Evaluation of Failure Criteria in Branch Members
Under Torsion and Bending Moment
Javier Avalos and Adolfo Sánchez
Abstract: Tree assessment relies on identifying and assessing structural conditions to predict failure. The tree is a complex structure made of live composite materials where multi-axial stress conditions exist in the interaction of the branches between external and internal forces. Failure criteria included bending moment and torsion, while also considering the wood as an orthotropic material. Ash (Fraxinus spp.) tree branches that failed in natural conditions demonstrated to be subject to both torsion and bending moment upon failure. Maximum stress values measured in controlled failure experiments demonstrated excellent agreement with the criteria used in the study, thus obtaining a curve extending from pure bending moment failure, pure torsion failure, and combination of both. From these experiments, the ultimate values determined for the tree species tested were X¯ = 75.5 MPa for pure bending and Z¯ = 11.2 MPa for pure torsion, which agrees well to previous reports. The methodology shown in this study may be applied to any tree species.
Keywords: Ash; Bending Moment; Failure; Failure Criteria; Fraxinus uhdei; Torsion; Orthotropic Material.