No abstract

No abstract

In biomechanical analyses, computational models are essential tools for simulating the behavior of a tree subjected to a load. However, such models allow only approximation of the actual behavior of the tree if the elastic parameters of the wood in different tree parts (stem, branches, and roots) and at least orthotropic behavior are not considered. In addition, as the wood is green, the parameters of strength and stiffness must be adequate for this level of moisture. However, even for stem wood, knowledge of elastic properties is not available for most species used in urban tree planting, and this scarcity of information is even greater for wood branches. The objective of this research was to evaluate methodology, based on wave propagation, in characterizing the 12 elastic constants of wood from branches. Complementarily, compression tests were performed to characterize the strength. The obtained elastic parameters using ultrasound tests were comparable with the values expected based on theoretical aspects related to the behavior of the wood. The results of the compression test complemented the ultrasound characterization, but the application of this method for the complete characterization of the elastic parameters is not feasible for tree branches because of their small size.

The dimensional variables of trees play an important role in biomechanical studies that seek to estimate the risk of falls, since they influence their biomechanical behavior in relation to the forces to which they are subjected, and therefore, their safety factor. The aim of this research is to evaluate the effect of dimensional variables of trees on their mechanical behavior. A finite-element model was used to perform linear static analysis. The wood from the tree was considered clean, and the architectural model was based on dimensional variables of species commonly used in urban afforestation in São Paulo, Brazil. Different slenderness, tapering, height, and load level were used to analyze the tree mechanical behavior. The numerical-simulation model facilitates the evaluation of the influence of dimensional parameters of trees on deflections and stresses. The behavior of the deflections varies according to height, diameter, and loading level. Since the model considers the geometric variations of the section, the stresses show smooth variations along the trunk. The maximum module values of positive and negative stresses are not equal, and can undergo sudden variations in position along the trunk when local maximum stresses become global maximums.

Resumo As atuais mudanças climáticas e os eventos extremos derivados das mesmas resultam em grande número de quedas de árvores, tornando a análise de risco de queda tema de grande interesse. Essa análise envolve conhecimentos multidisciplinares, dentre eles de biologia e de engenharia. O objetivo principal desse projeto de Iniciação Científica foi descrever os principais indicadores biomecânicos que devem ser levados em conta na análise do equilíbrio de árvores. A pesquisa foi realizada através de levantamento bibliográfico e de dados a respeito do equilíbrio de cargas que atuam nas árvores em função da espécie. Os principais indicadores necessários para análise do equilíbrio de árvores são as cargas (vento e gravitacionais), a morfologia externa (arquitetura e dimensões),os parâmetros físicos (densidade) e mecânicos da madeira saturada e proveniente das diferentes partes (galhos, tronco e raízes).