Microstructural and Mechanical Characterisation of Post-tensioning strands following Elevated Temperature Exposure

Conference paper by two MEng students, Robertson and Dudorova as a result of a supervised master student project by Tim Stratford, John Gales and Jane Blackford.This work was supported with additional experimental contribution from H.Smith, L. Bisby and E. Vega.Prestressing strands lose strength and become more susceptible to creep deformation when they are heated during a fire. The consequent loss in prestressing force could under certain conditions result in structural collapse, potentially outwith the heated region of the structure. This paper describes a test programme characterising the changes in microstructure of steel prestressing tendons exposed to elevated temperatures. The residual strength tests, hardness testing, and elevated temperature mechanical test were performed to demonstrate how recovery and recrystallisation of the initially work-hardened steel produce changes in its mechanical properties at elevated temperatures. The research results of this paper are beneficial not only in the fire design of post-tensioned structures using modern prestressing steel, but also in the assessment of the tendons’ residual strength after being affected by fire