| Summary: | According to the basic principles of bionics, internal forces are formed in the tree stem during its growth. Appearance and development of such forces are mainly caused by external effects, where the main external effect is a wind load. Internal forces develop in response to the powerful effect of the wind load on tree stems. Such forces ensure the resilience of tree stems. They prevent the tree stem from breaking and falling together with the roots.
The established system of internal forces does not disappear upon log sawing. All sawn-timber pieces obtained after log sawing are stressed to various extents. This affects the natural curvature and wood strength upon compression along fibers and static bending. The established mathematical relationship between the size of the core zone and the value of internal forces makes it possible to analyze changes in the wood strength upon compression along fibers along the board. The wood strength depends on the log taper, relative size of the core zone, and distribution of internal forces over the tree stem volume.
According to the obtained data, the ratio of wood ultimate strengths upon compression along fibers and static bending depends on the nature of internal forces' distribution over the tree stem section. The paper presents the results of theoretical studies on the wood strength upon compression along fibers under various laws of internal forces' variation along the length of the log.
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