Development and validation of a generalised engineering methodology for thermal analysis of structural members in fire
Stratford, Tim J
Kinsella, Emmett V
A novel methodology for generalising CFD-based approaches for thermal analysis of protected steelwork in fire has been developed, known as GeniSTELA. This is a quasi-3D approach with computation of a "steel temperature field" parameter in each computational cell. The methodology accommodates both uncertainties in the input parameters and possible variants to the specification by means of parallel calculations. A framework for the inclusion of temperature/time-dependent thermal properties, including the effects of moisture and intumescence, has been established. Indicative values of intumescent material properties have been obtained by means of cone calorimeter testing. These are dependent on initial thickness and exposure heat flux. GeniSTELA has been implemented as a submodel within the SOFIE RANS CFD code. The model is validated against measurements from the BRE large compartment fire tests, which involved well-instrumented post-flashover fires in a 12 x 12m compartment, including steel indicatives with and without protection. Sensitivity studies reveal the expected strong dependencies on structural member specification and properties of protection materials. The computational requirements are addressed, considering aspects such as the number of simultaneous cases and frequency of GeniSTELA call, in order to achieve a reasonable balance between fluid and solid-phase analyses. It is established that the model can be a practical tool, performing c. 10-100 simultaneous thermal calculations before becoming dominant. These steel temperature field predictions provided by GeniSTELA can provide far more flexibility in assessing the thermal response of structures to fire than is available via existing methods.
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