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Parametric investigation into the cross-sectional stress-strain behaviour, stiffness and thermal forces of steel, concrete and composite beams exposed to fire

Richard Walls (Department of Civil Engineering, Stellenbosch University, Saldanha, South Africa)
Celeste Viljoen (Department of Civil Engineering, Stellenbosch University, Saldanha, South Africa)
Hennie de Clercq (Department of Civil Engineering, Stellenbosch University, Saldanha, South Africa)

Journal of Structural Fire Engineering

ISSN: 2040-2317

Article publication date: 4 September 2019

Issue publication date: 26 February 2020

Abstract

Purpose

This paper aims to provide a parametric investigation into the behaviour of steel, concrete and composite beams exposed to fire. This investigation gives insight into the structural behaviour of elements experiencing thermal and mechanical loading illustrating reasons for observed global structural behaviour, and identifying how selected design parameters influence results obtained. Non-linear heating/thermal bowing behaviour is specifically considered.

Design/methodology/approach

Cross-sectional stresses and strains, resultant thermal forces, bending stiffness, axial stiffness and deflections are plotted for beams subjected to different fire regimes or input values. The impact of changes in input parameters on beam section properties is illustrated. Unusual structural responses, localised effects and general trends are identified in relation to variations in thermal gradients, concrete tensile capacity, standard fire exposure time and the assumed concrete flange widths of composite beams.

Findings

Stress-strain plots highlighting cross-sectional structural behaviour, trends in beam properties and the influence of design parameters are provided. Some counter-intuitive behaviour is explained, such as increased member stiffness being offset by increased thermal effects, leading to this parameter having negligible impact on global behaviour but a significant effect on local stresses and strains. Increased concrete strengths may lead to increased thermal deformations, whilst the inclusion of concrete tensile capacity typically has a minimal influence.

Research limitations/implications

The research focusses on cross-sectional properties, although results generated illustrate how global behaviour is affected.

Practical implications

Design engineers are made aware of how selected input values influence predicted structural response. Also, localised stress and strain behaviour relative to imposed loads and thermal effects can be identified.

Originality/value

This paper provides novel insight into the (sometimes counter-intuitive) behaviour of beams exposed to fire, highlighting trends and the influence of important input parameters on predicted response.

Keywords

Citation

Walls, R., Viljoen, C. and de Clercq, H. (2020), "Parametric investigation into the cross-sectional stress-strain behaviour, stiffness and thermal forces of steel, concrete and composite beams exposed to fire", Journal of Structural Fire Engineering, Vol. 11 No. 1, pp. 100-117. https://doi.org/10.1108/JSFE-10-2018-0031

Publisher

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Emerald Publishing Limited

Copyright © 2019, Emerald Publishing Limited