Rope bridge
A rope bridge (formerly knitting bridge or Tarabit ) is a special form of a suspension bridge made of natural fibers, synthetic fibers or steel cables, which was built without the usual pylons.
Designs
Single rope
The simplest rope bridge is a simple taut rope. A single rope is crossed hanging on the feet and hands, or sliding on the stomach with one leg on the rope and the other as a counterweight and hanging down to lower the center of gravity (a stick can be placed between the stomach and the rope as protection against chafing).
In rope acrobatics , the artist walks upright balancing over the rope, usually with a balancing pole. In the young sport of slacklining , a strap is used instead of a rope.
In a zip line or cable car, the crosser hangs on a snap hook or a pulley and rolls over the rope on wheels or is carried by a movable rope.
Double rope on top of each other
The lower rope is the suspension rope, the upper one the holding rope. Such a construction can only be used over short distances or with very high rope tension. Over longer distances, the two ropes twist in such a way that their different functions as suspension or holding rope are no longer guaranteed. Steel cables are mostly used for these bridges.
Double rope side by side
This construction is often seen on children's playgrounds as a play device for training the sense of balance. Steel cables are usually used for this. If the two ropes are connected by wooden rungs or a continuous wooden covering, the construction becomes somewhat more stable with a correspondingly high rope tension, at least as long as you only use the center line for walking. As soon as the center line is left, the construction begins to twist just like the bridge with “double ropes on top of each other”.
A special shape is the "Wild Woosey", two V-shaped diverging ropes that are crossed in pairs. The distance from about 40 cm increases to about 2 m, so that the two people crossing over have to support each other.
V-shaped three-rope bridge
This construction is also known as the Nepal Bridge and is often built over large spans in developing countries to cross ravines and rivers. In the mountains it is used in via ferrata . The lower rope is the carrying rope, the two upper ropes serve as the tether. At the sides, the ropes are connected to one another in a stabilizing manner so that vibrations and twisting are strongly dampened.
On the Burma Bridge , the three ropes are firmly connected to one another with short connecting ropes. These connections are made one step apart. When crossing, you do not step on the supporting rope, but much more stable in the V-shaped connecting rope.
A modification is a 2-rope bridge with shoulder-high loops hanging between the two ropes. You step from loop to loop and use the two ropes as a railing. Often seen in the climbing garden .
Rope bridges in outdoor training
Boy scouts , youth and sport and other youth groups build rope bridges in their tent camps over streams and gorges and between tree houses . In outdoor training , the construction and crossing of a rope bridge is a challenging project task for teams and managers. In the high ropes course , in the climbing forest and on adventure playgrounds , rope bridges are partially set up.
Crossing a rope bridge makes great demands on the sense of balance and on coping with fear .
safety
Only tested static ropes with low elongation may be used for rope bridges . An additional safety rope must always be used when crossing. For this purpose, a climbing harness is worn, which is attached to the safety rope with a sling and a screw carabiner, thus ensuring the necessary safety in the event of a fall.
Tensioning the ropes
Carrying and holding ropes (at least 10 mm in diameter with a tear strength of at least 2400 daN ) are tensioned with an auxiliary pulley block with around 300 to 600 daN . A via ferrata brake is often used for this, which limits the load to around 380 daN. When tensioning, the pulley must always be deflected with a pulley or alternatively with a carabiner (never directly in the rope, which leads to melt-burning of the rope material). The rope sag should be at least 10%, then the anchoring points are loaded with less than 1,000 daN. After the first load tests, the ropes may only be retensioned once, as they would be stretched impermissibly if they were tensioned several times.
Bark protection
If trees are used as anchoring, the bark must be protected. For this purpose, padding ( sleeping mat , remnants of carpet) is placed around the bark, and several pieces of wood around the trunk like a barrel to distribute the pressure (fix with a tension belt). If the device is set up for a limited time, double wide slings are sufficient.
Knot technique
Carrying and holding ropes are attached to a thick, firmly rooted tree on one side with a weaving line or carpenter's tack. On the other hand, they are tensioned with a pulley. Such a pulley system consists of belt slings or cords that are attached to suspension and auxiliary ropes with snap knots or Prusik knots . Deflections are always guided by pulleys or snap hooks so that the rope is not destroyed by friction. After tensioning, the support rope is looped around a thick tree several times and the end secured.
history
From prehistoric times until at least the last century, rope bridges made of natural fibers and leather straps played a major role in the mountainous regions of East Asia and South America. Steep, deep gorges and raging rivers that swelled when it rained called for bridges high above normal water levels, which inevitably meant bridges with large spans. Simple wooden yoke bridges or stone arch bridges with comparatively small spans could not meet these requirements. Rope bridges were therefore the only way to cross these rivers.
The simplest form was the single rope, on which the traveler shimmy across the river. At greater distances to the other bank, the person hung himself on the rope with a wooden hook and pulled himself forward with his hands, the hook being previously greased with butter in order to be able to slide better. In the case of large rivers, the rope was stretched diagonally downwards so that the slack did not lead to too great a rise on the other side. The more comfortable version had a separate pull rope with which the people attached to the suspension rope were pulled across the river. The horses of a caravan were also dragged across rivers in this way.
Bridges made of two suspension ropes next to each other, between which loops and braided nets were attached in a V shape and served as a walkway, were widespread. Sometimes the sidewalk was even made of long boards that were laid in the loops. V-shaped three-rope bridges with tightly woven ropes formed the larger version.
All of these bridges had to be constantly maintained and repaired and regularly replaced.
With the advent of wire ropes, ropes made of natural fibers have largely been replaced. However, wire rope bridges also have to be serviced and maintained.
The private Swiss organization Helvetas has developed rope bridges especially for Nepal and Bhutan over the last few decades and has installed over 4000 of these bridges.
Trivia
The Czech Robert Ospald managed to escape from Czechoslovakia in 1986 with the help of a self-made device by using the earth wire of a high voltage line as a rope bridge.
See also
- In the case of a cable-stayed bridge , the superstructure hangs on ropes stretched diagonally from a pylon.
- Zip line
- Charles Kuonen suspension bridge , longest pedestrian suspension bridge in the world (in Valais)
literature
- Romano Cotti, Herbert Oberholzer: Knowing and being able to: workbook of practical youth work . 10th edition. Rex-Verlag, Lucerne 1984, ISBN 978-3-7252-0291-1 .
Web links
Individual evidence
- ↑ Pierer's Universal Lexicon of the Past and Present . 4th edition. Verlagbuchhandlung von HA Pierer , Altenburg 1865 ( zeno.org [accessed June 12, 2019] encyclopedia entry "Strickbrücke").
- ↑ Pierer's Universal Lexicon of the Past and Present . 4th edition. Verlagbuchhandlung von HA Pierer , Altenburg 1865 ( zeno.org [accessed June 12, 2019] lexicon entry “Tarabiten”).
- ↑ Training documents J + S
- ↑ Risk management for zip lines.pdf on bergundstieg .at
- ↑ With 10% sag, the load is around 2.5 × body weight + pre-tensioning, for example with 80 kg body weight: 2.5 × 80 + 600 = 800 daN.
- ↑ Formula in Wikibook high ropes courses
- ↑ Safety working group of the DAV
- ^ Photo collection of the Royal Geographical Society Enterprises
- ↑ The Pundit AK reported that in 1878 in Yunnan , hanging on a leather rope, he crossed the Lancang Jiang, the upper reaches of the Mekong .
- ^ Helvetas - Nepal
- ↑ Robert Ospald: 380,000 volts hope of freedom