Speaker
Description
Tower yarders have been a well-established harvesting technology in European mountain forestry since the 1960s. Despite their long-standing practical relevance, the dynamic tensile force of the cable system under real operating conditions remains insufficiently understood. While in situ measurements of skyline forces are available, the contribution of guylines is commonly overlooked, even though guyline forces is fundamental to tower stability and anchorage safety. This lack of empirical evidence constrains the mechanical assessment, dimensioning, and safe installation of cable yarding systems.
The aim of this study was to quantify the dynamic forces response of skyline and guylines under operational conditions and to identify the work phases associated with critical peak loading. Tensile forces were recorded at a sampling frequency of 100 Hz on four cable yarder installations in Styria, Austria. More than 300 work cycles were monitored with more than 25 hours of productive machine operation. Tensile forces were measured in the skyline and in all four tower guylines. This enables an analysis of the working phases within the entire cable system.
Mean guyline forces ranged from 3 to 51 kN. Under certain system configurations, however, guyline forces reached up to 70% of the concurrent skyline tension. When adequate pretension was applied, guyline forces exhibited an approximately linear relationship with skyline tension, indicating a stable and mechanically consistent response of the guyed tower system. By contrast, insufficiently pretensioned guylines displayed distinctly non-linear load responses, pointing to irregular force sharing and reduced structural predictability.
The most critical loading conditions were observed during lateral skid and during the inhaul phase. Lateral skid produced abrupt force increases that were primarily associated with breakout and rapid load transfer. The inhaul phase, in turn, generated pronounced dynamic oscillations within the cable system. Frequency-domain analysis further showed that the dynamic response was dominated by low-frequency oscillations below 1 Hz.
The findings demonstrate that dynamic peak forces in both skyline and guylines must be explicitly considered in the mechanical design, pretensioning strategy, and safety assessment of tower yarder installations. In particular, guyline forces should no longer be regarded as a secondary aspect of system behaviour, since they can reach structurally relevant magnitudes and substantially influence the overall stability of the installation.
| Keywords | cable; force; safety; anchoring |
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