Calculation for safety against fracture

(Calculation of the load-bearing capacity of wood by means of edge fibre strain)

For calculation of safety against fracture, a simulated wind load (recorded via Dynaforce load cell) is introduced via a pulling device and a rope into the trunk during a tensile test. The consequence is that the elastic outer wood fibres are compressed against and/or extended in the pulling direction. This change in length of the edge fibres is recorded in a range of 1/1000 mm by means of high-resolution sensors (DynaStrain) that are carefully attached to the wood body.

These measured values are then projected by means of TSE and compared with statistical data on the properties and behaviour of green wood and their maximum strain capacities (Stuttgarter Festigkeitskatalog). From these data conclusions can be drawn for the critical limit. For values beyond this limit, the wood of the tested tree does no longer perform elastic movements under the applied force but reacts with failure (fracture, snapping, etc.) As a final result of the calculations by means of TSE, a value is obtained that illustrates the safety against fracture of the tested tree in case of hurricane-like wind.