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A Generalised Model for Direct Prediction of Stresses in Concrete at High Temperatures

Lookup NU author(s): Abbas Abubaker, Dr Colin Davie

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Abstract

© 2022 ICE Publishing: All rights reserved.A novel theoretical model capable of quantifying the stress causing transient thermal strain (TTS) in heated concrete has been proposed in this work. It can be used in finite element models or as a direct design equation to help structural designers in assessing the stress developed during heating of concrete members caused by combined actions of mechanical loads, heating fluxes and end restraints. The model classifies heated concrete problems into three categories; concrete members heated to a certain temperature then loaded; concrete members stressed to a certain level and then heated to a certain temperature under load; concrete members heated with fully restrained ends with or without external loading. The new TTS equation has been incorporated in a novel coupled thermo-mechanical finite element model in the framework of ABAQUS. Material models capable of capturing the constitutive behaviour and specifically the degradation of material properties experienced by concrete exposed to elevated temperatures, have been selected from the literature and have been adapted to include TTS and, where absent, temperature dependence. The FE model, along with the developed stress equation, has been validated against experimental results in which samples were tested under various loading configurations and boundary conditions. It has been shown to successfully reproduce the results for all of the studied cases. Furthermore, in exploring these scenarios a number of observations were made. Firstly, it was found that the stress developed under restraint is lower than under applied preload, but that stress relaxation in part due to TTS is higher in preloaded samples. Secondly, the limit of elastic behaviour appears to be reduced in samples subject to free thermal expansion compared to those under restraint. Finally, while free thermal expansion is critical to the overall stress-strain response there is evidence that it varies with the applied stress and significantly increases at high temperatures.


Publication metadata

Author(s): Abubaker AM, Davie CT

Publication type: Article

Publication status: Published

Journal: Magazine of Concrete Research

Year: 2022

Pages: epub ahead of print

Online publication date: 05/09/2022

Acceptance date: 03/07/2022

ISSN (print): 0024-9831

ISSN (electronic): 1751-763X

Publisher: ICE Publishing

URL: https://doi.org/10.1680/jmacr.21.00294

DOI: 10.1680/jmacr.21.00294


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