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Selecting wire rope design factors in cable yarding: a review and proposal

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https://ir.library.oregonstate.edu/concern/graduate_projects/02871190g

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  • Traditional rationale for design factors is briefly reviewed. Methodologies for determining these traditional design factors are lacking and are usually based upon subjective reasons which result in applying a design factor of 3.0 in all cases (western United States). Factors which affect wire rope life are discussed. These factors include steel properties (i.e. elastic limit), rope construction, types of loading (static and impact), bending stress, fatigue, wire rope maintenance, line length, line use, and expected life. Historically, the logging industry has not explicitly considered the economics of harvesting in selecting a design factor for harvest planning. Maximizing the service life of the wire rope may not maximize profit or minimize yarding costs. When cable yarding is considered, log production is a very important factor. The net payload which can be transported to the landing and the speed of the transport determine, to a large extent, the hourly production rate. In order to maximize production it is often necessary to operate at high line tensions. Although wire rope used in such a manner must be replaced more often (shorter life), work is accomplished which cannot be performed by any other means for the same cost. This paper presents a procedure for applying a design factor based on yarding costs. Since the planning of most skyline harvest systems starts with some design factor for the determining maximum tensions which can be used on a particular profile, the economic approach for determining a design factor seems like a reasonable strategy. To the operator of a cable yarding system, this strategy may be more appropriate than applying a design factor of 3.0 in all cases. Finding the optimum payload (or range of payloads) which minimizes overall yarding costs is a sound strategy for planning skyline harvest systems. The procedure in this report uses a yarding simulation model to determine yarding production, wire rope tensions, wire rope lives, and yarding cost per unit volume. The simulation was done on a hypothetical tintber stand with a running skyline system. Line lives were determined by accumulating the proportion of line life used as each turn was yarded. The nuntber of bends until failure was used as a yardstick for determining line life. Yarding cost per unit volume was then compared as logloads were increased until a minimum cost was identified. Design factors for both the mainline and skyline for each average logload were calculated and compared. The results of the simulation indicated that applying a design factor of 3.0 may not be appropriate when considering the effects of the design factor on yarding costs. Crew safety was not considered implicitly in the procedure. However, modifications of the procedure to include crew safety are discussed.
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