Rock Climbing Belay Device Analysis, Experiments and Modeling

Abstract

Amazingly no standard exists for belay devices used in rock or ice climbing. This paper presents an analysis performed on several belay devices that permits their comparison in terms of characteristics and efficiency. The belay device characterization consists in testing the brakes in the case of a given fall arrest in a testing room. Here, a belay device is characterized by its braking coefficient, the rope slip through the brake till the arrest of the fall and the impact load on the last runner. The braking coefficient is the ratio between the rope tensions on the tight and slack sides of the belay device. A device called “virtual hand” has been developed, it tries to reproduce the belayer hand action on the rope during the fall arrest, and it also enables the measurement of the load on the brake and the control of the rope tension on the belayer hand side. The fall arrest intensity or brutality is evaluated from the measurements of the rope slip in the brake and the load on the last runner. The analysis of the three measured characteristics enables the comparison of the six belay devices tested. It appears that these three quantities are related, indeed the larger the braking coefficient the lower the rope slip and the higher the impact load. The energy of the fall is absorbed over a shorter time period for belay device having a high braking coefficient. Therefore, an efficient braking gives way to a high impact force on the climber and a more brutal arrest of the fall. A basic model for the brake has been implemented in an already developed climber fall arrest model. Comparison of experimental and numerical results is made and is satisfactorily.