Simple suspension bridge

# Simple suspension bridge

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A simple suspension bridge (also rope bridge, swing bridge (NZ), suspended bridge, hanging bridge and catenary bridge) is an early type of bridge
Bridge
A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle...

that is supported entirely from anchors at either end, and has no towers or piers. However, it may have saddles. In such bridges, the deck of the bridge follows the downward and upward arc of the load-bearing cables, with additional light ropes at a higher level used to form a handrail. Alternatively, stout handrail cables supported on short piers at each end may be the primary load-bearing element, with the deck suspended below. Suspended well from two high locations over a river or canyon, simple suspension bridges follow a shallow downward catenary
Catenary
In physics and geometry, the catenary is the curve that an idealised hanging chain or cable assumes when supported at its ends and acted on only by its own weight. The curve is the graph of the hyperbolic cosine function, and has a U-like shape, superficially similar in appearance to a parabola...

arc and are not suited for modern roads and railroads. Owing to practical limitation in the grade (i.e., the deck being an arc, not flat) and the response to dynamic loads of the bridge deck, this type is quite restricted in its load-carrying capacity relative to its span
Span (architecture)
Span is the distance between two intermediate supports for a structure, e.g. a beam or a bridge.A span can be closed by a solid beam or of a rope...

. Yet, this type of bridge is considered the most efficient and sustainable design in developing countries, especially for river crossings that lie in non-flood plain topography like gorges.

## Comparison to other types

In some contexts the term "simple suspension bridge" refers not to this type of bridge but rather to a suspended deck bridge
Suspended deck bridge
A suspended bridge deck is a structural element of several different types of bridges. Many designs use a number of vertical cables or bars in tension to support the deck, these elements being attached to an overhead structure of some type:...

that is "simple" in that its deck is not stiffened. Although simple suspension bridges and "simple" suspended deck bridges are similar in many respects, they differ in their physics. On a simple suspension bridge, the main cables (or chains) follow a hyperbolic
Hyperbolic function
In mathematics, hyperbolic functions are analogs of the ordinary trigonometric, or circular, functions. The basic hyperbolic functions are the hyperbolic sine "sinh" , and the hyperbolic cosine "cosh" , from which are derived the hyperbolic tangent "tanh" and so on.Just as the points form a...

curve, the catenary
Catenary
In physics and geometry, the catenary is the curve that an idealised hanging chain or cable assumes when supported at its ends and acted on only by its own weight. The curve is the graph of the hyperbolic cosine function, and has a U-like shape, superficially similar in appearance to a parabola...

. This is because the main cables are free hanging. In contrast, on a suspended deck bridge (whether "simple" or not) the main cables follow a parabolic curve, the parabola
Parabola
In mathematics, the parabola is a conic section, the intersection of a right circular conical surface and a plane parallel to a generating straight line of that surface...

. This is because the main cables are tied at uniform intervals to the bridge deck below (see Catenary#Suspension bridge curve). The differences between these two curves was a question of importance in the 17th century, worked on by Isaac Newton
Isaac Newton
Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...

among others.

A stressed ribbon bridge
Stressed ribbon bridge
A stressed ribbon bridge is a tension structure . The suspension cables are embedded in the deck which follows a catenary arc between supports. Unlike the simple span the ribbon is stressed in compression, which adds to the stiffness of the structure...

also has one or more catenary curves and a deck laid on the main cables. Unlike a simple suspension bridge however, a stressed ribbon bridge has a stiff deck, usually due to the addition of compression elements (concrete slabs) laid over the main cables. This stiffness allows the bridge to be much heavier, wider, and more stable.

## History

The simple suspension bridge is the oldest known type of suspension bridge
Suspension bridge
A suspension bridge is a type of bridge in which the deck is hung below suspension cables on vertical suspenders. Outside Tibet and Bhutan, where the first examples of this type of bridge were built in the 15th century, this type of bridge dates from the early 19th century...

and, ignoring the possibility of pre-Columbian trans-oceanic contact
Pre-Columbian trans-oceanic contact
Theories of Pre-Columbian trans-oceanic contact are those theories that propose interaction between indigenous peoples of the Americas who settled the Americas before 10,000 BC, and peoples of other continents , which occurred before the arrival of Christopher Columbus in the Caribbean in 1492.Many...

, there were at least two independent inventions of the simple suspension bridge, in the wider Himalaya region and South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

.

The earliest reference to suspension bridges appear in Han dynasty
Han Dynasty
The Han Dynasty was the second imperial dynasty of China, preceded by the Qin Dynasty and succeeded by the Three Kingdoms . It was founded by the rebel leader Liu Bang, known posthumously as Emperor Gaozu of Han. It was briefly interrupted by the Xin Dynasty of the former regent Wang Mang...

records on the travels of Chinese diplomatic missions to the countries on the western and southern fringe of the Himalaya, namely the Hindukush range in Afghanistan
Afghanistan
Afghanistan , officially the Islamic Republic of Afghanistan, is a landlocked country located in the centre of Asia, forming South Asia, Central Asia and the Middle East. With a population of about 29 million, it has an area of , making it the 42nd most populous and 41st largest nation in the world...

, and the lands of Gandhara
Gandhara
Gandhāra , is the name of an ancient kingdom , located in northern Pakistan and eastern Afghanistan. Gandhara was located mainly in the vale of Peshawar, the Potohar plateau and on the Kabul River...

and Gilgit
Gilgit
Gilgit is a city in northern PakistanGilgit may refer to other terms related with the area of the city:* Gilgit River* Gilgit Valley* Gilgit District* Gilgit Agency * Gilgit Airport...

. These were simple suspension bridges of three or more cable
Cable
A cable is two or more wires running side by side and bonded, twisted or braided together to form a single assembly. In mechanics cables, otherwise known as wire ropes, are used for lifting, hauling and towing or conveying force through tension. In electrical engineering cables are used to carry...

Vine
A vine in the narrowest sense is the grapevine , but more generally it can refer to any plant with a growth habit of trailing or scandent, that is to say climbing, stems or runners...

s, where people walked directly on the ropes to cross. Later, they also used decking made from planks resting on two cables.

In South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

, Inca rope bridge
Inca rope bridge
Inca rope bridges were simple suspension bridges over canyons and gorges to provide access for the Inca Empire. Bridges of this type were suitable for use since the Inca people did not use wheeled transport—traffic was limited to pedestrians and livestock. The bridges were an integral part...

s predate the arrival of the Spanish in the Andes
Andes
The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...

in the 16th century. The oldest known suspension bridge, reported from ruins, dates from the 7th century in Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...

(see Maya Bridge at Yaxchilan
Maya Bridge at Yaxchilan
Academics have speculated that the Maya may have built a suspension bridge across the Usumacinta river. If so, the Maya Bridge at Yaxchilan would have been the longest bridge discovered in the ancient world, dating from its construction by the Maya civilization in the late 7th century at Yaxchilan...

).

Simple suspension bridges using iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

chain
Chain
A chain is a sequence of connected links.Chain may also refer to:Chain may refer to:* Necklace - a jewelry which is worn around the neck* Mail , a type of armor made of interlocking chain links...

s are also documented in Tibet
Tibet
Tibet is a plateau region in Asia, north-east of the Himalayas. It is the traditional homeland of the Tibetan people as well as some other ethnic groups such as Monpas, Qiang, and Lhobas, and is now also inhabited by considerable numbers of Han and Hui people...

and China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

, although their earliest date is unclear. Several are attributed to Tibetan monk Thang-stong rGyal-po, who reportedly built several in Tibet and Bhutan
Bhutan
Bhutan , officially the Kingdom of Bhutan, is a landlocked state in South Asia, located at the eastern end of the Himalayas and bordered to the south, east and west by the Republic of India and to the north by the People's Republic of China...

in the 15th century, including one at Chuka
Chuka, Tibet
Chuka is a village in the Tibet Autonomous Region of China. It lies at an altitude of 4095 metres . The village has a population of about 785.-See also:*List of towns and villages in Tibet...

. Another example, the Luding Bridge
Luding Bridge
Luding Bridge is a bridge over the Dadu River in Luding County, Garzê Tibetan Autonomous Prefecture, Sichuan, China, located about 80 kilometers west of the city of Ya'an. The bridge dates from the Qing Dynasty and is considered a historical landmark...

, dates from 1703, spanning 100 m using 11 iron chains.

Development of wire cable suspension bridge
Suspension bridge
A suspension bridge is a type of bridge in which the deck is hung below suspension cables on vertical suspenders. Outside Tibet and Bhutan, where the first examples of this type of bridge were built in the 15th century, this type of bridge dates from the early 19th century...

s dates to the temporary simple suspension bridge at Annonay
Annonay
Annonay is a commune in the north of the Ardèche department in the Rhône-Alpes region in southern France. It is the most populous commune in the Ardèche department, although it is not the capital, which resides in the smaller town of Privas.-Geography:...

built by Marc Seguin
Marc Seguin
Marc Seguin was a French engineer, inventor of the wire-cable suspension bridge and the multi-tubular steam-engine boiler.- Biography :...

and his brothers in 1822. It spanned only 18 m. However, simple suspension bridge designs were made largely obsolete by the 19th century invention and patent
Patent
A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....

of the suspended deck bridge
Suspended deck bridge
A suspended bridge deck is a structural element of several different types of bridges. Many designs use a number of vertical cables or bars in tension to support the deck, these elements being attached to an overhead structure of some type:...

by James Finley
James Finley (engineer)
James Finley , aka Judge James Finley, is widely recognized as the first designer and builder of the modern suspension bridge.Born in Maryland, Finley moved to a farm in Fayette County, Pennsylvania, near Uniontown...

. A late 18th century English
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

painting of a bridge in Srinagar
Srinagar
Srinagar is the summer seasonal capital of Jammu and Kashmir. It is situated in Kashmir Valley and lies on the banks of the Jhelum River, a tributary of the Indus. It is one of the largest cities in India not to have a Hindu majority. The city is famous for its gardens, lakes and houseboats...

, then part of the Garhwal Kingdom
Garhwal Kingdom
Garhwal Kingdom was a princely state in north-western Uttarakhand, India, ruled by the Panwar dynasty. It was founded in 888 AD and existed until it was annexed by the Gorkhas in 1803...

, anticipates the invention of the suspended deck bridge. This unusual bridge, built on a floodplain, had suspended deck ramps used to access a simple suspension bridge supported from towers.

## Materials

This type of bridge is known as a rope bridge due to its historical construction from rope
Rope
A rope is a length of fibres, twisted or braided together to improve strength for pulling and connecting. It has tensile strength but is too flexible to provide compressive strength...

. Inca rope bridge
Inca rope bridge
Inca rope bridges were simple suspension bridges over canyons and gorges to provide access for the Inca Empire. Bridges of this type were suitable for use since the Inca people did not use wheeled transport—traffic was limited to pedestrians and livestock. The bridges were an integral part...

s still are formed from native materials, chiefly rope, in some areas of South America. These rope bridges must be renewed periodically owing to the limited lifetime of the materials, and rope components are made by families as contributions to a community endeavor.

Simple suspension bridges, for use by pedestrian
Pedestrian
A pedestrian is a person traveling on foot, whether walking or running. In some communities, those traveling using roller skates or skateboards are also considered to be pedestrians. In modern times, the term mostly refers to someone walking on a road or footpath, but this was not the case...

s and livestock, are still constructed, based on the ancient Inca rope bridge
Inca rope bridge
Inca rope bridges were simple suspension bridges over canyons and gorges to provide access for the Inca Empire. Bridges of this type were suitable for use since the Inca people did not use wheeled transport—traffic was limited to pedestrians and livestock. The bridges were an integral part...

but using wire rope and sometimes steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

or aluminum grid decking, rather than wood.

In modern bridges, materials used instead of (fiber) rope include wire rope
Wire rope
thumb|Steel wire rope Wire rope is a type of rope which consists of several strands of metal wire laid into a helix. Initially wrought iron wires were used, but today steel is the main material used for wire ropes....

, chain
Chain
A chain is a sequence of connected links.Chain may also refer to:Chain may refer to:* Necklace - a jewelry which is worn around the neck* Mail , a type of armor made of interlocking chain links...

, and special-purpose articulated steel beams.

### Living bridges

Around Cherrapunji
Cherrapunji
Cherrapunji , is a subdivisional town in the East Khasi Hills district in the Indian state of Meghalaya. It is credited as being the second wettest place on Earth...

in northeast India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

there are "living root bridges", a form of tree shaping, which are simple suspension bridges made of living tree roots of some suitable species such as Ficus elastica
Ficus elastica
Ficus elastica, also called the rubber fig, rubber bush, rubber tree, rubber plant, or Indian rubber bush is a species of plant in the fig genus, native to northeast India and southern Indonesia....

growing alongside the gap to be bridged, by gradually training some of its roots to grow across the gap until they take root on the other side. There are examples with a span of over 100 feet. They are naturally self-renewing and self-strengthening as the component roots grow thicker.

In the Iya Valley
Iya Valley
The Iya Valley region in Tokushima Prefecture, Japan is a scenic area known for its dramatic mountain valleys and old vine bridges. Although access has improved in recent years, the Iya Valley and the inner parts of Shikoku have historically been remote and difficult to enter, making them a...

of Japan, bridges have been constructed using wisteria
Wisteria floribunda
Wisteria floribunda, the Japanese wisteria, is a woody liana of the Wisteria family. It was brought from Japan to the United States in 1860 by George Rogers Hall. Since then, it has become one of the most highly romanticized flowering garden plants...

vines. To build such a bridge, these vines were planted on opposite sides of a river and woven together when they grew long enough to span the gap. The addition of planks produced a serviceable bridge.

## Design

The arc of the bridge deck varies between a catenary
Catenary
In physics and geometry, the catenary is the curve that an idealised hanging chain or cable assumes when supported at its ends and acted on only by its own weight. The curve is the graph of the hyperbolic cosine function, and has a U-like shape, superficially similar in appearance to a parabola...

and a parabola
Parabola
In mathematics, the parabola is a conic section, the intersection of a right circular conical surface and a plane parallel to a generating straight line of that surface...

, depending on the weight of the bridge itself versus the load it carries.

The very lightest bridges of this type consist of a single footrope and nothing more. These are tightropes and slacklines, and require skill to use. More commonly, the footrope is accompanied by one or two handrail ropes, connected at intervals by vertical side ropes. This style is used by mountaineers. A slightly heavier variation has two ropes supporting a deck, and two handrail ropes. Handrails are necessary because these bridges are prone to oscillate side to side and end to end. Rarely, the footrope (or footrope plus handrails) is combined with an overhead rope similar to a zip-line
Zip-line
A zip-line consists of a pulley suspended on a cable mounted on an incline...

Ropeway
A ropeway is a form of naval lifting device used to transport light stores and equipment across rivers or ravines. It comprises a jackstay, slung between two sheers or gyns, one at either end, from which is suspended a block and tackle, that is free to travel along the rope and hauled back and...

).

In some cases, such as the Capilano Suspension Bridge
Capilano Suspension Bridge
The Capilano Suspension Bridge is a simple suspension bridge crossing the Capilano River in the District of North Vancouver, British Columbia, Canada. The current bridge is long and above the river...

, the primary supports form the handrails with the deck suspended below them. This makes for more motion side-to-side in the deck than when the primary supports are at deck level, but less motion in the handrails.

Disadvantages connected with simple suspension bridges are very great. The location of the deck is limited, massive anchorages and piers generally are required, and loading produces transient deformation of the deck. Solutions to these problems led to a wide variety of methods of stiffening the deck, resulting in several other types of suspension bridge. These include a stressed ribbon bridge
Stressed ribbon bridge
A stressed ribbon bridge is a tension structure . The suspension cables are embedded in the deck which follows a catenary arc between supports. Unlike the simple span the ribbon is stressed in compression, which adds to the stiffness of the structure...

, which is closely related to a simple suspension bridge but has a stiffened deck suitable for vehicle traffic.

A very light bridge, constructed with cables under high tension, may approach a suspended deck bridge
Suspended deck bridge
A suspended bridge deck is a structural element of several different types of bridges. Many designs use a number of vertical cables or bars in tension to support the deck, these elements being attached to an overhead structure of some type:...

in the nearly horizontal grade of its deck.

The bridge may be stiffened by the addition of cables that do not bear the primary structural or live loads and so may be relatively light. These also add stability in wind. An example is the 220-meter long bridge across the river Drac
Drac
Drac, from the Latin draco, is the word for dragon or devil in several languages, such as Catalan and Romanian.Drac or DRAC may also refer to:* Drac, abbreviation for the orchid genus Dracula...

at Lac de Monteynard-Avignonet
Lac de Monteynard-Avignonet
Lac de Monteynard-Avignonet is an artificial water reservoir for the Électricité de France power station on the Drac River. It belongs to the department of Isère. It is bounded by the canyons of the Drac and Ebron....

: this bridge has stabilizing cables below and to the side of the deck.

To reduce twisting motion in response to users a bridge may employ vertical drop cables from each side at the center of the bridge, anchored to the ground below.

## Use

The lightest of these bridges, without decking, are suitable for use only by pedestrians. Light bridges with decking, and sufficient tension that crossing the bridge does not approach climbing, may be used also by pack horses (and other animals), equestrians, and bicycle riders. To walk a lighter bridge of this type at a reasonable pace requires a particular gliding step, as the more normal walking step will induce traveling waves that can cause the traveler to pitch (uncomfortably) up and down or side-to-side. The exception is a stabilized bridge, which may be quite stable.

Simple suspension bridges have applications in outdoor recreation
Outdoor recreation
Outdoor recreation or outdoor activity is leisure pursuits engaged in outside, especially in natural or semi-natural settings out of town...

. They are a popular choice for tree-top trails and, where the terrain is suitable, for stream crossings. They may be designed without stabilizing so that the free movement of the bridge provides a more interesting experience for the user.

In French
French language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...

, a rudimentary simple suspension bridge is known by one of three names, depending on its form: pont himalayen ("Himalayan bridge": a single footrope and handrails on both sides, usually without a deck); pont de singe ("monkey bridge: a footrope with overhead rope); and tyrolienne ("Tyrolean": a zip-line). Zip-lines can be traversed by hanging below, or walked (by individuals with exceptional balance). A more developed version of the pont himalayen, provided with a deck between a pair of main cables, is known as a passerelle himalayen (French
French language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...

, "Himalayan footbridge"). Examples of this type include two bridges at Lac de Monteynard-Avignonet
Lac de Monteynard-Avignonet
Lac de Monteynard-Avignonet is an artificial water reservoir for the Électricité de France power station on the Drac River. It belongs to the department of Isère. It is bounded by the canyons of the Drac and Ebron....

in the French Alps
French Alps
The French Alps are those portions of the Alps mountain range which stand within France, located in the Rhône-Alpes and Provence-Alpes-Côte d'Azur regions....

; these bridges are exceptionally long, for bridges of this type.

## Notable bridges

Notable simple suspension bridges include:
Name Span
Span (architecture)
Span is the distance between two intermediate supports for a structure, e.g. a beam or a bridge.A span can be closed by a solid beam or of a rope...

length
Year built
Capilano Suspension Bridge
Capilano Suspension Bridge
The Capilano Suspension Bridge is a simple suspension bridge crossing the Capilano River in the District of North Vancouver, British Columbia, Canada. The current bridge is long and above the river...

136 metres (446.2 ft) 1888
Arroyo Cangrejillo Bridge 337 metres (1,105.6 ft) 1998
Lac de Monteynard-Avignonet
Lac de Monteynard-Avignonet
Lac de Monteynard-Avignonet is an artificial water reservoir for the Électricité de France power station on the Drac River. It belongs to the department of Isère. It is bounded by the canyons of the Drac and Ebron....

Drac bridge
220 metres (721.8 ft) 2007
Carrick-a-Rede Rope Bridge
Carrick-a-Rede Rope Bridge
Carrick-a-Rede Rope Bridge is a rope suspension bridge near Ballintoy, County Antrim, Northern Ireland. The bridge links the mainland to the tiny Carrick Island. The site is owned and maintained by the National Trust, spans twenty metres and is thirty metres above the rocks below. Today the bridge...

20 metres (65.6 ft) rebuilt 2008

• :Category:Simple suspension bridges
• Inca Bridge
• Stressed ribbon bridge
Stressed ribbon bridge
A stressed ribbon bridge is a tension structure . The suspension cables are embedded in the deck which follows a catenary arc between supports. Unlike the simple span the ribbon is stressed in compression, which adds to the stiffness of the structure...

(compression forces on the deck stabilize against swaying)
• Suspension bridge types
Suspension bridge types
A suspension bridge is any type of bridge that makes significant use of tension rather than or in addition to compression. A suspension bridge usually has main cables , anchored at each end of the bridge. Any load applied to the bridge is transformed into a tension in these main cables...