New Parameters to Describe High-Temperature Deformation of Prestressing Steel Determined Using Digital Image Correlation

This paper describes the results from a series of high-temperature tension tests on prestressing steel under sustained load (creep tests). Both steady-state and transient heating regimes are used. A novel digital image correlation (DIC) technique is evaluated, validated and used to measure tendon deformation during the high-temperature testing. The tests demonstrate that DIG is a reliable method for measuring strain at high temperatures and is not hampered by some of the limitations that prevent the usage of traditional strain measurement techniques at high temperatures and for high strains. It has also been shown that DIG can capture the reduction in cross-sectional area that occurs during necking, which appears to govern the tertiary creep phase. Testing and analysis demonstrate the importance of accurate creep parameters for modelling stress relaxation in heated prestressing steel tendons made from modern prestressing steel; creep parameters available before this work were developed almost 50 years ago and so modern prestressing steel can have very different creep properties. New creep parameters are developed in this paper that considerably improve the accuracy of stress relaxation modelling.