Dynamic parameters of lowering loads at gradual tree felling

The lowering of loads at gradual tree felling is the riskiest activity performed by tree climbers. During this activity, great forces emerge and act on the felled tree, while the tree climbers use the tree itself to anchor and secure their stance. This research aims to find out whether certain methods of work or the use of certain rigging for lowering loads exhibit positive features in reducing the forces acting on the anchoring point of the rigging system. The work methodology consists of three operations: (i) the calculation of the coefficient of shear friction for the combination of 4 ropes and 5 lowering devices - altogether 20 combinations; (ii) the mathematical modelling of the maximum forces acting on the lowering loads of known weight; and (iii) the verification of mathematical modelling using a series of measured experiments of lowering loads of known weight. The research results present the calculation of the shear friction coefficient for 20 combinations of rigging rope and lowering devices. The maximum magnitudes of the forces which may act on the upper anchoring point of the rigging system at the known load weight were additionally calculated. A total of 240 force values were measured when a load of 12 kg in weight falls according to a predetermined model situation. The results indicate that the greatest influence on decreasing the impact force generated by the falling load is that of the load attachment, reduced load weight, shortened length of the fall or elongation of the total rope length in the rigging system. The differences in the coefficients of shear friction are apparent in the results of measurements, too.