in detail. Mechanical models for bolts loaded in tension or in shear have been calibrated on the experimental results. The loss of resistance of bolts and welds due to their non-reversible behaviour under heating and subsequent cooling has been quantified.
Finally, a large part of the thesis is dedicated to the development of component-based models representing the action of common simple connections under natural fire conditions and to the analysis of the behaviour of these connections as a part of a sub-structure or large-scale structure. These simple models can be used for parametric analyses because it conciliate a reasonable time of definition of the data, an acceptable time of simulation and a good degree of accuracy of the results. Recommendations for the design of connections have been defined. The ductility of connections has a major influence on the occurrence of connection failures and classes of ductility for connections, dependant of the fire loading, have been defined in this work.

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