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Title: Microstructural characterisation of structural bolt assemblies in fire
Author: Johnson, Lucy
ISNI:       0000 0004 5350 4683
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2014
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In structural fire engineering, the importance of bolt assemblies is often overlooked. Connection design uses the temperature-dependent bolt strength-reduction factors prescribed in Eurocode 3, despite the existence of two distinct failure modes under tension; bolt breakage, and thread-stripping. This thesis investigates the factors which influence failure modes at ambient and elevated temperatures and a range of strain-rates through microstructural characterisation, tensile testing and finite element modelling. Microstructural characterisation carried out on M20 galvanised bolt assemblies consisting of Grade 8.8 bolts and Property Class 10 nuts from a range of manufacturers has highlighted that, despite a specified tempered-martensite microstructure, microstructural variations existed between different manufacturers and within a single batch. These microstructural variations not only affected the flow behaviour of the bolt material but determined the failure modes of bolt assemblies at ambient temperatures. Tensile testing of turned-down bolts allowed the temperature and strain-rate dependent flow behaviour of bolt material to be investigated, eliminating the effect of thread deformation. The flow curves obtained were input to a finite element model to represent true bolt material behaviour, which was validated against force-displacement curves obtained from uniaxial tensile testing of bolt assemblies from the same batch. Both experimental and finite element modelling work have highlighted the importance of using a tight thread tolerance class combination and a suitably tall nut to ensure ductile bolt breakage failures and avoid thread-stripping.
Supervisor: Palmiere, Eric ; Thackray, Richard ; Burgess, Ian ; Davison, Buick Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available