Rope elongation
The rope elongation is an important parameter to describe the properties of a rope . The following considerations relate in particular to climbing ropes .
A distinction must be made between:
- The elongation in use is a measure of the elasticity under (quasi) static load. A large static strain is e.g. As when top roping from a disadvantage, since again climb the rope slide into the last few meters must. Likewise, the least possible use elongation when pulling of loads in the big wall , desirable (hauling) because otherwise the work work is lost as a strain. The elongation in use is measured by increasing the load of a piece of rope preloaded with 5 kg to 80 kg. According to EN 892 or UIAA standard, the elongation in use may be:
- for single ropes a maximum of 10%
- with twin ropes in double strand a maximum of 10%
- for half ropes in a single strand a maximum of 12%.
- The impact force elongation describes the elongation in the fall event. This dynamic expansion absorbs part of the fall energy in the event of a fall - the other part of the energy is absorbed by the rest of the safety chain ( friction when the rope passes through the belay device and intermediate belay devices ; acceleration of the belayer). The impact shock elongation is measured on the first standard fall and must not exceed 40% according to the EN standard; if it were stretched more, the impact force would be lower, but there would be an increased risk of hitting ligaments or the ground in the event of a fall. With modern climbing ropes, the typical values are between 28% and 35%. In a normal sport climbing fall with a fall factor of 0.3, the dynamic elongation is in the order of 15%.
literature
Pit Schubert, Pepi Stückl: Alpine curriculum Volume 5, safety on the mountain, equipment, safety . BLV, Munich 2003, ISBN 3-405-16632-2 .