Two-Dimensional Analysis of Logging Tail Spars
A beam-column analysis of a skyline-logging tail spar was formulated and an example analysis made of a second-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) spar (15.-in. dbh) rigged at 40 ft. The analysis takes into account the taper of the spar tree, the flexibility of the base of the spar, and the eccentric restraining load at the top provided by guylines. Allowable skyline tension on the tail spar is shown to vary with skyline angle and guyline pretension. An optimum guyline pretension that produces the greatest capacity in the spar tree was found to be within a range attainable by hand tightening. The variation of allowable skyline tension with rigging height and spar diameter also is shown. For. Sci. 33(4):971-983.
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