Eurocode-based design method to evaluate the plastic bending moment capacity of demountable steel-concrete composite beams in the fire situation

In a context driven by the need to promote sustainability and circularity in construction, demountable steel-concrete composite beams offer a promising solution to reduce the carbon footprint by enabling the recovery and reuse of structural components during building deconstruction. However, ensuring their practical feasibility requires a thorough understanding of their mechanical behaviour at both room temperature and under fire conditions. This paper presents a novel methodology for the analytical evaluation of the plastic bending moment capacity of steel-concrete composite beams with demountable shear connectors under fire exposure, which is grounded on a thermo-mechanical finite element model presented in detail in this work. The numerical model accounted for the realistic characterization of the demountable shear connectors at elevated temperature, through the input of specific load-slip curves from push-out tests conducted in the framework of this research. Additionally, the numerical model was validated against the results of full-length beam tests, showing a very accurate representation of the flexural behaviour of the demountable steel-concrete composite beams at both ambient and fire conditions. The proposed calculation algorithm, using as a standpoint a previous room temperature design methodology, enables the calculation of the ultimate bending moment of the beams in the fire situation through a plastic design approach, extending the current applicability of the design rules in EN 1994-1-2 to cover demountable shear connections. To verify the developed analytical methodology, it was further tested to evaluate the flexural capacity of the studied steel-concrete composite beams at different standard fire periods, providing accurate and reliable predictions. • Numerical model for demountable steel-concrete composite beams subjected to fire • The numerical model was validated by comparison with real scale fire tests • Novel analytical method for fire-resistant moment of demountable composite beams • The algorithm accounts for the nonlinear load-slip behavior of the shear connections • The applicability of Eurocode 4 is extended to cover demountable shear connections