Fresh-stem bending of silver fir and Norway spruce
Tor Lundström (1, 2, 3), Markus Stoffel (2) and Veronika Stöckli (1)
1. WSL, Swiss Federal Institute for Snow and Avalanche Research SLF, 7260 Davos Dorf, Switzerland / 2. Laboratory of Dendrogeomorphology, University of Fribourg, 1700 Fribourg, Switzerland / 3. Corresponding author () / Received May 15, 2007; accepted July 24, 2007; published online January 2, 2008
Summary
The bending and growth characteristics of large fresh stems from four silver fir (Abies alba Mill.) and three Norway spruce (Picea abies (L.) Karst.) trees were studied. Twenty logs taken from different stem heights were subjected to four-point bending tests.
From the bending test records, we calculated stress–strain curves, which accounted for detailed log taper, shear deformation
and self weight. From these curves we determined, among other parameters, the modulus of elasticity (MOE), the modulus of
rupture (MOR) and the work absorbed in bending (W). No significant differences were found between species for the wood properties examined. Values of MOE, MOR and W generally decreased with stem height, with MOR in the range of 43 to 59 MPa and MOE ranging from 10.6 to 15.6 GPa. These
MOE values are twice or more those reported for stems of young Sitka spruce (Picea sitchensis (Bong.) Carr.) trees. Based on the radial growth properties measured in discs from the logs, we calculated predicted values
of MOE and MOR for the stem cross section. The predictions of MOE were precise, whereas those of MOR were approximate because
of a complex combination of different failure mechanisms. Methods to test and calculate MOE, MOR and W for the stems of living trees are discussed with the aim of improving analyses of tree biomechanics and assessments of forest
stability protection.
Keywords:
Abies alba, energy absorption, experiment, fresh wood, model validation, nonlinear behavior, Picea abies.
