Dynamic climbing ropes

The mass of a 50 m dynamic rope must be low (typically 3.5 kg) to enable it to be carried. The rope must be affordable and it must survive several years of use. Television series, showing expert climbers falling while attempting extreme routes, illustrate the required rope properties— tensile strength, low weight, easy bending to be clipped through belays, durability, low water absorption. 

In the case study, rope mechanical factors are analysed prior to discussing rope construction. Fibre selection and optimisation are then discussed, before considering durability and performance testing. 

For a rope to provide a certain tensile load capacity, it needs to contain a minimum cross-sectional area A of polymer. The analysis of Appendix C 

The mechanics analysis of the forces on the climber s body (Smith, 1998) assumes that the rope has negligible bending stiffness, and that a length L of rope has a linear force P versus extension x relationship with slope (tensile stiffness) Pl (Nm ). We see later (Fig. 15.7) that this is a reasonable approximation. The rope tensile parameter k is defined as the product of a rope s tensile stiffness and its length 

The peak force depends on the fall factor, defined by (Fig. 15.1a) 

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Figure 15.7 shows the rope force versus extension from a drop test on 1.8 m of dynamic climbing rope. A rigid mass of 11 kg was used with a fall factor of 1.0. The assumed linear loading response is a reasonable approximation once the load exceeds 0.6 kN and the strands have bedded-in . There is significant energy absorption on unloading. 

BSEN 892 1997 Mountaineering Equipment—Dynamic Climbing Ropes—Safety Requirements and Test Methods, BSI, London. 

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