Building Mechanical Model And Stress Analysis Under Ice And Snow Load Of Masson Pine

Nine provinces in South China has experienced ice and snow disaster in January 2008.Ice and snow damage not only threatens the productivity of forests but also has a significant impact on forest stability.Masson Pine are unique species in subtropical regions of our country,It is widely used in construction,mine timber,sleepers,bridges,etc.It is mainly species which produce resin.This paper study mechanical properties and stress under ice and snow load of Masson Pine.In order to provide a solid theoretical basis of forest management and regulation after ice and snow disaster.This article research Masson Pine which 20±2years old in forest farm of Forestry Research Institute of Subtropical in FuYang country of ZheJiang province.Masson Pine is studied by test approach,numerical simulation and theoretic analysis.Main studies are as following:1.Three-dimensional model of the mechanical structure of Masson Pine.There are a lot of scholars committed to fractal analysis and simulation.However,the fractal studies are directed at growth models basis on growth mechanism of plant and model of the form only consider of the appearance of plant,unlinked to Structural Mechanics of trees and conclude three-dimensional coordinates.This study attempts to provide space structure model through fractal theory to study the mechanical properties of trees.The results of fractal study is to build a mechanical structure of the model with three-dimensional coordinates and lay the foundation for analysis mechanical properties for the next step.2.Elastic constants of Masson Pine.Wood as an orthotnopic material,The elastic behavior described by Elastic modulus E,shear modulus G and Poisson's ratioμ.It is necessary to the determination of these constants if want to have deeply study of the mechanical properties.Twelve elastic constants of Masson Pine were measured by electrical strain gages.The results from expeiment show that the moduli of elasticity and Poisson' s ratios are related by Maxwell' s theory,verification the relationship between elastic constants and moisture content—modulus of elasticity and shear modulus and Poisson's ratioμ_LR decreased with moisture content increases,Poisson's ratioμ_RT,μ_TR,μ_LT increases with the moisture content increases—compared with the elastic constants which have known.So the elastic constants of measured by electrical strain gages are precise and consistent with the relations.3.Finite Element Analysis of Masson Pine.This article set up finite element model of single trees and use ANSYS software to analysis.Build up three kinds of branches structure model on base of three-dimensional Mechanics structural model:one-way eccentric branch model,two-way eccentric branch model,one-way eccentric branch model of symmetrical.Finding optimizing structure model under snow and ice disasters through analysis stress,strain,displacement map of these three models:On the upper of the tree,the diameter of the trunks and branches are closed,one-way eccentric branch model of symmetrical are the most reasonable,two-way eccentric branch model are the most unreasonable.On the lower of the tree,the diameter of the trunks and branches are larger difference, damage usually occurred in nodes of the trunk and branches.