© 2007 Heron Publishing—Victoria, Canada
Fresh-wood bending: linking the mechanical and growth properties of a Norway spruce stem
Tor Lundström (1, 2, 3), Urs Heiz (1), Markus Stoffel (3) and Veronika Stöckli (1)
1. WSL, Swiss Federal Institute for Snow and Avalanche Research SLF, 7260 Davos Dorf, Switzerland / 2. Corresponding author (t.lundstroem@sfl.ch) / 3. Laboratory of Dendrogeomorphology, University of Fribourg, 1700 Fribourg, Switzerland / Received September 27, 2006; accepted January 22, 2007; published online June 1, 2007
Summary
To provide data and methods for analyzing stem mechanics, we investigated bending, density and growth characteristics of 207
specimens of fresh wood from different heights and radial positions of the stem of one mature Norway spruce (Picea abies L. Karst.) tree. From the shape of each stress–strain curve, which was calculated from bending tests that accounted for shear
deformation, we determined the modulus of elasticity (MOE), the modulus of rupture (MOR), the completeness of the material,
an idealized stress–strain curve and the work involved in bending. In general, all mechanical properties increased with distance
from the pith, with values in the ranges of 5.7–18 GPa for MOE, 23–90 MPa for MOR and 370–630 and 430–1100 kg m–3 for dry and fresh wood densities, respectively. The first three properties generally decreased with stem height, whereas
fresh wood density increased. Multiple regression equations were calculated, relating MOR, MOE and dry wood density to growth
properties. We applied these equations to the growth of the entire stem and considered the annual rings as superimposed cylindrical
shells, resulting in stem-section values of MOE, MOR and dry and fresh densities as a function of stem height and cambial
age. The standing tree exhibits an inner stem structure that is well designed for bending, especially at a mature stage.
Keywords:
annual ring width, bending mechanics, bulk density, heartwood, knottiness, latewood, sapwood, stem growth, water content.
