A novel engineering tool for thermal analysis of structural members in natural fires

Abstract

A novel CFD-based methodology for generalised thermal analysis of protected steel structures in fire has been developed, in order to overcome some of the limitations of detailed thermal analysis methods. Relying on having an appropriate balance of semi-empirical methods and detailed numerical heat transfer approaches, in order to give solutions of sufficient accuracy for structural members in a generalised fashion, the novel methodology has been developed as an essentially 1D heat transfer model with appropriate representations for 2D and 3D effects to reconstruct a quasi-3D solution. The model has been implemented both in spreadsheet format, to facilitate sensitivity studies for model verification and identification of key parameters, and as a submodel within the SOFIE RANS CFD code. Parallel calculations are performed to consider a range of parameters of interest, including member size and protection material properties, as well as uncertainties in some of the essential input parameters (such as emissivities). Model sensitivities are demonstrated, revealing the expected strong dependencies on the properties of the thermal protection materials. Initial validation is undertaken with respect to the full-scale tests on a 12m x 12m compartment at BRE Cardington, comparing with the measured temperatures in a protected steel indicative, with satisfactory agreement. Predictions of steel temperatures for variations on the key input parameters will ultimately be provided as field variable predictions by the parallel calculations implemented in the CFD code, thereby providing a much more flexible means of assessing the thermal response of structure to fire than has been available hitherto. The final result is a comprehensive, but practical tool for structural fire design, with potential to improve the efficiency and safety of the relevant constructions.