ABSTRACT
Rock climbers have to trust their climbing ropes since falls while climbing are common and the consequences of rope failure are usually serious. Climbing ropes are designed to withstand numerous falls but have a finite life, therefore old ropes should be retired from use. Since no quantitative measure exists of the effect of a fall on the remaining life of a rope, work has been carried out to develop a theoretical analysis to predict the severity of a fall. This theoretical analysis relies on an understanding of the mechanical behaviour of a rope, therefore this paper describes experiments designed to measure this behaviour and how a model of the behaviour is included in the analysis of the climbing fall.
The mechanical behaviour of climbing ropes is difficult to measure by conventional methods since the rope can suffer large strains without failure and exhibits a strong strain rate dependency. The test method that has been followed here is to load the rope dynamically via a falling mass and record the load versus strain response of the rope. Tests can be carried out with different masses and fall distances to vary the strain rate. Although strain rate varies throughout each test during the initial part of the loading the strain rate is relatively constant and sufficient data can be derived to formulate a rope behaviour model.
The theoretical analysis of the climbing fall uses expressions relating increments of tension and strain for rope segments between two adjacent karabiners, allowing large strains and the dynamic non-linear behaviour of the rope to be accounted for. These expressions are combined with relationships governing slip of the rope past karabiners and through the belay device enabling an incremental solution for the tension in each rope segment during a fall. Predictions of forces developed during a fall show good agreement with experimental measurements.
