Characterization of old chestnut beams sections weakened by decay

• Main Author: Sousa, Hélder S.
• Publication Date: 2012
• Other Authors: Branco, Jorge M., Lourenço, Paulo B.
• Language: eng
• Source: Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
• Download full: http://hdl.handle.net/1822/20765
• topic: Timber structures; Weakened sections; Decay; Experimental evaluation; Compression parallel to grain; Science & Technology

The objective of this work was to experimentally assess the material properties of old chestnut (Castanea sativa Mill.) sections weakened by decay. Specimens were taken from critical zones of twenty floor beams, mostly corresponding to the ending parts in contact with granite masonry walls. These specimens were compared with clear wood reference specimens taken from undecayed parts of the same old beams. The experimental campaign comprised in visual inspection, non-destructive testing (ultra-sound, impact penetration and drilling resistance tests) and compression parallel to grain tests. Penetration tests presented an increase in the penetration depth of 36% for the decayed specimens, proving the decrease in resistance of the superficial layer. To evaluate the difference in the stiffness and strength results from the mechanical tests, the cross sections near the failure zones were identified and analyzed. The results of the decayed specimens exhibited a decrease of approximately 30% in the compression strength parallel to grain, mainly because of the presence of knots, misaligned fibers and decrease of the mechanical properties in the decayed areas. Also a reduction of approximately 5% was found for the dynamic and elastic moduli. For all cases, the coefficient of variation for decayed specimens results were significantly higher. Finally, the results of the experimental campaign were applied to calibrate a bi-parametrical decay model for above ground timber structures, considering a linear relation between time and decay depth.