Thermal Characterisation of Sprayed Plasters Response Under Non-Standard Heating Regimes

When exposed to fire, the strength and stiffness of steel reduce significantly. Being it highly conductive, the exposure of steel structural members to fire results in sudden temperature rises, which trigger a significant strength and stiffness decay in a short time, above all in the case of thin steel plates. Therefore, passive protective systems are generally adopted to prevent structural collapse. In the perspective of consistently adopting the performance-based approach, the thermo-mechanical analysis cannot disregard the variability of the thermal conductivity of such protective materials with temperature. Aiming to identify the relationship between thermal conductivity and temperature, recently, at the University of Naples, framed in the project PROSYSSIF, a methodology combining experimental evidence and numerical modelling has been developed for a commercial spray-applied fire-resistant plaster. The latter, applied on steel elements, are tested in transient and stationary heat flux conditions, along with an extensive chemo-physical characterisation at increasing temperatures. Afterwards, the experimental results are used to calibrate the Multiphysics-Lattice Discrete Particle Model, which simulates the moisture and heat transport phenomena occurring within the plaster. Then, the model is used to realise a parametric study, in which three design parameters (i.e., the thickness of the protective layer, input heat flux, and steel section factor) are analysed to quantify their effect on the protective material performance and to derive meaningful insights on its practical applications. The relationship between the thermal conductivity and the temperature is eventually implemented into an FE-based structural model to compare a benchmark structure's unprotected and protected response against natural fire scenarios.