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Abstract
Unguyed spar-trees are commonly used as a part of skyline cable logging systems. Finite Element Analysis is a robust method for determining spar-tree design load that can include virtually any field condition likely to be encountered. The results of Finite Element Analysis over a range of spar-trees similar in size to those typically found in second-growth Douglas-fir stands indicates that (1) some existing guidelines for use of unguyed spar-trees do not correspond to expected field behavior, and (2) lateral loads of a magnitude found in skyline cable yarding systems dominate the structural behavior of unguyed spar-trees. However, the Euler Buckling load which has been used as a guide to spar-tree capacity, may serve to normalize the results of Finite Element Analysis in such a way that simple linear relationships can be used to estimate spar-tree capacity.