Summary The authors present the first stage of their theoretical and experimental investigations focused on the fire protection of the steel structures using intumescent paint. In this initial stage, their results concerning the temperature distribution law (the theoretical law is validated by effective meticulously conducted measurements) are described. Their original testing bench destined to perform high‐accuracy monitoring of the temperature distribution along straight bars, having a given αg angular positioning with respect to the vertical direction is also described. By involving this testing bench in meticulously conducted experiments, the authors obtained both the effective temperature distribution along the bars and also validated the theoretical (exponential) thermal distribution law. By searching experiments, they also validate the m = const. hypothesis with respect to the massive cross‐sectional bars. Among their further goals, one can mention the searching experimental analysis on the validity of the m = const. hypothesis for the tubular cross‐sectional bars, followed by a combined experimental and numerical analysis of the 2‐D and 3‐D (unprotected and protected with intumescent paint layer) structures, as well as the paint layer's thickness optimisation, too.

This paper reports experimental and theoretical result derived from research on steel structural elements’ fire-protection with intumescent paint. The experimental results were obtained by means of an original testing bench, briefly described below and some basic cases, i.e., horizontally and vertically disposed, massive and square-tubular cross-sectioned, reduced-scale straight bars heated at one end. By means of the thermocouples mounted along the bars, the temperature distribution laws were monitored, depending on the heated end’s nominal temperature. The paper describes an original approach to the temperature distribution evaluation by means of some new parameters, based on the temperature distribution laws experimentally obtained with reduced-scale models. We involved the least-square method (LSM) and the curve-fitting one in order to obtain a more accurate temperature distribution law compared to the experimentally obtained ones. We also introduced some new parameters in order to define the amount of heat loss in a more accurate way. Based on the results obtained, the authors suggest that this approach to the temperature distribution law can be efficiently applied in further thermal analyses, for both 2D and 3D structures. The paper also includes a thorough analysis of “m” variation along the square-tubular-cross-section, reduced-scale straight bars, and similar new approaches are proposed by the authors. The sub-goals of this investigation were (1) to obtain useful correlations between the magnitudes of the massivity ζ = P/A and the parameter “m” along the bar, and (2) to analyze, on reduced-scale models, the heat distribution laws on unprotected and intumescent-paint-protected 2D and 3D steel structures.

In this contribution, the authors continued their initial study on the efficiency of the analysis of experimentally obtained temperature curves, in order to determine some basic parameters that are as simple and reliable as possible, such as “m”, the heat transfer coefficient. After the brief review of the previous results, on which the present article is based, the authors offered a brief argumentation of the importance of dimensional methods, especially the one called modern dimensional analysis, in these theoretical-experimental investigations regarding the propagation of the thermal field of structural elements with solid sections, and especially with tubular-rectangular sections. It could be concluded that modern experimental investigations mostly follow the behavior of models attached to the initial structures, i.e., prototypes, because there are clear advantages in this process of forecasting the behavior of the prototype based on the measurement results obtained on the attached model.