Operative loading in cable yarding systems: field observations of static and dynamic tensions in mobile anchor systems

Abstract

Cable yarding systems are an effective means of facilitating harvesting operations in steep terrain, but require sufficient anchoring for safe performance. Design and safe operation often dictates that cable loading remain at a safe level, yet the actual loads incurred for anchoring systems, particularly for “mobile” or “equipment” anchors, are ill-quantified. Furthermore, these anchors are subject to loading that is rather dynamic in nature, realizing impulse loads from various operation occurrences, particularly breakout. This study describes the measured static and dynamic cable loads during yarding for 21 mobile anchor systems operated by eight different contractors during active logging operations. The mean dynamic loading observed for guyline and skyline anchors was 49% and 44% greater than static tensions, respectively. Maximum dynamic loads exceeded approximately double static tensions. In the observed tests, cable tensions were well below the cable elastic and endurance limits but did approach the allowable tension in some cases. Although the monitored cable loads in this study were all within a safe range, the observed dynamic loads are useful guidance when considering higher static loads and consequently higher dynamic loads that may be unsafe.