Determining the Charred Layer of Wooden Beams with Finite Element Analysis Based on Enthalpy Approach

In the process of computer modeling the formation of a charred layer in wood materials, it is important to implement the correct material data. In thermal analysis, there exist two different approaches of implementation: the temperature-dependent material data properties, heat capacity approach and enthalpy approach, which is not commonly used but which has a few advantages. This approach should be examined in more detail because it can solve the problem associated with inaccurate results at temperatures around 100 °C. This scientific paper deals with the assessment of the computer-aided fire modeling and simulation suitability based on the enthalpy approach for determining the charred layer of structural elements. The structural elements selected for testing were spruce wooden beams with rectangular and circular cross-sections. A finite element model (FEM) was created in ANSYS software. The model was validated by medium-scale fire tests data of the spruce wooden beams loaded with a radiation panel. Boundary conditions were identical to the medium-scale fire test. Due to the enthalpy approach, the temperature curves from the simulations also faithfully simulated the section with a constant temperature around 100 °C. Within the temperature profiles, the accuracy of simulations averaged 91.7%. The accuracy of the simulations describing the total area of the charred layer was 93.0% on average. Presented FEM can be used in the search for new construction solutions for wooden elements and modifications to the design of cross-sections of wooden beams or wooden joints so that they can better withstand fire conditions.

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