Dimensionamento e otimização de sistemas de proteção térmica para elementos estruturais metálicos em situação de incêndio

Abstract

Steel structures undergo a significant reduction in strength and stiffness when subjected to elevated temperatures, making the adoption of passive fire protection systems essential in fire scenarios. Although different materials are available for this purpose, selecting the most suitable solution still depends on balancing regulatory requirements, thermal performance, material consumption, and installation costs. In this context, this study aims to conduct a comparative techno-economic analysis and propose the optimization of passive fire protection systems applied to a six-storey steel building model. To achieve this objective, the Required Fire Resistance Rating (TRRF), the section factors of the structural members, and the required fire protection thicknesses were determined based on coverage charts and the criteria established by ABNT NBR 14323 (2013). Subsequently, the material quantities and costs of three protection systems (intumescent coatings, sprayed fire-resistant mortars, and gypsum plasterboard systems) were estimated using products available on the Brazilian market. Finally, the Generalized Reduced Gradient (GRG) method was applied to evaluate fire protection thickness optimization scenarios and their economic implications. The results revealed significant differences among the protection systems analysed. Intumescent coatings presented the highest estimated costs, gypsum plasterboard systems exhibited intermediate costs, and sprayed mortars showed the lowest initial costs among the alternatives evaluated. Furthermore, the optimization process produced protection thicknesses that differed considerably from those specified in the manufacturers’ coverage charts, with higher values for intumescent coating and plasterboard systems and lower values for sprayed mortar systems. For the Thermo-X mortar, the optimization reduced the estimated material consumption from 68 to 29 bags, decreasing the cost from R$ 4,625.01 to R$ 1,962.33, corresponding to an approximate reduction of 57.6%. These differences indicate that the analytical formulation adopted is sensitive to the thermal properties considered and presents limitations in directly representing protection systems whose performance is strongly dependent on experimental testing and application conditions. It is concluded that the proposed procedure contributes to the preliminary techno-economic assessment of passive fire protection systems and may support decision-making in the design of steel structures subjected to fire conditions, provided that its results are interpreted in conjunction with regulatory provisions, technical catalogues, and experimental validations.