Analysis of Unguyed Spar-Trees

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

Capacity of Second-Growth Douglas-fir and Western Hemlock Stump Anchors for Cable Logging

The use of small instead of large stumps for cable logging anchors will usually result in applied loads approaching the load capacity of the anchors more closely. The use of small stump anchors is then contingent on better means of assessing their capacity. The results of field load tests of Douglas-fir and western hemlock stump anchors are reported. Ultimate loads were modeled as power functions of DBH. In addition, the relation between load and movement relationships for the stumps are modeled using a hyperbolic function that also provides an estimate of ultimate load. Practical use of the model equations requires knowledge of failure statistics and the acceptance of a probabilistic anchor capacity. Probability is applied to the re-rigging required when an anchor fails to perform adequately and to total pull-out failure