High temperatures in parallel or perpendicular wood grain direction: a numerical and experimental study
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Wood is a natural material and is submitted to many constantly changing influences. Wood as a construction material presents many advantages due its high strength and stiffness to height ratios. The main advantages of timber constructions, relatively to the use of other materials, are: ease of construction and maintenance, pleasant appearance, renewable resource, lightweight. The high vulnerability of wood due accidental conditions requires a rigorous thermal and mechanical assessment. Safety rules and others guidelines should be useful and used for wood applications. The fire safety of this type of material involves prevention, inhibition and detection. This involves appropriate design rules, installation, construction and maintenance of the wood material in different applications.
If wood is submitted to a sufficient heat, a degradation thermal process occurs, producing gases accompanied by loss in serviceable cross-section and its weight. The factors which affect the burning behaviour of wood will determine the charring rate. Design models of wood structures at high temperatures take into account the cross-section loss due to char formation.
This work contributes with an experimental program for evaluation of char-layer thickness in wood elements under high temperatures. Experimental results have shown a difference in charring rate and reproduced reasonably well by numerical results with the thermal properties of Eurocode 5 and a ratio of 1.5 applied by the Longitudinal/Transversal thermal conductivity. This study it allows to verify the evolution of the temperature and the char-layer throughout a wooden specimen, in different fibres orientation. The experimental results confirm that grain orientation of wood influences the char-layer evolution. The numerical program reveal of great importance also for char-layer determination. The char-layer thickness was calculated with the numerical results obtained from Ansys program and compared with experimental tests.
