Characterization of cross sections from old chestnut beams weakened by decay

Abstract

This work aims to experimentally assess the material properties of old chestnut (Castanea sativa Mill.) cross sections weakened by decay. Specimens were taken from critical zones of twenty floor beams, mostly corresponding to their ending parts, in contact with granite masonry walls. These specimens were compared with clear wood specimens taken from non-decayed parts . The experimental campaign comprised of visual inspection, non-destructive testing (ultra-sound, impact penetration and drilling resistance tests) and uniaxial compression tests, parallel to the grain. Pin penetration test evidenced a depth of penetration 36% higher for decayed specimens compared to non-decayed specimens, proving the loss of capacity in the superficial decayed layer. The results of decayed specimens exhibited a decrease of approximately 30% in the compressive strength parallel to the grain. A reduction of approximately 5% was found for the dynamic and elastic moduli. The coefficients of variation for decayed specimens are significantly higher than for sound specimens. Different decay models are considered and compared aiming at analyzing decay evolution along time and determining the decrease of load bearing cross section. Finally, the results were used to calibrate a bi-parametrical decay model for above ground timber structures, considering a linear relation between time and decay depth.