Capacity of Second-Growth Douglas-fir and Western Hemlock Stump Anchors for Cable Logging
Authors
Marvin R. Pyles
Oregon State University Corvallis, Oregon, USA
Jerry W. Anderson
Boise-Cascade Company Monmouth, Oregon, USA
Susan G. Stafford
Oregon State University Corvallis, Oregon, USA
Abstract
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.
