Development of an analytical model to predict the radiative heat flux to a vertical element due to a localised fire

Abstract

This paper describes an analytical model developed for design purposes with the aim to assess the radiative heat flux to a vertical element subjected to a localised fire. It focuses on the calculation of the radiative heat flux, which represents the main source of heating of vertical members that are not engulfed into the fire. The model exploits the concept of virtual solid flame whose height and temperature are determined according to the correlations provided in Annex C of EN1991-1-2 and relies on an analytical formulation easy to implement in any spreadsheet. A major enhancement of the proposed model is the capability of providing a way to predict the heat flux on all faces of a vertical member. Moreover, it is deemed valid for any range of heat fluxes that can be expected in a localised fire and it is inherently conservative to be used for design calculations. The proposed model was validated against several experimental tests performed within the European LOCAFI project, as well as against tests found in the literature. Moreover, a parametric numerical analysis was carried out by means of Computational Fluid Dynamics (CFD) numerical simulations that were calibrated on the basis of the experimental outcomes. In this way, the validation of the analytical model was also performed numerically and useful information about the main parameters that significantly influenced the numerical simulation of localised fires fire was drawn. Conservative agreement in terms of heat flux predictions between the proposed model and experimental as well as numerical outcomes was found.