An investigation of branch stresses induced by arboricultural operations

Abstract

This paper presents a method for assessing the safety of tree branches subject to unorthodox climbing approaches and possible falls. The method entails finite element modeling of the tree branch, experimentally or analytically determining loads associated with an ascending or falling climber, and computing stresses and safety factor along the length of the branch using dynamic structural analysis. A case study example is presented for an Ulmus americana L. branch on the campus of the University of Massachusetts, Amherst. This tree and branch were climbed using an unorthodox and controversial method during a competition in 2014. Case study models demonstrate that during an ascent, a climber’s skill has a significant effect on branch stresses, and during a simulated fall, the climber’s mass and fall distance are the key determinants of branch stresses. For loads induced during an ascent, safety factors for branches ranged between 3 and 4; for loads induced during a fall, safety factors were as low as 1.2. These values are dangerously low given the uncertainty of branch material properties. Climbers should be extremely cautious when attempting unorthodox climbing techniques.