316 Kane and Arwade: Effect of Climbing Line and Ascent Technique on Arboricultural Climbing Loads and 1.8 for the maximum load in an ascent (P100 The number of times each Pi of a climbing arborist’s weight tend to be consistent among ascent techniques and to vary between 1.1 for P75 ). is repeated during an ascent obviously depends on the duration of the ascent; assuming a loading frequency of 2.1 Hz (Fig- ure 3), the TIP would experience 21 peak loads for every 10 seconds of an ascent. The current study and previous work (Kane et al. 2020) have shown that the number of times each Pi ascent technique: excepting P100 is repeated also depends on , which tends to occur only once regardless of the ascent technique, the number of peak loads at P75 , P90 , P95 , and P99 ) to 1.8 (for P95 was larger when a climbing arborist used the ropewalking technique. In the current study, ropewalking induced anywhere from 1.4 (for P99 many peak loads as footlocking. In a previous study, ropewalking induced anywhere from 1.5 (for P99 1.9 (for P75 and P90 ) times as ) to ) times as many peak loads as foot- locking (Kane et al. 2020). Since ascents are dynamic loads that induce a dynamic tree response (swaying of the TIP), loading frequency is another important factor to consider. Results from the current study align with previous work (Kane et al. 2020): ropewalking tends to induce loads at 2 distinct frequencies—one approximately twice the other. In contrast, footlocking tends to induce loads at a wider range of frequencies. We speculate that the greater overall motion of a climb- ing arborist footlocking is responsible for this occur- rence. Anecdotally, the lead author observed that his hands exerted a downward force on the climbing line less frequently than his feet, but we did not quantify this. A careful analysis of the body motion of climb- ing arborists ascending using different techniques would clarify the biomechanics of various ascent techniques and may help explain why footlocking tends to induce loads at a wide range of frequencies. Similarly, it would be helpful in future studies to include a sample of climbing arborists of varying body types to investigate the effect of body type on loading frequency. None of the loading aspects that we investigated in the current study (magnitude, number of peak loads, frequency) varied significantly among climbing lines, which supports the speculation (Kane 2018) that the use of different climbing lines among many different climbing arborists did not meaningfully affect the results. The lack of an effect of different climbing lines with a wide range of elongation properties, ©2022 International Society of Arboriculture combined with the lack of an effect of different TIPs in the current and previous (Kane et al. 2020) studies, indicates that structural mechanics of the TIP-climbing line system does not influence the magnitude or fre- quency of loading during an ascent. While there are an infinite number of TIP geometries and many climbing lines and climbing arborists, the collective findings of the current and several previous (Kane 2018, 2020b; Kane et al. 2020) studies suggest that during ascents, (1) the magnitude of loading is pri- marily influenced by a climbing arborist’s weight, and (2) the frequency of loading is primarily influenced by ascent technique. CONCLUSIONS In combination with our previous studies, the current results provide a baseline understanding of loads associated with arboricultural tree climbing, includ- ing many of the relevant variables such as ascent technique and climbing line. In this and previous studies, maximum loads on a canopy-anchored climbing system have remained less than twice a climbing arborist’s weight; climbing arborists should conservatively assume that their chosen TIP must regularly bear twice their weight with climbing gear. But this is not an endorsement of §8.1.11 in the Z133 standard (American National Standards Institute 2017): a single proof load to assess the load-bearing capacity of a TIP grossly oversimplifies the dynamic structural mechanics of a climbing arborist ascending on a TIP. Future studies should also explore the load-bearing capacity of a TIP, which is critical to assessing the likelihood of TIP failure during arboricultural tree climbing. Relevant mechanical parameters of TIPs such as sway frequency, stiffness, and wood strength are largely absent from the literature. Finite element analysis may be a useful approach to assessing the likelihood of TIP failure, but mechanical parameters are necessary to create robust finite element models (Cetrangolo et al. 2018). Although TIP load-bearing capacity remains uncertain, climbing arborists can reduce the likelihood of TIP failure by choosing one conservatively. Three factors that meaningfully influ- ence a TIP’s load-bearing capacity and can be assessed from the ground are (1) the diameter of the stem below the TIP, (2) the degree to which the stem below the TIP diverges from vertical orientation, and (3) the presence of defects such as decay, cracks, or weakly attached branches on the stem below the TIP.
November 2022
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