Loss in moment capacity of tree stems induced by decay
Özet
Key message We model varying decay in tree crosssections by considering bending theory to estimate
moment capacity loss (MCL) for the sections. We
compare MCL with experiments on selected oak trees.
Abstract Tree failures can damage property and injure
people, sometimes with fatal consequences. Arborists
assess the likelihood of failure by examining many factors,
including strength loss in the stem or branch due to decay.
Current methods for assessing strength loss due to decay
are limited by not accounting for offset areas of decay and
assuming that the neutral axis of the cross-section corresponds to the centroidal axis. This paper considers that
strength loss of a tree can be related to moment capacity
loss (MCL) of the decayed tree cross-section, because tree
failures are assumed to occur when induced moments
exceed the moment capacity of the tree cross-section. An
estimation of MCL is theoretically derived to account for
offset areas of decay and for differences in properties of
wood under compressive and tensile stresses. Field measurements are used to validate the theoretical approach, and
predictions of loss in moment capacity are plotted for a
range of scenarios of decayed stems or branches. Results
show that the location and size of decay in the cross-section
and relative to the direction of sway are important to
determine MCL. The effect of wood properties on MCL
was most evident for concentric decay and decreased as the
location of decay moved to the periphery of the stem. The
effect of the ratio of tensile to compressive moduli of
elasticity on calculations of MCL was negligible. Practitioners are cautioned against using certain existing methods
because the degree to which they over- or underestimate
the likelihood of failure depended on the amount and
location of decay in the cross-section.
