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Finite element modeling of guyed back spars in cable logging

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Abstract:

In this study a finite element model of a back spar system was developed with three guylines opposing the skyline strap tension. In this paper the allowable skyline strap tension is the tension in the skyline strap that results in the maximum normal stress on a transverse cross section of the tree being equal to an assumed allowable stress. An iterative routine was developed to find the allowable skyline strap tension, and this routine was found to converge rapidly from initial values that were below and above the allowable skyline strap tension. Two algorithms were developed for finding the maximum normal stress on a transverse cross section of a tree, method 1 and method 2. If the plane that the tree displaced in was known a priori, then method 2 could be used, and it was found to be less sensitive to mesh coarseness. If the plane that the tree displaced in was not known a priori, then method 1 had to be used with a less coarse mesh. It was found that the stress concentrations due to simplified cable connections were not significant for rigging configurations that allowed a larger rigging point displacement. The rigging configurations that allowed larger rigging point displacements have stress fields that are dominated by bending, while for rigging configurations that allow only small rigging point displacements, the stress fields are dominated by axial compression.

Dans cette étude, un système de mât de queue avec trois haubans pour absorber la tension de la sangle du câble porteur a été modélisé par la méthode des éléments finis. Dans cet article, la tension de la sangle du câble porteur permise correspond à la tension dans la sangle engendrée par la contrainte normale maximale en section transversale de l'arbre. Cette tension correspond à la contrainte acceptable présumée. Une routine itérative a été développée afin de trouver la tension permise de la sangle du câble porteur. Cette routine converge rapidement à partir de valeurs initiales inférieures et supérieures à la tension permise. Deux algorithmes ont été développés pour trouver la contrainte normale maximale en section transversale d'un arbre : la méthode 1 et la méthode 2. Lorsque la zone de débardage est connue a priori, la méthode 2 peut être utilisée. Cette dernière s'est montrée moins sensible à la taille du maillage. Cependant, si la zone de débardage n'est pas connue a priori, la méthode 1 doit alors être utilisée avec un maillage plus fin. Les résultats montrent que la concentration des contraintes dues aux connections simplifiées des câbles n'est pas significative pour les configurations qui permettent de couvrir une plus grande surface. Les configurations de câblage qui permettent de couvrir de plus grandes zones ont des champs de contraintes dominés par le cintrage alors que les configurations de câblage couvrant de plus petites zones ont des champs de contraintes dominés par la compression axiale.[Traduit par le Rédaction]

Document Type: Research Article

Publication date: April 1, 2004

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  • Published since 1971, this monthly journal features articles, reviews, notes and commentaries on all aspects of forest science, including biometrics and mensuration, conservation, disturbance, ecology, economics, entomology, fire, genetics, management, operations, pathology, physiology, policy, remote sensing, social science, soil, silviculture, wildlife and wood science, contributed by internationally respected scientists. It also publishes special issues dedicated to a topic of current interest.
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