Numerical Modelling of Heat Transfer Through Protected Composite Structural Members

Abstract

Among many various types of passive fire protection materials (i.e. plaster boards, sprayed materials and intumescent coatings) thin film intumescent coatings have be-come the preferable option owing to their good advantages such as flexibility, good appearance (aesthetics), light weight to the structure and fast application. Despite their popularity, there is also a lack of good understanding of fire behaviour. In gen-eral, experimental methods are used to push this knowledge with labour and high-energy consumption and extremely expensive processes. With the development of computer technology, numerical models to predict the heat transfer phenomena of intumescent coatings have been developed with time. In this work, the numerical model has been established to predict the heat transfer performance including ma-terial properties such as thermal conductivity and dry film thickness of intumescent coating. The developed numerical model has been divided into different layers to un-derstand the sensitivity of steel temperature to the number of layers of intumescent coating and mesh sizes. The temperature-dependent thermal conductivity of intu-mescent coatings can be calculated based on inverse solution of the equation for cal-culating temperatures in protected steel according to the Eurocodes (EN 1993-1-2 and EN 1994-1-2). However, as the temperature distribution in the intumescent coat-ings is highly non-uniform, that Eurocode equation does not give accurate coating thermal conductivity-temperature relationship for use in numerical heat transfer modelling when the coating is divided into a number of layers, each having its char-acteristic thermal conductivity values. The comparison study of steel temperature under Standard (ISO 834) and Fast fire conditions against Eurocode analytical solu-tion has also been made by assuming both constant thermal conductivity and varia-ble thermal conductivity. The obtained results show close agreement with the Euro-code solution choosing a minimum certain mesh, number of layer and best-fitted thermal conductivity of the intumescent coating.